In regions of the Solar System distant from planetary magnetic fields, galactic cosmic rays (GCRs) have generally been assumed to be uniformly distributed over the Earth-Moon distance. However, our analysis of data from the LND (Lunar Lander Neutron and Dosimetry) experiment onboard the Chang'E-4 lander revealed a region of reduced GCR flux in the prenoon sector of the lunar orbit. Further investigation suggests the presence of an energetic particle cavity, formed by Earth's magnetic field acting as an obstacle to GCR propagation. This cavity indicates that the influence of Earth's magnetic field within the space environment extends unexpectedly up to and far beyond the lunar orbit. This finding offers the potential to avoid high radiation levels during future lunar exploration and deep-space missions.

In addition to the omnipresent Galactic Cosmic Rays, sudden Solar Energetic Particle (SEP) events present considerable health hazards for manned space missions. These events not only contribute to an increased long‐term cancer risk, but can, in extreme cases, cause acute radiation syndromes. Forecasting their imminent occurrence could significantly reduce radiation exposure by warning astronauts to move to shelter. However, all currently available tools are primarily designed for the Earth or Earth‐Moon system, which limits their applicability to future Mars missions. To address this, we developed a nowcasting system for SEP events applicable in deep space and on the Martian surface, which serves as a reliable last‐resort backup when forecasts fail. The methodology of this system is based on dose rates measured by the Radiation Assessment Detector onboard the Mars Science Laboratory, which recorded 5 SEP events during the 7‐month flight to Mars and 17 since its landing on Mars on 6 August 2012. An SEP event is triggered, and an astronaut is warned as soon as dose rates exceed the omnipresent background level by at least 25%. This approach suggests that our system can provide astronauts with at least 30 min to avoid both peak radiation exposure and the majority of the cumulative dose from SEP events. Our nowcasting system is robust, easily implementable in real‐life scenarios, and achieves a near‐zero false alarm rate both in deep space and on the Martian surface.

The particle acceleration and transport process during solar eruptions is one of the critical and long-standing problems in space plasma physics. Through decades of research, it is well accepted that particles with higher energies released during a solar eruption arrive at observers earlier than the particles with lower energies, forming a well-known structure in the dynamic energy spectrum called particle velocity dispersion (VD), as frequently observed by space missions. However, this picture is challenged by new observations from NASA's Parker Solar Probe and ESA's Solar Orbiter which show an unexpected inverse velocity dispersion (IVD) phenomenon, where particles with higher-energies arrive later at the observer. Facing on the challenge, we here report the recent discovery of such IVD structures with 10 solar energetic proton events observed by Solar Orbiter, and then analyze the mechanisms causing this unusual phenomenon. We suggest that shock diffusive acceleration, with respect to magnetic reconnection, is probably a dominant mechanism to accelerate protons to tens of MeV in such events where particles need longer time to reach higher energies. And we determine, innovatively, the physical conditions and time scales during the actual shock acceleration process that cannot be observed directly.

When solar wind plasma propagates outward, the electron density decreases rapidly with solar distance, and charge states of heavy ions freeze in at 1 to 5 solar radii. Thus, charge states of heavy ions carry important information about the temperature profile in the lower corona. Oxygen and Iron ions are the most abundant heavy ions in the solar wind, and their data quality is relatively higher than that of other heavy ion species.Statistically, the averaged charge states of O and Fe in the solar wind usually maintain a weak positive correlation, sometimes exhibiting a strong positive correlation in solar wind associated with Coronal Mass Ejections (CMEs). The averaged charge states of O and Fe also correlate with solar wind speed and the solar cycle. In this study, we use ten years of in-situ solar wind Oxygen and Iron ion data obtained from the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced Composition Explorer (ACE). The data set is derived from Pulse Height Analysis (PHA) data, ensuring high time resolution (12 minutes). We identify around one hundred structures (time periods) where the averaged charge states of Fe and O exhibit significant anti-correlations (Spearman rank correlation coefficient lower than -0.5). These structures have distinct signatures. We analyze the time scales of these structures, the magnitudes of the averaged charge state variations for O and Fe, the temporal lags between the onset and end of those variations , the distribution of structures in the solar wind (e.g., whether they are associated with Interplanetary Coronal Mass Ejections (ICMEs) and their relative position within ICMEs), and their distribution in the solar cycle. Compared to more widely occurring positive correlation structures, anti-correlation structures are rarer and more interesting, reflecting the complex variations in the radial temperature profile and electron density profile of the lower corona. Large-scale anti-correlation structures suggest the presence of a relatively stable radial energy transfer process within 1 to 5 solar radii.

