Passage of ICMEs, Their Associated Shock Structure, and Transient Modulation of Galactic Cosmic Rays

Abstract

Coronal mass ejections (CMEs) from the Sun propagate into interplanetary space and evolve to form a structure. When this structure is observed in near-Earth space, it consists in many cases of the CME ejecta and an extended shock region. Thus, while passing a point of observation (Earth/spacecraft), the interplanetary CME (ICME) structure may cross it from its near-central, intermediate, or near-end location. Therefore, galactic cosmic rays (GCRs) arriving at the Earth-based/space-borne detector may encounter solar plasma and field regimes of different strength, topology, and duration. We analyse the GCR intensity and the solar plasma/field parameters in three different situations when the ICME structure passes the detector from the central, intermediate, and the near-end portions of its extended structure. We study the behaviour of transient depressions in the GCR intensity in these three situations. Simultaneous changes in the solar plasma and field parameters are also studied. The differences in the amplitudes of the depression and the recovery characteristics during the passage of three groups of ICMEs are analysed and discussed.