Nina Dresing

We uncover a new pattern in the formation of fast coronal mass ejections (CMEs), consisting of three phases: a rapid lateral expansion ( hyperinflation ) lasting overexpansion ) and ending in the familiar self-similar expansion phase. The result is based on the analysis of 20 CMEs associated with flares and solar energetic particles (SEPs), which were comprehensively observed from multiple viewpoints at high cadence. To understand the role of the early expansion phase of CMEs in the formation of coronal shocks and consequent SEP acceleration, we studied the temporal relationship with other solar phenomena, including X-ray flares and radio emission. We find that (1) all events exhibit the three-stage formation sequence; (2) the overexpansion phase drives the shock and extreme-UV (EUV) wave, and explains why metric type II sources tend to form at CME flanks; (3) the hyperinflation phase is cotemporal to the flare impulsive phase, suggesting a common origin that is likely the addition of poloidal flux in the forming magnetic flux rope (MFR). Finally, we find that near-relativistic ∼53–105 keV) electrons are released first, near the flare peak and the onset of Type II. Note that ∼25 MeV protons are released later, toward the end of CME overexpansion, when shocks have formed. Our results clarify long-standing questions in the field and will contribute toward improved particle radiation forecasting schemes.

We present a study that combines remote-sensing and in situ observations of coronal mass ejections (CMEs) interacting with the nearby heliospheric current sheet (HCS). The sequence of eruptive events under study culminates in the largest directly observed flare of solar cycle 25 on 2024 October 3, producing a fast halo CME. Their source region can be linked to a so-called nested active region (or active longitude) that persisted over several solar rotations. Such long-lived regions reflect deep-seated magnetic structures that shape the global magnetic field configuration. By applying the drag-based CME propagation model, we connect the near-Sun observations from several CMEs during that activity period with in situ measurements. While one of the CMEs propagated on the opposite side of the HCS from Earth, and therefore did not produce in situ signatures near Earth, we detect, over the period 2024 October 5–10, a complex of HCS and CME structures propagating together with a shock ahead of them. The HCS seems to be locally replaced by the CME signatures, leading to a long-duration sector reversal of more than 48 hr. This event highlights the intrinsic connection between solar surface structures, the global magnetic field, and the evolution of complex eruptive events.

The Energetic Solar Eruptions: Data and Analysis Tools (SOLER) project presents a wide array of software tools to help in the analysis of solar energetic particle (SEP) events. The current heliospheric fleet of spacecraft, which has expanded significantly in recent years, offers an unprecedented number of simultaneous vantage points and, as such, uniquely extensive data on solar eruptions and their effects throughout the heliosphere. In an effort to utilize this data to its full potential, SOLER provides software tools in the form of easy-to-use open-source Python Jupyter Notebooks. The tools are designed such that even users with limited programming experience can get the most out of them, allowing one to focus on what matters most: the science. They are available online and require no installation by the user.The tools cover a wide range of functionalities. They include automatized data loaders that handle downloading from the web and enable visualization of SEP intensity-time profiles and other in-situ measurements made by various instruments aboard the heliospheric fleet. Additional tools assist in determining the Pitch-Angle Distributions (PAD) and capabilities for background-subtraction of SEPs and first-order anisotropies, their energy spectra, including the ability to fit the spectra using a variety of mathematical models. The final set of tools is dedicated to the determination of SEP event onset times and related analysis. These tools offer a linear regression method designed to identify the times at which SEP intensities change rapidly as well as a novel combination of a modified Poisson-CUSUM scheme, statistical bootstrapping, and methodological time-averaging to estimate the most probable onset time along with the associated confidence intervals.This project has received funding from the European Union's Horizon Europe research and innovation programme under grant agreement No 101134999 (SOLER). Views and opinions expressed are those of the authors only and do not necessarily reflect those of the European Union or HaDEA. Neither the European Union nor the granting authority can be held responsible for them.

