Abstract
An intense solar energetic particle (SEP) event was observed on 2021 October 9 by multiple spacecraft distributed near the ecliptic plane at heliocentric radial distances
R
≲ 1 au and within ...a narrow range of heliolongitudes. A stream interaction region (SIR), sequentially observed by Parker Solar Probe (PSP) at
R
= 0.76 au and 48° east from Earth (
ϕ
= E48°), STEREO-A (at
R
= 0.96 au,
ϕ
= E39°), Solar Orbiter (SolO; at
R
= 0.68 au,
ϕ
= E15°), BepiColombo (at
R
= 0.33 au,
ϕ
= W02°), and near-Earth spacecraft, regulated the observed intensity-time profiles and the anisotropic character of the SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at the onset of the SEP event, which resulted from the fact that PSP and STEREO-A were in the declining-speed region of the solar wind stream responsible for the SIR and from the passage of a steady magnetic field structure by SolO during the onset of the event. By contrast, the intensity-time profiles observed near Earth displayed a delayed onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV protons between the SIR and the shock driven by the parent coronal mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were nominally connected to the same region of the Sun, the intensity-time profiles at BepiColombo resemble those observed near Earth, with the bulk of low-energy ions also confined between the SIR and the CME-driven shock. This event exemplifies the impact that intervening large-scale interplanetary structures, such as corotating SIRs, have in shaping the properties of SEP events.
Solar energetic particle (SEP) events are a key ingredient of solar–terrestrial physics both for fundamental research and space weather applications. Multi-satellite observations are an important and ...incompletely exploited tool for studying the acceleration and the coronal and interplanetary propagation of the particles. While STEREO uses for this diagnostic two identical sets of instrumentation, there are many earlier observations carried out with different spacecraft. It is the aim of the SEPServer project to make these data and analysis tools available to a broad user community. The consortium will carry out data-driven analysis and simulation-based data analysis capable of deconvolving the effects of interplanetary transport and solar injection from SEP observations, and will compare the results with the electromagnetic signatures. The tools and results will be provided on the web server of the project in order to facilitate further analysis by the research community. This paper describes the data products and analysis strategies with one specific event, the case study of 13 July 2005. The release time of protons and electrons are derived using data-driven and simulation-based analyses, and compared with hard X-ray and radio signatures. The interconnection of the experimental and the simulation-based results are discussed in detail.
We applied a numerical modeling of the solar energetic particle (SEP) event inside a magnetic cloud in the solar wind to analyze the 17-22 MeV proton flux anisotropy observed on 1998 May 2 with the ...Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheric Observatory (SOHO), when SOHO was inside a magnetic cloud associated with a previous coronal mass ejection (CME). The analysis revealed a strong intermittency of the SEP transport parameters when different magnetic tubes were convected past the spacecraft. The estimated mean free path value varies over 1 order of magnitude, from 62 to 620 AU. The SEP event has been modeled with a prolonged injection of particles from a new CME into the previous ejecta comprising a set of magnetic loops. Both the prompt, direct proton flux and the delayed, counterstreaming flux were observed in the beginning and maximum phase of the event, but then the counterstreaming flux waned. The lack of counterstreaming protons can be explained either by the very fast escape of high-energy protons from the magnetic cloud, before they could complete one bounce in a narrow loop, or by the proton injection predominantly into one leg of a wide loop. An imprint of the magnetic compression at the leading part of the CME can be also found in the proton flux anisotropy data of SOHO/ERNE. These findings illustrate how high-precision anisotropy measurements and a numerical modeling can provide a kind of probe for the CME structure.