On November 27, 2021, Solar Orbiter has performed a gravity assist maneuver at the Earth and in December 2022 Solar Orbiter and STEREO-A were separated by less than 0.2 au. The periods around these two events provide unique opportunities to compare Solar Energetic Particle (SEP) observations from Solar Orbiter with corresponding observations from near-Earth missions and STEREO-A. The proximity of the different spacecraft offers a useful opportunity to compare the calibrations of the various particle instruments of the different spacecraft. Furthermore, the unique constellations can be used to study small-scale changes in the density distributions of the SEPs.We will present observations of near-relativistic electrons with energies from 50 keV to 400 keV as well as observations of protons with energies from 50 keV to 50 MeV. In particular, we use the period around the Earth gravity assist maneuver for a comparison of measurements from the Electron Proton Telescope (EPT) and the High Energy Telescope (HET) aboard Solar Orbiter with measurements from the Electron Proton and Alpha Monitor aboard the Advanced Composition Explorer (ACE), the 3DP instrument aboard Wind and the Electron Proton Helium Instrument (EPHIN) aboard SOHO. The period around the close encounter with STEREO-A is used for a comparison of EPT and HET observations with measurements from the High Energy Telescope (STA/HET) and the Solar Electron and Proton Telescope (SEPT) aboard the STEREO-A spacecraft. For both periods we discuss the instrument calibrations and possible physical explanations for differences in particle observations. Funding: This work was supported by the German Space Agency (Deutsches Zentrum für Luft- und Raumfahrt, e.V., (DLR)) under grant number 50OT2002 and has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 101004159 (SERPENTINE).

Impulsive solar energetic particle (SEP) events are typically associated with solar flares but the related particle injection and acceleration processes are still not well understood. We use in-situ and remote-sensing data from Solar Orbiter to establish a plausible link between a series of eruptions in a flaring region and a sequence of four SEP events measured at 0.5 AU between 5 and 6 March 2022. The direct comparison between these four events from the same source region allows to study the variability of the injected SEPs during an extended period of magnetic connectivity between Solar Orbiter and the flaring active region. In this study we analyze energetic electron, proton, and heavy ion data provided by the Energetic Particle Detector (EPD) suite onboard Solar Orbiter. Via a velocity dispersion analysis (VDA) of all measured particle species we estimate the solar event onset times which coincide with a series of solar eruptions that is observed by the Extreme Ultraviolet Imager (EUI) and the Spectrometer Telescope for Imaging X-rays (STIX) onboard Solar Orbiter. Further high-time-resolution EUV images and photospheric magnetic field information of the related active region is given by the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory. Solar Orbiter and Earth were nearly perfectly radially aligned at this time which enabled this additional remote sensing by SDO. We find that the energy spectra of the heavy ion in-situ measurements show significant differences between the four investigated SEP events in terms of overall particle intensity, spectral slope, and 3He / 4He abundances. By comparison with the remote-sensing observations we find that the two stronger SEP events (with higher 3He / 4He ratios) are related to solar eruptions with a more complex eruption pattern leading to extended brightening and restructuring of coronal loop structures. These new detailed observations can be used as starting point for quantitative modelling of flare-associated energetic particle acceleration and release in active regions.This work has been funded by the Spanish Ministerio de Ciencia, Innovación y Universidades project PID2019-104863RBI00/AEI/10.13039/501100011033.

