Ulysses Low-Energy Particle Observations over the Solar Poles

Details Ulysses Low-Energy Particle Observations over the Solar Poles Ulysses Low-Energy Particle Observations over the Solar Poles

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh51a..04l&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SH51A-04

Physics

7807 Charged Particle Motion And Acceleration, 2114 Energetic Particles, Heliospheric (7514), 2139 Interplanetary Shocks

Scientific paper

Ulysses has recently explored the polar regions of the heliosphere. In November 2000 and October 2001 Ulysses reached the most southerly and northerly latitudes, respectively, of its trajectory (80.2 deg). In this paper we will analyze the low-energy particle observations from the Heliosphere Instrument for Spectra Composition and Anisotropy at Low Energies (HI-SCALE) during the two Ulysses solar polar passes (understood as those time intervals that Ulysses spent at heliographic latitudes above 75 degrees). Unlike the first time that Ulysses explored these high-latitude regions (in September 1994 and August 1995), the heliosphere was dominated by solar maximum conditions. During the southern polar pass (November-December 2000) Ulysses observed several energetic particle enhancements associated with events of solar origin and with the arrival of interplanetary solar wind and field structures. The overall background particle flux level remained high throughout the southern polar pass. Ulysses observed predominantly low-speed solar wind (< ~300 - ~400 km/s) with occasional streams of faster ( ~500 km/s) wind. Two magnetic sectors were present up to a latitude of ~78 S above which a single inward polarity was observed. During the solar maximum northern polar pass (October-November 2001) Ulysses was immersed in the high-speed (>700 km/s) polar solar wind stream and only an inward magnetic field polarity was observed. Transient solar wind structures were clearly observed even at these high latitudes and under these high-speed solar wind conditions. Two long-lasting major solar energetic particle (SEP) events with onsets on days 267 and 309 of 2001 were observed at heliolatitudes above 77oN . The energetic particle fluxes returned to instrument background levels in the time interval between the two major SEP events. We correlate polar region observations from the Ulysses spacecraft with 1 AU measurements in the ecliptic from the ACE spacecraft. The two large SEP events during the northern polar pass were observed by both ACE and Ulysses. However there was no a one-to-one association between ACE and Ulysses for the less intense SEP events. Access of energetic particles at high latitudes through magnetic field lines originating at low latitudes under the different interplanetary conditions observed at northern and southern polar passes will be discussed.

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