Forbush Decreases and the Global Electric Circuit

Abstract

Solar wind is the driving force of the dynamics of Earth’s magnetosphere and ionosphere. When sudden changes of Interplanetary magnetic field (IMF) and pressure pulses in the solar wind impact the magnetosphere, the magnetosphere is compressed and/or temporarily weakened through magnetic reconnection. This will cause variations in the ionosphere as well as atmosphere, leading to various weather concerns. One extreme example of solar wind pressure pulse and magnetic field enhancement is the Coronal Mass Ejections (CMEs), where huge amount of plasma bobs are thrown off from the Sun with speeds as high as ~2000 km/second. When CMEs impact the Earth, they not only compress the magnetosphere, but can also lead to the suppression of high-energy cosmic rays, known as Forbush decreases (FDs).   FDs are promising candidates in influencing the global electric circuit (GEC) system. Researchers have delved into these effects by examining variations, often disruptive, of the potential gradient (PG) in ground-based measurements taken in fair weather regions. Here we aim to investigate deviations observed in the diurnal curve of the PG, as compared to the mean values derived from fair weather conditions, during both mild and strong FD events. Unlike the traditional classification of FDs, which are based on ground level neutron monitor data, we classify FDs using measurements of the Alpha Magnetic Spectrometer (AMS-02) on the International Space Station. Using the superposed epoch analysis (SEA) method, we examined PGs collected between January 2010 and December 2019 at a specific station situated at a low latitude and high altitude: the Complejo Astronómico El Leoncito (CASLEO) in Argentina. We find that events associated with mild FDs show no significant change in the PG. However, for strong FDs, a clear increase in the PG is seen. For these events, we also find a good correlation between the variation of DST and Kp indices and the increase of PG, suggesting that the compression of the magnetosphere and the increase of PG is intimately related through FDs