Open AccessRevisiting two‐step Forbush decreases
Author(s) -
Jordan A. P.,
Spence H. E.,
Blake J. B.,
Shaul D. N. A.
Publication year - 2011
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011ja016791
Subject(s) - interplanetary spaceflight , physics , forbush decrease , cosmic ray , coronal mass ejection , shock (circulatory) , neutron monitor , astrophysics , solar wind , astronomy , nuclear physics , plasma , medicine
Interplanetary coronal mass ejections (ICMEs) and their shocks can sweep out galactic cosmic rays (GCRs), thus creating Forbush decreases (FDs). The traditional model of FDs predicts that an ICME and its shock decrease the GCR intensity in a two‐step profile. This model, however, has been the focus of little testing. Thus, our goal is to discover whether a passing ICME and its shock inevitably lead to a two‐step FD, as predicted by the model. We use cosmic ray data from 14 neutron monitors and, when possible, high time resolution GCR data from the spacecraft International Gamma Ray Astrophysical Laboratory (INTEGRAL). We analyze 233 ICMEs that should have created two‐step FDs. Of these, only 80 created FDs, and only 13 created two‐step FDs. FDs are thus less common than predicted by the model. The majority of events indicates that profiles of FDs are more complicated, particularly within the ICME sheath, than predicted by the model. We conclude that the traditional model of FDs as having one or two steps should be discarded. We also conclude that generally ignored small‐scale interplanetary magnetic field structure can contribute to the observed variety of FD profiles.