ST – Solar-Terrestrial Sciences

ST1.1 – Open Session on the Sun and Heliosphere

Solar activity is an essential factor for the study of many aspects of the geophysical and astronomical sciences. A very simple measure of solar activity is counting sunspots using telescopes. This task can be done even with small telescopes since the Sun is apparently a very large and luminous star. For this reason, it is possible to rescue the ancient observations of sunspots made in the past centuries to obtain an image of the evolution of solar activity during the last four centuries.

The first attempt to reconstruct solar activity from these records was made by Rudolf Wolf, who defined the Sunspot Number index in the 19th century. The Zurich Observatory (and later the Brussels Observatory) was in charge of continuing Wolf's work to the present day. In 1998, Hoyt and Schatten presented a new reconstruction of solar activity that was very different from Wolf's reconstruction (Vaquero and Vázquez, 2009). Many of these differences were solved by Clette et al. (2014).

Currently, research to improve the Sunspot Number is focused on (i) improving the database by reviewing old observations, and (ii) improving the methodologies to convert raw data into the Sunspot Number index. In this work, we try to present the latest advances in this task (Muñoz-Jaramillo and Vaquero, 2019; Arlt and Vaquero, 2020).



Arlt, R., Vaquero, J.M. (2020) Living Reviews in Solar Physics 17, 1.

Clette, F. et al. (2014) Space Science Reviews 186, 35.

Muñoz-Jaramillo, A., Vaquero, J.M. (2019) Nature Astronomy 3, 205.

Vaquero, J.M. and Vázquez, M. (2009) The Sun recorded through history (Springer).

How to cite: Vaquero, J. M.: A long-term geophysical and astronomical dataset: sunspot counting from 1610 to 2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15499,, 2021.

EGU21-2555 | vPICO presentations | ST1.1

A clock for the Sun's magnetic Hale cycle and 27 day recurrences in the aa geomagnetic index

Sandra Chapman, Scott McIntosh, Robert Leamon, and Nicholas Watkins

We construct a new solar cycle phase clock which maps each of the last 18 solar cycles onto a single normalized epoch for the approximately 22 year Hale (magnetic polarity) cycle, using the Hilbert transform of daily sunspot numbers (SSN) since 1818. We use the clock to study solar and geomagnetic climatology as seen in datasets available over multiple solar cycles. The occurrence of solar maxima on the clock shows almost no Hale cycle dependence, confirming that the clock is synchronized with polarity reversals.  The odd cycle minima lead the even cycle minima by ~ 1.1 normalized years, whereas the odd cycle terminators (when sunspot bands from opposite hemispheres have moved to the equator and coincide, thus terminating the cycle, McIntosh(2019)) lag the even cycle terminators  by ~ 2.3 normalized years.  The average interval between each minimum and terminator  is thus relatively extended for odd cycles and shortened for even ones. We re-engineer the R27 index that was orignally proposed by Sargent(1985) to parameterize 27 day recurrences in the aa index. We perform an epoch analysis of autocovariance in the aa index using the Hale cycle clock to obtain a high time resolution parameter for 27 day recurrence, <acv(27)>. This reveals that the transition to recurrence, that is, to an ordered solar wind dominated by high speed streams, is fast, occurring within 2-3 solar rotations or less. It resolves an extended late declining phase which is approximately twice as long on even Schwabe cycles as odd ones. We find that Galactic Cosmic Ray flux rises in step with <acv(27)> but then stays high. Our analysis also identifies a slow timescale trend in SSN that simply tracks the Gleissberg cycle. We find that this trend is in phase with the slow timescale trend in the modulus of sunspot latitudes, and in antiphase with that of the R27 index.

How to cite: Chapman, S., McIntosh, S., Leamon, R., and Watkins, N.: A clock for the Sun's magnetic Hale cycle and 27 day recurrences in the aa geomagnetic index, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2555,, 2021.

EGU21-14168 | vPICO presentations | ST1.1

 First radio evidence for ubiquitous magnetic reconnections and impulsive heating in the quiet solar corona 

Surajit Mondal, Divya Oberoi, Ayan Biswas, Shabbir Bawaji, Ujjaini Alam, Arpit Behera, Devojyoti Kansabanik, Nick Swainston, Ramesh Bhat, and John Morgan

It has been a long standing problem as to how the solar corona can maintain its million K temperature, while the photosphere, which is the lowest layer of the solar atmosphere, is only at a temperature of 5800 K. A very promising theory to explain this is the “nanoflare” hypothesis, which suggests that numerous flares of energies ~1024 ergs are always happening in the solar corona, and maintain its million K temperature. However, detecting these nanoflares directly is challenging with the current instrumentation as they are hypothesised to occur at very small spatial, temporal and energy scales. These nanoflares are expected to produce nonthermal electrons, which are expected to emit in the radio band. These nonthermal emissions are often brighter than their thermal counterparts and might be detectable with current radio instruments. Due to their importance multiple searches for these nonthermal emissions have been done, but thus far they have been  limited to active regions. The quiet corona is also hot, and often comprises the bulk of the coronal region, so it is equally important to understand the physical processes which maintain this medium at MK temperatures. We describe the results from our effort to use the data from the Murchison Widefield Array (MWA) to search for impulsive radio emissions in the quiet solar corona. By pushing the detection threshold of nonthermal emission by about two orders of magnitude lower than previous studies, we have uncovered ubiquitous very impulsive nonthermal emissions from the quiet sun. We refer to these emissions as Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs). Using independent observations spanning very different solar conditions we show that WINQSEs are present throughout the quiet corona at all times. Their occurrence rate lies in the range of many hundreds to about a thousand per minute, implying that on average order 10 or so WINQSEs are present in every 0.5 s MWA image. Preliminary estimates suggest that WINQSEs have a bandwidth of ~2 MHz. Buoyed by  their possible connection to the hypothesised “nanoflares”, we are pursuing several projects to characterise and understand them. These include developing machine learning algorithms to identify WINQSEs in radio images and characterise their morphologies; exploring the ability of the present generation EUV and X-ray instruments to estimate the energy corresponding to the brightest of WINQSEs; and attempting very high time resolution imaging to explore their temporal structure. In this talk, I will present the results from the past and ongoing projects about WINQSEs and argue that these might be a key step towards detecting “nanoflares” and the resolution of the coronal heating problem.



How to cite: Mondal, S., Oberoi, D., Biswas, A., Bawaji, S., Alam, U., Behera, A., Kansabanik, D., Swainston, N., Bhat, R., and Morgan, J.:  First radio evidence for ubiquitous magnetic reconnections and impulsive heating in the quiet solar corona , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14168,, 2021.

EGU21-14293 | vPICO presentations | ST1.1

Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare   

Rohit Sharma, Marina Battaglia, Yingjie Luo, Bin Chen, and Sijie Yu

Solar flares release enormous magnetic energy into the corona, producing the heating of ambient plasma and acceleration of particles. The flaring process is complex and often shows multiple spatially separated temporal individual episodes of energy releases, which can be hard to resolve based on the instrument capability. We analysed the multi-wavelength imaging and spectroscopy observations of multiple electron acceleration episodes during a GOES B1.7-class two-ribbon flare observed simultaneously with the Karl G. Jansky Very Large Array (VLA) at 1--2 GHz, the Reuven Ramatay High Energy Solar Spectroscopic Imager (RHESSI) in X-rays, and the Solar Dynamics Observatory in extreme ultraviolet (EUV).
We observed a total of six radio bursts. First three bursts were co-temporal, but not co-spatial nonthermal X-ray source and represent multiple electron acceleration episodes. We model the radio spectra by optically thick gyrosynchrotron emission and estimate the magnetic field strength and nonthermal electron spectral parameters in each acceleration episode. We note that the nonthermal parameters derived from X-rays differ considerably from the nonthermal parameters inferred from the radio and originates in the lower corona. Although co-temporal, our multi-wavelength analysis shows that different electron populations produce multiple acceleration episodes in radio and X-rays wavelengths. 

How to cite: Sharma, R., Battaglia, M., Luo, Y., Chen, B., and Yu, S.: Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare   , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14293,, 2021.

EGU21-4954 | vPICO presentations | ST1.1

Surges of the weak magnetic field in the photosphere of the Sun

Dmitrii Baranov, Elena Vernova, and Marta Tyasto

The properties of the magnetic fields of the solar photosphere are investigated, in particular, the distribution of fields of different polarity over the solar surface. As primary data, synoptic maps of the photospheric magnetic field of the Kitt Peak National Solar Observatory for 1978-2016 were used. Using the vector summation method, the non-axisymmetric component of the magnetic field is determined. It was found that the nonaxisymmetric component of weak magnetic fields B < 5 G changes in antiphase with the flux of these fields. Magnetic fields of B < 5 G constitute a significant part of the total magnetic field of the Sun, since they occupy more than 60% of the area of the photosphere. The fine structure of the distribution of weak fields can  be observed by setting the upper limit to the strength of the  fields  included in the time–latitude diagram. This allows to eliminate the contribution of the strong fields of sunspots.

On the time-latitude diagram for weak magnetic fields (B < 5 G), bands of differing colors correspond to the streams of the magnetic fields moving in the direction to the Sun’s poles.. These streams or surges show the alternation of the dominant polarity - positive or negative - which is clearly seen in all four cycles. The slopes of the bands indicate the velocity of the fields movement towards the poles. The surges can be divided into two groups. The surges of the first group belong to the so-called Rush-to-the-Poles. These are bands with the width of about three years, which begin at approximately 40° of latitude and have the same polarity as the trailing sunspots. They reach high latitudes and cause the polarity reversal of the polar field. However, in addition to these surges, for most of the solar  cycle (the descending phase, the minimum and the ascending phase), there are narrower surges of both polarities (with the width less than one year), which extend from the equator almost to the poles. These surges are most clearly visible in the southern hemisphere when the southern pole is positive. Consideration of the latitude-time diagrams separately for positive and negative polarities showed that the alternating dominance of one of the polarities is associated with the antiphase development  of the positive and negative fields of the surges. The widths of surges and the periodicity of their appearance vary significantly for the two hemispheres and from one solar cycle to the other. The mean period of the polarity alternation is about 1.5 years.

How to cite: Baranov, D., Vernova, E., and Tyasto, M.: Surges of the weak magnetic field in the photosphere of the Sun, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4954,, 2021.

EGU21-2445 | vPICO presentations | ST1.1

Prominence Formation by Levitation-Condensation at Extreme Resolutions

Jack Jenkins and Rony Keppens

We revisit the so-called levitation-condensation mechanism for the ab-inito formation of solar prominences: cool and dense clouds in the million-degree solar atmosphere. Levitation-condensation occurs following the formation of a flux rope in response to the deformation of a force-free coronal arcade by controlled magnetic footpoint motions and subsequent reconnection. Existing coronal plasma gets lifted within the forming rope, therein isolating a collection of matter now more dense than its immediate surroundings. This denser region ultimately suffers a thermal instability driven by radiative losses, and a prominence forms. We improve on various aspects that were left unanswered in the early work, by revisiting this model with our modern open-source grid- adaptive simulation code []. Most notably, this tool enables a resolution of 5.6 km within a 24 Mm x 25 Mm domain size; the full global flux rope dynamics and local plasma dynamics are captured in unprecedented detail. Our 2.5D simulation (where the flux rope has realistic helical magnetic field lines) demonstrates that the thermal runaway condensation can happen at any location, not solely in the bottom part of the flux rope where the majority of prominence material is assumed to reside. Intricate thermodynamic evolution and shearing flows develop spontaneously, themselves inducing further fine-scale (magneto)hydrodynamic instabilities. Our analysis touches base with advanced linear magnetohydrodynamic stability theory, e.g. with the Convective Continuum Instability or CCI process as well as with in-situ thermal instability studies. We find that condensing prominence plasma evolves according to the internal pressure and density gradients as found previously for coronal rain condensations, but also misalignments therein suggesting the relevance of the Rayleigh-Taylor instability or RTI process in 3D. We also find evidence for resistively-driven dynamics in the prominence body, in close analogy with analytical predictions. These findings are relevant for modern studies of full 3D prominence formation and structuring. Most notably, we anticipate obtaining similar resolutions within a fully 3D setup. Such an achievement will afford us the exciting opportunity to offer crucial explanations as to the persistent discrepancy in prominence appearance when projected off- or on-disk.

How to cite: Jenkins, J. and Keppens, R.: Prominence Formation by Levitation-Condensation at Extreme Resolutions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2445,, 2021.

EGU21-3616 | vPICO presentations | ST1.1

Direct Observation of A Large-scale CME Flux Rope Event Arising from an Unwinding Coronal Jet 

Hechao Chen, Jiayan Yang, Junchao Hong, Haidong Li, and Yadan Duan

Increasing observations show that coronal jets may result in bubble-shaped coronal mass ejections (CMEs), but the genesis of jet-driven CMEs and their nature are not fully understood. Here, we report a direct stereoscopic observation on the magnetic coupling from a coronal blowout jet to a stellar-sized CME.  Observations in the EUV passbands of SDO/AIA show that this whole event starts with a small-scale active-region filament whose eruption occurs at a coronal geyser site due to flux emergence and cancellation. By interacting with an overlying null-point configuration, this erupting filament first breaks one of its legs and triggers an unwinding blowout jet. The release of magnetic twist in its jet spire is estimated at around 1.5−2.0 turns. This prominent twist transport in jet spire rapidly creates a newborn large-scale flux rope from the jet base to a remote site. As a result, the newborn large-scale flux rope erupts into the outer coronae causing an Earth-directed bubble-shaped CME. In particular, two sets of distinct flare post-flare loops form in its source region in sequence, indicating this eruptive event couples with twice flare reconnection. This observation highlights a real pathway for jet-CME magnetic coupling and provides a new hint for the buildup of large-scale CME flux ropes. 

How to cite: Chen, H., Yang, J., Hong, J., Li, H., and Duan, Y.: Direct Observation of A Large-scale CME Flux Rope Event Arising from an Unwinding Coronal Jet , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3616,, 2021.

EGU21-1461 | vPICO presentations | ST1.1

Characteristics of Sunquake Events Observed in Solar Cycle 24

Alexander Kosovichev and Ivan Sharykin

Helioseismic response to solar flares ("sunquakes") occurs due to localized force or/and momentum impacts observed during the flare impulsive phase in the lower atmosphere. Such impacts may be caused by precipitation of high-energy particles, downward shocks, or magnetic Lorentz force. Understanding the mechanism of sunquakes is a key problem of the flare energy release and transport. Our statistical analysis of M-X class flares observed by the Solar Dynamics Observatory during Solar Cycle 24 has shown that contrary to expectations, many relatively weak M-class flares produced strong sunquakes, while for some powerful X-class flares, helioseismic waves were not observed or were weak. The analysis also revealed that there were active regions characterized by the most efficient generation of sunquakes during the solar cycle. We found that the sunquake power correlates with maximal values of the X-ray flux derivative better than with the X-ray class. The sunquake data challenge the current theories of solar flares.

How to cite: Kosovichev, A. and Sharykin, I.: Characteristics of Sunquake Events Observed in Solar Cycle 24, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1461,, 2021.

EGU21-13091 | vPICO presentations | ST1.1

Coronal loops in a box: 3D models of their internal structure, dynamics and heating

Cosima Breu, Hardi Peter, Robert Cameron, Sami Solanki, Pradeep Chitta, and Damien Przybylski

The corona of the Sun, and probably also of other stars, is built up by loops defined through the magnetic field. They vividly appear in solar observations in the extreme UV and X-rays. High-resolution observations show individual strands with diameters down to a few 100 km, and so far it remains open what defines these strands, in particular their width, and where the energy to heat them is generated.

