Testing the Simultaneity of Forbush Decreases Using Latitudinal Dependent Neutron Monitors

Abstract

Forbush decrease (FD) is a transient reduction in the galactic cosmic ray (GCR) flow intensity. In this work, the simultaneity of Forbush decreases was tested. This was done using the daily and hourly cosmic ray (CR) counts from three latitudinal-dependent stations of South Pole (SOPO), Climax (CLMX), and Moscow (MOSC). The semi-manual method of FD selection was used in this work. The daily CR counts were obtained from the above mentioned CR stations. They were sorted and arranged in a text editor. A source FD table was obtained from the internet. The daily variations of these source dates were shown to indicate FDs. The magnitudes of the detected FDs were further determined using R. statistical software. A threshold of >-1.5% was used as a baseline for FD selection. A total of 64 FDs were generated for SOPO stations, while 77 and 81 FDs were generated for CLMX and MOSC stations respectively. These selected FDs and their corresponding magnitudes were arranged and displayed in tabular form. The simultaneous FDs were manually sorted from the FD list. The epoch approach was used to test the simultaneous events by plotting their hourly variations. The main phase of the simultaneous FDs revealed a universal time (UT) overlap. The magnitudes of the Simultaneous FDs were found to be similarly strong. These are in agreement with previous findings that simultaneous events are strong in magnitude and their main phase overlap in UT. A correlation between these FDs was tested. Strong and positive correlations were found between the FDs of the three latitudinal-dependent stations. These correlations indicate that FDs are latitudinal-dependent.