This contribution will summarise recent science highlights of the ESA/NASA Solar Orbiter mission and provide a mission status update. Solar Orbiter started its nominal mission phase in December 2021, with perihelia around 0.29 au occurring every six months. The ten instruments onboard provide high-resolution imaging and spectroscopy of the Sun and corona, as well as detailed in-situ measurements of the surrounding heliosphere. Together, these observations enable us to comprehensively study the Sun in unprecedented detail and determine the linkage between observed solar wind streams and their source regions on the Sun. Solar Orbiter’s science return is significantly enhanced by coordinated observations with other space missions, including Parker Solar Probe, SDO, SOHO, STEREO, Hinode and IRIS, as well as new ground-based telescopes like DKIST. Starting in 2025, Solar Orbiter’s highly elliptical orbit will get progressively more inclined to the ecliptic plane, which will enable the first detailed observations of the Sun’s unexplored polar regions.

How to cite: Mueller, D., Zouganelis, Y., De Groof, A., Williams, D., Walsh, A., Janvier, M., Nieves-Chinchilla, T., and Lario, D.: Solar Orbiter: Recent science highlights and mission status , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7975, https://doi.org/10.5194/egusphere-egu24-7975, 2024.

ESA’s Solar Orbiter mission, launched in February 2020, is designed to investigate how the Sun creates and controls the Heliosphere, and why solar activity changes with time. To achieve its objectives, Solar Orbiter is equipped with a comprehensive suite of remote sensing and in situ instruments that work in concert to connect coronal structures and phenomena to their heliospheric counterparts. It aims to advance our understanding of the solar dynamo, responsible for the Sun’s magnetic cycle, by venturing out of the ecliptic plane to directly observe the Sun’s polar regions, providing an unprecedented view of our star. Since its launch, Solar Orbiter has completed 5 perihelion passes below the orbit of Mercury where it has taken the most detailed images of the Sun to date. The high resolution images have revealed previously unresolved coronal features that deepen our knowledge of how the corona is heated and the solar wind is formed, as well as how eruptions are triggered and release energy. As we now enter farther into solar maximum, the mission is perfectly placed to gain fresh insight to how transients drive heliospheric variability and impact local space weather. As such, the talk will present a brief overview of the overarching Solar Orbiter science objectives, discuss recent discoveries by the mission, and outlook for future observations and its exciting journey out of the ecliptic plane.

How to cite: Rivera, Y.: Solar Orbiter: Mission Goals, Recent Discoveries, and Future Outlook, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11461, https://doi.org/10.5194/egusphere-egu24-11461, 2024.

The emission of radiation associated with the release of energy in solar flares is in many cases modulated according to a quasi-oscillatory pattern. This behavior is known as Quasi-Periodic Pulsations (QPPs). STIX instrument on board  Solar Orbiter offers new opportunities to study these types of phenomena. We reviewed Quick-Look light curves of the STIX instrument recorded from the beginning of the mission (April 14, 2020) to the end of March 202. 129 flares with the clearest pulses were selected, for which the periodicity analysis was carried out using the Lomb-Scargle periodogram and the autocorrelation method. It was found that 70% of those flares showed statistically significant oscillations. The observed periods ranged from 43 to 1355 s. It was found that longer periods occur less frequently than shorter ones. It has also been shown that there is a relationship between the period and the time interval in which the oscillations were observed.

How to cite: Szaforz, Ż., Mrozek, T., and Tomczak, M.: Investigation of solar flares showing quasi-periodicity based on STIX Quick-Look light curves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8631, https://doi.org/10.5194/egusphere-egu24-8631, 2024.

This talk shows that imaging-spectroscopy analyses from data recorded by the Spectrometer/Telescope for Imaging X-rays (STIX) on-board Solar Orbiter allow to disentangle the two factors that determine the observed hard X-ray spectrum of a solar flare, i.e., the density of the accelerated electrons and the ambient target density. More specifically, we show, for the first time in a quantitative way, that in the case of some peculiar events characterized by a significant coronal emission, the number of non-thermal electrons accelerated by the flare is relatively small and that a high rate of such electrons is stopped before they can reach the chromosphere

How to cite: piana, M., volpara, A., massa, P., emslie, G., krucker, S., and massone, A. M.:  STIX electron flux maps allow the quantitative determination of the number of accelerated electrons in solar flares, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15888, https://doi.org/10.5194/egusphere-egu24-15888, 2024.