The aim of our study is to understand how the magnetic field couples the different layers of the solar atmosphere, how the energy generated by magnetoconvection is transported into the upper atmosphere and dissipated, and how this process determines the scales of observed bright strands in the loop.

To this end, we conduct 3D resistive MHD simulations with the MURaM code. We include the effects of heat conduction, radiative transfer and optically thin radiative losses.
We study an isolated coronal loop that is rooted with both footpoints in a shallow convection zone layer. To properly resolve the internal structure of the loop while limiting the size of the computational box, the coronal loop is modelled as a straightened magnetic flux tube. By including part of the convection zone, we drive the evolution of the corona self-consistently by magnetoconvection.

We find that the energy injected into the loop is generated by internal coherent motions within strong magnetic elements. 
The resulting Poynting flux is channelled into the loop in vortex tubes forming a magnetic connection between the photosphere and corona, where it is dissipated and heats the upper atmosphere.

The coronal emission as it would be observed in solar extreme UV or X-ray observations, e.g. with AIA or XRT, shows transient bright strands.
The widths of these strands are consistent with observations. From our model we find that the width of the strands is governed by the size of the individual photospheric magnetic field concentrations where the field lines through these strands are rooted. Essentially, each coronal strand is mainly rooted in a single magnetic patch in the photosphere, and the energy to heat the strand is generated by internal motions within this magnetic concentration.

With this model we can build a coherent picture of how energy and matter are transported into the upper solar atmosphere and how these processes structure the interior of coronal loops.

How to cite: Breu, C., Peter, H., Cameron, R., Solanki, S., Chitta, P., and Przybylski, D.: Coronal loops in a box: 3D models of their internal structure, dynamics and heating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13091,, 2021.

EGU21-1013 | vPICO presentations | ST1.1

Formation of solar coronal loops through magnetic reconnection in an emerging active region

Zhenyong Hou, Hui Tian, Hechao Chen, Xiaoshuai Zhu, Jiansen He, Xianyong Bai, Zhenghua Huang, and Lidong Xia

Coronal loops are building blocks of solar active regions (ARs). However, their formation is not well understood. Here we present direct observational evidence for the formation of coronal loops through magnetic reconnection as new magnetic fluxes emerge to the solar atmosphere. Observations in the EUV passbands of SDO/AIA clearly show the newly formed loops following magnetic reconnection within a vertical current sheet. Formation of the loops is also seen in the Hα images taken by NVST. The SDO/HMI observations show that a positive-polarity flux concentration moves toward a negative-polarity one with a speed of ~0.5 km s-1 before the apparent formation of coronal loops. During the formation of coronal loops, we found signatures of flux cancellation and subsequent enhancement of the transverse field between the two polarities. We have reconstructed the three-dimensional magnetic field structure through a magnetohydrostatic model, which shows field lines consistent with the loops in AIA images. Numerous bright blobs with a width of ~1.5 Mm appear intermittently in the current sheet and move upward with apparent velocities of ~80 km s-1. We have also identified plasma blobs moving to the footpoints of the newly formed large loops, with apparent velocities ranging from 30 to 50 km s-1. A differential emission measure analysis shows that the temperature, emission measure and density of the bright blobs are 2.5-3.5 MK, 1.1-2.3×1028 cm-5 and 8.9-12.9×109 cm-3, respectively. Power spectral analysis of these blobs indicates that the magnetic reconnection is inconsistent with the turbulent reconnection scenario.

How to cite: Hou, Z., Tian, H., Chen, H., Zhu, X., He, J., Bai, X., Huang, Z., and Xia, L.: Formation of solar coronal loops through magnetic reconnection in an emerging active region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1013,, 2021.

EGU21-3134 | vPICO presentations | ST1.1

Coronal dimmings associated with coronal mass ejections on the solar limb

Galina Chikunova, Karin Dissauer, Tatiana Podladchikova, and Astrid Veronig

We studied 43 coronal dimming events associated with Earth-directed coronal mass ejections (CMEs) that were observed in quasi-quadrature by the SDO and STEREO satellites. We derived the properties of the dimmings as observed above the limb by STEREO EUVI, and compared them with the mass and speed of the associated CMEs. The unique satellite constellation allowed us to compare our findings with the results from Dissauer et al. (2018, 2019), who studied these events observed against the solar disk by SDO AIA. Such statistics is done for the first time and confirms the close relation between characteristic dimming and CME parameters for the off-limb viewpoint. We find that the dimming areas are typically larger for off-limb observations (mean value of 1.24±1.23×1011 km2 against 3.51±0.71×1010 km2 for on-disk), while the decrease in the total extreme ultraviolet intensity is similar (c=0.60±0.14). The off-limb dimming areas and brightnesses are strongly correlated with the CME mass (c=0.82±0.06 and 0.75±0.08), whereas the dimming area and brightness change rate correlate with the CME speed (c∼0.6). Our findings suggest that coronal dimmings have the potential to provide early estimates of the Earth-directed CMEs parameters, relevant for space weather forecasts, for satellite locations at both L1 and L5.

How to cite: Chikunova, G., Dissauer, K., Podladchikova, T., and Veronig, A.: Coronal dimmings associated with coronal mass ejections on the solar limb, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3134,, 2021.

EGU21-31 | vPICO presentations | ST1.1

The Source Locations of Major Flares and CMEs in the Emerging Active Regions

Lijuan Liu, Yuming Wang, Zhenjuan Zhou, and Jun Cui

Major flares and coronal mass ejections (CMEs) tend to originate from the compact polarity inversion lines (PILs) in the solar active regions (ARs). Recently, a scenario named as “collisional shearing” is proposed by Chintzoglou et al. (2019) to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form the compact PIL, driving the shearing and flux cancellation that are responsible to the subsequent large activities. In this work, through tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of “collisional shearing”. We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, 6 from the conjoined systems of sPIL and cPIL, and 2 from the conjoined systems of sPIL and ePIL (external  PIL between the AR and the nearby preexisting polarities). Collision accompanied by shearing and flux cancellation is found developing at all PILs prior to the eruptions, with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the intenser activities tend to originate from the PILs with severer collision. The results suggest that the “collisional shearing”, i.e., bipole-bipole interaction during the flux emergence is a common process in driving the major activities in emerging ARs.

How to cite: Liu, L., Wang, Y., Zhou, Z., and Cui, J.: The Source Locations of Major Flares and CMEs in the Emerging Active Regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-31,, 2021.

We present a novel method to derive the shock density compression ratio of coronal shock waves that are occasionally observed as halo coronal mass ejections (CMEs). Our method uses the three-dimensional (3-D) geometry and enables us to access the reliable shock density compression ratio. We show the 3-D properties of coronal shock waves seen from multiple vantage point observations, i.e., geometry, kinematics, and compression ratio (Mach number). The significant findings are as follows: (1) Halo CMEs are the manifestation of spherically shaped fast-mode waves/shocks, rather than a matter of the projection of expanding flux ropes. The footprints of halo CMEs on the coronal base are the so-called EIT/EUV waves. (2) These spherical fronts arise from a driven shock (bow- or piston-type) close to the CME nose, and it is gradually becoming a freely propagating (decaying) fast-mode shock wave at the flank. (3) The shock density compressions peak around the CME nose and decrease at larger position angles (flank). (4) Finally, the supercritical region extends over a large area of the shock and lasts longer than past reports.  These results offer a simple unified picture of the different manifestations for CME-associated (shock) waves, such as EUV waves and SEP events observed in various regimes and heliocentric distances. We conclude that CME shocks can accelerate energetic particles in the corona over extended spatial and temporal scales and are likely responsible for the wide longitudinal distribution of these particles in the inner heliosphere.

How to cite: Kwon, R. Y.: The three-dimensional density compression ratio of shock fronts observed as halo coronal mass ejections , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10578,, 2021.

EGU21-642 | vPICO presentations | ST1.1

Mapping the global magnetic field in the solar corona through magnetoseismology

Zihao Yang, Christian Bethge, Hui Tian, Steven Tomczyk, Richard Morton, Giulio Del Zanna, Scott McIntosh, Bidya Binay Karak, Sarah Gibson, Tanmoy Samanta, Jiansen He, Yajie Chen, Linghua Wang, and Xianyong Bai

Magnetoseismology, a technique of magnetic field diagnostics based on observations of magnetohydrodynamic (MHD) waves, has been widely used to estimate the field strengths of oscillating structures in the solar corona. However, previously magnetoseismology was mostly applied to occasionally occurring oscillation events, providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure. This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter (CoMP). Using several CoMP observations of the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of the plasma density and wave phase speed in the corona, which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky. We also examined distributions of the electron density and magnetic field strength, and compared their variations with height in the quiet Sun and active regions. Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

How to cite: Yang, Z., Bethge, C., Tian, H., Tomczyk, S., Morton, R., Del Zanna, G., McIntosh, S., Binay Karak, B., Gibson, S., Samanta, T., He, J., Chen, Y., Wang, L., and Bai, X.: Mapping the global magnetic field in the solar corona through magnetoseismology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-642,, 2021.

EGU21-3990 | vPICO presentations | ST1.1

Clustering of Fast Coronal Mass Ejections during Solar Cycles 23 and 24 and Implications for CME–CME Interactions

Jenny Marcela Rodriguez Gomez, Tatiana Podlachikova, Astrid Veronig, Alexander Ruzmaikin, Joan Feynman, and Anatoly Petrukovich

Coronal Mass Ejections (CMEs) and their interplanetary counterparts (ICMEs) are the major sources for strong space weather disturbances. We present a study of statistical properties of fast CMEs (v≥1000 km/s) that occurred during solar cycles 23 and 24. We apply the Max Spectrum and the declustering threshold time methods. The Max Spectrum can detect the predominant clusters, and the declustering threshold time method provides details on the typical clustering properties and timescales. Our analysis shows that during the different phases of solar cycles 23 and 24, fast CMEs preferentially occur as isolated events and in clusters with, on average, two members. However, clusters with more members appear, particularly during the maximum phases of the solar cycles. During different solar cycle phases, the typical declustering timescales of fast CMEs are τc =28-32 hrs, irrespective of the very different occurrence frequencies of CMEs during a solar minimum and maximum. These findings suggest that  τc   for extreme events may reflect the characteristic energy build-up time for large flare and CME-prolific active regions. Statistically associating the clustering properties of fast CMEs with the disturbance storm time index at Earth suggests that fast CMEs occurring in clusters tend to produce larger geomagnetic storms than isolated fast CMEs. Our results highlight the importance of CME-CME interaction and their impact on Space Weather.

How to cite: Rodriguez Gomez, J. M., Podlachikova, T., Veronig, A., Ruzmaikin, A., Feynman, J., and Petrukovich, A.: Clustering of Fast Coronal Mass Ejections during Solar Cycles 23 and 24 and Implications for CME–CME Interactions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3990,, 2021.

EGU21-7602 | vPICO presentations | ST1.1

LOFAR observations of a jet-driven piston shock in the low solar corona

Ciara Maguire, Eoin Carley, Pietro Zucca, Nicole Vilmer, and Peter Gallagher

The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite a large number of type II radio bursts observations, the precise origin of coronal shocks is still subject to investigation. Here we present a well-observed solar eruptive event that occurred on 16 October 2015, focusing on a jet observed in the extreme ultraviolet by the SDO Atmospheric Imaging Assembly, a streamer observed in white-light by the Large Angle and  Spectrometric Coronagraph, and a metric type II radio burst observed by the LOw-Frequency Array (LOFAR) radio telescope. For the first time, LOFAR has interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be co-spatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model which accounts for the scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5 Rsun above the jet and propagated at a speed of ∼1000 km s−1, which was significantly faster than the jet speed of ∼200 km s−1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

How to cite: Maguire, C., Carley, E., Zucca, P., Vilmer, N., and Gallagher, P.: LOFAR observations of a jet-driven piston shock in the low solar corona, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7602,, 2021.

EGU21-11089 | vPICO presentations | ST1.1

High fidelity spectroscopic imaging at low radio frequencies to estimate plasma parameters of solar coronal mass ejections at higher coronal heights

Devojyoti Kansabanik, Surajit Mondal, Divya Oberoi, and Angelos Vourlidas

Coronal Mass Ejections (CMEs) are large-scale explosive eruptions of magnetised plasma from the Sun into the Heliosphere. Measuring the physical parameters of CMEs is crucial for understanding their physics and for assessing their geo-effectiveness. Radio observations offer the most direct means for estimating these plasma parameters when gyrosynchrotron (GS) emission is detected from the CME plasma. However, since the first detection by Bastian et al.2001, only a handful of studies have successfully detected GS emission from CME plasma. This is usually attributed to the challenges involved in obtaining the high dynamic range imaging required for observing this faint gyrosynchrotron emission in the vicinity of active solar emissions.

The newly developed imaging pipeline (Mondal et al., 2019) designed for the data from Murchison Widefield Array (MWA) marks a significant improvement in metrewave solar radio imaging. Our work suggests that we should now be able to routinely detect GS emission from CME plasma. We present an example where we have successfully detected radio emission from CME plasma and modelled it as GS emission, leading to reliable estimates of CME magnetic field as well as the distribution of energetic electrons (Mondal et al. 2020). In a different example we are able to detect the radio emission from the CME plasma out to as far as 8.3 solar radii. We find that the observed spectra are not always consistent with simple GS models. This highlights that more complicated physics might be at play and points to the need for building more detailed models for interpreting these emissions. We hope that with the availability of polarimetric imaging capability, which we are in the process of developing, this technique will provide a robust way to routinely measure CME magnetic fields along with its other physical parameters. We note that these are the weakest detections of GS emissions from CME plasma reported yet.

How to cite: Kansabanik, D., Mondal, S., Oberoi, D., and Vourlidas, A.: High fidelity spectroscopic imaging at low radio frequencies to estimate plasma parameters of solar coronal mass ejections at higher coronal heights, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11089,, 2021.

EGU21-13004 | vPICO presentations | ST1.1

Detailed Calibration of the Off-Axis Optical Characteristics for the X-Ray Telescope onboard Hinode

Junho Shin, Ryouhei Kano, Takashi Sakurai, Yeon-Han Kim, and Yong-Jae Moon

The X-Ray Telescope (XRT) onboard the Hinode satellite has a specially designed Wolter type grazing-incidence (GI) optics with a paraboloid-hyperboloid mirror assembly to measure the solar coronal plasma of temperatures up to 10 MK with a resolution of about one arc sec. One of the main purposes of this scientific mission is to investigate the detailed mechanism of energy transfer processes from the photosphere to the upper coronal region leading to its heating and the solar wind acceleration. An astronomical telescope is in general designed such that the best-focused image of an object is achieved at or very close to the optical axis, and inevitably the optical performance deteriorates away from the on-axis position. The Sun is, however, a large astronomical object and thus targets near the limb of full-disk images are placed at the outskirt of the field of view. The design of a solar telescope should thus consider the uniformity of imaging quality over a wide FOV, and it is particularly so for X-ray telescopes whose targets can be in the corona high above the limb.


