Solar maximum low-energy particle observations at heliographic latitudes above 75 degrees

Abstract

We present a preliminary analysis of low-energy particle observations by the Ulysses and ACE spacecraft during the time intervals that Ulysses spent at heliographic latitudes above 75 degrees during its solar maximum orbit. The most southerly and northerly latitudes (80.2°) were reached by Ulysses in November 2000 and October 2001, respectively. These two periods were characterized by high levels of solar activity. During its passage through the highest southern latitudes, Ulysses encountered complex magnetic field and solar wind configurations, with numerous energetic particle events of either solar origin or associated with solar wind stream interaction regions. By contrast, during its high northern latitude passage, Ulysses remained immersed in the high-speed (∼700 km s −1) solar wind coronal hole flow bearing magnetic field of negative polarity and detected three intense solar energetic particle (SEP) events. We correlate observations from Ulysses at high heliographic latitudes with 1 AU measurements in the ecliptic from the ACE spacecraft. Large SEP events were observed simultaneously by both spacecraft. Periods with comparable particle intensities at ACE and Ulysses occurred during the decay phase of large SEP events. We discuss the formation of these periods of nearly identical particle intensities (i.e., “reservoirs”) in terms of both fresh injections of solar energetic particles and the formation of compressed magnetic field regions in the heliosphere beyond the Earth orbit (∼2–5 AU). We discuss the implications of these observations for models of solar energetic particle propagation to both high and low heliographic latitudes.