Context. Solar energetic particle (SEP) events are critical for understanding particle acceleration and transport in the heliosphere. While most SEP events involve outward streaming particles along open magnetic field lines, bidirectional events characterized by simultaneous sunward and anti-sunward particle flows offer unique insights into magnetic field topology and the interplay of multiple acceleration sources. Aims. We investigate the origin and transport of energetic particles in two rare bidirectional anisotropic SEP events observed by Solar Orbiter, with a particular emphasis on their association with magnetic flux ropes. Methods. Energetic particles, solar wind plasma, magnetic field, and solar radio measurements were analysed. Via the velocity dispersion analysis, we determined release times and path lengths for distinct particle populations. Automated flux rope identification and magnetic helicity diagnostics were used to characterize magnetic flux ropes. Results. Both events showed two clear velocity dispersion signatures with opposite particle anisotropies during their onset phase. The sunward streaming protons, characterized by a delayed release time, a harder spectral index, and higher intensities, may be due to coronal mass ejection-driven shock acceleration, while the promptly released anti-sunward streaming protons are likely linked to flare acceleration. Notably, in both cases, small-scale flux ropes were identified in situ during the time intervals corresponding to the bidirectional particle streaming. Path lengths derived for sunward and anti-sunward injections were substantially greater than nominal values of the Parker field lines, further evidence of the role of the flux rope in shaping particle trajectories. Conclusions. These observations demonstrate that magnetic flux ropes can significantly affect magnetic connectivity to the source region and SEP propagation in the inner heliosphere, and that simultaneous velocity dispersion from two distinct particle sources can be used to place direct constraints on the topology of the flux rope. Our results highlight the value of combining particle anisotropy, release time, source spectra, and magnetic structure diagnostics to unravel SEP transport in complex transient magnetic structures, and also present new challenges for the current SEP transport model.

Predictions of the intensities of solar particle events are often fraught with uncertainties. Insufficient knowledge and understanding of the solar sources of the particles, and the conditions in the corona and in the inner heliosphere, as well as magnetic connectivity, have been limiting factors in making further progress. This presentation covers a study done by one of the Work Packages of the SERPENTINE project, and is based on the analysis of lists prepared by two other work packages of the same project, and logically consists of two parts. In the first part we performed a statistical analysis of a list of 45 multi-spacecraft events in solar cycle 25 observed by five spacecraft located in the inner Heliosphere (Solar Orbiter, Parker Solar Probe, Stereo A, Bepi Colombo), and one located at 1 AU close to the Earth (SOHO or Wind). The list, while prepared with a focus on the detection of protons above 25 MeV by two or more spacecraft, contains also information about electron observations around 100 keV and 1 MeV, respectively. Aiming to investigate the processes which are responsible for spreading energetic particles in longitude and latitude, and to estimate the importance of perpendicular diffusion in the latitudinal direction, we considered, together with other parameters, not only the longitudinal distances to the source, but also the differences in the total angle. In this part of our study we used methods such as correlation analysis and principal component analysis, and applied them to the list as a whole, as well as to different types of events. For example, we found that in the case of narrow-spread events perpendicular diffusion is sufficient to explain the spreading of particles from the solar source into the heliosphere, while in the case of wide-spread events an additional acceleration source is needed. We also evaluated the role of the speeds and sizes of the associated coronal mass ejections, as well as features of EUV waves appearing in the events, and relate different types of microwave (radio) emission to different groups of events. In the second part of this work we performed a statistical analysis of a list of 61 interplanetary shocks, observed by Solar Orbiter. By using a superposed epoch analysis, we built a statistical picture of ion time profiles around the shock front in several energy ranges. We also investigated which shock parameters are more important for particle energization by propagating interplanetary shocks, particularly in the case of an overlap in these lists.This study has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 101004159 (SERPENTINE).