We will explain in this presentation the importance of detailed calibration of the off-axis optical characteristics for Hinode/XRT. It have been revealed that the scattered light caused by the GI mirror surface has a power-law distribution and shows an energy dependence. We will also introduce the basic scheme of how the level of scattering wing is determined and connected to the core from the analysis of highly saturated in-flight data. Vignetting is another important optical characteristics for describing the telescope's performance, which reflects the ability to collect incoming light at different locations and photon energies. We have evaluated the vignetting effect in Hinode/XRT by analyzing the ground experimental data and found that the degree of vignetting varies linearly from the optical center and its pattern shows an energy dependence. Many interesting results on the calibration of Hinode/XRT optical characteristics will be introduced and discussed thoroughly. 

How to cite: Shin, J., Kano, R., Sakurai, T., Kim, Y.-H., and Moon, Y.-J.: Detailed Calibration of the Off-Axis Optical Characteristics for the X-Ray Telescope onboard Hinode, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13004,, 2021.

EGU21-6760 | vPICO presentations | ST1.1

Two classes of eruptive events during Solar Minimum

Prantika Bhowmik and Anthony Yeates

During Solar Minimum, the Sun is perceived to be quite inactive with barely any spots emerging on the solar surface. Consequently, we observe a drop in the number of highly energetic events such as solar flares and coronal mass ejections (CMEs), which are often associated with active regions on the photosphere. However, our magnetofrictional simulations during the minimum period suggest that the solar corona could still be significantly dynamic while evolving in response to the large-scale shearing velocities on the solar surface. The non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically lost through eruptive events. Our study shows that these events can be categorised into two distinct classes. One set of events are caused due to full-scale eruption of low-lying coronal flux ropes and could be associated with occasional filament erupting CMEs observed during Solar Minimum. The other set of events are not driven by destabilisation of low-lying structures but rather by eruption from overlying sheared arcades. These could be linked with streamer blowouts or stealth CMEs. The two classes differ considerably in the amount of magnetic flux and helicity shed through the outer coronal boundary. We additionally investigate how other measurables such as current, open magnetic flux, free energy, coronal holes area, and the horizontal component of the magnetic field on the outer model boundary vary during the two classes of event. This study demonstrates and emphasises the importance and necessity of understanding the dynamics of the coronal magnetic field during Solar Minimum.

How to cite: Bhowmik, P. and Yeates, A.: Two classes of eruptive events during Solar Minimum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6760,, 2021.

EGU21-2076 | vPICO presentations | ST1.1

Extreme event theory applied to the solar wind

Carlos Larrodera, Lidia Nikitina, and Consuelo Cid

Society’s dependence on technology has increased during the past years. Therefore, understanding the hazardous events including space weather events that lead to technological problems is now critical. As solar wind is the driver of space weather, identifying extreme solar wind is important. In this work extreme value theory is used to characterize the solar wind parameters most relevant to space weather: interplanetary magnetic field strength and proton speed. This is done using an extreme value distribution for all data above a certain threshold for each parameter. Analysis demonstrates that these thresholds are around 900 km/s for the proton speed and around 95 nT for the interplanetary magnetic field. Based on 20 years of solar wind data, we made an estimation for the interplanetary magnetic field and solar wind proton speed with return periods corresponding to 4 and 6 solar cycles with a 99% confidence interval.

How to cite: Larrodera, C., Nikitina, L., and Cid, C.: Extreme event theory applied to the solar wind, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2076,, 2021.

EGU21-14653 | vPICO presentations | ST1.1

Probing the solar corona magnetic field with sungrazing comets

Giuseppe Nisticò, Valery M. Nakariakov, Timothy Duckenfield, Miloslav Druckmüller, and Gaetano Zimbardo

Space telescopes of the SoHO, STEREO and SDO missions have occasionally acquired observations of comets, providing an interesting opportunity to investigate the structure and dynamics of the heliospheric plasma.  Cometary plasma tails exhibit a wave-like motion, which is believed to be a response to the physical conditions of the local interplanetary medium. Furthermore, sungrazing comets diving in the solar atmosphere provide us with an unprecedented way to diagnose the coronal plasma at distances which are unaccessible from the current spacecraft. Here, we present observations of Comet Lovejoy C/2011 W3 from SDO/AIA, which was seen to cross the EUV solar corona in December 2011. The cometary ions produced by the sublimation of the comet nucleus were channelled along the magnetic field lines forming some filamented structures. Such structures appear to show small amplitude kink oscillations, which are used to determine the magnitude of the coronal magnetic field by coronal seismology.

How to cite: Nisticò, G., Nakariakov, V. M., Duckenfield, T., Druckmüller, M., and Zimbardo, G.: Probing the solar corona magnetic field with sungrazing comets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14653,, 2021.

EGU21-11094 | vPICO presentations | ST1.1

LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse

Aoife Maria Ryan, Peter T. Gallagher, Eoin P. Carley, Michiel A. Brentjens, Pearse C. Murphy, Christian Vocks, Diana E. Morosan, Hamish Reid, Jasmina Magdalenic, Frank Breitling, Pietro Zucca, Richard Fallows, Gottfried Mann, Alain Kerdraon, and Ronald Halfwerk

The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.

How to cite: Ryan, A. M., Gallagher, P. T., Carley, E. P., Brentjens, M. A., Murphy, P. C., Vocks, C., Morosan, D. E., Reid, H., Magdalenic, J., Breitling, F., Zucca, P., Fallows, R., Mann, G., Kerdraon, A., and Halfwerk, R.: LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11094,, 2021.

EGU21-4795 | vPICO presentations | ST1.1

Quality assessment for objective inter-comparison of coronal models

Andreas Wagner, Manuela Temmer, and Eleanna Asvestari

With the increasing amount of space weather forecasting simulation codes being developed, assessing their performance becomes crucial. Especially the errors resulting from coronal magnetic field models are a critical factor, because these will get propagated further by various solar wind models. We present a first result for a benchmarking system that allows a rather easy-to-implement  assessment of the performance quality of any coronal magnetic field model. This will allow for a standardized comparison between different models. The benchmarking system is based on stepwise visual and semi-automatized comparisons between model output and EUV on-disk and coronograph white-light data. We are using various viewpoints and instrumental data provided by STEREO, SOHO and SDO. 
In our work we exemplarily apply this scheme to the coronal model currently implemented in EUHFORIA, an adaption of the Wang-Sheeley-Arge (WSA) model, with varying input parameters. Furthermore, with this system we also show its possible usage for the derivation of an ideal parameter set. 

How to cite: Wagner, A., Temmer, M., and Asvestari, E.: Quality assessment for objective inter-comparison of coronal models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4795,, 2021.

EGU21-2864 | vPICO presentations | ST1.1

Study of alpha particle properties across rarefaction regions

Tereza Durovcova, Jana Šafránková, and Zdeněk Němeček

Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.

How to cite: Durovcova, T., Šafránková, J., and Němeček, Z.: Study of alpha particle properties across rarefaction regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2864,, 2021.

EGU21-12772 | vPICO presentations | ST1.1

3He rich periods measured by the Suprathermal Ion Telescope (SIT) on STEREO-A during solar cycle 24

Marlon Köberle, Radoslav Bucik, Nina Dresing, Bernd Heber, Andreas Klassen, and Linghua Wang

3He-rich solar energetic particle (SEP) events are characterized by a peculiar elemental composition with rare species like 3He or ultra-heavy ions tremendously enhanced over the solar system abundances.
We report on 3He rich SEP periods measured by the Suprathermal Ion Telescope (SIT) onboard STEREO-A beginning in 2007 until 2020, covering the whole solar cycle 24.
The mass resolution capabilities of SIT do not allow to easily distinguish between 3He and 4He especially in cases of a low 3He to 4He ratio.
We therefore developed a semi-automatic detection algorithm to find time periods during which a 3He enhancement can be statistically determined.
Using this method we found 112 3He rich periods.
These periods were further examined in regards of their 3He/4He and Fe/O ratio. 
Previously about ten 3He-rich SEP periods measured by SIT on STEREO-A have been reported.
An association with in-situ electron measurements by STEREO-SEPT and STEREO-STE showed that ~60% of the 112 periods are accompanied with electron events.
The here presented catalogue of 3He rich periods is intended to serve as a reference for the community.

How to cite: Köberle, M., Bucik, R., Dresing, N., Heber, B., Klassen, A., and Wang, L.: 3He rich periods measured by the Suprathermal Ion Telescope (SIT) on STEREO-A during solar cycle 24, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12772,, 2021.

EGU21-11921 | vPICO presentations | ST1.1

Evolution of solar wind flows from the inner corona to 1 AU: constraints provided by SOHO UVCS and SWAN data

Alessandro Bemporad, Olga Katushkina, Vladislav Izmodenov, Dimitra Koutroumpa, and Eric Quemerais

The Sun modulates with the solar wind flow the shape of the whole Heliosphere interacting with the surrounding interstellar medium. Recent results from IBEX and INCA experiments, as well as recent measurements from Voyager 1 and 2, demonstrated that this interaction is much more complex and subject to temporal and heliolatitudinal variations than previously thought. These variations could be also related with the evolution of solar wind during its journey through the Heliosphere. Hence, understanding how the solar wind evolves from its acceleration region in the inner corona to the Heliospheric boundaries is very important.

In this work, SWAN Lyman-α full-sky observations from SOHO are combined for the very first time with measurements acquired in the inner corona by SOHO UVCS and LASCO instruments, to trace the solar wind expansion from the Sun to 1 AU. The solar wind mass flux in the inner corona was derived over one full solar rotation period in 1997, based on LASCO polarized brightness measurements, and on the Doppler dimming technique applied to UVCS Lyman-α emission from neutral H coronal atoms due to resonant scattering of chromospheric radiation. On the other hand, the SWAN Lyman-α emission (due to back-scattering from neutral H atoms in the interstellar medium) was analyzed based on numerical models of the interstellar hydrogen distribution in the heliosphere and the radiation transfer. The SWAN full-sky Lyman-α intensity maps are used for solving of the inverse problem and deriving of the solar wind mass flux at 1 AU from the Sun as a function of heliolatitude. First results from this comparison for a chosen time period in 1997 are described here, and possible future applications for Solar Orbiter data are discussed.

How to cite: Bemporad, A., Katushkina, O., Izmodenov, V., Koutroumpa, D., and Quemerais, E.: Evolution of solar wind flows from the inner corona to 1 AU: constraints provided by SOHO UVCS and SWAN data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11921,, 2021.

We study the 27-day variations of galactic cosmic rays (GCRs) based on neutron monitor (NM), ACE/CRIS, STEREO and SOHO/EPHIN measurements, in solar minima 23/24 and 24/25 characterized by the opposite polarities of solar magnetic cycle. Now there is an opportunity to re-analyze the polarity dependence of the amplitudes of the recurrent GCR variations in 2007-2009 for negative A < 0 solar magnetic polarity and to compare it with the clear periodic variations related to solar rotation in 2017-2019 for positive A > 0. We use the Fourier analysis method to study the periodicity in the GCR fluxes. Since the GCR recurrence is a consequence of solar rotation, we analyze not only GCR fluxes, but also solar and heliospheric parameters examining the relationships between the 27-day GCR variations and heliospheric, as well as, solar wind parameters. We find that the polarity dependence of the amplitudes of the 27-day variations of the GCR intensity and anisotropy for NMs data is kept for the last two solar minima: 23/24 (2007-2009) and 24/25 (2017-2019) with greater amplitudes in positive A > 0 solar magnetic polarity. ACE/CRIS, SOHO/EPHIN and STEREO measurements are not governed by this principle of greater amplitudes in positive A > 0 polarity. GCR recurrence caused by the solar rotation for low energy (< 1GeV) cosmic rays is more sensitive to the enhanced diffusion effects, resulting in the same level of the 27-day amplitudes for positive and negative polarities. While high energy (> 1GeV) cosmic rays registered by NMs, are more sensitive to the large-scale drift effect leading to the 22-year Hale cycle in the 27-day GCR variation, with the larger amplitudes in the A > 0 polarity than in the A < 0.

How to cite: Modzelewska, R. and Gil, A.: 27-day variations of the galactic cosmic rays intensity and anisotropy in solar minima 23/24 and 24/25 by ACE/CRIS, STEREO, SOHO/EPHIN and neutron monitors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13185,, 2021.

EGU21-13829 | vPICO presentations | ST1.1

Statistical analysis of flow direction and its variations in different types of solar wind streams

Anastasiia Moskaleva, Maria Riazantseva, Yuri Yermolaev, and Irina Lodkina

The efficiency of the solar wind interaction with the Earth's magnetosphere is determined not only by the values of solar wind parameters, but also by the direction of its flow.  As a rule, the slow quiet and uniform solar wind extends radially, but at the same time there are different large-scale solar wind streams, that differ in the values of the plasma parameters and in the flow direction. The most significant changes of solar wind flow direction can be observed in areas of stream interaction, for example Sheath (compression regions before the fast interplanetary coronal mass ejections) and CIR (corotating interaction regions, that are predate high-speed flows from coronal holes) [1]. In the present study, using plasma measurements on the WIND spacecraft, the statistical distributions of the values and fluctuations of flow direction angles in the solar wind were analyzed.  The angles variations were considered on temporal scales from several ten seconds to an hour. The statistical distributions in the quiet solar wind and in various large-scale solar wind streams using the catalog of large-scale solar wind phenomena from the were compared [2].

At the result of this work, it was shown , that maximum values of modules longitude (φ) and latitude (θ) angles, and of their variations are observed for Sheath and CIR regions, the probability of large deviations from the radial direction (>5 degrees)  also increases. Meanwhile the dependence on the solar wind type reduces with decreasing scale. The relation of the values and fluctuations of the direction angles on the values of the plasma parameters in the solar wind were also analyzed.

The work was supported by the RFBR, grant № 19-02-00177а.

1.Yermolaev Y. I., Lodkina I. G., Nikolaeva N. S., Yermolaev M. Y. 2017, Solar Physics, 292 (12),193,
2. Yermolaev, Yu.I., Nikolaeva, N.S., Lodkina, I.G., Yermolaev, M.Yu.: 2009, Catalog of large-scale solar wind phenomena during 1976 – 2000. Cosm. Res. 47(2),81;Eng.transl.Kosm.Issled.47(2),99,

How to cite: Moskaleva, A., Riazantseva, M., Yermolaev, Y., and Lodkina, I.: Statistical analysis of flow direction and its variations in different types of solar wind streams, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13829,, 2021.

EGU21-14937 | vPICO presentations | ST1.1

Sampling the heliosphere through low-frequency observations of pulsars

Caterina Tiburzi, Golam Shaifullah, and Pietro Zucca

Pulsars are highly-magnetized, fast-rotating neutron stars whose radiation is mainly detected at radio frequencies. Their clock-like emission and high degree of linear polarization make them ideal background sources to probe the electron density and magnetic field of the interplanetary medium.
The Soltrack project is a cutting-edge experiment that combines high-quality pulsar observations carried out with LOFAR with the study of the heliosphere and its phenomena. It recently confirmed the first evidence of the Solar cycle's impact on pulsar data, developed a new software to detect pulsar occultations by coronal mass ejections, identified the influence of Solar streamers on pulsar observations and applied pulsar-derived measurements to the validation efforts of the EUHFORIA magneto-hydrodynamic software, that simulate the Solar wind properties for Space weather purposes.
Here I will describe the fundamental concepts at the basis of the Soltrack experiments, and describe the results reached while paving the road for the application of pulsar data to heliospheric analyses.

