26-day Analysis of Energetic Ion Observations at High and Low Heliolatitudes: Ulysses and ACE |
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Authors: | Lario D Roelof EC Forsyth RJ Gosling JT |
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Institution: | (1) Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, U.S.A;(2) The Blackett Laboratory, Imperial College, London, U.K;(3) Los Alamos National Laboratory, Los Alamos, New Mexico, U.S.A |
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Abstract: | We present observations of energetic (0.34–8 MeV) ions from the Ulysses spacecraft during its second ascent to southern high latitude regions of the heliosphere. We cover the period from January
1999 until mid-2000 as Ulysses moved from 5.2 AU and 18° S to 3.5 AU and 55° S. In contrast to the long-lived and well-defined ∼26-day recurrences that
were observed throughout Ulysses‘ first southern pass, energetic ion fluxes during the first portion of the Ulysses’ second polar orbit are highly irregular. Although corotating interaction regions (CIRs) are clearly present in solar wind
and magnetic field data throughout the first half of 1999, their effects on energetic ion intensities are quite different
from what they were in 1992–1993. No dominant strictly recurrent ion flux increases are observed in association with the arrival
of these CIRs. Correspondingly, there is no stable structure of large polar coronal holes during the same period. Isolated
transient solar energetic particle (SEP) events are observed at low and high latitudes. We compare energetic ion observations
from the ACE and Ulysses spacecraft during the first half of 1999 to determine the influence of these SEP events in the observed recurrent CIR structure.
Such SEP events occurred only occasionally during 1992–1993, but when they occurred, they obscured the recurrences in a manner
similar to that observed in 1999–2000. We therefore conclude that the basic differences in the behavior of energetic ion events
between the first and second southern passes are due to the short life of the corotating structure and the higher frequency
of SEP events occurring in 1999–2000.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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