arXiv subjects

C. Palmroos

Publications and source records attributed to C. Palmroos.

8 recordsLinked to original sources

arXiv2026

Catalogue and statistics of greater than 100 MeV solar proton events during solar cycles 23-25 from SOHO-ERNE observations

The SPEARHEAD (specification, analysis, and re-calibration of high-energy particle data) project, funded by the European Union Horizon Europe programme, enhances the accuracy and usability of high-energy particle measurements. It investigates particle acceleration, release, and transport during solar eruptions by refining instrument response functions and cross-calibrating datasets. We present a comprehensive catalogue of greater than 100 MeV proton events identified from May 1996 to August 2024 using SOHO-ERNE penetrating-particle rates, together with associated solar phenomena derived from multi-instrument observations. The SEP events were detected through a systematic scan of ERNE-HED counter data and cross-calibrated with SOHO-EPHIN to derive peak fluxes and fluences. Each event was associated with its likely parent eruption using X-ray (XR) (GOES-XRS, RHESSI, SolO-STIX), radio (Wind-WAVES, STEREO-WAVES, ground-based observatories), and gamma-ray (Fermi-LAT) observations, CMEs (SOHO-LASCO), and ground-level enhancements (GLEs) (neutron monitors). Timings and physical properties were systematically compared to investigate the relationships between SEP onset, flare evolution, CME kinematics, and radio signatures. Statistical analyses reveal that most SEP releases closely follow flare and CME onsets, with moderate SEP-XR-CME correlations, and a strong SEP-GLE fluence link. These results indicate that high-energy SEP events are typically associated with strong solar activity signatures, with the observed intensities and timings strongly modulated by magnetic connectivity and coronal conditions. This catalogue provides the most extensive reference to date for high-energy SEP events over solar cycles 23-25, establishing a unified framework for future investigations of extreme particle acceleration.

astro-ph.SR↗

arXiv2025

The high-energy protons of the ground level enhancement (GLE74) event on 11 May 2024

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 eruption responsible for the emission of the primary particles, utilizing both in situ and remote-sensing. Observations spanning proton energies from a few MeV to around 1.64 GeV, collected from the Solar and Heliospheric Observatory (SOHO), the Geostationary Operational Environmental Satellite (GOES), the Solar Terrestrial Relations Observatory (STEREO-A), and neutron monitors, were integrated with records of the associated solar soft X-ray flare, coronal mass ejection, and radio bursts, to identify the solar origin of the GLE74. Additionally, a time-shift analysis was conducted to link the detected particles to their solar sources. Finally, a comparison of GLE74 to previous ones is carried out. GLE74 reached a maximum particle rigidity of at least 2.4 GV and was associated with a series of type III, type II, and type IV radio bursts. The release time of the primary solar energetic particles (SEPs) with an energy of 500 MeV was estimated to be around 01:21 UT. A significant SEP flux was observed from the anti-Sun direction with a relatively broad angular distribution, rather than a narrow, beam-like pattern, particularly during the main phase at the particle peak flux. Comparisons with previous GLEs suggest that GLE74 was a typical event in terms of solar eruption dynamics.

astro-ph.SR↗

arXiv2025

On the reason for the widespread energetic storm particle event of 13 March 2023

On 13 March 2023, when the Parker Solar Probe was situated on the far side of the Sun as seen from Earth, a large solar eruption took place creating a strong solar energetic particle (SEP) event observed by multiple spacecraft (S/C). The energetic event was observed at six well-separated locations: Parker Solar Probe, Solar Orbiter, BepiColombo, STEREO~A, near-Earth S/C, and MAVEN. An in-situ shock crossing and a related energetic storm particle (ESP) event were observed at all inner-heliospheric S/C, suggesting that the interplanetary coronal mass ejection (CME)-driven shock extended all around the Sun. However, the solar event was accompanied by a series of pre-event CMEs. We aim to characterize this extreme widespread SEP event and to provide an explanation for the unusual observation of a circumsolar interplanetary shock and corresponding circumsolar ESP event. We analyse data from seven space missions to characterize the solar eruption at the Sun, the energetic particle event, and the interplanetary context at each observer location as well as the magnetic connectivity of each observer to the Sun. We employ magnetohydrodynamic simulations of the solar wind in which we inject various CMEs that were launched before as well as contemporaneously with the solar eruption under study. In particular, we test two different scenarios that could have produced the observed global ESP event: 1) a single circumsolar blast-wave-like shock launched by the associated solar eruption, and 2) the combination of multiple CMEs driving shocks into different directions. By comparing the simulations of the two scenarios with observations we find that both settings are able to explain the observations. However, the blast-wave scenario performs slightly better in terms of the predicted shock arrival times at the various observers.

