A survey of the cosmic ray diurnal variation during 1973–1979—I. Persistence of solar diurnal variation

Abstract

We find that the solar diurnal variation in cosmic ray intensity is a persistent phenomenon over the years 1973–1979. That is, even during solar minimum, conditions in the heliosphere lead to a net flux of cosmic rays from a particular (time-varying) direction in space. If we regard the daily fluctuations in the amplitude and phase of the diurnal variation as random perturbations about the mean vector, we are able to quantify the relative magnitude of the random component.