Automated detection of simultaneous/non-simultaneous Forbush decreases and the associated cosmic ray phenomena

Abstract

The knowledge of the periodic diurnal anisotropy in the cosmic ray (CR) flux intensity as well as the enhanced anisotropy that might accompany Forbush events is not novel. Theoretical models and several methodological approaches such as Fourier techniques developed to predict the diurnal vectors started appearing in the literature since 1960s’. Consequently, the vectors have been successfully calculated on both annual, monthly and day to day basis. The amplitude and the phase of the unusually large diurnal wave trains that happen at the time of FDs have also been estimated by the method of Fourier analysis. However, direct application of Fourier transform algorithms to account for the enhanced CR diurnal anisotropies during the period of Forbush events is one of the open questions in CR research. Manual FD event identification technique, traditionally employed to select the short-term rapid depressions (Forbush decreases, FDs) in CR intensity is inefficient to handle the characteristic CR flux superposition tendencies. Identifications of FDs and the accompanying enhanced amplitude of the CR diurnal anisotropies are rarely investigated simultaneously. This poses a drawback on quantitative prediction of the impact of CR anisotropies on the detectable number of global and location dependent FDs as well as their magnitudes. A detailed and rigorous analysis involving simultaneous application of Fourier analysis to FDs and diurnal anisotropies, selections of FDs from Fourier transformed and raw CR data are attempted in the current work. The results are discussed with emphasis on simultaneity of FDs detected at different locations at Earth.