How to cite: Tiburzi, C., Shaifullah, G., and Zucca, P.: Sampling the heliosphere through low-frequency observations of pulsars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14937,, 2021.

The Nancay Radioheliograph is dedicated to imaging the solar corona at decimetre-to-metre wavelengths. The imaged structures are the quiet corona, through thermal bremsstrahlung, and bright collective emissions due to electrons accelerated in quiescent, flaring and eruptive active regions. The instrument produced nearly daily maps of the Sun between 1996 and 2015, at several frequencies in the 150-450 MHz range with sub-second cadence. The observations were stopped in 2015 for a major technical upgrade through the replacement of the correlator and the data acquisition system. They were resumed in November 2020, and at the time of writing the commissioning of the instrument is well underway. This contribution will give a brief overview of the technical changes and present observations at eight frequencies of solar activity since November 2020, including the coronal mass ejection (CME) of December 14 seen in some images of the total solar eclipse, observations conducted during the present perihelion passage of the Parker Solar Probe mission, as well as during periods of interest to the Solar Orbiter mission. The data are freely available, and special products of common visualisation with the space missions will be illustrated.

How to cite: Klein, K.-L. and the NRH team: Solar observations with the Nancay Radioheliograph in support of the Solar Orbiter and Parker Solar Probe missions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7107,, 2021.

TianQin is a proposed space-borne gravitational wave (GW) observatory composed of three identical satellites orbiting around the geocenter with a distance of 105 km. It aims at detecting GWs in 0.1 mHz – 1 Hz. The detection of GW relies on the high precision measurement of optical path length at 10−12 m level. The dispersion of space plasma can lead to the optical path difference (OPD, ∆l) along the propagation of laser beams between a pair of satellites. Here, we study the OPD noises for TianQin. The Space Weather Modeling Framework is used to simulate the interaction between the Earth magnetosphere and solar wind. From the simulations, we extract the magnetic field and plasma parameters on the orbits of TianQin at four relative positions of the satellite constellation in the Earth magnetosphere. We calculate the OPD noise for single link, Michelson, and Time-Delay Interferometry (TDI) data combinations (α and X). For single link and Michelson interferometer, the maxima of ∆l are on the order of 1 pm. For the TDI combinations, these can be suppressed to about 0.05 pm. The OPD noise of Michelson combination is colored in the concerned frequency range; while the ones for the TDI combinations are roughly white. Furthermore, we calculate the ratio of the equivalent strain of the OPD noise to that of TQ, and find that the OPD noises for the TDI combinations can be neglected in the most sensitive frequency range of f < 0.1 Hz.

How to cite: Wei, S.: Analyses of Laser Propagation Noise for TianQin Gravitational Wave Observatory Based on the Global Magnetosphere MHD Simulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10868,, 2021.

Understanding and modelling the complex state of the Sun-solar wind-heliosphere system, requires a comprehensive set of multiwavelength observations. LOFAR has unique capabilities in the radio domain. Some examples of these include: a) the ability to take high-resolution solar dynamic spectra and radio images of the Sun; b) observing the scintillation (interplanetary scintillation - IPS) of distant, compact, astronomical radio sources to determine the density, velocity and turbulence structure of the solar wind; and c) the use of Faraday rotation as a tool to probe the interplanetary magnetic-field strength and direction. However, to better understand and predict how the Sun, its atmosphere, and more in general the Heliosphere works and impacts Earth, the combination of in-situ spacecraft measurements and ground-based remote-sensing observations of coronal and heliospheric plasma parameters is extremely useful. Ground-based observations can be used to infer a global picture of the inner heliosphere, providing the essential context into which in-situ measurements from spacecraft can be placed. Conversely, remote-sensing observations usually contain information from extended lines of sight, with some deconvolution and modelling necessary to build up a three-dimensional (3-D) picture. Precise spacecraft measurements, when calibrated, can provide ground truth to constrain these models. The PSP mission is observing the solar corona and near-Sun interplanetary space. It has a highly-elliptical orbit taking the spacecraft as close as nearly 36 sola radii from the Sun centre on its first perihelion passage, and subsequent passages ultimately reaching as close as 9.8 solar radii. Four instruments are on the spacecraft’s payload: FIELDS measuring the radio emission, electric and magnetic fields, Poynting flux, and plasma waves as well as the electron density and temperature; ISOIS measuring energetic electrons, protons, and heavy ions in the energy range 10 keV-100 MeV; SWEAP measuring the density, temperature, and flow speed of electrons, protons, and alphas in the solar wind; and finally, WISPR imaging coronal streamers, coronal mass ejections (CMEs), their associated shocks, and other solar wind structures in the corona and near-Sun interplanetary space, and provide context for the other three in-situ instruments. In this talk, the different observing modes of LOFAR and several results of the joint LOFAR/PSP campaign will be presented, including fine structures of radio bursts, localization and kinematics of propagating radio sources in the heliosphere, and the challenges and plans for future observing campaigns including PSP and Solar Orbiter.


How to cite: Zucca, P.: Observing the Sun with LOFAR: an overview of the telescope capabilities and the recent results from the PSP groud base support campaign., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15048,, 2021.

EGU21-9506 | vPICO presentations | ST1.1

Response of the interplanetary hydrogen population to global changes of solar activity: a quantitative analysis based on SOHO/SWAN and SOHO/LASCO-C2 data comparison.

Dimitra Koutroumpa, Eric Quémerais, Lucile Conan, Philippe Lamy, Stéphane Ferron, and Hugo Gilardy

For more than two decades the SOHO/SWAN instrument has been monitoring the full-sky hydrogen backscattered Lyman-α emission, and the derived three-dimensional solar wind proton flux. We present a comparison of the time series of the latitude-integrated hydrogen ionization rates (β) derived from the inversion of the SWAN full-sky maps with the integrated coronal electron density derived from the inversion of SOHO/LASCO-C2 white light images. The analysis shows a variable time lag of the SWAN β of a few Carrington rotations, correlated with the solar cycle phase (larger delay during solar maxima compared to minima). This is a direct consequence of the variation of the size of the hydrogen ionization cavity and the time it takes for hydrogen atoms to propagate in the inner heliosphere. This effect should be taken into account in studies of the interstellar neutral populations in interplanetary space.

How to cite: Koutroumpa, D., Quémerais, E., Conan, L., Lamy, P., Ferron, S., and Gilardy, H.: Response of the interplanetary hydrogen population to global changes of solar activity: a quantitative analysis based on SOHO/SWAN and SOHO/LASCO-C2 data comparison., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9506,, 2021.

EGU21-14279 | vPICO presentations | ST1.1

Shock Acceleration of ~1-100 Kev Electrons at Earth's Bow Shock

Zixuan Liu, Linghua Wang, Liu Yang, Wimmer-Schweingruber Robert, Quanqi Shi, and Bale Stuart

We present a statistical study of in-situ shock acceleration of ~1-100 keV solar wind suprathermal electrons at Earth’s bow shock, by using Wind 3D plasma and energetic particle measurements in ambient solar wind and MMS measurements in shock downstream. We pick out 74 shock cases (1 quasi-parallel shock, 73 quasi-perpendicular shocks) during 2015 October - 2017 January, and classify them into 4 types according to their energy spectra in downstream: type 0 (23 cases) without significant electron acceleration after shock passage, type 1 (24 cases) with power-law spectrum, J ∝εβ1_dn, at ~0.8-10 keV, type 2 (16 cases) with power-law-spectrum at ~0.8-10 keV and significant flux enhancement above 30 keV, and type 3 (11 cases) with a clear double-power-law spectrum, J ∝ εβ1_dn (J ∝ εβ2_dn) when ε « εdntr  (ε » εdntr), bending down at εdntr ~20-90 keV. The spectral indexes at lower energies for type 1, type 2 and type 3, β1dn, range from 2.5 to 5, while the spectral indexes at higher energies for type 3, β2dn, range from 4 to 9, and all the spectral indexes have no significant correlation with those in ambient solar wind. Among the 4 types, type 3 is the strongest acceleration with the largest flux enhancement and the lowest β1dn. Besides, we find that the flux ratio between downstream and ambient solar wind Jdn/Jab is field-perpendicular for most cases in both low and high energies, and Jdn/Jab1dn) has positive (negative) correlations with θBn and magnetic field compression ratio, rB, which favor the shock drift acceleration (SDA) mechanism. However, Jdn/Jab has no correlation with the drift electric field Ed, while the normalized drift time, Td/Ttr, has a positive correlation with θBn, it suggests that θBn can influence electron drift time and thus influence the acceleration efficiency.

How to cite: Liu, Z., Wang, L., Yang, L., Robert, W.-S., Shi, Q., and Stuart, B.: Shock Acceleration of ~1-100 Kev Electrons at Earth's Bow Shock, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14279,, 2021.

EGU21-10504 | vPICO presentations | ST1.1

Unique heliophysics science opportunities along the Interstellar Probe journey up to 1000 AU from the Sun

Elena Provornikova, Pontus C. Brandt, Ralph L. McNutt, Jr., Robert DeMajistre, Edmond C. Roelof, Parisa Mostafavi, Drew Turner, Matthew E. Hill, Jeffrey L. Linsky, Seth Redfield, Andre Galli, Carey Lisse, Kathleen Mandt, Abigail Rymer, and Kirby Runyon

The Interstellar Probe is a space mission to discover physical interactions shaping globally the boundary of our Sun`s heliosphere and its dynamics and for the first time directly sample the properties of the local interstellar medium (LISM). Interstellar Probe will go through the boundary of the heliosphere to the LISM enabling for the first time to explore the boundary with a dedicated instrumentation, to take the image of the global heliosphere by looking back and explore in-situ the unknown LISM. The pragmatic concept study of such mission with a lifetime 50 years that can be implemented by 2030 was funded by NASA and has been led by the Johns Hopkins University Applied Physics Laboratory (APL). The study brought together a diverse community of more than 400 scientists and engineers spanning a wide range of science disciplines across the world.

Compelling science questions for the Interstellar Probe mission have been with us for many decades. Recent discoveries from a number of space missions exploring the heliosphere raised new questions strengthening the science case. The very shape of the heliosphere, a manifestation of complex global interactions between the solar wind and the LISM, remains the biggest mystery. Interpretations of imaging the heliosphere in energetic neutral atoms (ENAs) in different energy ranges on IBEX and Cassini/INCA from inside show contradictory pictures. Global physics-based models also do not agree on the global shape. Interstellar Probe on outbound trajectory will image the heliosphere from outside for the first time and will provide a unique determination of the global shape.

The LISM is a completely new area for exploration and discovery. We have a crude understanding of the LISM inferred from in-situ measurements inside the heliosphere of interstellar helium, pick-up-ions, ENAs, remote observations of solar backscattered Lyman-alpha emission and absorption line spectroscopy in the lines of sight of stars. We have no in-situ measurements of most LISM properties, e.g. ionization, plasma and neutral gas, magnetic field, composition, dust, and scales of possible inhomogeneities. Voyagers with limited capabilities have explored 30 AU beyond the heliosphere which appeared to be a region of significant heliospheric influence. The LISM properties are among the key unknowns to understand the Sun`s galactic neighborhood and how it shapes our heliosphere. Interstellar Probe will be the first NASA mission to discover the very nature of the LISM and shed light on whether the Sun enters a new region in the LISM in the near future.

In this presentation we give an overview of heliophysics science for the Interstellar Probe mission focusing on the critical science questions of the three objectives for the mission. We will discuss in more details a need for direct measurements in the LISM uniquely enabled by the Interstellar Probe.

How to cite: Provornikova, E., Brandt, P. C., McNutt, Jr., R. L., DeMajistre, R., Roelof, E. C., Mostafavi, P., Turner, D., Hill, M. E., Linsky, J. L., Redfield, S., Galli, A., Lisse, C., Mandt, K., Rymer, A., and Runyon, K.: Unique heliophysics science opportunities along the Interstellar Probe journey up to 1000 AU from the Sun, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10504,, 2021.

EGU21-3308 | vPICO presentations | ST1.1

Interstellar Probe: A Mission to the Heliospheric Boundary and Interstellar Medium for the Next Decade

Pontus Brandt, Ralph McNutt, Elena Provornikova, Carey Lisse, Kathleen Mandt, Kirby Runyon, Abigail Rymer, Parisa Mostafavi, Robert DeMajistre, Edmond Roelof, Drew Turner, Matthew Hill, James Kinnison, Gabe Rogers, Clayton Smith, Glen Fountain, David Copeland, Peter Kollmann, Reza Ashtari, and Robert Stough and the The Interstellar Probe Study Team

An Interstellar Probe mission to the Very Local Interstellar Medium (VLISM) would bring new scientific discoveries of the mechanisms upholding our vast heliosphere and directly sample the unexplored Local Interstellar Clouds that our Sun is moving through in relatively short galactic timescales. As such, it would represent Humanity's first explicit step in to the galaxy and become perhaps NASA's boldest step in space exploration. Such a mission has been discussed and studied since 1960, but the stumbling block has often been propulsion. Now this hurdle has been overcome by the availability of new and larger launch vehicles. An international team of scientists and experts are now progressing towards the final year of a NASA-funded study led by The Johns Hopkins University Applied Physics Laboratory (APL) to develop pragmatic example mission concepts for an Interstellar Probe with a nominal design lifetime of 50 years. Together with the Space Launch System (SLS) Office at the NASA Marshall Space Flight Center, the team has analyzed dozens of launch configurations and demonstrate that asymptotic speeds in excess of 7.5 Astronomical Units (AU) per year can be achieved using existing or near-term propulsion stages with a powered or passive Jupiter Gravity Assist (JGA). These speeds are more than twice that of the fastest escaping man-made spacecraft to date, which is Voyager 1 currently at 3.59 AU/year. An Interstellar Probe would therefore reach the Termination Shock (TS) in less than 12 years and cross the Heliopause into the VLISM after about 16 years from launch.

In this presentation we provide an overview and update of the study, the science mission concept, discuss the compelling discoveries that await, and the associated example science payload, measurements and operations ensuring a historic data return that would push the boundaries of space exploration by going where no one has gone before.

How to cite: Brandt, P., McNutt, R., Provornikova, E., Lisse, C., Mandt, K., Runyon, K., Rymer, A., Mostafavi, P., DeMajistre, R., Roelof, E., Turner, D., Hill, M., Kinnison, J., Rogers, G., Smith, C., Fountain, G., Copeland, D., Kollmann, P., Ashtari, R., and Stough, R. and the The Interstellar Probe Study Team: Interstellar Probe: A Mission to the Heliospheric Boundary and Interstellar Medium for the Next Decade, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3308,, 2021.

ST1.2 – Energetic Particles in the Heliosphere and their influence on the Atmosphere

EGU21-6212 | vPICO presentations | ST1.2

Cosmic rays at ground level; a brief introduction

Du Toit Strauss

Galactic cosmic rays, and sporadic high energy solar energetic particles, are energetic enough to pierce the Earth’s protective magnetosphere and interact with the atmosphere. Here, a secondary particle cascade leads to enhanced radiation levels which is of importance, for instance, to aviation dosimetry and related studies. At ground level, these secondary particles can be observed (indirectly) by means of neutron monitors, and this has been done for more than 70 years, providing a valuable long-term cosmic ray record. In this talk, we introduce the different primary particle populations, discuss their acceleration and modulation, and connect this with long-term neutron monitor measurements.

