Investigating The Dependence Of Forbush Decrease On Geomagnetic Cutoff Rigidity

Abstract

The dependence of Forbush decreases on geomagnetic cutoff rigidity has been studied. The study aimed to investigate the implications of geomagnetic cutoff rigidity on forbush decrease. To achieve this aim, the data of cosmic ray daily count from six neutron stations of Tibet, Esoi, Tsumeb, Oulu, Apatity, and Magadan were used. These data covered a period of six (6) years from the year 2010 to 2015. An advanced manual method developed by Okike and Umahi (2019b) was used to select the FDs through R. statistical software.  A sharp depression in the intensity of cosmic ray variation known as Forbush decrease (FD) was detected. A large number of FDs were recorded. The results of our analysis was grouped into stations of high, low and middle rigidity. The stations of low rigidity recorded the highest number of FDs followed by stations of middle rigidity while the stations of high rigidity recorded the least number of FDs. The magnitude of these FDs was determined. It was observed that FD magnitudes vary inversely with the station's rigidity. A correlation between the FD magnitudes of the cosmic ray (CR) stations was also tested. It was observed that stations of low rigidity indicated the best correlation followed by the stations of middle rigidity, while the stations of high rigidity indicated the least correlation. A regression was further tested between the FD magnitudes of the different stations. The result of the regression between FDs of different stations was 99.8% , 98% and 97.5% significant for stations low, high and middle rigidity stations respectively. In summary, this study used a large number of events to test the rigidity dependence of FDs, and it was observed that FDs are inversely related to the cutoff rigidity. Thus, FDs measured at the CR stations can be used to examine the effects of rigidity between the stations.