Case study of Forbush decreases: Energy dependence of the recovery

Abstract

Case study is presented for three Forbush decreases in 2004-2005, using cosmic ray data from ground-based detectors - neutron monitors and a muon detector. One of them was a typical event (September 2005), while two other were quite unusual (November 2004 and January 2005). Two unusual features, not expected from the standard theory, are revealed: (1) the recovery time of a Forbush decrease can strongly depend on the energy; (2) an over-recovery is observed in the most energetic cosmic ray data (muon detector). A simple scenario is suggested for the observed phenomenon. © 2007 COSPAR.