How to cite: Strauss, D. T.: Cosmic rays at ground level; a brief introduction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6212,, 2021.

EGU21-6394 | vPICO presentations | ST1.2

Energetic particles and the solar cycle: Impact of solar magnetic field amplitude and geometry on SEPs and GCRs diffusion coefficients

Barbara Perri, Allan Sacha Brun, Antoine Strugarek, and Victor Réville

SEPs are correlated with the 11-year solar cycle due to their production by flares and interaction with the inner heliosphere, while GCRs are anti-correlated with it due to the modulation of the heliospheric magnetic field. The solar magnetic field along the cycle varies in amplitude but also in geometry, causing diffusion of the particles along and across the field lines; the solar wind distribution also evolves, and its turbulence affects particle trajectories.

We combine 3D MHD compressible numerical simulations to compute the configuration of the magnetic field and the associated polytropic solar wind up to 1 AU, with analytical prescriptions of the corresponding parallel and perpendicular diffusion coefficients for SEPs and GCRs. First, we analyze separately the impact of the magnetic field amplitude and geometry for a 100 MeV proton. By varying the amplitude, we change the amplitude of the diffusion by the same factor, and the radial gradients by changing the spread of the current sheet. By varying the geometry, we change the latitudinal gradients of diffusion by changing the position of the current sheets. We also vary the energy, and show that the statistical distribution of parallel diffusion is different for SEPs and GCRs. Then, we use realistic solar configurations, showing that diffusion is highly non-axisymmetric due to the configuration of the current sheets, and that the distribution varies a lot with the distance to the Sun, especially at minimum of activity. With this model, we are thus able to study the direct influence of the Sun on Earth spatial environment in terms of energetic particles. 

How to cite: Perri, B., Brun, A. S., Strugarek, A., and Réville, V.: Energetic particles and the solar cycle: Impact of solar magnetic field amplitude and geometry on SEPs and GCRs diffusion coefficients, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6394,, 2021.

EGU21-3719 | vPICO presentations | ST1.2

Random Walk and Trapping of Interplanetary Magnetic Field Lines: Global Simulation, Magnetic Connectivity, and Implications for Solar Energetic Particles

David Ruffolo, Rohit Chhiber, William H. Matthaeus, Arcadi V. Usmanov, Paisan Tooprakai, Piyanate Chuychai, and Melvyn L. Goldstein

The random walk of magnetic field lines is an important ingredient in understanding how the connectivity of the magnetic field affects the spatial transport and diffusion of charged particles. As solar energetic particles (SEPs) propagate away from near-solar sources, they interact with the fluctuating magnetic field, which modifies their distributions. We develop a formalism in which the differential equation describing the field line random walk contains both effects due to localized magnetic displacements and a non-stochastic contribution from the large-scale expansion. We use this formalism together with a global magnetohydrodynamic simulation of the inner-heliospheric solar wind, which includes a turbulence transport model, to estimate the diffusive spreading of magnetic field lines that originate in different regions of the solar atmosphere. We first use this model to quantify field line spreading at 1 au, starting from a localized solar source region, and find rms angular spreads of about 20 – 60 degrees. In the second instance, we use the model to estimate the size of the source regions from which field lines observed at 1 au may have originated, thus quantifying the uncertainty in calculations of magnetic connectivity; the angular uncertainty is estimated to be about 20 degrees. Finally, we estimate the filamentation distance, i.e., the heliocentric distance up to which field lines originating in magnetic islands can remain strongly trapped in filamentary structures. We emphasize the key role of slab-like fluctuations in the transition from filamentary to more diffusive transport at greater heliocentric distances. This research has been supported in part by grant RTA6280002 from Thailand Science Research and Innovation and the Parker Solar Probe mission under the ISOIS project (contract NNN06AA01C) and a subcontract to University of Delaware from Princeton University (SUB0000165).  MLG acknowledges support from the Parker Solar Probe FIELDS MAG team.  Additional support is acknowledged from the  NASA LWS program  (NNX17AB79G) and the HSR program (80NSSC18K1210 & 80NSSC18K1648).

How to cite: Ruffolo, D., Chhiber, R., Matthaeus, W. H., Usmanov, A. V., Tooprakai, P., Chuychai, P., and Goldstein, M. L.: Random Walk and Trapping of Interplanetary Magnetic Field Lines: Global Simulation, Magnetic Connectivity, and Implications for Solar Energetic Particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3719,, 2021.

EGU21-134 | vPICO presentations | ST1.2

The Unusual Widespread Solar Energetic Particle Event on 2013 August 19: Solar origin, CME-driven shock evolution and particle longitudinal distribution

Laura Rodríguez-García, Raúl Gómez-Herrero, Yannis Zouganelis, Laura Balmaceda, Teresa Nieves-Chinchilla, Nina Dresing, Mateja Dumbovic, Nariaki Nitta, Fernando Carcaboso, Luiz Fernando Guedes dos Santos, Lan Jian, Leila Mays, David Williams, and Javier Rodríguez-Pacheco

Context: Late on 2013 August 19, STEREO-A, STEREO-B, MESSENGER, Mars Odyssey, and L1 spacecraft, spanning a longitudinal range of 222° in the ecliptic plane, observed an energetic particle flux increase. The widespread solar energetic particle (SEP) event was associated with a coronal mass ejection (CME) that came from a region located near the far-side central meridian from Earth's perspective. The CME appeared to consist of two eruptions, and was accompanied by a ~M3 flare as a post-eruption arcade, and low-frequency (interplanetary) type II and shock-accelerated type III radio bursts.

Aims: The main objectives of this study are two, disentangling the reasons of the different intensity-time profiles observed by MESSENGER and STEREO-A, longitudinally separated by only 15°, and unravelling the single solar source related with the SEP event.

Results: The solar source associated with the widespread SEP event is the shock driven by the two-stages CME, as the flare observed as a posteruptive arcade is too late to explain the estimated particle onset. The different intensity-time profiles observed by STEREO-A, located at 0.97 au, and MESSENGER, at 0.33 au, can be interpreted as enhanced particle scattering beyond Mercury's orbit. The longitudinal extent of the shock does not explain by itself the wide spread of particles in the heliosphere. The particle increase observed at L1 may be attributed to cross-field diffusion transport, and this is also the case for STEREO-B, at least until the spacecraft is eventually magnetically connected to the shock at ~0.6 au. The CME-driven shock may have suffered distortion in its evolution in the heliosphere, such that the shock flank overtakes the shock nose at 1 au.

How to cite: Rodríguez-García, L., Gómez-Herrero, R., Zouganelis, Y., Balmaceda, L., Nieves-Chinchilla, T., Dresing, N., Dumbovic, M., Nitta, N., Carcaboso, F., dos Santos, L. F. G., Jian, L., Mays, L., Williams, D., and Rodríguez-Pacheco, J.: The Unusual Widespread Solar Energetic Particle Event on 2013 August 19: Solar origin, CME-driven shock evolution and particle longitudinal distribution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-134,, 2021.

The influence of the heliospheric current sheet (HCS) on the propagation of high energy solar protons is explored using 3D test particle modelling. The test particle model, which includes drift effects, is used to simulate specific past ground level enhancement (GLE) events which cover a range of HCS configurations. For example, the effects of a source location close to and far from the HCS for events both poorly and well-connected to Earth are examined. Similarly, the effect of the Earth’s location relative to the HCS is explored. The modelling is performed for high energy (300-1200 MeV) protons to represent the energetic conditions under which GLEs occur. The derived intensity profiles at 1AU are compared to observations from HEPAD onboard GOES, as well as STEREO (at locations away from Earth) and neutron monitor data. 

How to cite: Waterfall, C. and Dalla, S.: Role of the heliospheric current sheet in high energy proton transport through modelling of historic GLE events , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6223,, 2021.

EGU21-8189 | vPICO presentations | ST1.2

A self-consistent simulation of proton acceleration and transport near a high-speed solar wind stream

Nicolas Wijsen, Evangelia Samara, Àngels Aran, David Lario, Jens Pomoell, and Stefaan Poedts

Solar wind stream interaction regions (SIRs)  are often characterised by energetic ion enhancements. The mechanisms accelerating these particles as well as the locations where the acceleration occurs, remains debated. Here, we report the findings of a simulation of a SIR-event observed by Parker Solar Probe at 0.56 au and the Solar Terrestrial Relations Observatory-Ahead at 0.96 au in September 2019 when both spacecraft were approximately radially aligned with the Sun. The simulation reproduces the solar wind configuration and the energetic particle enhancements observed by both spacecraft. Our results show that the energetic particles are produced at the compression waves associated with the SIR and that the suprathermal tail of the solar wind is a good candidate to provide the seed population for particle acceleration. The simulation confirms that the acceleration process does not require shock waves and can already commence within Earth's orbit, with an energy dependence on the precise location where particles are accelerated. The three-dimensional configuration  of the solar wind streams strongly modulates the energetic particle distributions, illustrating the necessity of advanced models to understand  these particle events.

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0).


How to cite: Wijsen, N., Samara, E., Aran, À., Lario, D., Pomoell, J., and Poedts, S.: A self-consistent simulation of proton acceleration and transport near a high-speed solar wind stream, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8189,, 2021.

EGU21-10734 | vPICO presentations | ST1.2

Solar Energetic Electron Events Associated with Hard X-ray Flares 

Wen Wang, Linghua Wang, Sam Krucker, Glenn M. Mason, Yang Su, and Radoslav Bucik

We investigate 16 solar energetic electron (SEE) events measured by WIND/3DP with a double power-law spectrum and the associated western hard X-ray (HXR) flares measured by RHESSI with good count statistics, from 2002 February to 2016 December. In all 16 cases, the presence of an SEE power-law spectrum extending down to 65 keV at 1 AU implies that the SEE source would be high in the corona, at a heliocentric distance of >1.3 solar radii, while the footpoint or footpoint-like emissions shown in HXR images suggest that the observed HXRs are likely produced mainly by thick target bremsstrahlung processes very low in the corona. We find that in 8 cases (the other 8 cases), the power-law spectral index of HXR-producing electrons, estimated under the relativistic thick-target bremsstrahlung model, is significantly larger than (similar to) the observed high-energy spectral index of SEEs, with a positive correlation. In addition, the estimated number of SEEs is only 10-4 - 10-2 of the estimated number of HXRproducing electrons at energies above 30 keV, but also with a positive correlation. These results suggest that in these cases, SEEs are likely formed by upward-traveling electrons from an acceleration source high in the corona, while their downward-traveling counterparts may undergo a secondary acceleration before producing HXRs via thick-target bremsstrahlung processes. In addition, the associated 3He=4He ratio is positively correlated with the observed high-energy spectral index of SEEs, indicating a possible relation of the 3He ion acceleration with high-energy SEEs

How to cite: Wang, W., Wang, L., Krucker, S., Mason, G. M., Su, Y., and Bucik, R.: Solar Energetic Electron Events Associated with Hard X-ray Flares , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10734,, 2021.

EGU21-9543 | vPICO presentations | ST1.2

Connecting solar flare hard X-ray spectra to in-situ electron spectra using RHESSI and STEREO/SEPT observations

Nina Dresing, Alexander Warmuth, Frederic Effenberger, Ludwig Klein, Lindsay Glesener, Sophie Musset, and Maximilian Bruedern

In-situ observations of solar energetic particle events are determined by a combination of acceleration, injection, and transport processes which are often hard to disentangle. However, the energy spectrum of impulsive electron events is believed to carry the imprint of the flare acceleration process which can be studied by analyzing the hard X-ray (HXR) spectrum of the flare.

Using STEREO/SEPT electron data of the whole STEREO mission we have identified 64 solar energetic electron event candidates where the HXR solar counterpart of the event was observed by RHESSI. After cleaning of the data set and an independent verification by the timing of associated interplanetary type III radio bursts, we find 17 events which lend themselves for a comparison of the spectral indices observed in situ and at the Sun.

Special attention is paid to the choice of the in-situ electron spectral index used for comparison as most of the events show spectral transitions (breaks) in the measurement range of SEPT. We find that both the lower and higher spectral indices correlate similarly well with the HXR spectra yielding correlation coefficients of 0.8 but indicating opposite relations with the flare spectrum in terms of the thin- or thick target model. The correlations show no dependence on the electron onset delay, nor on the longitudinal separation between flare and spacecraft magnetic footpoint at the Sun. However, the correlations increase, if only events with significant anisotropy are used indicating that transport effects play a role in shaping the spectra observed in-situ. We will discuss the different transport effects that need to be taken into account and which may even lead to a vanishing imprint of the flare acceleration.

How to cite: Dresing, N., Warmuth, A., Effenberger, F., Klein, L., Glesener, L., Musset, S., and Bruedern, M.: Connecting solar flare hard X-ray spectra to in-situ electron spectra using RHESSI and STEREO/SEPT observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9543,, 2021.

Solar type III radio bursts contain a wealth of information about the dynamics of near-relativistic electron beams in the solar corona and the inner heliosphere; this information is currently unobtainable through other means.  Whilst electron beams expand along their trajectory, the motion of different regions of an electron beam (front, middle, and back) had never been systematically analysed before.  Using LOw Frequency ARray (LOFAR) observations between 30-70 MHz of type III radio bursts, and kinetic simulations of electron beams producing derived type III radio brightness temperatures, we explored the expansion as electrons propagate away from the Sun.  From relatively moderate intensity type III bursts, we found mean electron beam speeds for the front, middle and back of 0.2, 0.17 and 0.15 c, respectively.  Simulations demonstrated that the electron beam energy density, controlled by the initial beam density and energy distribution have a significant effect on the beam speeds, with high energy density beams reaching front and back velocities of 0.7 and 0.35 c, respectively.  Both observations and simulations found that higher inferred velocities correlated with shorter FWHM durations of radio emission at individual frequencies.  Our radial predictions of electron beam speed and expansion can be tested by the upcoming in situ electron beam measurements made by Solar Orbiter and Parker Solar Probe.

How to cite: Reid, H. and Kontar, E.: Nonrelativistic electron beam expansion in the solar corona/wind  and their type III radio bursts observed with LOFAR, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11109,, 2021.

EGU21-10101 | vPICO presentations | ST1.2

Detection of stratospheric X-rays with a novel microscintillator sensor

Karen Aplin, Graeme Marlton, Victoria Race, and Clare Watt

A new energetic particle detector based on a 1 cm3 CsI(Tl) scintillator crystal responds to both particle count and energy. This offers increased measurement capability over the long-established Geiger counter technology for investigating the role of energetic particles in the atmosphere during meteorological radiosonde flights. Here we present results from three flights over the UK in 2017-18 where the detector was flown alongside Geiger counters to test its capability for measuring ionising radiation in the atmosphere. Operation of the microscintillator detector was verified by both it and the Geiger counters showing the anticipated Regener-Pfotzer maximum at around 17km. Unexpectedly however, two of the flights also detected lower energy signals at 10-100 keV. Laboratory experiments investigating the thermal response of the microscintillator, in combination with careful error analysis, can be used to show that the signals detected do not originate from instrument artefacts, and are statistically significant. These are most likely to be stratospheric X rays, usually associated with bremsstrahlung radiation generated by precipitating electrons from the radiation belts.

How to cite: Aplin, K., Marlton, G., Race, V., and Watt, C.: Detection of stratospheric X-rays with a novel microscintillator sensor, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10101,, 2021.

