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GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 19, 8037, doi:10.1029/2003GL017154, 2003

Steady-state event-excluded proton spectra at solar minimum at all heliolatitudes

J. D. Patterson

Fundamental Technologies, LLC, Lawrence, Kansas, USA


T. P. Armstrong

Fundamental Technologies, LLC, Lawrence, Kansas, USA


Abstract

We present spectra of a steady foreground population of particles in the inner heliosphere observed by the Heliosphere Instrument for Spectra, Composition, and Anisotopy at Low Energies (HISCALE) on board the Ulysses spacecraft. The observed spectra come from the full range of heliolatitudes visited by Ulysses, −80 to +80 degrees, during Ulysses' first full orbit of the Sun during solar minimum. New corrections for background were applied resulting in a more sensitive and higher energy resolution data set that we used here to analyze quiet-time (event-excluded) spectra. We found a persistent foreground population of energetic protons that permeate the inner heliosphere. These protons have complex energy spectra suggesting multiple acceleration sources, and these particles move predominently in non-radial directions. These findings support the idea that the inner heliosphere acts as a reservoir for energetic protons.

Received 18 February 2003; accepted 21 May 2003; published 11 September 2003.

Index Terms: 2114 Interplanetary Physics: Energetic particles, heliospheric (7514); 2118 Interplanetary Physics: Energetic particles, solar; 2162 Interplanetary Physics: Solar cycle variations (7536).

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Citation: Patterson, J. D., and T. P. Armstrong (2003), Steady-state event-excluded proton spectra at solar minimum at all heliolatitudes, Geophys. Res. Lett., 30(19), 8037, doi:10.1029/2003GL017154.