First results from the Solar Orbiter mission

ESA/NASA's mission Solar Orbiter was launched in February 2020, and the in-situ instruments have started their science operations in June. The mission’s unique design will enable breakthrough science focusing on the linkage between the Sun and the heliosphere. By approaching as close as 0.28 AU from the Sun and orbiting the Sun in a plane up to 33 degrees heliographic latitude, Solar Orbiter will view the Sun and corona with remote imaging with high spatial resolution, and acquire in-situ measurements of the surrounding heliosphere. Solar Orbiter had its first perihelion near 0.51 AU in June 2020, its first Venus flyby in December and its second perihelion at 0.49 AU on 10 February 2021. Presentations covering instrument performance during commissioning and calibration, initial data and first scientific results from the first perihelia and the cruise phase (together with contextual ground and space-based observations), and theoretical predictions are solicited.

Convener: Yannis Zouganelis | Co-conveners: David Lario, Daniel Mueller, Teresa Nieves-Chinchilla
vPICO presentations
| Tue, 27 Apr, 11:00–15:00 (CEST)

vPICO presentations: Tue, 27 Apr

Chairpersons: Yannis Zouganelis, David Lario
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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Lunch break
Chairpersons: Daniel Mueller, Teresa Nieves-Chinchilla
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.

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 present concern a wide range of phenomena including: Langmuir and Whistler Waves, dust impacts, Solar Type III bursts and observations during the recently visited Venus environment.

How to cite: Maksimovic, M. and the RPW, MAG, SWA and EPD teams: The Radio and Plasma Waves (RPW) Instrument on Solar Orbiter: latest observations and results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11899,, 2021.

Arnaud Zaslavsky, Ingrid Mann, Stuart Bale, Andrzej Czechowski, Karine Issautier, Eric Lorfèvre, Milan Maksimovic, Nicole Meyer-Vernet, David Pisa, Kristina Rackovic-Babic, Jan Soucek, and Jakub Vaverka

Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals are, as could be expected, routinely detected by the radio and plasma waves (RPW) instrument aboard Solar Orbiter, therefore providing in-situ measurements of the interplanetary dust density along the spacecraft trajectory.

We present a statistical analysis of the first year and half of dust impact data recorded by Solar Orbiter RPW between 1 AU and 0.5 AU. We discuss the results in terms of constraints that can be put on beta-meteoroids and interstellar dust fluxes, and compare them to results obtained by STEREO at 1 AU and more recently by Parker Solar Probe at 0.5 AU.

How to cite: Zaslavsky, A., Mann, I., Bale, S., Czechowski, A., Issautier, K., Lorfèvre, E., Maksimovic, M., Meyer-Vernet, N., Pisa, D., Rackovic-Babic, K., Soucek, J., and Vaverka, J.: Interplanetary dust observations with the Solar Orbiter RPW instrument: a first year of data., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4482,, 2021.

Niklas J. T. Edberg, Lina Hadid, Milan Maksimovic, Stuart D. Bale, Thomas Chust, Yuri Khotyaintsev, Volodya Krasnoselskikh, Matthieu Kretzschmar, Eric Lorfèvre, Dirk Plettemeier, Jan Souček, Manfred Steller, Štěpán Štverák, Pavel Trávníček, Andris Vaivads, Antonio Vecchio, and Tim Horbury and the RPW team & MAG team

We present measurements from the Radio and Plasma Wave (RPW) instrument suite onboard the Solar Orbiter mission during the first Venus encounter. RPW consists of several units and is capable of measuring both the electric and magnetic field fluctuations with three electric antennas and a search-coil magnetometer: The Low Frequency Receiver (LFR) cover the range from DC up to 10kHz when measuring the electric and magnetic waveform and spectra; the Thermal Noise and High Frequency Receiver (TNR-HFR) determines the electric power spectra and magnetic power spectra from 4kHz-20MHz, and 4kHz to 500kHz, respectively, to determine properties of the electron population; the Time Domain Sampler (TDS) measures and digitizes onboard the electric and magnetic field waveforms from 100 Hz to 250 kHz. The BIAS subunit measures DC and LF electric fields as well as the spacecraft potential, which gives a high cadence measure of the local plasma density when calibrated to the low-cadence tracking of the plasma peak from the TNR. Solar Orbiter approached Venus from the induced magnetotail and had its closest approach at an altitude of 7500 km over the north pole of Venus on 27 Dec 2020. The RPW instruments observed a tail region that extended several 10’s of Venus radii downstream of the planet. The induced magnetosphere was characterized to be a highly dynamic environment as Solar Orbiter traversed the downstream tail and magnetosheath before it crossed the Bow Shock outbound at ~12:40 UT. Polarized whistler waves, high frequency electrostatic waves, narrow-banded emissions, possible electron double layers were observed. The fine structure of the bow shock could also be investigated in detail. Solar Orbiter could hence enhance the knowledge of the structure of the solar wind-Venus interaction.

