Coherence of Charged Particle Oscillations in the Heliosphere (f∼5 µHz): Implications for a Solar Modulation Source

Abstract

Time series analysis of low energy electron and high energy proton cosmic ray fluxes, both measured on the Ulysses spacecraft, shows that they are coherent in some frequency bands in the energy range 0-6 µHz, especially near 5 µHz. Interplanetary particle fluxes with very different kinematic properties (e.g., gyrofrequencies) are modulated coherently in the heliosphere at discrete frequencies; one specific example, discussed here, has a period of ∼2.2 days. The analyzed data spans the interval 1 January 1993 to 20 April 1994 when Ulysses traveled between 22° and 60° south heliographic latitude and was about 4 AU from the Sun. The frequency at 5.26 µHz is tentatively identified as a zonal harmonic mode with l = 2, m = 0.