Contribution of obliquely incident particles to neutron monitor counting rate

We describe a new method for calculating geomagnetic cutoffs that incorporates obliquely incident primaries, and we use it to interpret a sea level neutron monitor latitude survey. Effects due to obliquely incident primaries are significant and may be responsible for anomalies observed in this and other latitude surveys. We define an "apparent" cutoff that takes these obliquely incident particles into account. Use of our apparent cutoff in a Dorman function fit to the 1994-1995 Bartol Research Institute-University of Tasmania latitude survey data results in a significant improvement over use of the more conventional effective vertical cutoff. Copyright 1997 by the American Geophysical Union.