IV. Geographically smoothed geomagnetic cutoffs

Abstract

Detailed calculations of effective vertical-trajectory cutoff rigidities have failed to eliminate a discontinuity in the neutron-monitor latitude variation in the vicinity of Mexico City noted after the 1965 survey described in paper I of this set of five papers. Since a similar discontinuity appears when the vertical cutoffs are plotted against geographical latitude, the irregularity seems to be a function of the vertical rigidity cutoffs. Extensive calculations of cutoffs at, intervals of one degree of latitude along meridians 260 °E and 285° E have delineated the systematic nature of the irregularity. A set of cutoff values, which orders the observations satisfactorily for the analysis in the present papers, was obtained by smoothing a 5° latitude by 15° longitude grid of calculated values within a sector of the northern hemisphere bounded by meridians 195 °E and 285 °E.