EGU21-7498 | vPICO presentations | ST1.2

The effect of Forbush decreases on the polar-night HOx concentration

Irina Mironova

It is well-known that energetic particle precipitations during solar proton events increase ionization rates in the middle atmosphere enhancing the production of hydrogen oxide radicals (HOx) involved in the catalytic ozone destruction cycle. There are many studies where the contribution of energetic particles to the formation of hydrogen oxide radicals and ozone loss has been widely investigated. However, until now, there was no solid evidence that the reduction in galactic cosmic ray fluxes during a magnetic storm, known as Forbush-effect, directly and noticeably affects the polar-night stratospheric chemistry.
Here, the impact of the Forbush decrease on the behaviour of hydrogen oxide radicals was explored using the chemistry-climate model SOCOL.
We found that hydrogen oxide radical lost about half of its concentration over the polar boreal night stratosphere owing to a reduction in ionization rates caused by Forbush decreases after solar proton events occurred on 17 and 20 of January 2005. A robust response in ozone was not found. There is not any statistically significant response in (NOx) on Forbush decrease events as well as over summertime in the southern polar region.
The results of this study can be used to increase the veracity of ozone loss estimation if stronger Forbush events can have a place.

Reference: Mironova I, Karagodin-Doyennel A and Rozanov E (2021) , The effect of Forbush decreases on the polar-night HOx concentration affecting stratospheric ozone. Front. Earth Sci. 8:618583. doi: 10.3389/feart.2020.618583

The study was supported by the Russian Science Foundation grant (RSF project No. 20-67-46016).

How to cite: Mironova, I.: The effect of Forbush decreases on the polar-night HOx concentration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7498,, 2021.

EGU21-858 | vPICO presentations | ST1.2

The Effect of Forbush Decreases on Atmospheric Aerosols and Clouds from The PATMOS-x Satellite from 1978 to 2018

Haruka Matsumoto, Henrik Svensmark, and Martin Enghoff

The solar system is constantly changing, and it is important for us to understand how our climate and weather changes in response to the solar activity during both long-time scales (e.g. the 11-year solar cycle) and short time scales (e.g. days to weeks during For-bush Decreases (FDs)). Solar variability causes a corresponding modulation of the incident number of cosmic rays in Earth's atmosphere. Previous work by [Veretenenko and Pudovkin, 1997], [Svensmark and Friis-Christensen, 1997], [Palle Bago and Butler, 2000], [Svensmark et al., 2016], [Harrison and Ambaum, 2010], and other researchers have discussed this cause-effect relationship from an experimental and theoretical approach. Since the 1970s, global observations of the Earth's system by satellites are offering an invaluable source of information about cloud parameters.

In this study, we used the newly calibrated PATMOS-x (Pathfinder Atmospheres Extended) data set during the period from 1978 to the present. A method for capturing the connection between cosmic rays and meteorological measurements has been conducted by superposition analysis of FD events for time series (36 days) and the Monte Carlo bootstrap test to evaluate significance level of the integrated signal for 9 days after the minimum in FD. We have reviewed results, primarily about cloud emissivity (Achieved Significance Level (ASL >99%), surface brightness temperature (ASL >99%), and cloud fraction (ASL >99%). Some of the results support the proposed relationship between solar activity and temperature. This result indicates that the amount of incident cosmic rays decreases due to FDs, global average temperature increases [Friis-Christensen and Lassen, 1991], [Harrison and Ambaum, 2010]. In addition, PATMOS-x parameters of cloud probability, cloud mask, and cloud fraction, which all means cloud coverage on the Earth shows statistically significant signals following FDs. In some previous research, IR-detected cloud fraction from International Satellite Cloud Climate Project (ISCCP) and combined liquid and ice cloud fraction, effective emissivity from the Moderate Resolution Imaging Spectroradiometer (MODIS) also show connection with FDs, see [Svensmark et al., 2009], [Svensmark et al., 2016], [Marsh and Svensmark, 2000a], Todd and Kniveton [2004]. The relationship between the observed changes in cloud amount and the resulting solar forcing is discussed. On the other hand, “Cloud water content" from Special Sensor Microwave Imager (SSM/I), “Liquid water path", and “Optical thickness" from MODIS also showed as significant signals by FDs, see [Svensmark et al., 2009], [Svensmark et al., 2016], however a similar parameter about “optical thickness" and “integrated total cloud water over whole column g/m2" from PATMOS-x dataset does not have high significant signals by a bootstrap test with ASL of 77.03 and 92.51% respectively. Moreover, significant results are reported for several new cloud parameters from the PATMOS-x dataset (e.g. cloud type, brightness temperature, measurements by different wavelength 0.65, 0.86, 3.75, 11.0, and 12.0 μm and others) and Fu-Liou model is used for estimation of changed radiations in the atmosphere. An interaction between CCN and radiation has not been investigated well yet. It is necessary to still more to learn about these results for further understanding of Earth’s atmosphere.

How to cite: Matsumoto, H., Svensmark, H., and Enghoff, M.: The Effect of Forbush Decreases on Atmospheric Aerosols and Clouds from The PATMOS-x Satellite from 1978 to 2018, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-858,, 2021.

EGU21-3376 | vPICO presentations | ST1.2

Influence of energetic particle precipitation on polar vortex mediated by planetary wave activity

Timo Asikainen, Antti Salminen, Ville Maliniemi, and Kalevi Mursula

The northern polar vortex experiences considerable inter-annual variability, which is also reflected to tropospheric weather. Recent research has established a link between polar vortex variations and energetic electron precipitation (EEP) from the near-Earth space into the polar atmosphere, which is mediated by EEP-induced chemical changes causing ozone loss in the mesosphere and stratosphere. However, the most dramatic changes in the polar vortex are due to strong enhancements of planetary wave activity, which typically result in a sudden stratospheric warming (SSW), a momentary breakdown of the polar vortex. Here we use the SSWs as an indicator of high planetary wave activity and consider their influence of SSWs on the atmospheric response to EEP in 1957-2017 using combined ERA-40 and ERA-Interim re-analysis data and geomagnetic activity as a proxy of EEP. We find that the EEP-related enhancement of the polar vortex and other associated dynamical responses are seen only during winters when a SSW occurs, and that the EEP-related changes take place slightly before the SSW onset. We show that the atmospheric conditions preceding SSWs favor enhanced wave-mean-flow interaction, which can dynamically amplify the initial polar vortex enhancement caused by ozone loss. These results highlight the importance of considering SSWs and sufficient level of planetary wave activity as a necessary condition for observing the effects of EEP on the polar vortex dynamics.

How to cite: Asikainen, T., Salminen, A., Maliniemi, V., and Mursula, K.: Influence of energetic particle precipitation on polar vortex mediated by planetary wave activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3376,, 2021.

EGU21-15895 | vPICO presentations | ST1.2

The Atmospheric Ionization during Substorm Model

Olesya Yakovchuk and Jan Maik Wissing

The Atmospheric Ionization during Substorm Model (AISstorm) is the successor of the Atmospheric Ionization Module Osnabrück (AIMOS) and thus may also be considered as AIMOS 2.0 - AISStorm.

The overall structure was kept mostly unaltered and splits up into an empirical model that determines the 2D precipitating particle flux and a numerical model that determines the ionization profile of single particles. The combination of these two results in a high resolution 3D particle ionization pattern.

The internal structure of the model has been completely revised with the main aspects being: a) an internal magnetic coordinate system, b) including substorms characteristics, c) higher time resolution, d) higher spatial resolution, e) energy specific separate handling of drift loss cone, auroal precipitation and polar cap precipitation, partly even in separate coordinate systems, f) better MLT resolution and g) covering a longer time period. All these tasks have been matched while keeping the output data format identical, allowing easy transition to the new version.

How to cite: Yakovchuk, O. and Wissing, J. M.: The Atmospheric Ionization during Substorm Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15895,, 2021.

EGU21-2362 | vPICO presentations | ST1.2

The Mansurov Effect: Real or a statistical artefact?

Jone Edvartsen, Ville Maliniemi, Hilde Tyssøy, Timo Asikainen, and Spencer Hatch

The Mansurov Effect is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit, which is further hypothesized to impact the polar troposphere through cloud generation processes. In this paper we investigate the connection between IMF By-component and polar surface pressure by using daily ERA5 reanalysis for geopotential height since 1980. Previous studies have shown to produce a significant 27-day cyclic response during solar cycle 23. However, when appropriate statistical tests are applied, the correlation is not significant at the 95% level. Our results also show that data from three other solar cycles, which have not been investigated before, produce similar cyclic responses as during solar cycle 23, but with seemingly random offset in the timing of the signal. We examine the origin of the cyclic pattern occurring in the super epoch/lead lag regression methods commonly used to support the Mansurov hypothesis in all recent papers, as well as other phenomena in this community. By generating random normally distributed noise with different levels of temporal autocorrelation, and using the real IMF By-index as forcing, we show that the methods applied to support the Mansurov hypothesis up to now, are highly susceptible, as cyclic patterns always occurs as artefacts of the methods. This, in addition to the lack of significance, suggests that there is no adequate evidence in support of the Mansurov Effect.

How to cite: Edvartsen, J., Maliniemi, V., Tyssøy, H., Asikainen, T., and Hatch, S.: The Mansurov Effect: Real or a statistical artefact?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2362,, 2021.

ST1.3 – First results from the Solar Orbiter mission

EGU21-2981 | vPICO presentations | ST1.3 | Highlight

The Solar Orbiter mission – Exploring the Sun and heliosphere

Daniel Mueller, Yannis Zouganelis, Teresa Nieves-Chinchilla, and Chris St. Cyr

Solar Orbiter, launched on 10 February 2020, is a space mission of international collaboration between ESA and NASA. It is exploring the linkage between the Sun and the heliosphere and has started to collect unique data at solar distances down to 0.49 AU. By ultimately approaching as close as 0.28 AU, Solar Orbiter will view the Sun with very high spatial resolution and combine this with in-situ measurements of the surrounding heliosphere. Over the course of the mission, the highly elliptical orbit will get progressively more inclined to the ecliptic plane. Thanks to this new perspective, Solar Orbiter will deliver images and comprehensive data of the unexplored Sun’s polar regions and the side of the Sun not visible from Earth. This talk will highlight first science results from Solar Orbiter and provide a mission status update.

How to cite: Mueller, D., Zouganelis, Y., Nieves-Chinchilla, T., and St. Cyr, C.: The Solar Orbiter mission – Exploring the Sun and heliosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2981,, 2021.

EGU21-15792 | vPICO presentations | ST1.3 | Highlight

First Results from Solar Orbiter’s Energetic Particle Detector

Javier Rodriguez-Pacheco and the EPD Team

In this presentation, we will show the first measurements performed by EPD since the end of the commissioning phase until the latest results obtained. During these months EPD has been scanning the inner heliosphere at different heliocentric distances and heliolongitues allowing - together with other spacecraft - to investigate the spatio-temporal behavior of the particle populations in the inner heliosphere during solar minimum conditions. Solar Orbiter was launched from Cape Canaveral on February 10th, 2020, thus beginning the journey to its encounter with the Sun. Solar Orbiter carries ten scientific instruments, six remote sensing and four in situ, that will allow the mission main goal: how the Sun creates and controls the heliosphere. Among the in situ instruments, the Energetic Particle Detector (EPD) measures electrons, protons and heavy ions with high temporal resolution over a wide energy range, from suprathermal energies up to several hundreds of MeV/nucleon.

How to cite: Rodriguez-Pacheco, J. and the EPD Team: First Results from Solar Orbiter’s Energetic Particle Detector, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15792,, 2021.

EGU21-5927 | vPICO presentations | ST1.3

The Energetic Particle Detector (EPD) Electron-Proton Telescope (EPT) on Solar Orbiter: In-flight calibration and background correction of science data.

Daniel Pacheco, Alexander Kollhoff, Robert F. Wimmer-Schweingruber, Johan L. Freiherr von Forstner, Christoph Terasa, Robert Elftmann, Sebastian Boden, Lars Berger, Sandra Eldrum, Zigong Xu, Javier Rodríguez-Pacheco, George Ho, and Raúl Gómez-Herrero and the The EPD Team

Solar Orbiter was launched in February 2020 carrying the most complete set of in-situ and remote sensing instruments, for the study of the Sun and the heliosphere. The Energetic Particle Detector (EPD) on board of Solar Orbiter was switched on on 28 February 2020 and, since then, it has provided us with measurements of the energetic particles traveling through the inner heliosphere. The EPD suite is composed of a set of different sensors measuring electrons, protons and ions in a wide range of energies.

The Electron-Proton Telescope (EPT) was designed to measure electrons and ions with energies of 35-4000keV and 45-7000keV respectively. By utilizing the so-called magnet/foil-technique, EPT is capable of measuring energetic particles with a high temporal and energy resolution while obtaining directional information from its four different fields of view. Although EPT is well suited for the study of solar energetic particle events, instrumental effects such as the contamination of EPT data products by GCR particles need to be understood for a correct interpretation of the data.

We will present our current understanding of the background and calibration of EPT based on the data gathered during the first year of Solar Orbiter’s mission.

How to cite: Pacheco, D., Kollhoff, A., Wimmer-Schweingruber, R. F., von Forstner, J. L. F., Terasa, C., Elftmann, R., Boden, S., Berger, L., Eldrum, S., Xu, Z., Rodríguez-Pacheco, J., Ho, G., and Gómez-Herrero, R. and the The EPD Team: The Energetic Particle Detector (EPD) Electron-Proton Telescope (EPT) on Solar Orbiter: In-flight calibration and background correction of science data., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5927,, 2021.

EGU21-15152 | vPICO presentations | ST1.3

The Energetic Particle Detector (EPD) Electron-Proton Telescope (EPT) on Solar Orbiter: First Data

Alexander Kollhoff, Daniel Pacheco, Robert F. Wimmer-Schweingruber, Johan von Forstner, Lars Berger, Sandra Eldrum, Zigong Xu, Bernd Heber, Javier Rodriguez-Pacheco, and George Ho and the EPD team

Solar Orbiter’s Energetic Particle Detector (EPD) was commissioned in early 2020 and has since been returning data from the inner heliosphere. Despite the low activity in the current deep and extended solar minimum, EPD has observed a number of solar particle events and numerous other enhancements of energetic particles. As one of the four complementary EPD sensors, the Electron-Proton Telescope (EPT) covers the gap between the high and low particle-energy measurements of HET and STEP. With four double-ended telescopes, EPT is capable of measuring electrons and ions in an energy range of 35-400keV and 45-7000keV respectively, while providing anisotropy information from four different viewing directions.

We will present a first overview of EPT measurements, exhibiting some of the EPT data products which are made available by the European Space Agency (ESA).

In order to provide the community a deep insight into the data, we will go through different aspects of the measurements, including the current status of the intercalibration with the other EPD instruments.

How to cite: Kollhoff, A., Pacheco, D., Wimmer-Schweingruber, R. F., von Forstner, J., Berger, L., Eldrum, S., Xu, Z., Heber, B., Rodriguez-Pacheco, J., and Ho, G. and the EPD team: The Energetic Particle Detector (EPD) Electron-Proton Telescope (EPT) on Solar Orbiter: First Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15152,, 2021.

