Features of Solar Activity Manifestations in Cosmic Rays May 10–11, 2024

The paper presents the results of an analysis of solar and geomagnetic activity, variations in cosmic ray fluxes during the period of May 10–11, 2024. At that time, the largest geomagnetic storm in the last 20 years occurred, caused by the arrival of several solar coronal plasma emissions to the Earth, which initiated the Forbush decrease in galactic cosmic rays (GCL) on May 10–11, 2024. This event was registered by the global network of ground-based neutron monitors (NM). The peculiarity of this period lies in the fact that, along with a significant decrease in GCL fluxes in the main phase of the geomagnetic storm, the GOES and SOHO spacecraft recorded the arrival of a stream of high-energy solar cosmic rays into near-Earth space. The source of these particles was a powerful solar flare of magnitude X5.8/2B (coordinates S17W44), which began on May 11 at 01:10 UT. SCL fluxes in a wide range of energies began to be observed on spacecraft almost simultaneously, and at ~02:10 UT, a short-term increase in cosmic rays began, recorded by high-latitude terrestrial NM, marked as the GLE 74 event. Thus, the ground-based installations demonstrated a complex behavior of particle fluxes due to the superposition of SCL fluxes on modulated HCL fluxes during Forbush lowering. The main focus of the work is on the assessment of the possible contribution of SCL fluxes to the observed increases in the NM count. The analysis uses data from the ground-based NM network, as well as data from CL measurements by CARPET instruments and neutron detectors located at the Dolgoprudnenskaya Scientific Station of the FIAN, at the Eurasian National University (Astana, Republic of Kazakhstan) and at the CASLEO Astronomical Complex (Argentine Andes). To determine the energy spectra of the SCL, measurement data from the GOES and SOHO spacecraft are used. Cosmic ray flux measurements are analyzed in conjunction with data on solar, interplanetary, and geomagnetic activity.