Time Lag in Diurnal Correlations vs. Asymptotic Longitudinal Separation

Abstract

The correlation between two neutron monitor count rates vs. time lag τ can be fit by the sum of a linear function of |τ| (a triangular function of τ), representing temporal correlation, and a sinusoid with phase ϕ, representing the diurnal correlation associated with cosmic ray anisotropy at directional separation ϕ. Comparing 1-minute count rates from pairs of neutron monitors with similar cutoff rigidities but different asymptotic longitudes, we measure ϕ from the diurnal correlation between count rates and find this to be closely related to the separation of asymptotic longitudes of the primary cosmic rays. We propose that this technique provides an alternative measurement of the diurnal anisotropy at various cutoff rigidities disentangled from temporal variations.