Large solar energetic particle (SEP) events occur in association with fast coronal mass ejections (CMEs) and flares. We have studied in detail the rise phase of the SEP event of 1998 May 2 observed ...with the particle telescope ERNE aboard the Solar and Heliospheric Observatory (SOHO) spacecraft and ground-based neutron monitors. Using the ERNE data and numerical modeling of the SEP transport, we present improved evaluations of the solar release profile of deka-MeV protons. The SOHO EIT images are used to study the CME liftoff processes and possible sources of deka-MeV and hecto-MeV proton streams. In a first stage of the deka-MeV proton production, which starts not later than 4 minutes after the radio flash and the Moreton wave start, particles get accelerated from a few MeV through 20 MeV In approximately 15 minutes. Both ERNE and neutron monitor data are used to study the release of solar protons in the hecto-MeV range. The proton acceleration to above 400 MeV was completed not later than 15-20 minutes after the onset of the eruption. However, injection profiles of deka-MeV protons and hecto-MeV protons were different. Differences in the release scenarios, energy spectra, and composition of deka-MeV protons versus hecto-MeV protons suggest two different acceleration regions involved, perhaps situated on initially open lines and initially closed lines of the coronal magnetic field. The first SEP productions were followed by a prolonged period of proton reacceleration, which continued in the similar to 10-100 MeV range for many hours and during which a common energy spectrum was formed.
An intense solar energetic particle (SEP) event was observed on 2021 October 9 by multiple spacecraft distributed near the ecliptic plane at heliocentric radial distances R ≲ 1 au and within a narrow ...range of heliolongitudes. A stream interaction region (SIR), sequentially observed by Parker Solar Probe (PSP) at R = 0.76 au and 48° east from Earth (ϕ = E48°), STEREO-A (at R = 0.96 au, ϕ = E39°), Solar Orbiter (SolO; at R = 0.68 au, ϕ = E15°), BepiColombo (at R = 0.33 au, ϕ = W02°), and near-Earth spacecraft, regulated the observed intensity-time profiles and the anisotropic character of the SEP event. PSP, STEREO-A, and SolO detected strong anisotropies at the onset of the SEP event, which resulted from the fact that PSP and STEREO-A were in the declining-speed region of the solar wind stream responsible for the SIR and from the passage of a steady magnetic field structure by SolO during the onset of the event. By contrast, the intensity-time profiles observed near Earth displayed a delayed onset at proton energies ≳13 MeV and an accumulation of ≲5 MeV protons between the SIR and the shock driven by the parent coronal mass ejection (CME). Even though BepiColombo, STEREO-A, and SolO were nominally connected to the same region of the Sun, the intensity-time profiles at BepiColombo resemble those observed near Earth, with the bulk of low-energy ions also confined between the SIR and the CME-driven shock. This event exemplifies the impact that intervening large-scale interplanetary structures, such as corotating SIRs, have in shaping the properties of SEP events.
We report on an energetic storm particle event on 2000 August 11 observed by ERNE on board SOHO, A large-intensity enhancement started simultaneously in all energy channels between 2 and 50 MeV at 11 ...UT. The concurrence of the onsets indicates the local nature of the particle event. Intensities increased 100-fold from the background level before 11 UT to the maximum of the event around 15:30 UT. Three hours after the maximum, at 18:19 UT, the SOHO CELIAS Proton Monitor observed the passage of an interplanetary shock. Our analysis of the proton energy spectrum during the event indicates that the interplanetary shock was capable of accelerating particles up to energies of an order of 50 MeV. Assuming that the energy spectrum prevailing in the event describes the seed particle population for shock reaceeleration, we find that the energy spectrum during major phases of the energetic storm particle event matches well with the assumption of a constant energy conversion power by the shock over the whole energy range from 2 to 50 MeV. We analyze the evolution of anisotropy of the proton flux in the 16-20 MeV channel of ERNE. The distribution of the directional intensity was observed to be relatively flat in the beginning of the event. Then the upstream distribution developed into a loss-cone-like distribution, and the intensity along the magnetic field relative to the intensity in the perpendicular direction was systematically reduced. At the shock passage, the distribution resembled a pancake.