How to cite: Edberg, N. J. T., Hadid, L., Maksimovic, M., Bale, S. D., Chust, T., Khotyaintsev, Y., Krasnoselskikh, V., Kretzschmar, M., Lorfèvre, E., Plettemeier, D., Souček, J., Steller, M., Štverák, Š., Trávníček, P., Vaivads, A., Vecchio, A., and Horbury, T. and the RPW team & MAG team: Solar Orbiter/Radio and Plasma Wave observations during the first Venus flyby, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12198,, 2021.

Michiko Morooka, Yuri Khotyaintsev, Anders Eriksson, Niklas Edberg, Erik Johansson, Milan Maksimovic, Stuart Bale, Thomas Chust, Volodya Krasnoselskikh, Matthieu Kretzschmar, Eric Lorfèvre, Dirk Plettemeier, Jan Souček, Manfred Steller, Štěpán Štverák, Pavel Trávníček, Andris Vaivads, and Antonio Vecchio

A large-amplitude impact-induced like electric field signal is often observed by the Radio and Plasma Wave (RPW) Instrument onboard Solar Orbiter. The signal has a sharp increase followed by an exponential decay, typically observed when spacecraft experiences a dust impact. The amplitude can reach several V/m. The impact dust size can be estimated from the electric field amplitude and is similar to the characteristic dust size near the sun expected from the zodiacal-light observations. On the other hand, the signal's decay time is the order of second, unusually long compared to the dust impact signals previously reported by the other spacecraft. We will show the characteristics of these signals and discuss the origin.

How to cite: Morooka, M., Khotyaintsev, Y., Eriksson, A., Edberg, N., Johansson, E., Maksimovic, M., Bale, S., Chust, T., Krasnoselskikh, V., Kretzschmar, M., Lorfèvre, E., Plettemeier, D., Souček, J., Steller, M., Štverák, Š., Trávníček, P., Vaivads, A., and Vecchio, A.: Impact induced electric field signals observed by the Solar Orbiter/RPW, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13801,, 2021.

Matthieu Kretschmar, Thomas Chust, Daniel Graham, Volodya Krasnosekskikh, Lucas Colomban, Milan Maksimovic, Timothy Horbury, Christofer Owen, and Philippe Louarn

Plasma waves can play an important role in the evolution of the solar wind and the particle velocity distribution functions in particular. We analyzed the electromagnetic waves observed above a few Hz by the Radio Plasma Waves (RPW) instrument suite onboard Solar Orbiter, during its first orbit, which covered a distance from the Sun between 1 AU and 0.5 AU.  We identified the majority of the detected waves as whistler waves with frequency around  0.1 f_ce and right handed circular polarisation. We found these waves to be mostly aligned or anti aligned with the ambient magnetic field, and rarely oblique. We also present and discuss their direction of propagation and the variation of the waves' properties with heliocentric distance.

How to cite: Kretschmar, M., Chust, T., Graham, D., Krasnosekskikh, V., Colomban, L., Maksimovic, M., Horbury, T., Owen, C., and Louarn, P.: Whistler waves observed by Solar Orbiter during its first orbit, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15195,, 2021.

Yuri Khotyaintsev, Daniel B Graham, Konrad Steinvall, Andris Vaivads, Milan Maksimovic, Niklas J. T. Edberg, Erik P.G. Johansson, and Anders I. Eriksson and the RPW, MAG and SWA Teams

We report Solar Orbiter observations of electromagnetic waves near the proton cyclotron frequency during the first perihelion. The waves have polarization close to circular and have wave vectors closely aligned with the background magnetic field. Such waves are potentially important for heating of the solar wind as their frequency and polarization allows effective energy exchange with solar wind protons. The Radio and Plasma Waves (RPW) instrument provides a high-cadence measurement of plasma density and electric field which we use together with the magnetic field measured by MAG to characterize these waves. In particular we compute the compressibility and the phase between the density fluctuations and the parallel component of the magnetic field, and show that these have a distinct behavior for the waves compared to the Alfvénic turbulence. We compare the observations to multi-fluid plasma dispersion and identify the waves modes corresponding to the observed waves. We discuss the importance of the waves for solar wind heating.

