R. F. Wimmer-Schweingruber

• PhD, Prof. Dr.
• Kiel University

High energy solar protons were observed by particle detectors aboard spacecraft in near-Earth orbit on May 11, 2024 and produced the 74th ground level enhancement (GLE74) event registered by ground-based neutron monitors. This study involves a detailed reconstruction of the neutron monitor response, along with the identification of the solar erupti...

High energy solar protons were observed by particle detectors aboard spacecraft in near-Earth orbit on May 11, 2024 and produced the 74th ground level enhancement (GLE74) event registered by ground-based neutron monitors. This study involves a detailed reconstruction of the neutron monitor response, along with the identification of the solar erupti...

High energy solar protons were observed by particle detectors aboard spacecraft in near-Earth orbit on May 11, 2024 and produced the 74 th ground level enhancement (GLE74) event registered by ground-based neutron monitors. This study involves a detailed reconstruction of the neutron monitor response, along with the identification of the solar erupt...

We studied energetic particle intensity profiles observed by Solar Orbiter during the time period from April 2020 to April 2023, associated with the passage of interplanetary (IP) shocks. For our study we considered 58 IP forward shocks and analysed the possible correlations between some IP shock parameters and the electron and proton responses to...

We performed a survey of ³ He-rich events using observations from the Suprathermal Ion Spectrograph on the Solar Orbiter mission from 2020 to 2024. We identified 57 ³ He-rich events, each showing clear ³ He enhancements above the background and ³ He/ ⁴ He abundance ratios greater than 1 in at least one energy channel in the range from 193.2 keV nuc...

We report on the 2024 September 9 sustained gamma ray emission (SGRE) event observed by the Large Area Telescope onboard the Fermi satellite. The event was associated with a backside solar eruption observed by multiple spacecraft such as the Solar and Heliospheric Observatory (SOHO), Solar Terrestrial Relations Observatory (STEREO), Parker Solar Pr...

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...

With the launch of Solar Orbiter, the intensity and composition of suprathermal particles have been sampled within the inner heliosphere at distances between ∼0.3 and 1 au. This includes a multitude of observations of suprathermal ions associated with stream interaction regions (SIRs) measured by the Solar Orbiter Energetic Particle Detector, with...

Context. Solar energetic particle (SEP) events provide crucial insights into particle acceleration and transport mechanisms in the heliosphere. Inverse velocity dispersion (IVD) events, characterized by higher-energy particles that arrive later than lower-energy particles, challenge the classical understanding of SEP events and are increasingly obs...

Context. Freshly injected interstellar pick-up ion (PUIs) are expected to exhibit a simple, torus-shaped velocity distribution function (VDF). The PUI velocity in the solar wind (SW) frame depends on the velocity of the interstellar neutral (ISN) population at the pick-up position. Aims. We directly compare PUI VDFs measured by the plasma and supra...

In this study, a four-grid retarding potential analyzer (RPA) with drilled grid holes is investigated, focusing on correlations between grid orientations and resulting characteristics. The individual grids have a hexagonal hole pattern and can be mounted rotated relative to each other in multiples of 90°. An ion beam with a small divergence and a n...

Inverse velocity dispersion (IVD) events, characterized by higher-energy particles arriving later than lower-energy particles, challenge the classical understanding of SEP events and are increasingly observed by spacecraft, such as Parker Solar Probe (PSP) and Solar Orbiter (SolO). However, the mechanisms underlying IVD events remain poorly underst...

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 SupraTh...

Context. The Energetic Particle Detector (EPD) suite on board Solar Orbiter provides unprecedented high-resolution measurements of suprathermal and energetic particles in interplanetary space. These data can resolve particle dynamics near interplanetary shocks, offering new insights into particle acceleration and transport processes. Aims. We prese...

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 mea...

Interplanetary (IP) shocks are fundamental constituents of the heliosphere, where they form as a result of solar activity. We use previously unavailable measurements of IP shocks in the inner heliosphere provided by Solar Orbiter, and present a survey of the first 100 shocks observed in situ at different heliocentric distances during the rising pha...

In addition to the omnipresent Galactic Cosmic Rays (GCRs), 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 signif...