EGU21-6776 | vPICO presentations | ST1.3

The High Energy Telescope (HET) on the SolarOrbiter Mission: Overview and First Data

Zigong Xu, Johan L. Freiherr von Forstner, Patrick Kühl, Nils Janitzek, César Martín, Shrinivasrao R. Kulkarni, Stephan I. Böttcher, Robert F. Wimmer-Schweingruber, Javier Rodríguez-Pacheco, Glenn M. Mason, and George C. Ho and the Solar Orbiter EPD team

As part of the Energetic Particle Detector (EPD) suite onboard Solar Orbiter, the High Energy Telescope has been launched on its mission to the Sun on February 9, 2020, and has been measuring energetic particles since it was first switched on about two weeks after launch. Using their double-ended telescopes, the two HET units provide measurements of ions above 7 MeV/nuc and electrons above 300 keV in four viewing directions. HET observed several Solar Energetic Particle (SEPs) events during the cruise phase, including the first one with a broad energy coverage (up to ~100MeV) on 29 Nov 2020. Being the first larger SEP event in a phase of rising solar activity, these measurements have already attracted extensive attention of the community. Apart from the SEPs, the HET can be used to observe the Galactic cosmic radiation (GCR) and its temporal variation. The GCR measurements can be also utilized for the validation of the energy response of HET. The overall spectra observed by HET are as expected, except for calibration issues in some specific energy bins that we are still investigating. Finally, the HET also observed several Forbush Decreases (FD), i.e. cosmic ray decreases caused by CMEs and their embedded magnetic field. Here, the capabilities and data products of HET, as well as first measurements of SEPs, GCR and FDs are presented. 

How to cite: Xu, Z., Freiherr von Forstner, J. L., Kühl, P., Janitzek, N., Martín, C., Kulkarni, S. R., Böttcher, S. I., Wimmer-Schweingruber, R. F., Rodríguez-Pacheco, J., Mason, G. M., and Ho, G. C. and the Solar Orbiter EPD team: The High Energy Telescope (HET) on the SolarOrbiter Mission: Overview and First Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6776,, 2021.

EGU21-13329 | vPICO presentations | ST1.3

First solar electron events observed by EPD aboard Solar Orbiter

Raúl Gómez-Herrero, Daniel Pacheco, Alexander Kollhoff, Francisco Espinosa Lara, Johan L. Freiherr von Forstner, Nina Dresing, David Lario, Laura Balmaceda, Vratislav Krupar, Olga E. Malandraki, Angels Aran, Radoslav Bucik, Andreas Klassen, Karl-Ludwig Klein, Ignacio Cernuda, Sandra Eldrum, Hamish Reid, John G. Mitchell, Glenn M. Mason, and George C. Ho and the Solar Orbiter EPD/RPW/MAG/SWA Teams

The first solar electron events detected by Solar Orbiter were observed by the Energetic Particle Detector (EPD) suite during July 11-23, 2020, when the spacecraft was at heliocentric distances between 0.61 and 0.69 au. We combined EPD electron observations from 4 keV to the relativistic range (few MeV), radio dynamic spectra and extreme ultraviolet (EUV) observations from multiple spacecraft in order to identify the solar origin of these electron events. Electron anisotropies and timing as well as the plasma and magnetic field environment were evaluated to characterize the interplanetary transport conditions. We found that all the electron events were clearly associated with type III radio bursts. EUV jets were also found in association with all of them except one. A diversity of time profiles and pitch-angle distributions (ranging from almost isotropic to beam-like) was observed. These observations indicate that different source locations and different magnetic connectivity and transport conditions were likely involved. The broad spectral range covered by EPD with excellent energy resolution and the high time cadence ensure that future observations close to the Sun will contribute to the understanding of the acceleration, release, and transport processes of energetic particles. EPD observations will play a key role in the identification of the sources of impulsive events and the links between the near-relativistic electrons and the ion populations enriched in 3He and heavy ions


How to cite: Gómez-Herrero, R., Pacheco, D., Kollhoff, A., Espinosa Lara, F., Freiherr von Forstner, J. L., Dresing, N., Lario, D., Balmaceda, L., Krupar, V., Malandraki, O. E., Aran, A., Bucik, R., Klassen, A., Klein, K.-L., Cernuda, I., Eldrum, S., Reid, H., Mitchell, J. G., Mason, G. M., and Ho, G. C. and the Solar Orbiter EPD/RPW/MAG/SWA Teams: First solar electron events observed by EPD aboard Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13329,, 2021.

EGU21-15864 | vPICO presentations | ST1.3

The low-energy ion event on 2020 June 19 measured by Solar Orbiter

Angels Aran, Daniel Pacheco, Monica Laurenza, Nicolas Wijsen, Evangelia Samara, David Lario, Laura Balmaceda, Johan L. Freiherr von Forstner, Simone Benella, Luciano Rodriguez, and Raúl Gómez-Herrero and the The low-energy ion event on 2020 June 19 study Team

Shortly after reaching the first perihelion, the Energetic Particle Detector (EPD) onboard Solar Orbiter measured a low-energy (<1 MeV/nuc) ion event whose duration varied with the energy of the particles. The increase above pre-event intensity levels was detected early on June 19 for ions in the energy range from ~50 keV to ~1 MeV and lasted up to ~12:00 UT on June 20. In the energy range from ~10 keV to < 40 keV, the ion event spanned from June 18 to 21. This latter low-energy ion intensity enhancement coincided with a two-step Forbush decrease (FD) as displayed in the EPD > 17 MeV/nuc ion measurements. On the other hand, no electron increases were detected. As seen from 1 au, there is no clear evidence of solar activity from the visible disk that could be associated with the origin of this ion event. We hypothesize about the origin of this event as due to either a possible solar eruption occurring behind the visible part of the Sun or to an interplanetary spatial structure. We use interplanetary magnetic field data from the Solar Orbiter Magnetometer (MAG), solar wind electron density derived from measurements of the Solar Orbiter Radio and Plasma Waves (RPW) instrument to specify the in-situ solar wind conditions where the ion event was observed. In addition, we use solar wind plasma measurements from the Solar Orbiter Solar Wind Analyser (SWA) suite gathered during the following solar rotation, for comparison purposes. In order to seek for possible associated solar sources, we use images from the Extreme Ultraviolet Imager (EUI) instrument onboard Solar Orbiter. Together with the lack of electron observations and Type III radio bursts, the simultaneous response of the ion intensity-time profiles at various energies indicates an interplanetary source for the particles. The two-step FD shape observed during this event suggests that the first step early on June 18 was due to a transient structure, whereas the second step on June 19, together with the ~50 –1000 keV/nuc ion enhancement, was due to a solar wind stream interaction region. The observation of a similar FD in the next solar rotation favours this interpretation, although a more complex structure cannot be discarded due to the lack of concurrent solar wind temperature and velocity observations.

Different parts of this research have received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870405 (EUHFORIA 2.0) and grant agreement No 01004159 (SERPENTINE).

How to cite: Aran, A., Pacheco, D., Laurenza, M., Wijsen, N., Samara, E., Lario, D., Balmaceda, L., von Forstner, J. L. F., Benella, S., Rodriguez, L., and Gómez-Herrero, R. and the The low-energy ion event on 2020 June 19 study Team: The low-energy ion event on 2020 June 19 measured by Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15864,, 2021.

EGU21-12501 | vPICO presentations | ST1.3 | Highlight

Early Observations from the Solar Orbiter SWA/Electron Analyser System

Christopher Owen and the the International SWA, MAG and RPW teams.

Solar Orbiter carries a total of 10 instrument suites making up the payload for the mission.  One of these, the Solar Wind Analyser (SWA) instrument, is comprised of 3 sensor units which are together served by a central DPU unit.  Of particular focus in this presentation are the early measurements from one of these sensors, the Electron Analyser System (EAS).  EAS is a dual-head, top-hat electrostatic analyser system that is capable of making 3D measurements of solar wind electrons at energies below ~5 keV from a vantage point at the end of a 4-metre boom extending into the shadow of the spacecraft.  The sensor was accommodated in this location to both maximise the unobstructed field of view and to minimise the effect of spacecraft related disturbances on the low-energy (less than a few tens of eV) electrons expected the core population of the solar wind.

To date the SWA instrument sensors have operated sporadically during the mission cruise phase, which began in June 2020.  This is due to a number of operational issues faced by the SWA team, which mean we have not been able to take data in a continuous manner.  However, the data that has been taken shows the clear promise of the SWA measurements, in general, once these issues can be overcome.  For example, EAS is using a novel sample steering mechanism in burst mode which, with reference to a magnetic field vector shared onboard by the MAG instrument, allows the capture of the electron pitch angle distribution at unusually high time resolution.  We discuss these observations here, and illustrate the potential science returns from the burst mode.  We also present results from the new EAS observations in the vicinity of reconnecting current sheets in the solar wind, to more generally illustrate the capability of the sensor. 

How to cite: Owen, C. and the the International SWA, MAG and RPW teams.: Early Observations from the Solar Orbiter SWA/Electron Analyser System, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12501,, 2021.

EGU21-12435 | vPICO presentations | ST1.3

Updates and Early Results from the Heavy Ion Sensor on Solar Orbiter

Susan T. Lepri, Stefano A. Livi, Jim M. Raines, Antoinette B. Galvin, Lynn M. Kistler, Ryan M. Dewey, Benjamin L. Alterman, Frederic Allegrini, Michael R. Collier, and Christopher J. Owen


The Solar Orbiter mission was launched in 2020 into an orbit that will explore the inner heliosphere. During its orbit, periods of quasi-corotation with the Sun will enable determination of the source regions on the Sun for solar wind structures.  The Solar Wind Analyser (SWA) is a suite of instruments that provide in-situ measurements of solar wind electrons, protons, alpha particles, and heavy ions.  The SWA-Heavy Ion Sensor (HIS) is optimized to measure heavy ions in the solar wind, pickup ions, and suprathermal ions in an energy range spanning from 0.5- 75keV/e.  We present measurements of heavy ion composition from SWA-HIS taken during the cruise phase of the mission to highlight the capabilities of the instrument and the observations we expect to collect over the next 10 years. We discuss how SWA-HIS will enable linkages between the Sun and the solar wind to reveal the nature of the acceleration and release of the solar wind and the sources and structure of the solar wind.  We will also provide an overview of the available data and accessibility of the public datasets. 

How to cite: Lepri, S. T., Livi, S. A., Raines, J. M., Galvin, A. B., Kistler, L. M., Dewey, R. M., Alterman, B. L., Allegrini, F., Collier, M. R., and Owen, C. J.: Updates and Early Results from the Heavy Ion Sensor on Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12435,, 2021.

EGU21-592 | vPICO presentations | ST1.3 | Highlight

Overview of interplanetary coronal mass ejections observed by Solar Orbiter, Parker Solar Probe, Bepi Colombo, Wind and STEREO-A

Christian Möstl, Andreas J. Weiss, Rachel L. Bailey, Martin A. Reiss, Tanja Amerstorfer, Jürgen Hinterreiter, Maike Bauer, Ute V. Amerstorfer, Emma E. Davies, Tim Horbury, David Barnes, Jackie A. Davies, Richard A. Harrison, Daniel Heyner, Ingo Richter, Hans-Ulrich Auster, Werner Magnes, and Wolfgang Baumjohann

We show in situ observations of ICMEs during the first year of Solar Orbiter observations based on magnetic field data from the MAG instrument in conjunction with in situ and imaging observations from the Heliospheric System Observatory. The in situ magnetic field data from four other currently active spacecraft - Parker Solar Probe, BepiColombo, STEREO-Ahead and Wind -  are also searched for ICME signatures, and all clear ICME events that could be identified by classic signatures such as elevated and rotating magnetic fields of sufficiently long durations are included in a living online catalog. Furthermore, we provide a visualization of the in situ magnetic field data alongside spacecraft positions and propagating CME fronts, which are based on modeling of STEREO-A heliospheric imager data. This allows us to identify ICME events that could be unambiguously followed from their inception on the Sun to their impact at the aforementioned spacecraft, and highlights sought-after lineup events, in which the same ICME is observed at multiple points in space, such as the well-studied 2020 April 15-20 ICME. We discuss the ICME rate observed so far, and provide an outlook on the expected ICME rate in solar cycle 25 based on different forecasts for the cycle amplitude (see Möstl et al. 2020,

How to cite: Möstl, C., Weiss, A. J., Bailey, R. L., Reiss, M. A., Amerstorfer, T., Hinterreiter, J., Bauer, M., Amerstorfer, U. V., Davies, E. E., Horbury, T., Barnes, D., Davies, J. A., Harrison, R. A., Heyner, D., Richter, I., Auster, H.-U., Magnes, W., and Baumjohann, W.: Overview of interplanetary coronal mass ejections observed by Solar Orbiter, Parker Solar Probe, Bepi Colombo, Wind and STEREO-A, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-592,, 2021.

EGU21-8878 | vPICO presentations | ST1.3

Triple-point magnetic flux rope analysis for the 2020 April 19 CME observed in situ by Solar Orbiter, Bepi Colombo, and WIND

Andreas J. Weiss, Christian Möstl, Emma Davies, Matthew J. Owens, Tanja Amerstorfer, Maike Bauer, Jürgen Hinterreiter, Rachel L. Bailey, Martin A. Reiss, Tim Horbury, Helen O'Brien, Vincent Evans, Virginia Angelini, Daniel Heyner, Ingo Richter, Uli Auster, Werner Magnes, and Wolfgang Baumjohann

We present initial results for a triple-point analysis for the in situ magnetic field measurements of a CME observed at three independent locations. On the 19th of April 2020, Solar Orbiter observed a CME in situ at a radial distance of around 0.8 au. This CME was subsequently also detected by the Wind and Bepi Colombo satellites closer to Earth. This triple in situ measurement of a CME provides us the unique opportunity to test the consistency of the measurements with our own 3D Coronal Rope Ejection (3DCORE) model. A triple measurement allows for up to seven different data combinations to be analyzed (three single-point, three dual-point, and one single triple-point combination) which gives us information on how our analysis pipeline responds to multi-point measurements and how the results change with measurements at differing radial and longitudinal distances. The goal of this study is to test whether all three in situ measurements can still be described by a slightly bent flux rope geometry and how adding additional measurements can improve the accuracy of inferred model parameters.

How to cite: Weiss, A. J., Möstl, C., Davies, E., Owens, M. J., Amerstorfer, T., Bauer, M., Hinterreiter, J., Bailey, R. L., Reiss, M. A., Horbury, T., O'Brien, H., Evans, V., Angelini, V., Heyner, D., Richter, I., Auster, U., Magnes, W., and Baumjohann, W.: Triple-point magnetic flux rope analysis for the 2020 April 19 CME observed in situ by Solar Orbiter, Bepi Colombo, and WIND, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8878,, 2021.

EGU21-4996 | vPICO presentations | ST1.3

Switchback-like structures observed by Solar Orbiter

Andrey Fedorov, Philippe Louarn, Christopher Owen, Lubomir Prech, Timothy Horbury, Alain Barthe, Alexis Rouillard, Justin Kasper, Stuart Bale, Roberto Bruno, Helen O’Brien, Vincent Evans, Virginia Angelini, Davin Larson, and Roberto Livi and the SWA-PAS, MAG, SWEAP, and FIELDS teams

During 27th September 2020 NASA Parker Solar Probe (PSP) and ESA-NASA Solar Orbiter (SolO) have been located around the same Carrington longitude and their latitudinal separation was very small as well. Solar wind plasma and magnetic field data obtained throughout this time interval  allows to consider that sometimes the solar wind, observed by both spacecrafts, originates from the same coronal hole region. Inside these time intervals the SolO radial magnetic field experiences several short variations similar to the "switchbacks" regularly observed by PSP. We used the SolO SWA-PAS proton analyzer data to analyze the ion distribution function variations inside such switchback-like events to understand if such events are really "remains" of the alfvenic structures observed below 60 Rs.

