  Cosmic ray Forbush decreases (FDs) are usually thought to be due to
Earth-directed coronal mass ejections (CMEs) from the Sun and their associated
shocks. When CMEs and their shocks reach the Earth, they cause magnetic field
compressions. We seek to understand the relation between these magnetic field
compressions and FDs at rigidities between 12 and 42 GV using data from the
GRAPES-3 instrument at Ooty. We find that the shapes of the Forbush decrease
profiles show a startling similarity to that of the magnetic field compression
in the near-Earth IP medium. We seek to understand the implications of this
interesting result.