Context. The parameters of solar energetic particle (SEP) event profiles such as the onset time and peak time have been researched extensively to obtain information on the acceleration and transport of SEPs. The corotation of particle-filled magnetic flux tubes with the Sun is generally thought to play a minor role in determining intensity profiles...

The 2021 October 28 solar energetic particle (SEP) event was a rare ground level enhancement (GLE) event, where secondary particles from the interactions of SEPs with the Earth’s atmosphere were detected by neutron monitors on the ground. A number of papers have examined the solar signatures, neutron monitor observations, and the characteristics of...

Solar wind is frequently categorized based on its respective solar source region. 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...

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 insight...

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 diffe...

On 2022 March 10 a coronal mass ejection erupted from the Sun, resulting in Solar Orbiter observations at 0.45 au of both dispersive solar energetic particles arriving prior to the interplanetary coronal mass ejection (ICME) and locally accelerated particles near the ICME-associated shock structure as it passed the spacecraft on 2022 March 11. This...

Context. Observations of the Fe and O charge states in the solar wind and interplanetary coronal mass ejections (ICMEs) generally exhibit a positive correlation between the average charge states of Fe and O (avQ Fe and avQ O ). Because Fe and O charge states freeze at different heights in the corona, this positive correlation indicates that conditi...

In regions of the solar system distant from planetary magnetic fields, galactic cosmic rays (GCRs) have generally been assumed to be uniformly distributed throughout interplanetary space. However, our analysis of data from the Chang’E-4 lander revealed a region of reduced GCR flux in the pre-noon sector of the lunar orbit. Further investigation sug...

Context: Parameters of solar energetic particle (SEP) event profiles such as the onset time and peak time have been researched extensively to obtain information on acceleration and transport of SEPs. Corotation of particle-filled magnetic flux tubes with the Sun is generally thought to play a minor role in determining intensity profiles. However re...

In this study, we employ the combined charged particle measurements from Integrated Science Investigation of the Sun on board the Parker Solar Probe (PSP) and Energetic Particle Detector on board the Solar Orbiter (SolO) to study the composition variation of the solar energetic particle (SEP) event occurring on 2023 May 16. During the event, SolO a...

Interplanetary shocks are fundamental constituents of the heliosphere, where they form as a result of solar activity. We use previously unavailable measurements of interplanetary shocks in the inner heliosphere provided by Solar Orbiter, and present a survey of the first 100 shocks observed in situ at different heliocentric distances during the ris...

In this study, we employ the combined charged particle measurements from Integrated Science Investigation of the Sun (\ISOIS) onboard the Parker Solar Probe (PSP) and Energetic Particle Detector (EPD) onboard the Solar Orbiter (SolO) to study the composition variation of the solar energetic particle (SEP) event occurring on May 16, 2023. During the...

Multispacecraft observations of ³ He-rich solar energetic particle (SEP) events are scarce, but much needed in order to understand and properly constrain the source and transport of these remarkably enriched ³ He SEP events. In this paper, we report 15 ³ He-rich SEP events that were detected by the Advanced Composition Explorer, the Solar Terrestri...

We have surveyed ³ He-rich events on the Solar Orbiter mission from 2020 April to 2024 April, selecting isolated injections whose rollover ³ He spectral shape is presumed to represent the initial acceleration state, unprocessed by subsequent activity such as coronal mass ejections or jets. A main goal has been to find relationships between the spec...

On 2022‐02‐15, solar eruptions caused one of the most intensive Solar Particle Events (SPEs) in Solar Cycle 25 observed at various heliospheric locations. This study focuses on the enhancements of energetic proton flux observed by multiple detectors located at the orbit and on the surface of Mars. We carry out the first analysis by the Mars Energet...

On 2022 March 10, a coronal mass ejection (CME) erupted from the Sun, resulting in Solar Orbiter observations at 0.45 au of both dispersive solar energetic particles arriving prior to the interplanetary CME (ICME) and locally accelerated particles near the ICME-associated shock structure as it passed the spacecraft on 2022 March 11. This shock was...

