Populating the inner heliosphere (<5 AU) with heavy ions

Abstract

Heavy ion (Z > 2) and electron measurements were made on the ACE (1 AU) and Ulysses (3.2 AU) spacecraft in the inner heliosphere during the July 14, 2000 solar events. Following the last interplanetary shock event at ∼1437 UT on July 15, the heavy ion fluxes at 1 AU began to decay with an e-folding decay time for both O and Fe ions (0.5-1 MeV/nucl) of ∼1 day. In contrast, the heavy ion fluxes at Ulysses (heliolatitude ∼62o S; ∼ 90o in longitude from the ACE-Sun line) abruptly increased in intensity on July 14, and continued to increase slowly thereafter. The ion and electron fluxes were essentially equal at both locations on July 21, indicating that the inner heliosphere (to ∼3.2 AU) then contained an approximately uniform reservoir of charged particles in a volume of ∼ 102 AU3 (∼3.4·1024 km3 ). The equality of the decaying fluxes at the two locations persisted for more than two weeks, at times modulated more noticeably at 1 AU by solar activity.