Understanding the general properties of the various solar winds requires an understanding of the phenomena at their source. The properties of the solar wind are influenced by the exchange of energy at the base of the solar corona. For example, the speed of the solar wind is strongly influenced by the level of heating below the sonic point. The heating that occurs in the collisional part of the atmosphere modifies the ionisation level of the heavy elements and therefore their charge state. This is why the charge state ratios of heavy ions measured in the solar wind are good parameters for distinguishing between fast and slow solar winds. In this study, we use the new Irap solar atmospheric model (ISAM) to study the level of ionisation of heavy ions transported in fast and slow solar winds. ISAM is a 16-moment multi-species model that self-consistently couples the transport equations for neutral and ionised particles (H, p, e, He, O and Mg) from the lower chromosphere through the solar corona to the solar wind. The lower corona is a region that is strongly coupled to the transition region by the downward heat flux.

By solving first for H, p and e, we recover the results of previous modelling showing that variations in the source temperature modify the pressure of the transition region which, in turn, modulates the mass flux of the solar wind. Using an ad-hoc heating function characterised by a scale height inversely proportional to the expansion factor of the magnetic field lines channelling the solar wind, we first recover the general properties of the fast and slow solar winds, as well as the known observation that the source temperature of the slow wind is higher than that of the fast wind. We then solve explicitly the ionisation processes and the coupled transport of oxygen with the major species (H, p, e) in order to isolate the different processes that contribute to the ionisation level of the heavy ions. We compare the results of our modelling with spectroscopic and in situ data. This work was funded by the ERC SLOW SOURCE - DLV - 819189.

How to cite: Lomazzi, P., Thomas, S., Rouillard, A., Poirier, N., Réville, V., Lavarra, M., and Blelly, P.-L.: Modeling the source temperature of fast and slow winds using a 16 moments multi-species model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16348, https://doi.org/10.5194/egusphere-egu24-16348, 2024.

The distribution of charged particles in the heliosphere covers more than 16 orders of magnitude in particle flux and more than 6 orders of magnitude in energy. While the majority of these particles are ionized hydrogen (protons) and fully ionized helium (alpha particles), heavier ions are also present. Because of the large parameter space that must be covered, different instruments are required and these instruments must be optimized to specific energy and particle flux ranges. They must also be designed to target specific ion species. To properly characterize the means by which different energy ranges are populated, the observations from these different instruments must be intercalibrated.

We present initial progress intercalibrating observations from Solar Orbiter’s Heavy Ion Sensor (HIS) and Suprathermal Ion Spectrograph (SIS). HIS is a heavy ion composition experiment that targets the solar wind through the low energy range of suprathermal energies with mass and charge state resolution. SIS covers the suprathermal and low range energetic particles with high mass resolution but without charge state resolution. Together, these two sensors cover heavy ion composition from solar wind to suprathermal energies. During advantageous conditions, proton distributions across both instruments are also available. Properly intercalibrated observations across these instruments enable studies of charged particle energization across the energy ranges, which is essential for characterizing a wide range of phenomena in heliosphere.

How to cite: Alterman, B., Allen, R., Dewey, R., Livi, S., Raines, J., Lepri, S., Spitzer, S., Bert, C., Owen, C., Ho, G., Galvin, A., Kistler, L., Allegrini, F., Ogasawara, K., Wurz, P., Philips, M., D'Amicis, R., Mason, G., Wimmer-Schweingruber, R. F., and Rodriquez-Pacheco, J.: Inter-Calibration of Solar Orbiter’s Heavy Ion Sensor and Suprathermal Ion Spectrograph, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13328, https://doi.org/10.5194/egusphere-egu24-13328, 2024.

Solar Energetic Particles (SEPs), accelerated during solar eruptions, are observed using instruments onboard spacecraft in interplanetary space, at a large distance from their source. As SEPs propagate in the solar wind, they are guided by the interplanetary magnetic field (IMF), which consists of a large-scale Parker spiral magnetic field superposed by turbulent fluctuations. The turbulence causes the SEPs to scatter along the magnetic field lines, resulting in some cases in delayed arrival of SEPs to spacecraft in interplanetary space. It also gives rise to meandering of field lines, which helps to spread SEPs across heliolongitudes, and eventually results in diffusive cross-field propagation of the particles. To investigate how turbulence affects SEP propagation and arrival to observing spacecraft in different locations in the heliosphere, we have developed a novel analytical model of the IMF, where the Parker spiral is superposed with Fourier modes that represent the turbulence. Unlike any previous models, our description reproduces the observed geometry for the main mode of turbulence, the so-called 2D mode, with both the magnetic field disturbance vector and the wavenumber vector normal to the background Parker spiral field. We use 3D test particle simulations to study the propagation of energetic protons in our new turbulent IMF description. Particles are injected close to the Sun and observables derived at different radial distances and heliolongitudes, representing the locations of near-Earth spacecraft as well as locations accessible to Solar Orbiter and Parker Solar Probe. We compare the SEP onset times obtained from our simulations to those obtained with a 1D focused transport model. We find that the turbulence prolongs the field lines, and thus when particle are simulated in our new IMF model, the SEP intensity onsets are delayed compared to those obtained by using a 1D focused transport model. Further, we find that onset delay depends on the longitudinal separation of the SEP source and the heliolongitude of the location where the observables are derived. We discuss the implications of our findings on current understanding of the sources and transport of SEPs.