We report direct observations of a fast magnetosonic forward–reverse shock pair observed by Solar Orbiter on 2022 March 8 at the short heliocentric distance of 0.5 au. The structure, sharing some features with fully-formed stream interaction regions, is due to the interaction between two successive coronal mass ejections (CMEs), never previously ob...

Observations of the Fe and O charge states in the solar wind and interplanetary coronal mass ejections (ICMEs) generally exhibit a positive correlation between the averaged charge states of Fe and O (avQ Fe and avQ O). Because Fe and O charge states freeze in at different heights in the corona, this positive correlation indicates that conditions at...

The Sun drives a supersonic wind which inflates a giant plasma bubble in our very local interstellar neighborhood, the heliosphere. It is bathed in an extremely variable background of energetic ions and electrons which originate from a number of sources. Solar energetic particles (SEPs) are accelerated in the vicinity of the Sun, whereas shocks dri...

The energy spectral shape of solar energetic electron events carries important information on the energetic electron source/acceleration at the Sun. We investigate the association of six newly identified solar energetic electron spectral types with solar eruptive phenomena, including the downward double-power-law (DDPL) spectrum with break energy E...

We present the first observations of in situ electron acceleration at corotating interaction region (CIR) shocks near 1 au, utilizing measurements from Wind and Magnetospheric Multiscale (MMS) mission in the interplanetary medium. As the forward (reverse) shock of the 2018 January CIR (the 2020 February CIR) moves from Wind at [206, 92, −7] R E ([2...

Context. Interplanetary collisionless shocks are known to be capable of accelerating charged particles up to hundreds of MeV. However, the underlying acceleration mechanisms are still under debate. Aims. We present the dynamic behaviors of energetic protons that are accelerated by an interplanetary shock that was observed with unprecedented high-re...

Context. The Solar Orbiter Metis coronagraph captures images of the solar corona in both visible (VL) and ultraviolet (UV) light. Tracks ascribable to the passage of galactic and solar particles appear in the Metis images. An algorithm implemented in the Metis processing electronics allows us to separate the pixels fired by VL photons from those cr...

The Parker Solar Probe (PSP) and Solar Orbiter (SolO) missions opened a new observational window in the inner heliosphere, which is finally accessible to direct measurements. On 2022 September 5, a coronal mass ejection (CME)-driven interplanetary (IP) shock was observed as close as 0.07 au by PSP. The CME then reached SolO, which was radially well...

Aims.We studied the first multi-spacecraft high-energy solar energetic particle (SEP) event of solar cycle 25, which triggered a ground level enhancement (GLE) on 28 October 2021, using data from multiple observers (Parker Solar Probe, STEREO-A, Solar Orbiter, GOES, SOHO, BepiColombo, and the Mars Science Laboratory) that were widely distributed th...

Context. When describing the relationships between two data sets, four crucial aspects must be considered, namely: timescales, intrinsic lags, linear relationships, and non-linear relationships. We present a tool that combines these four aspects and visualizes the underlying structure where two data sets are highly related. The basic mathematical m...

Context. By coupling the EUropean Heliospheric FORcasting Information Asset (EUHFORIA) and the improved Particle Acceleration and Transport in the Heliosphere (iPATH) models, we model two energetic storm particle (ESP) events originating from the same active region (AR 13088) and observed by Solar Orbiter (SolO) on August 31, 2022, and September 5,...

Context. When describing the relationships between two data sets, time scales, intrinsic lags, linear relationships and non-linear relationships are four crucial aspects. We present a tool that combines these four aspects together and visualizes the underlying structure where two data sets are highly related. The basic mathematical methods used are...

Context. By coupling the EUropean Heliospheric FORcasting Information Asset (EUHFORIA) and the improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, two energetic storm particle (ESP) events, originating from the same active region (AR 13088) and observed by Solar Orbiter (SolO) on August 31 2022 and September 05 2022, are...

We present Solar Orbiter energetic particle observations of two ³ He-rich events with features more clearly observed than in prior studies. The event of 2022 November 9 observed from 0.59 au contained hundreds of ultraheavy (UH; mass >78 amu) ions whereas previous observations at 1 au have shown only an occasional count or two. The event of 2023 Ap...

