Testing the Empirical Relationship between Forbush Decreases and Cosmic Ray Diurnal Anisotropy

Abstract

The abrupt aperiodic modulation of cosmic ray (CR) flux intensity, often referred to as Forbush decrease (FD), plays a significant role in our understanding of the Sun–Earth electrodynamics. Accurate and precise determinations of FD magnitude and timing are among the intractable problems in FD-based analysis. FD identification is complicated by CR diurnal anisotropy. CR anisotropy can increase or reduce the number and amplitude of FDs. It is therefore important to remove its contributions from CR raw data before FD identification. Recently, an attempt was made, using a combination of the Fourier transform technique and FD-location machine, to address this. Thus, two FD catalogs and amplitude diurnal variation (ADV) were calculated from filtered (FD1 and ADV) and raw (FD2) CR data. In the current work, we test the empirical relationship between FD1, FD2, ADV and solar-geophysical characteristics. Our analysis shows that two types of magnetic fields - interplanetary and geomagnetic (Dst) - govern the evolution of CR flux intensity reductions.