  Forbush decrease (FD), discovered by Scott E. Forbush about 80 years ago, is
reffered to as the non-repetitive short-term depression in galactic cosmic ray
(GCR) flux, presumed to be associated with large-scale perturbations in solar
wind and interplanetary magnetic field (IMF). It is the most spectacular
variability in the GCR intensity which appear to be the compass for
investigators seeking solar-terrestrial relationships. The method of selection
and validation of FD events are very important to cosmic ray scientists. We
have deployed a new computer software to determine the amplitude and timing of
FDs from daily-averaged cosmic ray (CR) data at OULU neutron monitor station.
The code selected 230 FDs between 1998 and 2002. In an attempt to validate the
new FD automated catalog, the relationship between the amplitude of FDs, and
IMF, solar wind speed (SWS) and geomagnetic storm indices (Dst, kp, ap) is
tested here. A two-dimensional regression analysis indicates significant linear
relationship between large FDs (CR(\%) $\leq-3$) and solar wind data and
geomagnetic storm indices in the present sample. The implications of the
relationship among these parameters are discussed.