How thermal particles are accelerated to suprathermal energies is an unsolved issue, crucial for many astrophysical systems. We report novel observations of irregular, dispersive enhancements of the suprathermal particle population upstream of a high-Mach-number interplanetary shock. We interpret the observed behavior as irregular “injections” of s...

Observations of Solar Energetic Particles (SEPs) using the Suprathermal Ion Spectrograph (SIS), which is part of the Energetic Particle Detector suite on the Solar Orbiter mission, present an unprecedented opportunity to investigate the composition and evolution of SEPs in close proximity to the Sun. By analyzing data from the SIS instrument, we ha...

Context. Solar Orbiter, a mission developed by the European Space Agency, explores in situ plasma across the inner heliosphere while providing remote-sensing observations of the Sun. The mission aims to study the solar wind, but also transient structures such as interplanetary coronal mass ejections and stream interaction regions. These structures...

Astronauts will be facing many risks when they are away from Earth's environment, among which radiation is one of the most vital and troublesome issues. Space radiation exposure from energetic particles of Solar Energetic Particles (SEPs) and Galactic Cosmic Rays (GCRs) can adversely impact the Central Nervous System (CNS) by inducing acute (i.e.,...

Solar wind properties are determined by the conditions of their solar source region and transport history. Solar wind parameters, such as proton speed, proton density, proton temperature, magnetic field strength, and the charge state composition of oxygen, are used as proxies to investigate the solar source region of the solar wind. The transport a...

Context. After their acceleration and release at the Sun, solar energetic particles (SEPs) are injected into the interplanetary medium and are bound to the interplanetary magnetic field (IMF) by the Lorentz force. The expansion of the IMF close to the Sun focuses the particle pitch-angle distribution, and scattering counteracts this focusing. Solar...

Context. Solar wind properties are determined by the conditions of their solar source region and transport history. Solar wind parameters, such as proton speed, proton density, proton temperature, magnetic field strength, and the charge state composition of oxygen, are used as proxies to investigate the solar source region of the solar wind. The so...

Plain Language Summary Human beings are considering going back to the Moon and eventually to Mars within the next decades. However, we are still facing one major hurdle “space radiation” which is a significant and unavoidable risk for crews' health, especially for long‐term stays at future lunar or martian stations. In particular, sporadic solar en...

Despite the growing importance of planetary Space Weather forecasting and radiation protection for science and robotic exploration and the need for accurate Space Weather monitoring and predictions, only a limited number of spacecraft have dedicated instrumentation for this purpose. However, every spacecraft (planetary or astronomical) has hundreds...

We highlight the importance of magnetic reconnection at the heliopause, both asone of the key processes driving the interaction between solar and interstellar media,but also as an element of the definition of the heliopause itself. We highlight the mainobservations that have fed the current debates on the definition, location and shapeof the heliop...

Aims. This study analyses relativistic electron measurements obtained by the High Energy Telescope (HET) aboard Solar Orbiter in the energy range from 200 keV to above 10 MeV. Caveats of these measurements are discussed. The purpose of this study is to analyse anisotropies of relativistic solar energetic electrons utilising the different viewing di...

Aims. We study the radial evolution of near-relativistic solar energetic electron (SEE) events observed by at least two spacecraft at different heliocentric distances and with small separation angles between their magnetic footpoints at the Sun. Methods. We identified SEE events for which Solar Orbiter and either Wind or STEREO-A had a small longit...

Context. The Solar Orbiter spacecraft made its first close perihelion passes in 2022, reaching 0.32 au on 26 March and 0.29 au on 12 October. Transient activity was relatively low, making it possible to perform measurements of the quiet-time suprathermal ion pool over multi-day periods. Aims. The inner heliosphere suprathermal ion pool is a source...

Solar energetic particles (SEPs) from suprathermal (few keV) up to relativistic (∼few GeV) energies are accelerated at the Sun in association with solar flares and coronal mass ejection-driven shock waves. Although our knowledge of the origin, acceleration, and transport of these particles from close to the Sun through the interplanetary medium has...

We investigate the peak flux energy spectrum of 458 solar energetic electron (SEE) events with a clear velocity dispersion detected at energies from ≤4.2 to ≥108 keV by Wind/3DP from 1994 December through 2019 December, utilizing a pan-spectrum fitting method. According to the fitted spectral parameters, these 458 events are self-consistently class...