How to cite: Fedorov, A., Louarn, P., Owen, C., Prech, L., Horbury, T., Barthe, A., Rouillard, A., Kasper, J., Bale, S., Bruno, R., O’Brien, H., Evans, V., Angelini, V., Larson, D., and Livi, R. and the SWA-PAS, MAG, SWEAP, and FIELDS teams: Switchback-like structures observed by Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4996,, 2021.

EGU21-6306 | vPICO presentations | ST1.3

The solar wind angular-momentum flux observed during Solar Orbiter's first orbit

Daniel Verscharen, David Stansby, Adam Finley, Christopher Owen, Timothy Horbury, Marco Velli, Stuart Bale, Philippe Louarn, Andrei Fedorov, Roberto Bruno, Stefano Livi, Gethyn Lewis, Chandrasekhar Anekallu, Christopher Kelly, Gillian Watson, Dhiren Kataria, Helen O'Brien, Vincent Evans, and Virginia Angelini

The Solar Orbiter mission is currently in its cruise phase, during which the spacecraft's in-situ instrumentation measures the solar wind and the electromagnetic fields at different heliocentric distances. 

We evaluate the solar wind angular-momentum flux by combining proton data from the Solar Wind Analyser (SWA) Proton-Alpha Sensor (PAS) and magnetic-field data from the Magnetometer (MAG) instruments on board Solar Orbiter during its first orbit. This allows us to evaluate the angular momentum in the protons in addition to that stored in magnetic-field stresses, and compare these to previous observations from other spacecraft. We discuss the statistical properties of the angular-momentum flux and its dependence on solar-wind properties. 

Our results largely agree with previous measurements of the solar wind’s angular-momentum flux in the inner heliosphere and demonstrate the potential for future detailed studies of large-scale properties of the solar wind with the data from Solar Orbiter.

How to cite: Verscharen, D., Stansby, D., Finley, A., Owen, C., Horbury, T., Velli, M., Bale, S., Louarn, P., Fedorov, A., Bruno, R., Livi, S., Lewis, G., Anekallu, C., Kelly, C., Watson, G., Kataria, D., O'Brien, H., Evans, V., and Angelini, V.: The solar wind angular-momentum flux observed during Solar Orbiter's first orbit, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6306,, 2021.

EGU21-5247 | vPICO presentations | ST1.3

Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind

Rungployphan Kieokaew, Benoit Lavraud, David Ruffolo, William Matthaeus, Yan Yang, Julia Stawarz, Sae Aizawa, Philippe Louarn, Alexis Rouillard, Vincent Génot, Andrey Fedorov, Rui Pinto, Claire Foullon, Christopher Owen, and Timothy Horbury

The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interfaces between shear flows in plasmas. KHI is ubiquitous in plasmas and has been observed in situ at planetary interfaces and at the boundaries of coronal mass ejections in remote-sensing observations. KHI is also expected to develop at flow shear interfaces in the solar wind, but while it was hypothesized to play an important role in the mixing of plasmas and exciting solar wind fluctuations, its direct observation in the solar wind was still lacking. We report first in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind near the Heliospheric Current Sheet. We find that the observed conditions satisfy the KHI onset criterion from linear theory and the steepening of the shear boundary layer is consistent with the development of KH vortices. We further investigate the solar wind source of this event to understand the conditions that support KH growth. In addition, we set up a local MHD simulation using the empirical values to reproduce the observed KHI. This observed KHI in the solar wind provides robust evidence that shear instability develops in the solar wind, with obvious implications in the driving of solar wind fluctuations and turbulence. The reasons for the lack of previous such measurements are also discussed.

How to cite: Kieokaew, R., Lavraud, B., Ruffolo, D., Matthaeus, W., Yang, Y., Stawarz, J., Aizawa, S., Louarn, P., Rouillard, A., Génot, V., Fedorov, A., Pinto, R., Foullon, C., Owen, C., and Horbury, T.: Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5247,, 2021.

EGU21-9288 | vPICO presentations | ST1.3

The sheath region of April 2020 magnetic cloud and the associated energetic ions 

Emilia Kilpua, Simon Good, Nina Dresing, Rami Vainio, Emma Davies, Robert Forsyth, Benoit Lavraud, Daniel Heyner, Tim Horbury, Virginia Angeli, Helen O'Brien, Vincent Evans, Bob Wimmer, Javier Rodriguez-Pacheco, Raul Gomez-Herrero, and George Ho

Acceleration of energetic particles is a fundamental and ubiquitous mechanism in space and astrophysical plasmas. One of the open questions is the role of the sheath region behind the shock in the acceleration process. We analyze observations by Solar Orbiter, BepiColombo and the L1 spacecraft to explore the structure of a coronal mass ejection (CME)-driven sheath and its relation to enhancements of energetic ions that occurred on April 19-20, 2020. Our detailed analysis of the magnetic field, plasma and particle observations show that the enhancements were related to the Heliospheric Current Sheet crossings related to the reconnecting current sheets in the vicinity of the shock and a mini flux rope that was compressed at the leading edge of the CME ejecta. This study highlights the importance of smaller-scale sheath structures for the energization process. These structures likely formed already closer to the Sun and were swept and compressed from the upstream wind past the shock into the sheath. The upcoming observations by the recent missions (Solar Orbiter, Parker Solar Probe and BepiColombo) provide an excellent opportunity to explore further their role.  

How to cite: Kilpua, E., Good, S., Dresing, N., Vainio, R., Davies, E., Forsyth, R., Lavraud, B., Heyner, D., Horbury, T., Angeli, V., O'Brien, H., Evans, V., Wimmer, B., Rodriguez-Pacheco, J., Gomez-Herrero, R., and Ho, G.: The sheath region of April 2020 magnetic cloud and the associated energetic ions , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9288,, 2021.

EGU21-9712 | vPICO presentations | ST1.3

Turbulence and intermittency of electron density fluctuations in the inner heliosphere: Solar Orbiter first data.

Luca Sorriso-Valvo, Francesco Carbone, Yuri Yuri Khotyaintsev, Daniel Graham, Konrad Steinvall, and Daniele Telloni and the The Solar Orbiter RPW and MAG Teams

The recently released spacecraft potential measured by the RPW instrument onboard Solar Orbiter has been used to estimate the solar wind electron density in the inner heliosphere. Selected intervals have been extracted to study and quantify the properties of turbulence. Empirical Mode Decomposition was used to obtain the generalized marginal Hilbert spectrum, equivalent to the structure functions analysis, additionally reducing issues typical of nonstationary time series. Results show the presence of a well defined inertial range with Kolmogorov scaling. However, the turbulence shows intermittency only in part of the samples, while other intervals have homogeneous scale-dependent fluctuations. These are observed predominantly during intervals of ion-frequency wave activity. Comparisons with compressible magnetic field intermittency (from the MAG instrument) and with an estimate of the solar wind velocity (using electric and magnetic field) are also provided to provide general context and help determine the cause for the absence of intermittency.

How to cite: Sorriso-Valvo, L., Carbone, F., Yuri Khotyaintsev, Y., Graham, D., Steinvall, K., and Telloni, D. and the The Solar Orbiter RPW and MAG Teams: Turbulence and intermittency of electron density fluctuations in the inner heliosphere: Solar Orbiter first data., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9712,, 2021.

EGU21-10023 | vPICO presentations | ST1.3

Large amplitude ion-acoustic waves observed in the solar wind by the Solar Orbiter

David Pisa, Jan Soucek, Ondrej Santolik, Milan Maksimovic, Timothy Horbury, and Christopher Owen and the SolO RPW, MAG, and SWA instrument teams

Electric field observations of the Time Domain Sampler (TDS) receiver, a part of the Radio and Plasma Waves (RPW) instrument onboard Solar Orbiter, often exhibit very intense broadband emissions at frequencies below 10 kHz in the spacecraft frame. The RPW instrument has been operating almost continuously during the commissioning phase of the mission from March to May, the first perihelion in June, and through the first flyby of Venus in late December 2020. Nearly a year of observations allow us to perform a statistical study of ion-acoustic waves in the solar wind covering an interval of heliocentric distances between 0.5 AU to 1 AU. The occurrence of low-frequency waves peaks around perihelion in June at distances of 0.5 AU and decreases with increasing distances, with only a few waves detected per day in late September at ~1 AU. A more detailed analysis of triggered waveform snapshots shows the typical wave frequency at about 3 kHz and wave power about 5e-2 mV2/m2. The distribution of the relative phase between two components of the projected E-field in the Spacecraft Reference Frame (SRF) shows a mostly linear wave polarization. These waves are interpreted as strongly Doppler-shifted ion-acoustic waves, generated by solar wind ion beams and often accompany large-scale solar wind structures. A detailed analysis of the Doppler-shift using solar wind data from a Proton and Alpha particle Sensor (PAS), a part of Solar Wind Analyzer (SWA), is done for several examples.

How to cite: Pisa, D., Soucek, J., Santolik, O., Maksimovic, M., Horbury, T., and Owen, C. and the SolO RPW, MAG, and SWA instrument teams: Large amplitude ion-acoustic waves observed in the solar wind by the Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10023,, 2021.

EGU21-10238 | vPICO presentations | ST1.3

Analysis of Alfvénic flows with Solar Orbiter: particle and magnetic observations down to kinetic scales.

Philippe Louarn, Andrei fedorov, alexis Rouillard, Benoit Lavraud, Vincent Génot, Christopher J Owen, Roberto Bruno, Lubomir Prech, Stephano Livi, Timothy S Horbury, and Milan Maksimovic and the SWA and MAG Solar Orbiter

The magnetic and velocity fluctuations of the solar wind may be strongly correlated. This characterizes the  ‘Alfvenic’ flows. Using the observations of the Proton Alfa sensor (PAS/SWA) and the magnetometer (MAG) onboard Solar Orbiter, we analyze a period of 100 hours of such alfvenic flows, at different scales. Several parameters of the turbulence are computed (V-B correlation, various spectral indexes, cross-helicity, residual energy). We explore how these parameters may vary with time and characterize different turbulent states of the flow. More specifically, using the unprecedented time resolution of PAS during burst mode, especially its capability to measure 3D distribution functions at time scale below the proton gyroperiod, we study the connection of the turbulence to the dissipation domain and analyze the fine structure of the distribution functions and their evolutions at sub-second scales. The goal is to investigate whether some characteristics of the distributions, as their more or less pronounced temperature anisotropy, may be related to the turbulence parameters and the degree of V-B correlation.

How to cite: Louarn, P., fedorov, A., Rouillard, A., Lavraud, B., Génot, V., Owen, C. J., Bruno, R., Prech, L., Livi, S., Horbury, T. S., and Maksimovic, M. and the SWA and MAG Solar Orbiter: Analysis of Alfvénic flows with Solar Orbiter: particle and magnetic observations down to kinetic scales., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10238,, 2021.

EGU21-10630 | vPICO presentations | ST1.3

Solar Orbiter observations of solar wind current sheets and their deHoffman-Teller frames

Konrad Steinvall, Yuri Khotyaintsev, Giulia Cozzani, Andris Vaivads, Christopher Owen, Andrey Fedorov, and Philippe Louarn and the RPW Team, SWA Team, MAG Team

Solar wind current sheets have been extensively studied at 1 AU. The recent advent of Parker Solar Probe and Solar Orbiter (SolO) has enabled us to study these structures at a range of heliocentric distances.

We present SolO observations of current sheets in the solar wind at heliocentric distances between 0.55 and 0.85 AU, some of which show signatures of ongoing magnetic reconnection. We develop a method to find the deHoffman-Teller frame which minimizes the Y-component (the component tangential to the spacecraft orbit) of the electric field. Using the electric field measurements from RPW and magnetic field measurements from MAG, we use our method to determine the deHoffman-Teller frame of solar wind current sheets. The same method can also be used on the Alfvénic turbulence and structures found in the solar wind to obtain a measure of the solar wind velocity.

Our preliminary results show a good agreement between our modified deHoffmann-Teller analysis based on the single component E-field, and the conventional deHoffman-Teller analysis based on 3D plasma velocity measurements from PAS. This opens up the possibility to use the RPW and MAG data to obtain an estimate of the solar wind velocity when particle data is unavailable.

How to cite: Steinvall, K., Khotyaintsev, Y., Cozzani, G., Vaivads, A., Owen, C., Fedorov, A., and Louarn, P. and the RPW Team, SWA Team, MAG Team: Solar Orbiter observations of solar wind current sheets and their deHoffman-Teller frames, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10630,, 2021.

EGU21-12941 | vPICO presentations | ST1.3

Ripples in the Heliospheric Current Sheet: Dependence on Latitude and Transient Outflows

Ronan Laker, Timothy Horbury, Lorenzo Matteini, Thomas Woolley, Lloyd Woodham, Julia Stawarz, Stuart Bale, Emma Davies, Jonathan Eastwood, Helen O'Brien, Vincent Evans, Virginia Angelini, Ingo Richter, Daniel Heyner, Chris Owen, Philippe Louarn, and Andrei Fedorov

The recent launches of Parker Solar Probe (PSP), Solar Orbiter (SO) and BepiColombo, along with several legacy spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously. We take advantage of this unique spacecraft constellation, along with low solar activity between May and July 2020, to investigate how latitude affects the solar wind and Heliospheric Current Sheet (HCS) structure. We use ballistic mapping to compare polarity and solar wind velocity between several spacecraft, showing that fine scale ripples in the HCS can be resolved down to several degrees in longitude. We show that considering solar wind velocity is also useful when investigating the HCS structure, as it can reveal times when the spacecraft is within slow, dense streamer belt wind without changing magnetic polarity. We measured the local orientation of planar magnetic structures associated with HCS crossings, finding that these were broadly consistent with the shape of the HCS but at much steeper angles due to compression from stream interaction regions. We identified several transient magnetic clouds associated with HCS crossings, and have shown that these can disrupt the local HCS orientation up to four days after their passage, but did not significantly affect the position of the HCS. This work highlights that the heliosphere should always be treated as three-dimensional, especially at solar minimum, where a few degrees in latitude can create a considerable difference in solar wind conditions.

How to cite: Laker, R., Horbury, T., Matteini, L., Woolley, T., Woodham, L., Stawarz, J., Bale, S., Davies, E., Eastwood, J., O'Brien, H., Evans, V., Angelini, V., Richter, I., Heyner, D., Owen, C., Louarn, P., and Fedorov, A.: Ripples in the Heliospheric Current Sheet: Dependence on Latitude and Transient Outflows, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12941,, 2021.

EGU21-11899 | vPICO presentations | ST1.3 | Highlight

The Radio and Plasma Waves (RPW) Instrument on Solar Orbiter: latest observations and results

Milan Maksimovic and the RPW, MAG, SWA and EPD teams

We will review the very latest observations and results obtained by the Radio and Plasma Waves (RPW) Instrument on the recently launched Solar Orbiter mission. RPW is designed to measure in-situ magnetic and electric fields and waves from 'DC' to a few hundreds of kHz. RPW is also capable of measuring solar radio emissions up to 16 MHz and link them to solar flares observed by the onboard remote sensing instruments. The latest results we will prese