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Ann. Geophys., 21, 1245-1248, 2003
www.ann-geophys.net/21/1245/2003/
© European Geosciences Union 2003
A survey of 3He enhancements at 2–20 MeV/nucleon: Ulysses COSPIN/LET
C. Tranquille, R. G. Marsden, T. R. Sanderson, and M. Y. Hofer
Research and Scientific Support Department of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
Abstract. We present the results of
a survey of enhancements in the ratio of 3He/4 He as measured by the
COSPIN/LET instrument on board the Ulysses spacecraft in the energy range 2–20
MeV/n. In the context of this study, all ratios of 3He/4 He above
0.05 are considered to be enhanced compared with the solar system value of
~0.0004. Previous studies have shown that enhanced fluxes of 3He are
frequently associated with small, impulsive solar flare events in which the
observer is well connected to the flare site. These events also often show
enrichments in heavy ion composition compared with standard coronal values.
Recent attention has also focused on 3He enrichments as evidence for
re-acceleration of remnant particle populations that are present in the inner
heliosphere following periods of enhanced solar activity. For this study, we
have examined the Ulysses data set from launch (October 1990) up to the
present, representing a full solar cycle. The spatial coverage extends from 1–5.4
AU in heliocentric distance, and effectively includes the complete range of
heliomagnetic latitudes from pole to pole. We have identified 12 periods of
enhanced 3He/4 He, occurring at heliocentric distances out to 5 AU,
and heliolatitudes up to 48°. We investigate the characteristics of the
events, many of which last for several days, in order to establish possible
origins.
Key words. Interplanetary physics
(energetic particles) – Solar physics, astrophysics and astronomy (energetic
particles; flares and mass ejections)
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