How to cite: Khotyaintsev, Y., Graham, D. B., Steinvall, K., Vaivads, A., Maksimovic, M., Edberg, N. J. T., Johansson, E. P. G., and Eriksson, A. I. and the RPW, MAG and SWA Teams: Using Compressibility and Electric Field to Characterize Circularly-Polarized Waves Near the Proton Cyclotron Frequency Observed by Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15746,, 2021.

Daniel Graham, Yuri Khotyaintsev, Konrad Steinvall, Andris Vaivads, Milan Maksimovic, Niklas Edberg, Erik Johansson, Anders Eriksson, Matthieu Kretzschmar, and Thomas Chust and the RPW, MAG and SWA Solar Orbiter teams

Thin current sheets are routinely observed in the solar wind. Here we report observations of thin current sheets and the associated plasma waves using the Solar Orbiter spacecraft. The Radio and Plasma Waves (RPW) instrument provides high-resolution measurements of the electric field, number density perturbations, and magnetic field fluctuations, which we use to identify and characterise the observed waves, while the magnetic field provided by the MAG instrument is used to characterise the current sheets. We discuss the role of current sheets in the generation of the observed waves and the effects of the waves on the current sheets. 

How to cite: Graham, D., Khotyaintsev, Y., Steinvall, K., Vaivads, A., Maksimovic, M., Edberg, N., Johansson, E., Eriksson, A., Kretzschmar, M., and Chust, T. and the RPW, MAG and SWA Solar Orbiter teams: Thin current sheets and the associated wave activity observed by Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15860,, 2021.

Lucas Colomban, Matthieu Kretzschmar, Volodya Krasnoselskikh, Laura Bercic, Chris Owen, and Milan Maksimovic

Whistler waves are thought to play an important role on the evolution of the electron distribution function as a function of distance. In particular, oblique whistler waves may diffuse the Strahl electrons  into the halo population.  Using AC magnetic field from the RPW/SCM (search coil magnetometer) of Solar Orbiter, we search for the presence of oblique Whistler waves in the frequency range between 3 Hz and 128 Hz .  We perform a minimum variance analysis of the SCM data in combination with the MAG (magnetometer) data to determine the inclination of the waves with respect to the ambiant magnetic field. As the emphasis is placed on the search for oblique whistler, we also analyze the RPW electric field data and the evolution of the electron distribution function during these Whistler events.

How to cite: Colomban, L., Kretzschmar, M., Krasnoselskikh, V., Bercic, L., Owen, C., and Maksimovic, M.: Search for oblique Whistler waves using solar orbiter data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16006,, 2021.

Laura Bercic and the et al.

The solar coronal plasma which escapes the Sun’s gravity and expands through our solar system is called the solar wind. It consists mainly of electrons and protons, carries the Sun’s magnetic field and, at most heliocentric distances, remains weakly-collisional. Due to their small mass, the solar wind electrons have much higher thermal velocity than their positively charged counterpart, and play an important role in the solar wind energetics by carrying the heat flux away from the Sun. Their velocity distribution functions (VDFs) are complex, usually modeled by three components. While the majority of electrons belong to the low-energetic thermal Maxwellian core population, some reach higher velocities, forming either the magnetic field aligned strahl population, or an isotropic high-energy halo population. This shape of the electron VDF is a product of the interplay between
Coulomb collisions, adiabatic expansion, global and local electro-magnetic fields and turbulence.
In this work we focus on the effects of local electro-magnetic wave activity on electron VDF, taking advantage of the early measurements made by the novel heliospheric Solar Orbiter mission. The high- cadence sampling of 2-dimensional electron VDFs by the electrostatic analyser SWA-EAS, together with the EM wave data collected by the seach-coil magnetometers and electric-field antennas, part of

the RPW instrument suit, allow a direct investigation of the wave-particle energy and momentum exchange. We present the evolution of the electron VDF in the presence of quasi-parallel and oblique whistler waves, believed to be responsible for scattering the strahl and creating the halo population (Verscharen et al. 2019; Micera et al. 2020).

How to cite: Bercic, L. and the et al.: Evolution of the electron velocity distribution under the presence of whistler waves in the solar wind (high-cadence Solar Orbiter observations), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16455,, 2021.

