Role of low-frequency modes in organizing the inner heliosphere

Abstract

Cosmic ray proton data (125 to >2000 MeV) measured in the inner three-dimensional (3-D) heliosphere over the years from 1993 into 2000 by the KET instrument on the Ulysses spacecraft are examined. The data are parameterized and characterized by fitting products of spherical harmonic and sinusoidal frequency functions to three individual proton energy data sets. It is found that the time dependence of the cosmic ray data sets can be rather well characterized by relatively few variables consisting of low-order spherical harmonic modes and a few frequencies of the order of a solar cycle. The results can be useful for analytical and computational studies of cosmic rays in the inner 3-D heliosphere.