Collisionless shocks are often modelled as smooth, planar surfaces - but many show organized corrugations that steer how particles get accelerated and how they radiate. We present a simple, linear magnetohydrodynamic (MHD) model that treats the shock as an evolving interface. This lets us separate two things: (1) the shock’s own properties and geometry, and (2) the statistics of the upstream turbulence that hits it. With this separation, we obtain adirect map from incoming fluctuations to the corrugation patterns they create, including their drift speed and coherence. In our model, the interface acts like an “impedance” that focuses broad-band turbulent power into fast-mode waves that skim along the shock. The shock responds most strongly when the wave’s normal group speed is small (a sharp, single-peaked response). Corrugation strength increases with compression, while the shock geometry and plasma beta control how long these patterns persist. The framework makes testable predictions linking upstream turbulence and shock shape to finestructure in electromagnetic signals from heliospheric and supernova-remnant shocks.

We investigate combined remote-sensing and in-situ data for a case study on a coronal mass ejection (CME) interacting with the nearby located heliospheric current sheet (HCS). The CME is related to the largest directly observed flare (X9.0) of solar cycle 25 on October 3, 2024. We find the CME source region to be a so-called nested active region, hence, persisting over several solar rotations. The active region and its evolution is therefore significantly linked to the structure of the global magnetic field. In-situ measurements indicate that a combined system of HCS and CME structures is propagating outward and generating a weak shock front ahead of it. The CME itself is highly interrupted by clear HCS-related structures, i.e., the heliospheric plasma sheet. The interaction process might have caused the CME-related shock-sheath region to be separated from the magnetic ejecta part by almost 40 hours. This event shows the intrinsic relation between solar surface structures, global magnetic field and the evolution of complex eruptive events.

On 11 November 2025, Solar Orbiter’s STIX instrument observed an X5-class solar flare, which peaked at approximately 10:01 UTC, originating from active region AR 14274 located at N23W23. Associated with this flare, a fast coronal mass ejection (CME) was observed by several coronagraphs, with a reconstructed 3D speed of about 2100 km s⁻¹. Solar Orbiter, near 0.82 au and ~18° west of Earth in heliolongitude, encountered the associated interplanetary CME (ICME) at around 09:00 UTC on 12 November, as observed by the MAG and SWA instruments. The ICME arrived at Earth roughly 9 hours later, around 18:00 UTC on 12 November.Solar Orbiter/EPD detected electrons with energies above 7 MeV, as well as penetrating ions exceeding 400 MeV. At Earth, the neutron monitor network recorded the ground level enhancement 77 (GLE 77), showing increases at least above a rigidity of 8 GV shortly after 10:00 UTC on 11 November. This event represents the largest GLE of Solar Cycle 25 observed to date and displays clear prompt and delayed components, presumably associated with flare-related and CME-driven particle acceleration.In this study, we analyze Solar Orbiter and near-Earth observations of the flare, CME, and associated solar energetic particle (SEP) event. We also include multi-spacecraft SEP measurements, in particular from ESA’s BepiColombo mission, which was nominally well connected to the parent active region.

The Sun is the most efficient particle accelerator in the solar system, capable of accelerating particles such as electrons and protons to relativistic energies. Solar Energetic Particles (SEPs) are known to be accelerated both at solar flare reconnection sites and by shocks driven by coronal mass ejections. One way to distinguish between these two SEP acceleration mechanisms is through their energy spectra, either fluence or peak intensity.While the spectral breaks commonly observed in solar energetic electron (SEE) spectra may represent signatures of the acceleration process, several transport-related effects have also been proposed as their origin. In this study, we analyse the energy spectra of intense SEE events measured by Solar Orbiter’s Energetic Particle Detector (EPD) between December 2020 and December 2022. EPD’s unprecedented energy resolution enables us to identify spectral features with greater detail than previously possible.We investigate the shape of SEE spectra by fitting them with a range of mathematical models. Our results are compared with previous studies, and we explore possible connections to transport-related effects. In addition, we examine potential correlations between spectral features and parameters such as radial distance or properties of the associated solar events.Our analysis reveals four distinct spectral shapes: single power-law, double power-law, and two types of triple power-law spectra, namely knee–knee (KK) and ankle–knee (AK) forms. No significant correlations with radial distance are found. However, the observed spectral shapes exhibit an ordering with respect to the longitudinal separation between the spacecraft and the associated solar flare.We conclude that multiple processes likely contribute to shaping SEE spectra. Our results suggest that the two breaks observed in KK triple power-law spectra arise from distinct physical effects, namely Langmuir-wave generation and pitch-angle scattering. Furthermore, the break in double power-law spectra may represent a merger of the first and second breaks seen in KK triple power-law spectra.