Yajie Chen, Damien Przybylski, Hardi Peter, and Hui Tian

Recent observations by the Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter have revealed prevalent small-scale transient brightenings in the quiet solar corona termed campfires. To understand the generation mechanism of these coronal brightenings, we constructed a self- consistent and time-dependent quiet-Sun model extending from the upper convection zone to the lower corona using a realistic 3D radiation MHD simulation. From the model we have synthesized the coronal emission in the EUI 174 Å passband. We identified several transient coronal brightenings similar to those in EUI observations. The size and lifetime of these coronal brightenings are 2–4 Mm and ∼2 min, respectively. These brightenings are located at a height of 2–4 Mm above the photosphere, and the surrounding plasma is often heated above 1 MK. These findings are consistent with the observational characterisation of the campfires. Through a comparison of the magnetic field structures before and after the occurrence of brightenings, we conclude that these coronal brightenings are generated by component magnetic reconnection between interacting bundles of field lines or the relaxation of highly twisted flux ropes. Occurring in the coronal part of the atmosphere, these events show no measurable signature in the photosphere. These transient coronal brightenings may play an important role in heating of the local coronal plasma.

How to cite: Chen, Y., Przybylski, D., Peter, H., and Tian, H.: Transient small-scale brightenings in the quiet Sun corona: a model for "campfires" observed with Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5061,, 2021.

Luca Teriaca and the EUI and SPICE Teams

The Solar Orbiter spacecraft carries a powerful set of remote sensing instruments that allow studying the solar atmosphere with unprecedented diagnostic capabilities. Many such diagnostics require the simultaneous usage of more than one instrument. One example of that is the capability, for the first time, to obtain (near) simultaneous spatially resolved observations of the emission from the first three lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact, the SPectral Imaging of the Coronal Environment (SPICE) spectrometer can observe the Lyman beta and gamma lines in its long wavelength (SPICE-LW) channel, the High Resolution Lyman Alpha (HRILYA) telescope of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take images dominated by the Lyman alpha line of ionized Helium at 30.4 nm (FSI-304). Being hydrogen and helium the main components of our star, these very bright transitions play an important role in the energy budget of the outer atmosphere via radiative losses and the measurement of their profiles and radiance ratios is a fundamental constraint to any comprehensive modelization effort of the upper solar chromosphere and transition region. Additionally, monitoring their average ratios can serve as a check out for the relative radiometric performance of the two instruments throughout the mission.

Although the engineering data acquired so far are far from ideal in terms of time simultaneity (often only within about 1 h) and line coverage (often only Lyman beta was acquired by SPICE and not always near simultaneous images from all three telescopes are available) the analysis we present here still offers a great opportunity to have a first look at the potential of this diagnostic from the two instruments.

In fact, we have identified a series of datasets obtained at disk center and at various positions at the solar limb that allow studying the Lyman alpha to beta radiance ratio and their relation to He II 30.4 as a function of the position on the Sun (disk center versus limb and quiet Sun versus coronal holes).

How to cite: Teriaca, L. and the EUI and SPICE Teams: First results from combined EUI and SPICE observations of Lyman lines of Hydrogen and He II, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14801,, 2021.

Andrzej Fludra and the SPICE Team

SPICE (Spectral Imaging of Coronal Environment) is an EUV imaging spectrometer onboard Solar Orbiter. SPICE observes the Sun in two wavelength bands: 69.6-79.4 nm and 96.6-105.1 nm and is capable of recording full spectra in these bands with exposures as short as 1s. SPICE can measure spectra from the disk and low corona, and records all spectral lines simultaneously, using one of three narrow slits: 2”x11’, 4’’x11’, 6’’x11’, or a wide slit 30’’x14’. The primary mirror can be scanned in a direction perpendicular to the slit, allowing raster images of up to 16’ in size.

The first SPICE data were taken during the instrument commissioning carried out by the RAL Space team between 2020 April 21 and 2020 June 14, and at the first Solar Orbiter perihelion at 0.52AU between June 16-21.  We give examples of full spectra from the quiet Sun near disk centre and provide a list of key spectral lines from neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur and magnesium. These lines cover the temperature range between 10,000 K and 1 million K (10MK in flares), providing slices of the Sun’s atmosphere in narrow temperature intervals. We show examples of raster images in several strong lines, obtained with different slits and a range of exposure times between 5s and 180s.

We have found several unusually bright, compact structures (named “beacons”) in the quiet Sun network, with extreme intensities up to 22 times greater than the average intensity across the image. The lifetimes of these sources are longer than 1 hour. We will derive plasma velocities in the beacon area, and co-align the SPICE rasters with the SDO/AIA 304 and 171 images and the HMI magnetic field to better understand the origin and properties of beacons.

