Search

The first ground-level enhancement of the current Solar Cycle 25 occurred on 28 October 2021. It was observed by several space-borne and ground-based instruments, specifically neutron monitors. A moderate count-rate increase over the background was observed by high-altitude polar stations on the South Pole and Dome C stations at the Antarctic plateau. Most of the neutron monitors registered only marginal count-rate increases. Using detrended records and employing a method verified by direct space-borne measurements, we derive the rigidity spectra and angular distributions of the incoming solar protons in the vicinity of Earth. For the analysis, we employed a newly computed and parameterized neutron-monitor yield function. The rigidity spectra and anisotropy of solar protons were obtained in their time evolution throughout the event. A comparison with the Solar and Heliospheric Observatory/Energetic and Relativistic Nuclei and Electron (SOHO/ENRE) experiment data is also performed. We briefly discuss the results derived from our analysis.

Using the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheric Observatory (SOHO), we have measured the 17-22 MeV proton flux anisotropy during the 1998 May 2-3 solar energetic particle (SEP) event, when SOHO was inside a magnetic cloud associated with a previous coronal mass ejection (CME). The ability of the SOHO/ERNE to measure particle fluxes with high angular resolution makes it a unique instrument for observing SEPs under weak scattering conditions. During most of the first 4 hr of the SEP event that started shortly after 14 UT on 1998 May 2, the proton intensity parallel to the magnetic field was ~1000 times higher than in the perpendicular direction. The ERNE observations indicate that the magnetic flux-rope structure of the CME provides a "highway" for transport of solar energetic protons with a parallel mean free path of at least 10 AU. The particle telescope ERNE/High Energy Detector was able to measure the proton angular distribution, which was narrow to an extent that it could not be resolved with other instruments. Within 30-45 minutes after the onset of the proton event, a counterstreaming flux was also identified. The ERNE data also revealed a narrow magnetic tube in which protons were much less anisotropic than in the rest of the rope. We briefly discuss the implications of these findings for the origin and structure of the CME.

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 (~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