During the period from January through mid‐May, 1997, four large Earth‐directed CMEs were observed by the Large Angle Spectroscopic Coronograph (LASCO). These CMEs were associated with long‐lasting ...fluxes of >1.6 MeV protons detected by the Energetic and Relativistic Nuclei and Electron instrument (ERNE). However, the magnitudes of energetic proton events differed dramatically on different occasions. In strong proton events, production of 10‐50 MeV protons started during expansion of the coronal Moreton wave in the western hemisphere of the Sun. The new SOHO observations suggest that potentialities of CMEs to produce energetic particles in the interplanetary medium crucially depend on the previous evolution of the explosion below ∼2R⊙. Forecasting of the near‐Earth >10 MeV proton intensity requires multiwavelength observations of the early phase of an event particularly the Extreme‐ultraviolet Imaging Telescope (EIT) observations.
SEPServer is a three-year collaborative project funded by the seventh framework programme (FP7-SPACE) of the European Union. The objective of the project is to provide access to state-of-the-art ...observations and analysis tools for the scientific community on solar energetic particle (SEP) events and related electromagnetic (EM) emissions. The project will eventually lead to better understanding of the particle acceleration and transport processes at the Sun and in the inner heliosphere. These processes lead to SEP events that form one of the key elements of space weather. In this paper we present the first results from the systematic analysis work performed on the following datasets: SOHO/ERNE, SOHO/EPHIN, ACE/EPAM, Wind/WAVES and GOES X-rays. A catalogue of SEP events at 1 AU, with complete coverage over solar cycle 23, based on high-energy ( similar to 68-MeV) protons from SOHO/ERNE and electron recordings of the events by SOHO/EPHIN and ACE/EPAM are presented. A total of 115 energetic particle events have been identified and analysed using velocity dispersion analysis (VDA) for protons and time-shifting analysis (TSA) for electrons and protons in order to infer the SEP release times at the Sun. EM observations during the times of the SEP event onset have been gathered and compared to the release time estimates of particles. Data from those events that occurred during the European day-time, i.e., those that also have observations from ground-based observatories included in SEPServer, are listed and a preliminary analysis of their associations is presented. We find that VDA results for protons can be a useful tool for the analysis of proton release times, but if the derived proton path length is out of a range of 1 AU < s3 AU, the result of the analysis may be compromised, as indicated by the anti-correlation of the derived path length and release time delay from the associated X-ray flare. The average path length derived from VDA is about 1.9 times the nominal length of the spiral magnetic field line. This implies that the path length of first-arriving MeV to deka-MeV protons is affected by interplanetary scattering. TSA of near-relativistic electrons results in a release time that shows significant scatter with respect to the EM emissions but with a trend of being delayed more with increasing distance between the flare and the nominal footpoint of the Earth-connected field line.
The onset of the >10‐MeV proton event of August 13–14, 1996, revealed a velocity dispersion, which is a signature of its solar origin, but no associated soft X ray flare was observed. The LASCO CME ...observations, the presence of AR 7981 beyond the west limb, and type II and IV radio burst timing with respect to the proton event onset indicate that the parent solar eruption may be centered on the back side of the Sun, at ∼150°W. In such a case, expanding CME‐associated wave can reach the Earth‐connected interplanetary magnetic field line in ∼1 hour and so give rise to the >10‐MeV proton event observed with the Energetic and Relativistic Nuclei and Electron (ERNE) instrument onboard SOHO. We verify this hypothesis against observational data and conclude that a solar back side eruption is the most plausible explanation of the August 13, 1996, event. We compare the August 13, 1996, event with events associated with Earth directed CMEs and show that the August 13, 1996, event reveals many properties common to >10‐MeV proton events originating from solar eruptions centered ∼90° away from the root of the Earth‐connected interplanetary magnetic field line. In such events, the first detected protons are released ∼1 hour after the start time of type II and IV radio bursts. The first injection spectrum is essentially harder than the spectrum at the intensity maximum; that is, the hard but less intensive proton production is followed by the major soft‐spectrum production when CME expands farther from the Sun.
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