astro-ph.SR↗

arXiv2024

Determining the acceleration regions of in situ electrons using remote radio and X-ray observations

Solar energetic particles in the heliosphere are produced by flaring processes on the Sun or shocks driven by coronal mass ejections. These particles are regularly detected remotely as electromagnetic radiation (X-rays or radio emission), which they generate through various processes, or in situ by spacecraft monitoring the Sun and the heliosphere. We aim to combine remote-sensing and in situ observations of energetic electrons to determine the origin and acceleration mechanism of these particles. Here, we investigate the acceleration location, escape, and propagation directions of electron beams producing radio bursts observed with the Low Frequency Array (LOFAR), hard X-ray (HXR) emission and, in situ electrons observed at Solar Orbiter (SolO) on 3 October 2023. These observations are combined with a three-dimensional (3D) representation of the electron acceleration locations and results from a magneto-hydrodynamic (MHD) model of the solar corona in order to investigate the origin and connectivity of electrons observed remotely at the Sun to in situ electrons. We observed a type II radio burst with good connectivity to SolO, where a significant electron event was detected. However, type III radio bursts and Hard X-rays were also observed co-temporally with the elctron event but likely connected to SolO by different far-sided field lines. The injection times of the SolO electrons are simultaneous with both the onset of the type II radio burst, the group of type III bursts and the presence of a second HXR peak, however, the most direct connection to SolO is that of the type II burst location. The in situ electron spectra point to shock acceleration of electrons with a short-term connection to the source region.

astro-ph.SR↗

arXiv2024

Solar energetic particles injected inside and outside a magnetic cloud: The widespread solar energetic particle event on 2022 January 20

Context. On 2022 January 20, the Energetic Particle Detector (EPD) on board Solar Orbiter measured a solar energetic particle (SEP) event showing unusual first arriving particles from the anti-Sun direction. Near-Earth spacecraft separated 17{\deg} in longitude to the west from Solar Orbiter measured classic antisunward-directed fluxes. STEREO-A and MAVEN, separated 18{\deg} to the east and 143{\deg} to the west from Solar Orbiter respectively, also observed the event, suggesting that particles spread over at least 160{\deg} in the heliosphere. Results. Solar Orbiter was embedded in a MC erupting on 16 January from the same active region as that related to the SEP event on 20 January. The SEP event is related to a M5.5 flare and a fast CME-driven shock of 1433 km/s, which injected particles within and outside the MC. Taken together, the hard SEP spectra, the presence of a Type II radio burst, and the co-temporal Type III radio burst being observed from 80 MHz that appears to emanate from the Type II burst, suggest that the shock is likely the main accelerator of the particles. Conclusions. Our detailed analysis of the SEP event strongly suggests that the energetic particles are mainly accelerated by a CME-driven shock and are injected into and outside of a previous MC present in the heliosphere at the time of the particle onset. The sunward-propagating SEPs measured by Solar Orbiter are produced by the injection of particles along the longer (western) leg of the MC still connected to the Sun at the time of the release of the particles. The determined electron propagation path length inside the MC is around 30% longer than the estimated length of the loop leg of the MC itself (based on the graduated cylindrical shell model), which is consistent with the low number of field line rotations.

astro-ph.SR↗

arXiv2024

The solar cycle 25 multi-spacecraft solar energetic particle event catalog of the SERPENTINE project

