Περίληψη:
The study of space-weather effects and more specifically Forbush decreases of the cosmic-ray intensity depends on space and ground measurements. Very often Forbush decreases and geomagnetic storms are accompanied by pre-increases and/or pre-decreases manifested in cosmic-ray behavior, known as precursory signs. These cosmic-ray intensity variations do not coincide with the shock arrival but begin well before (up to 24 hours) the onset of the main event. In this study a group of large Forbush decreases with amplitude ≥ 4% was examined for precursors. According to the helio-longitude of the solar source, the events were separated into three categories: western (21 ∘≤ helio-longitude ≤ 60∘), eastern (− 60 ∘≤ helio-longitude ≤ − 21 ∘), and central (− 20 ∘≤ helio-longitude ≤ 20 ∘). The selected events cover 1967 – 2017. The analysis of the Forbush decreases and the plotting of the asymptotic longitudinal cosmic-ray distribution diagrams were based on the “Global Survey Method” and the “Ring of Stations” method, respectively. Data on solar flares, solar-wind speed, interplanetary magnetic field, and geomagnetic indices (Kp and Dst) were also used. The results show the clear signs of precursors in a significant number of events. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Συγγραφείς:
Papailiou, M.
Abunina, M.
Mavromichalaki, H.
Belov, A.
Abunin, A.
Eroshenko, E.
Yanke, V.