We also show the first above-limb measurements with SPICE in Mg IX, Ne VIII and O VI lines, as obtained when the spacecraft pointed at the limb. Maps of Mg/Ne abundance ratios on disk can be derived and compared with in situ measurements to help confirm the magnetic connection between the spacecraft location and the Sun’s surface, and locate the sources of the solar wind.

How to cite: Fludra, A. and the SPICE Team: First Results From SPICE EUV Spectrometer on Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5577,, 2021.

Natalia Zambrana Prado, Éric Buchlin, and Hardi Peter and the SPICE consortium team

Linking solar activity on the surface and in the corona to the heliosphere is one of Solar Orbiter’s main goals. Its EUV spectrometer SPICE (SPectral Imaging of the Coronal Environment) will provide relative abundance measurements which will be key in this quest, as different structures on the Sun have different abundances as a consequence of the FIP (First Ionization Potential) effect. From the 16th to the 22nd of November 2020,  the Solar Orbiter remote sensing checkout window STP-122 was carried out. During this period of observations, SPICE was lucky to catch a small AR in its field of view. We carried out abundance specific observations in order to provide relative FIP bias measurements with SPICE. Furthermore, data from other types of observations carried out during that same week allow us to identify the spectral lines that could be used for abundance diagnostics. We take the SPICE instrument characteristics into account to give recommendations regarding the types of studies to carry out to obtain such abundance measurements.

How to cite: Zambrana Prado, N., Buchlin, É., and Peter, H. and the SPICE consortium team: First data for abundance diagnostics with SPICE, the EUV spectrometer on-board Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15555,, 2021.

Andrea Francesco Battaglia, Jonas Saqri, Ewan Dickson, Hualin Xiao, Astrid Veronig, Alexander Warmuth, Marina Battaglia, and Säm Krucker and the STIX Team

With the launch and commissioning of Solar Orbiter, the Spectrometer/Telescope for Imaging X-rays (STIX) is the latest hard X-ray telescope to study solar flares over a large range of flare sizes. STIX uses hard X-ray imaging spectroscopy in the range from 4 to 150 keV to diagnose the hottest temperature of solar flare plasma and the related nonthermal accelerated electrons. The unique orbit away from the Earth-Sun line in combination with the opportunity of joint observations with other Solar Orbiter instruments, STIX will provide new inputs into understanding the magnetic energy release and particle acceleration in solar flares. Commissioning observations showed that STIX is working as designed and therefore we report on the first solar microflare observations recorded on June 2020, when the spacecraft was at 0.52 AU from the Sun. STIX’s measurements are compared with Earth-orbiting observatories, such as GOES and SDO/AIA, for which we investigate and interpret the different temporal evolution. The detected early peak of the STIX profiles relative to GOES is due either by nonthermal X-ray emission of accelerated particles interacting with the dense chromosphere or the higher sensitivity of STIX toward hotter plasma.

How to cite: Battaglia, A. F., Saqri, J., Dickson, E., Xiao, H., Veronig, A., Warmuth, A., Battaglia, M., and Krucker, S. and the STIX Team: First results of the STIX hard X-ray telescope onboard Solar Orbiter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4390,, 2021.

Ewan Dickson and the STIX team

The Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter (Krucker et al., 2020) uses an indirect imaging system to measure flare location, size and morphology. Pairs of tungsten grids create Moiré fringes on its coarsely pixelated CdTe detectors. Images are then reconstructed on the ground, using sophisticated imaging algorithms, after the data containing the counts in each pixel for 30 imaging detectors has been download. 

STIX therefore uses a dedicated sub-collimator to estimate a rough (within a few arcminutes), but unambiguous, flare location on board in near real time. The Coarse Flare Locator (CFL) consists of a single grid with a specific pattern which selectively illuminates pixels of a dedicated detector based on the source location. The correlation between the counts in the pixels of this detector, combined with sums of counts from the other detectors, and a look up table of pre-caculated expectations allows the location to be estimated promptly, within the constraints of on board processing. 

Using the downloaded measured counts in each pixel the coarse flare location can also be reconstructed on the ground. This allows for more sophisticated algorithms which require greater computational power than is available on board; greater flexibility as to which time and energy intervals are combined; and more careful background subtraction possible. 

The first estimates of STIX flare locations calculated using the STIX Ground Processing Software (GSW) from data taken during commissioning and subsequent Remote Sensing Checkout Windows are presented here. Comparisons are made to the expected active region and source locations, using data from several other instruments. 