Understanding the zenith angle dependence of the Martian surface radiation environment is crucial for planning future human exploration missions to Mars. In our previous research (Wimmer et al. 2015; Guo et al. 2021; Khaksarighiri et al. 2023) we extensively studied the zenith-angle dependence of the Martian surface radiation dose rate. Leveraging the same validated radiation model, calibrated with data from the Radiation Assessment Detector (RAD) on Mars, we calculated the flux of secondary downward particles reaching to the surface of Mars from various zenith angles resulting from the interaction of primary particles with the Martian atmosphere. These flux of secondary particles, coming from different zenith angles, can be integrated into a comprehensive topographic map of Mars, providing a detailed depiction of the global radiation landscape.The construction of this radiation map requires careful consideration of various factors, including atmospheric column density, local and large-scale topography offering potential shielding effects, and the input spectrum is affected by heliospheric modulation. Additionally, accounting for seasonal pressure cycles and daily atmospheric surface pressure due to thermal tides is essential. Our model specifically focused on the influence of zenith angle on atmospheric column depth and simulations tailored to the Gale Crater region, a region explored by the Curiosity rover. Applying this methodology allows us to create lookup tables of all secondary particles reaching the Martian surface from various zenith angles and evaluate the atmospheric impact. Employing these matrices alongside the incident spectrum enables the calculation of secondary particle flux from all zenith angles on the Martian surface.This method provides valuable insights into the fluctuations in radiation flux on Mars, facilitating thorough assessments of potential radiation hazards. Mission planners can leverage these data, obtaining vital information to identify secure landing areas and sheltered regions for astronauts on the Martian surface.

The interaction between waves and particles plays a pivotal role in particle acceleration near interplanetary shocks. Previously, detailed investigations about these processes were limited due to data availability and coarse time resolution from interplanetary missions. However, recent observations from the Solar Orbiter mission, with its high-resolution capabilities, have shed new light on this topic. In this work, we conduct a comprehensive study of wave-particle interactions near interplanetary shocks, using four years of data obtained by the Energetic Particle Detector (EPD), Magnetometer (MAG), Radio and Plasma Wave Analyzer (RPW) and Solar Wind Analyzer (SWA) onboard the Solar Orbiter. We analyze the propagation and polarization properties of waves associated with shocks through wavelet analysis. In addition, we reconstruct the pitch angle distributions and gyrophase distributions of particles in the solar wind frame of reference. These reconstructions help us identify wave-particle interactions in the data and investigate the energy transport during these events. We report on results from this ongoing analysis. Our results advance the understanding of particle acceleration induced by waves near interplanetary shocks, highlighting the role of wave-particle interactions in dynamic processes occurring in the inner heliosphere.

Since its start in 2021, the Solar EneRgetic ParticlE aNalysis plaTform for the INner hEliosphere (SERPENTINE) Project funded by EU H2020 program is using multi-spacecraft observations to investigate the origin of Solar Energetic Particles (SEPs) and providing new tools and datasets for the heliophysics community. SERPENTINE distributes new catalogues covering past and recent multipoint observations of SEP events, as well as their associated coronal mass ejections and interplanetary shocks. New SEP-related high-level data products from BepiColombo and Solar Orbiter missions, with added scientific value will be also provided in the near future. In this work, we summarize the structure, contents, and functionalities of the SERPENTINE Project Data Center (https://data.serpentine-h2020.eu/), a web-based interface providing open access to the various catalogues and high-level data products resulting from the project. This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004159 (SERPENTINE).

The Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory's Curiosity rover is the first-ever instrument continuously monitoring energetic particles on the surface of Mars. Since the rover's landing on August 6, 2012, RAD has accumulated valuable data, providing an unprecedented opportunity to assess the radiation environment across a solar cycle on an another planet.Understanding the radiation environment on Mars is crucial for a more accurate assessment of the risks posed to manned future space missions. Moreover, it also serves to further investigate planetary conditions, properties of the Sun, and galactic cosmic rays (GCRs). The radiation field on the surface of Mars primarily consists of charged particles, including primary GCRs propagating to the Martian surface and secondary particles generated through the interaction of primary GCRs with the Martian atmosphere or soil. Furthermore, it undergoes temporal changes caused by factors such as atmospheric pressure variations due to thermal tides, seasonal changes, geographical and topographical shielding effects, heliospheric modulation of GCRs, as well as Martian soil and subsurface conditions. Considering all these factors is essential for a comprehensive description of the radiation environment. Here we utilize the extensive RAD dataset spanning the last 11 years to delve into the intricate variations in particle flux. Our analysis encompasses a diverse array of particle species, providing a comprehensive understanding of how particle flux evolves over the course of one complete solar cycle. This extended time frame allows us to capture and analyze long-term trends, offering valuable insights into the dynamic nature of particle interactions within the Martian environment. By exploring the temporal patterns of particle flux across different species, we aim to contribute to a more nuanced comprehension of the complex radiation dynamics on Mars and its implications for future space missions and potential habitation. Additionally, we endeavored to understand the impacts of subsurface composition on the Martian surface radiation field, particularly in generating additional upward particles. This investigation is significant as it contributes to the exploration of potential subsurface water content on the surface of Mars.

Context. Solar wind is frequently categorized based on its respective solar source region. Solar wind that originates in coronal holes is consequently called coronal hole wind. Two well-established categorizations of the coronal hole wind, the scheme based on the charge-state composition, and the scheme based on proton plasma, identify a very different fraction of solar wind in the data from the Advanced Composition Explorer (ACE) as coronal hole wind during the solar activity minimum at the end of solar cycle 24. Aims. We investigate possible explanations for the different identifications of the coronal wind in 2009 in the scheme based on the charge-state composition (almost only coronal hole wind) and in the scheme based on the proton plasma (almost no coronal hole wind at the same time). The high fraction of coronal hole wind observed in the scheme based on the charge-state composition in 2009 was also addressed previously. Methods. We compared the properties of the respective coronal hole wind types and their changes with solar activity cycle in 2001-2010. As a comparison reference, we included the coronal hole wind as identified by an unsupervised machine-learning approach, k-means, in our analysis. Results. Because the ratio of the O7+ to O6+ densities drops systematically for the entire solar wind during the solar activity minimum, which cannot be captured by the fixed threshold on the O charge-state ratio suggested in the scheme based on the charge-state composition, we find that this solar wind classification likely misidentifies some slow solar wind as coronal hole wind during the solar activity minimum. The k-means coronal hole wind agrees with the very low fraction of coronal hole wind observed in the classification based on the proton plasma. In addition, the k-means classification we considered includes two types of coronal hole wind, the first of which is dominant during the solar activity maximum and exhibits comparatively higher O and Fe charge states, whereas the second is dominant during the solar activity minimum and features lower O and Fe charge states. A low fraction of coronal hole wind from low-latitude coronal holes observed by ACE in 2009 is plausible because during this time period, a very small number of low-latitude coronal holes was observed. The scheme based on proton plasma and 7-means also relies on fixed decision boundaries, wherein the decision boundary in the scheme based on the proton plasma for coronal hole wind appears to be better adapted for conditions at solar activity minimum than maximum. Conclusions. The results imply that the origin-oriented solar wind classification needs to be revisited, and they also suggest that an explicit inclusion of the phase of the solar activity cycle can be expected to improve the classification of the solar wind.

