The Forbush decrease observed by the SEVAN particle detector network in the 25th solar activity cycle

The temporal variations of cosmic-ray intensity, measured by ground-based detectors at various latitudes, longitudes, and altitudes, are related to the geophysical and solar phenomena. The latter are interplanetary coronal mass ejections and fast solar wind from coronal holes, which cause interplanetary magnetic field (IMF) abrupt variations near Earth. Interacting with the magnetosphere, they cause worldwide sudden decreases (Forbush decreases, FDs) of intensity followed by gradual recovery. The amplitude of the flux depletion depends on the type and energy of the registered particle, which in turn depends on geographical coordinates and the detector's energy threshold and selective power. SEVAN particle detector network with nodes in Europe and Armenia selects three types of particles that demonstrate coherent depletion and recovery and correspond to different energy galactic protons interacting with disturbed magnetospheric plasmas.

On November 3–4, 2021, an interplanetary coronal mass injection (ICME) hit the magnetosphere, sparking a strong G3-class geomagnetic storm and auroras as far south as California and New Mexico. All detectors of the SEVAN network have registered an (FD) of ≈5% depletion in a 1-min time series of count rates. Approaching the maximum solar activity cycle, large variations of the particle flux intensity were registered on February 27, March 23, 2023, and March 24, 2024.

In this work, we present measurements of these FDs performed on mountain altitudes on Aragats (Armenia), Lomnicky Stit (Slovakia), Mileshovka (Czechia), and at sea level DESY (Hamburg, Germany). We compared FD measurements made by SEVAN detectors and neutron monitors located on Aragats and Lomnicky Stit and made a correlation analysis of FD registration at different locations.