Krucker, S et al. The Spectrometer/Telescope for Imaging X-rays (STIX). Astronomy and Astrophysics, v. 642, Oct. 2020. DOI: 10.1051/0004-6361/201937362.

How to cite: Dickson, E. and the STIX team: The First STIX Coarse Flare Locations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16460,, 2021.

michele piana, paolo massa, emma perracchione, andrea francesco battaglia, federico benvenuto, anna maria massone, gordon hurford, and sam krucker

The Spectrometer/Telescope for Imaging X-rays (STIX) is the instrument of the Solar Orbiter mission conceived for the observation of the hard X-ray flaring emission, with the objective of providing insights on the diagnosis of thermal and non-thermal accelerated electrons at the Sun. The STIX imaging system is composed of 30 pairs of tungsten grids, each one placed in front of a four-pixel detector, and produces as many Fourier components of the angular distribution of the flaring source, via Moiré pattern modulation. Therefore, the data recorded by STIX, named visibilities, can be interpreted as a sparse sampling of the Fourier transform of the X-ray signal and the corresponding image reconstruction problem requires the inversion of the Fourier transform from limited data, usually addressed with regularization techniques. Since the current calibration status of STIX measurements still prevents the use of visibility phases for imaging purposes, here we propose a parameter identification process based on forward fitting  just the amplitude of the experimental visibilities. Specifically, we have parameterized the flaring source by means of pre-assigned source shapes (e.g., circular and elliptical bi-variate Gaussian functions), and we relied on several approaches to non-linear optimization in order to estimating the shape parameters. In particular, we have implemented a forward-fit method based on deterministic chi-squared minimization, a stochastic optimization algorithm and a deep neural approach based on ensemble learning, also equipping them with an ad hoc statistical technique for uncertainty quantification. The performances of the three approaches are compared in the case of both microflares and M class events recorded by STIX during its commissioning phase and the validation of results is realized also exploiting the EUV information provided by the Atmospheric Imaging Assembly within the Solar Dynamics Observatory.

How to cite: piana, M., massa, P., perracchione, E., battaglia, A. F., benvenuto, F., massone, A. M., hurford, G., and krucker, S.: Early results for the STIX image reconstruction problem: imaging from visibility amplitudes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9422,, 2021.

Jonas Saqri, Astrid Veronig, Ewan Dickson, Säm Krucker, Andrea Francesco Battaglia, Marina Battaglia, Hualin Xiao, Alexander Warmuth, and the STIX Team

Solar flares are generally thought to be the impulsive release of magnetic energy giving rise to a wide range of solar phenomena that influence the heliosphere and in some cases even conditions of earth. Part of this liberated energy is used for particle acceleration and to heat up the solar plasma. The Spectrometer/Telescope for Imaging X-rays (STIX) instrument onboard the Solar Orbiter mission launched on February 10th 2020 promises advances in the study of solar flares of various sizes. It is capable of measuring X-ray spectra from 4 to 150 keV with 1 keV resolution binned into 32 energy bins before downlinking. With this energy range and sensitivity, STIX is capable of sampling thermal plasma with temperatures of≳10 MK, and to diagnose the nonthermal bremsstrahlung emission of flare-accelerated electrons. During the spacecraft commissioning phase in the first half of the year 2020, STIX observed 68 microflares. Of this set, 26 events could clearly be identified in at least two energy channels, all of which originated in an active region that was also visible from earth. These events provided a great opportunity to combine the STIX observations with the multi-band EUV imagery from the Atmospheric Imaging Assembly (AIA) instrument on board the earth orbiting Solar Dynamics Observatory (SDO). For the microflares that could be identified in two STIX science energy bands, it was possible to derive the temperature and emission measure (EM) of the flaring plasma assuming an isothermal source. For larger events where more detailed spectra could be derived, a more accurate analysis was performed by fitting the spectra assuming various thermal and nonthermal sources. These results are compared to the diagnostics derived from AIA images. To this aim, the Differential EmissionMeasure (DEM) was reconstructed from AIA observations to infer plasma temperatures and EM in the flaring regions. Combined with the the relative timing between the emission seen by STIX and AIA, this allows us to get deeper insight into the flare energy release and transport processes.

How to cite: Saqri, J., Veronig, A., Dickson, E., Krucker, S., Battaglia, A. F., Battaglia, M., Xiao, H., Warmuth, A., and STIX Team, T.: Plasma Diagnostics of Microflares observed by STIX and AIA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7966,, 2021.