Acceleration of charged particles in solar flares, during reconnection of magnetic field lines in coronal loops, and by shock waves in the solar corona and interplanetary space are some of the substantial physical processes being studied by the Solar Orbiter mission. Cross-analysis of the light curves of the non-thermal parts of X-ray flares energy spectra registered by the Spectrometer Telescope for Imaging X-rays (STIX), and high-energy charged particle spectrograms recorded by the Energetic Particle Detector (EPD) suite assist us in furthering our understanding of these events. The anomalies and events in interplanetary space such as shocks, CIRs, ICMEs, solar and interplanetary radio bursts, SEPs being investigated in situ regime are typically associated with solar X-ray flares and/or SDO/AIA measurements of the solar atmosphere in multiple wavelengths when sources are on the visible side of the solar disk. In cases where the powerful flare occurs on the Sun's backside, the massive CME can reach the volumes in the interplanetary space right at the opposite side of the CME’s seed and manifests in different forms of irregularities in the solar wind parameters and magnetic field components as well in enhanced energetic particle fluxes. Such types of occasions are of particular interest due to their near-global impact on the inner heliosphere. In this study, we conduct a cross-analysis of the data derived from the Solar Wind Analyzer Proton-Alpha Sensor (SWA-PAS), Magnetometer (MAG), and EPD suite onboard the Solar Orbiter for the period of 13-14 March 2023, when a high-speed CME launched from near 180° from Earth accelerated an enormous quantity of high energy charged particles, from electrons to iron ions. At the time SolO was located 26°East of the Earth-Sun line at a distance of about 0.6 au. Even so, the CME quickly reached the spacecraft and manifested as a very sharp and strong shock at the front of which particles were accelerated additionally. In the analysis, we involve the data from the Suprathermal Ion Spectrograph (SIS), the SupraThermal Electrons and Protons (STEP), and the Electron Proton Telescope (EPT) of the EPD suite. This work is supported by the “Long-term program of support of the Ukrainian research teams at the Polish Academy of Sciences carried out in collaboration with the U.S. National Academy of Sciences with the financial support of external partners”.

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.

Freshly injected interstellar Pickup Ions (PUIs) are expected to exhibit a simple, torus-shaped velocity distribution function. The PUI velocity in the solar wind frame depends on the velocity of the interstellar neutral (ISN) population at the pick-up position. In this study, we compare PUI velocity distributions measured by the PLasma And SupraThermal Ion Composition (PLASTIC) instrument over the full orbit of Solar TErestrial RElations Observatory-Ahead (STEREO-A) directly. We define a new position-independent velocity measure for PUIs that takes the local direction of the interstellar neutral inflow into account. The resulting new PUI velocity measure corrects thereby for the position-dependent contribution of the ISN velocity. Pitch-angle distributions are then analysed depending on the magnetic-field azimuthal angle for different orbital positions and different values of the PUI velocity measure. The new PUI velocity measure shows an approximately constant cut-off over the complete orbit of STEREO-A. A torus signature is visible everywhere. Therein, a broadening of the torus signature outside the focusing cone and crescent regions and for lower velocity measure observed. In addition, we illustrate the symmetry between the primary and secondary ISN trajectory in the vicinity of the focusing cone. A torus signature associated with freshly injected PUIs is visible over the complete orbit of STEREO-A with increased density in the focusing cone. At least remnants of a torus signature remain for smaller values of the PUI velocity measure. The new velocity measure also prepares for PUI studies with Solar Orbiter.

Solar Energetic Particle Analysis Platform for the Inner Heliosphere (SERPENTINE) is a 42-months-long EU/H2020 project that started in January 2021 and focuses on the physics of Solar Energetic Particle (SEP) acceleration and transport. The project (see https://serpentine-h2020.eu) provides answers for three science questions: (Q1) what are the primary reasons for widespread SEP events; (Q2) what are the mechanisms responsible for acceleration ions from suprathermal to near-relativistic energies in coronal and interplanetary shocks; and (Q3) what is the role of shocks in the acceleration of electrons in SEP events. SERPENTINE makes use of the present capabilities provided by inner heliospheric missions such as Solar Orbiter, Parker Solar Probe and BepiColombo. In addition to the scientific objectives, the project develops and releases to the community a large number of analysis tools to facilitate the interpretation of observations. Also event catalogs and high-level datasets are produced and distributed. We will give a summary of the results of the project. Some of the science highlights include the several identified causes of widespread events related to both sources and transport (Q1), the role of local and averaged properties of shocks in ion acceleration (Q2), and the observational evidence of shocks as the primary accelerators of MeV electrons in gradual SEP events (Q3).