The Solar energetic particle analysis platform for the inner heliosphere (SERPENTINE) project presents it's new multi-spacecraft SEP event catalog for events observed in solar cycle 25. Observations from five different viewpoints are utilized, provided by Solar Orbiter, Parker Solar Probe, STEREO A, BepiColombo, and the near-Earth spacecraft Wind and SOHO. The catalog contains key SEP parameters for 25-40 MeV protons, 1 MeV electrons, and 100 keV electrons. Furthermore, basic parameters of the associated flare and type-II radio burst are listed, as well as the coordinates of the observer and solar source locations. SEP onset times are determined using the Poisson-CUSUM method. SEP peak times and intensities refer to the global intensity maximum. If different viewing directions are available, we use the one with the earliest onset for the onset determination and the one with the highest peak intensity for the peak identification. Associated flares are identified using observations from near Earth and Solar Orbiter. Associated type II radio bursts are determined from ground-based observations in the metric frequency range and from spacecraft observations in the decametric range. The current version of the catalog contains 45 multi-spacecraft events observed in the period from Nov 2020 until May 2023, of which 13 were widespread events and four were classified as narrow-spread events. Using X-ray observations by GOES/XRS and Solar Orbiter/STIX, we were able to identify the associated flare in all but four events. Using ground-based and space-borne radio observations, we found an associated type-II radio burst for 40 events. In total, the catalog contains 142 single event observations, of which 20 (45) have been observed at radial distances below 0.6 AU (0.8 AU).

physics.space-ph↗

arXiv2023

Connecting remote and in situ observations of shock-accelerated electrons associated with a coronal mass ejection

One of the most prominent sources for energetic particles in our solar system are huge eruptions of magnetised plasma from the Sun called coronal mass ejections (CMEs), which usually drive shocks that accelerate charged particles up to relativistic energies. In particular, energetic electron beams can generate radio bursts through the plasma emission mechanism, for example, type II and accompanying herringbone bursts. Here, we investigate the acceleration location, escape, and propagation directions of various electron beams in the solar corona and compare them to the arrival of electrons at spacecraft. To track energetic electron beams, we use a synthesis of remote and direct observations combined with coronal modelling. Remote observations include ground-based radio observations from the Nancay Radioheliograph (NRH) combined with space-based extreme-ultraviolet and white-light observations from the Solar Dynamics Observatory (SDO), the Solar Terrestrial Relations Observatory (STEREO) and Solar Orbiter (SolO). We also use direct observations of energetic electrons from the STEREO and Wind spacecraft. These observations are then combined with a three-dimensional (3D) representation of the electron acceleration locations that combined with results from magneto-hydrodynamic models of the solar corona is used to investigate the origin and link of electrons observed remotely at the Sun to in situ electrons. We observed a type II radio burst followed by herringbone bursts that show single-frequency movement through time in NRH images. The movement of the type II burst and herringbone radio sources seems to be influenced by the regions in the corona where the CME is more capable of driving a shock. We also found similar inferred injection times of near-relativistic electrons at spacecraft to the emission time of the type II and herringbone bursts.

astro-ph.SR↗

arXiv2023

The 17 April 2021 widespread solar energetic particle event

Context. A solar eruption on 17 April 2021 produced a widespread Solar Energetic Particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere at heliocentric distances of 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare and a medium fast Coronal Mass Ejection (CME) with a speed of 880 km/s driving a shock, an EUV wave as well as long-lasting radio burst activity showing four distinct type III burst. Methods. A multi-spacecraft analysis of remote-sensing and in-situ observations is applied to attribute the SEP observations at the different locations to the various potential source regions at the Sun. An ENLIL simulation is used to characterize the interplanetary state and its role for the energetic particle transport. The magnetic connection between each spacecraft and the Sun is determined. Based on a reconstruction of the coronal shock front we determine the times when the shock establishes magnetic connections with the different observers. Radio observations are used to characterize the directivity of the four main injection episodes, which are then employed in a 2D SEP transport simulation. Results. Timing analysis of the inferred SEP solar injection suggests different source processes being important for the electron and the proton event. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source of the electron event. Conclusions. We find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110 degrees covered by distinct SEP injections.

astro-ph.SR↗