How to cite: Laitinen, T. and Dalla, S.: Modelling Solar Energetic Particle event onsets in the turbulent heliosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11192, https://doi.org/10.5194/egusphere-egu24-11192, 2024.

Ever since the first ³He-enhanced solar energetic particle (SEP) event was reported in the literature in 1970, the exact mechanism by which the isotope is enhanced orders of magnitude higher than its solar wind value remains unknown.  But the source, acceleration, and transport of SEP events can only be studied by multi-point simultaneous in-situ measurement within the heliosphere.  However, multi-spacecraft observations of ³He-rich solar energetic particle (SEP) event are scarce.  Further observations are much needed in order to understand and properly constrain the source and transport of the remarkable enriched ³He SEP event. In this paper, we report six ³He-rich SEP events that were detected by ACE, STEREO and Solar Orbiter near 1 au during Solar Orbiter’s aphelion pass at the end of 2022 and early 2023.  Many of these events were detected simultaneously by at least two or three spacecraft at up to ~40° longitudal separation, while some events were detected by only a single spacecraft even though an adjacent spacecraft was less than 20° away. These fortuitous multi-spacecraft observations of ³He-rich SEP events thus provide us observational constraint on the acceleration and propagation of this special class of SEP events. In addition, we will show in this paper how multi-spacecraft measurements could also be used to constraint the solar source region of ³He-rich SEP event.

How to cite: Ho, G., Mason, G., Kouloumvakes, A., Allen, R., Wimmer-Schweingruber, R., and Rodríguez-Pacheco, J.: Longitudinal Extent of 3He-rich Solar Energetic Particle Events near 1 AU, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6724, https://doi.org/10.5194/egusphere-egu24-6724, 2024.

Solar Orbiter (SO) observations provide an unprecedented opportunity to study the evolution of solar energetic particle (SEP) events from different locations within the heliosphere. In this work, we have compiled a catalogue of SEP events based on observations of both electrons and protons from the High Energy Telescope (HET) of the Energetic Particle Detector (EPD) that occurred in 2020 to 2023 during the ascending phase of Solar Cycle 25. A scan of simultaneous So/HET intensity-time observations for ~10 MeV protons and near relativistic (~1 MeV) electrons has been performed. We have identified all enhancements observed above the background levels of these particular channels and surveyed available solar wind data by the SO/ Solar Wind Analyzer (SWA) and the SO/Magnetometer (MAG) during the identified events. Moreover, we employed Velocity Dispersion Analysis (VDA) for protons and electrons and Time-shifting Analysis (TSA) for electrons, alone, with the aim to infer the SEP release times at the Sun. Our resulting catalogue includes 75 SEP events. For each of these events (and for each species), we provide the onset and peak time, the peak flux value and fluence. We also identify the solar associations/sources for the SEP events, by comparing the inferred release times of the SEPs to the related light curves from the SO/Spectrometer/Telescope for Imaging X-rays (STIX), the standard flare list obtained from the GOES X-ray Sensor and their associated coronal mass ejections (CMEs). We find that a significant portion of all SEP events in our sample (48%; 36/75) reached 50 MeV for protons and thus are Space Weather relevant. Finally, a statistical analysis of our observations is presented. We have investigated correlations between peak particle fluxes (for protons and electrons) and event fluences, as well as peak particle fluxes (event fluences), flare magnitude and CME speed. We also calculate the connection angle to the apparent source and identify a subsample of the events that are better connected to the solar event. In addition, the e/p ratio is calculated and a division of the sample based on Fe-rich and ³He-rich events is discussed. 

Acknowledgement: Research leading to these results has received funding from the Horizon Europe programme project No 101135044 (SPEARHEAD).

How to cite: Papaioannou, A., Rodríguez-García, L., Gomez Herrero, R., Lavasa, E., Kouloumvakos, A., Vasalos, G., Warmuth, A., Richardson, I. G., Lario, D., Zouganelis, I., Espinosa Lara, F., Cernuda Cangas, I., Kuel, P., Schuller, F., Barczynski, K., Fleth, S., Anastasiadis, A., Walsh, A., Mueller, D., and Rodriguez-Pacheco, J. and the A Solar Orbiter Team: A catalogue of large solar energetic particle events observed by Solar Orbiter for the first ~ four years of measurements (2020–2023), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17889, https://doi.org/10.5194/egusphere-egu24-17889, 2024.