Statistical comparison of time profiles of Forbush decreases associated with coronal mass ejections and streams from coronal holes in solar cycles 23–24

Abstract

ABSTRACTIn this paper, Forbush decrease (FD) profiles are compared for events associated with (i) coronal mass ejections from active regions accompanied by solar flares (AR CMEs), (ii) filament eruptions away from active regions (non-AR CMEs), and (iii) high-speed streams (HSSs) from coronal holes (CHs). FD profiles are described by time parameters that are delayed from an FD onset to the registration of maximum values of cosmic ray (CR) density variations, CR density hourly decrease, CR equatorial anisotropy, solar wind (SW) speed, interplanetary magnetic field (IMF) strength and minimum Dst index. Distributions of these parameters from 1997 to 2020 and within maxima and minima of the last solar cycles (SCs) were compared by statistical methods. The results obtained reveal that statistical properties of the time parameters depend both on the FD source and on the solar activity period. FDs associated with AR CMEs develop even at close values of SW parameters faster than those associated with non-AR CMEs and HSS from CHs. Differences between typical FD profiles for events associated with AR and non-AR CMEs are more significant when the interplanetary disturbance contains a magnetic cloud. The difference between FD profiles for events associated with AR and non-AR CMEs is less distinguishable within maximum SC 24 than within maximum SC 23. For FDs associated with HSS from CHs, the main phase durations and the time delays of maximal SW speed are longer within SC 23–24 minimum, while the time delays of maximal IMF strength differ insignificantly between 23–24 and 24–25 minima.