Low energy charged particles in the high latitude heliosphere: Comparing solar maximum and solar minimum

Abstract

Low energy charged particles in the global (3‐D) heliosphere within ∼2.3 AU of the Sun are compared during the two fast latitude scans by the Ulysses spacecraft at solar minimum and maximum. This comparison of data taken by the HISCALE instrument illustrates quantitatively the differences in the population of the heliosphere during the only two solar cycles for which 3‐dimensional information are available. At solar minimum the largest intensities of particles are found in and near the heliospheric current sheet, whereas at solar maximum the entire 3‐D volume is filled. An example is presented of solar‐produced charged particles (electrons and heavy ions measured when Ulysses was at its highest heliolatitude) that provide evidence of a heliosphere ‘reservoir’ with a volume as much as 50 AU3; this reservoir subsequently decays with an e‐folding time of the order of 3 days. Anomalous He, O, and Ne ions are clearly measured at high heliolatitudes at solar minimum, whereas during solar maximum their fluxes, if present, are completely swamped at these energies by the higher intensities of solar particles.