Future expeditions into interplanetary space, and in particular to the Moon and Mars, will expose astronauts to very high levels of cosmic radiation, which are known due to years of research and instruments that have been sent to space. It is, however, a limitation in understanding the risks of this radiation for the human body due to difficulties...

Energy spectra of X-ray solar flares observed by the Spectrometer-Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter consist of both thermal and non-thermal parts. The thermal part is present in all solar events. When the non-thermal part of the energy spectrum begins to dominate, we can expect detection in interplanetary space of high-e...

The properties of the solar wind represent a mixture of indicators for solar origin and transport effects. Both are of interest for the understanding of heliophysics and space weather effects. Most available solar wind classifications focus on the solar origin, in part based on transport effected properties. We aim to identify the solar wind proper...

We report Solar Orbiter observations of six recurrent solar energetic particle injections in 2022 March 3−6 at ∼0.5 au. All but one were associated with jets emanating from a plage near a large sunspot in active region 12 957. We saw large jets in injections with high ³ He and Fe enrichments and minor jets in injections with no or lower enrichments...

The Radiation Assessment Detector (RAD) on board the Mars Science Laboratory's Curiosity rover has been monitoring the surface radiation environment on Mars for just over 10 years. It has been found by Wimmer‐Schweingruber et al. (2015, https://doi.org/10.1002/2015gl066664) that within the narrow view cone of RAD, the directionality of the radiatio...

Aims. We perform a statistical study of the relations between the properties of solar energetic electron (SEE) events measured by the MESSENGER mission from 2010 to 2015 and the parameters of the respective parent solar activity phenomena in order to identify the potential correlations between them. During the time of analysis, the MESSENGER helioc...

Context. Interplanetary collisionless shocks are known to be sources of energetic charged particles up to hundreds of MeV. However, the underlying acceleration mechanisms are still under debate. Aims. We determine the properties of suprathermal protons accelerated by the interplanetary shock on 2021 November 3 with the unprecedented high-resolution...

A detailed overview of the knowledge gaps in our understanding of the heliospheric interaction with the largely unexplored Very Local Interstellar Medium (VLISM) are provided along with predictions of with the scientific discoveries that await. The new measurements required to make progress in this expanding frontier of space physics are discussed...

The Sun drives a supersonic wind which inflates a giant plasma bubble in our very local interstellar neighborhood, the heliosphere. Its boundaries and the turbulent magnetic field shield the solar system from much of the interstellar medium as well as the low-energy portion of galactic cosmic rays (GCRs) which are accelerated primarily by super-nov...

We highlight the importance of magnetic reconnection at the heliopause, both as one of the key processes driving the interaction between solar and interstellar media, but also as an element of the definition of the heliopause itself. We highlight the main observations that have fed the current debates on the definition, location and shape of the he...

Context. Coronal mass ejections (CMEs) are extremely dynamical, large-scale events in which plasma – but not only the coronal plasma – is ejected into interplanetary space. If a CME is detected in situ by a spacecraft located in the interplanetary medium, it is then called an interplanetary coronal mass ejection (ICME). This solar activity has been...

Context. During the first close perihelion pass of Solar Orbiter, a series of impulsive ³ He-rich solar particle events was observed on 18–19 March 2022 from a distance of 0.36 au. In addition to the energetic particle, radio, and X-ray data from Solar Orbiter, the events were observed in radio and/or extreme ultraviolet by STEREO-A, SDO, Wind, and...

Context. We present a list of 61 solar energetic electron (SEE) events measured by the MESSENGER mission and the radial dependences of some parameters associated with these SEE events. The analysis covers the period from 2010 to 2015, when the heliocentric distance of MESSENGER varied between 0.31 and 0.47 au. We also show the radial dependences fo...

Aims. We perform a statistical study of the relations between the properties of solar energetic electron (SEE) events measured by the MESSENGER mission from 2010 to 2015 and the parameters of the respective parent solar activity phenomena to identify the potential correlations between them. During the time of analysis MESSENGER heliocentric distanc...