ST1.3

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, https://doi.org/10.5194/egusphere-egu21-15792, 2021.

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, https://doi.org/10.5194/egusphere-egu21-6776, 2021.

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, https://doi.org/10.5194/egusphere-egu21-12501, 2021.

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, https://doi.org/10.5194/egusphere-egu21-12435, 2021.

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, https://doi.org/10.3847/1538-4357/abb9a1).

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, https://doi.org/10.5194/egusphere-egu21-592, 2021.

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, https://doi.org/10.5194/egusphere-egu21-8878, 2021.

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, https://doi.org/10.5194/egusphere-egu21-4996, 2021.

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, https://doi.org/10.5194/egusphere-egu21-9712, 2021.

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, https://doi.org/10.5194/egusphere-egu21-10023, 2021.

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, https://doi.org/10.5194/egusphere-egu21-10238, 2021.

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, https://doi.org/10.5194/egusphere-egu21-10630, 2021.

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, https://doi.org/10.5194/egusphere-egu21-12941, 2021.

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, https://doi.org/10.5194/egusphere-egu21-11899, 2021.

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, https://doi.org/10.5194/egusphere-egu21-4482, 2021.

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, https://doi.org/10.5194/egusphere-egu21-12198, 2021.

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, https://doi.org/10.5194/egusphere-egu21-13801, 2021.

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, https://doi.org/10.5194/egusphere-egu21-15195, 2021.

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, https://doi.org/10.5194/egusphere-egu21-15746, 2021.

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, https://doi.org/10.5194/egusphere-egu21-15860, 2021.

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, https://doi.org/10.5194/egusphere-egu21-16455, 2021.

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, https://doi.org/10.5194/egusphere-egu21-5061, 2021.

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, https://doi.org/10.5194/egusphere-egu21-14801, 2021.

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, https://doi.org/10.5194/egusphere-egu21-15555, 2021.

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, https://doi.org/10.5194/egusphere-egu21-4390, 2021.

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, https://doi.org/10.5194/egusphere-egu21-9422, 2021.

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, https://doi.org/10.5194/egusphere-egu21-7966, 2021.