The cosmic ray radial and latitudinal gradients in the heliosphere near solar minima

Abstract

Based on existing measurements of galactic and anomalous cosmic ray gradients obtained by the heliopsheric network spacecraft in the last three solar minima, we found that there is an approximately linear relationship between the magnitudes of the radial gradient and latitudinal gradient. Cosmic rays of a particular species/energy that exhibit a large latitudinal gradient tend to have a large radial gradient too and vice versus. This linear relationship is not affected by the sign of solar magnetic polarity. A similar linear relationship between the amplitude of 27-day recurrent variations and the magnitude of the latitudinal gradient was discovered earlier. These relationships mean that the 3-dimensional distributions of cosmic rays in the heliosphere have a scaling similarity among cosmic rays of different species/energies. Analytical approximations for the gradients and recurrent variation amplitude were derived using the stochastic process theory of cosmic ray modulation. The linear correlation exists because all the variations of cosmic ray at high energies are mainly determined by the adiabatic energy loss.