Context. The energy spectra of energetic particles offer valuable insights into particle acceleration processes. While the commonly observed spectral breaks in solar energetic electron (SEE) spectra could serve as fingerprints of the acceleration process, several transport-related effects have been proposed to be responsible as well. Here, we analyse the energy spectra of intense SEE events measured with Solar Orbiter’s Energetic Particle Detector (EPD) between December 2020 and December 2022. Aims. We investigate the shape of SEE spectra by fitting them with various mathematical models. We compare our results with previous studies and explore possible links to transport-related effects. We aim to identify potential correlations between spectral features and meaningful parameters, such as the radial distance, or the properties of associated solar events. Methods. We determined the background-subtracted peak-intensity spectra as observed by EPD, accounting for velocity dispersion. We fit the spectra of STEP and EPT with various mathematical models, using an automated method that chooses the best possible fit. Results. We found four different spectral shapes in our analysis: single power law, double power law and two types of triple power law: a knee-knee (KK) and an ankle-knee (AK) triple power law. No significant correlations with radial distance were identified; although the observed spectral shapes display an ordering with the longitudinal separation between the spacecraft and the associated solar flare. We also observed a correlation between the spectral index in the intermediate energy range at 70 keV and the strength of the associated solar flare. The correlation disappears at lower and higher energies, suggesting a stronger influence of transport effects at those energies. Conclusions. We conclude that multiple processes are likely involved in shaping SEE spectra. Our results suggest that the two breaks of the KK triple power law spectra arise from distinct effects, Langmuir-wave generation, and pitch-angle scattering, respectively. Our results also suggest that the break in the double power laws could represent a merger between the first and second breaks of KK triple power laws.

Context. Following its launch in April 2023, JUICE is now in its cruise phase to Jupiter, where it is scheduled to arrive in July 2031. JUICE carries a radiation monitor, namely the RADiation hard Electron Monitor (RADEM) to measure protons, electrons, and ions, detecting particles coming mainly from the anti-Sunwards direction. On 13 May 2024, a large solar energetic particle (SEP) event took place in association with an eruption close to the western limb of the Sun, as seen from Earth. Providentially, at that time, JUICE was located very close to STEREO-A, separated by only 0.13 au in radial distance, 0.3° in latitude, and 1.6° in longitude. Aims. Our main aims are to characterise the observations within the interplanetary (IP) context whereby SEPs propagated to near-Earth, JUICE, and STEREO-A observers, while performing a first comparison of energetic particle instruments on board JUICE and STEREO-A spacecraft. Methods. We analysed the IP context using in situ measurements and studied the proton anisotropies measured by near-Earth spacecraft and STEREO-A. We focussed on an isotropic period during the decay phase of the SEP event to compute the proton energy spectrum. We fit the STEREO-A spectrum and compared it to the one measured by SOHO and JUICE. Results. We find the proton spectral indices measured by JUICE, SOHO, and STEREO-A to be similar. The proton fluxes measured by RADEM are in agreement with those from STEREO-A, with a deviation of less than 25%. Conclusions. The RADEM instrument aboard JUICE is a valuable tool for measuring SEP events in the heliosphere, providing an excellent opportunity to study and characterise the energetic particle environment in the solar wind between 0.65 and 5.2 au. The intercalibration factors between the fluxes measured by STEREO-A and JUICE at the effective energies of 6.9 MeV, 13.3 MeV, 21.6 MeV, and 31.2 MeV are 1.02, 1.23, 1.12, and 0.95, respectively. We note that these intercalibration factors are valid only until 2024 July 10, when the configuration of the RADEM instrument was changed.