Context. The interaction between waves and particles is crucial for particle acceleration near interplanetary shocks. Previously, research on these processes was constrained by limited data and the coarse time resolution of interplanetary missions. However, recent high-resolution observations from the Solar Orbiter mission are providing new insights into this area. Aims. We analyzed data measured by the Energetic Particle Detector, the Magnetometer, and the Solar Wind Analyzer on board Solar Orbiter, to investigate wave-proton interactions upstream an interplanetary shock observed on April 8, 2022. Methods. We performed a mean-field-transformed wavelet analysis on the magnetic field data to derive the wave properties. We reconstructed pitch angle distributions and gyrophase distributions in the solar wind frame of reference to analyze the proton behavior. Results. We find that the observed waves are quasi-parallel propagating, ion-scale transverse waves that exhibit alternating left-handed and right-handed polarization. Fluxes of suprathermal protons oscillate quasi-periodically with these waves and show signs of wave modulation. In addition, signatures hinting at resonance, such as phase shifts across energy, are revealed in proton fluxes. The proton phase space density near the calculated resonant energy increases during the interaction, which indicates the acceleration or scattering of protons. Conclusions. We present direct observations of particles resonating with waves close to an interplanetary shock, which captures these dynamics within single wave periods. Our results highlight the role of wave-particle interactions in dynamic processes occurring in the inner heliosphere.

We examine ^3 He-rich solar energetic particles (SEPs) detected on 2023 October 24–25 by Solar Orbiter at 0.47 au. Measurements reveal that heavy-ion enhancements increase irregularly with mass, peaking at S. C, and especially N, Si, and S, stand out in the enhancement pattern with large abundances. Except for ^3 He, heavy-ion spectra can only be measured below 0.5 MeV nucleon ^−1 . At 0.386 MeV nucleon ^−1 , the event shows a huge ^3 He/ ^4 He ratio of 75.2 ± 33.9, larger than previously observed. Solar Dynamics Observatory extreme-ultraviolet data show a minifilament eruption at the solar source of ^3 He-rich SEPs that triggered a straight tiny jet. Located at the boundary of a low-latitude coronal hole, the jet base is a bright, small-scale region with a supergranulation scale size. The emission measure (EM) provides relatively cold source temperatures of 1.5–1.7 MK between the filament eruption and nonthermal type III radio burst onset. Analysis suggests that the EM distribution of temperature in the solar source could be a factor that affects the preferential selection of heavy ions for heating or acceleration, thus shaping the observed enhancement pattern. Including previously reported similar events indicates that the eruption of the minifilament is a common feature of events with heavy-ion enhancement not ordered by mass. Surprisingly, sources with weak magnetic fields show extreme ^3 He enrichment in these events. Moreover, the energy attained by heavy ions seems to be influenced by the size and form of the jets.

The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind, ultimately being vital in controlling solar activities and driving space weather. Despite numerous efforts to explore these regions, to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane, leaving their behavior and evolution poorly understood. This observation gap has left three top-level scientific questions unanswered: How does the solar dynamo work and drive the solar magnetic cycle? What drives the fast solar wind? How do space weather processes globally originate from the Sun and propagate throughout the solar system? The Solar Polarorbit Observatory(SPO) mission, a solar polar exploration spacecraft, is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes. In order to achieve its scientific goals, SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere, to observe the Sun in the extreme ultraviolet, X-ray, and radio wavelengths, to image the corona and the heliosphere up to 45 Rs, and to perform in-situ detection of magnetic fields,and low-and high-energy particles in the solar wind. The SPO mission is capable of providing critical vector magnetic fields and Doppler velocities of the polar regions to advance our understanding of the origin of the solar magnetic cycle, providing unprecedented imaging observations of the solar poles alongside in-situ measurements of charged particles and magnetic fields from high heliolatitudes to unveil the mass and energy supply that drive the fast solar wind, and providing observational constraints for improving our ability to model and predict the three-dimensional(3D) structures and propagation of space weather events.