HR: 09:35h
AN: SH11A-06 [PDF]
TI: Event Fluences of Energetic $^{3}$He and $^{4}$He: Different Behavior During the Rise and the Maximum
of Solar Cycle 23
AU: * Ho, G C
EM: george.ho@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723 United States
AU: Roelof, E C
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723 United States
AU: Haggerty, D K
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723 United States
AU: Mason, G M
AF: Department of Physics and I.P.S.T., University of Maryland, College Park, MD 20742 United States
AB:
The ACE/ULEIS instrument allows us to study the behavior of the $^{3}$He/$^{4}$He ratio at low energies (0.4-2.0 MeV/nuc) in
a large number of solar particle events (SEPs). We had previously investigated 27 $^{3}$He-enhanced events between ACE
launch in 1997 and the end of 1999 [Ho $et$ $al., ApJ., 552,$ 863, 2001]. The event fluences (F) varied by a factor $\sim$30
for both $^{3}$He and $^{4}$He. They showed a reasonable correlation so that F($^{3}$He)/F($^{4}$He) lay predominantly
within the range 0.1$<$$^{3}$He/$^{4}$He$<$1.0. We have now added 57 more events for the years 2000-2002. F($^{3}$He) still
varied by a factor of $\sim$30, but F($^{4}$He) now varied by $\sim$300. Remarkably, in the lower range of F($^{4}$He), the
correlation with F($^{3}$He) is about the same as before, but in the upper decade of the range, there is no correlation.
Consequently, the ratio of event fluences (F) for the 84 events over the period 1997-2002 covered the range
0.004$<$$^{3}$He/$^{4}$He$<$20.0, but these ratios do not reflect the above-mentioned structure in the fluences. The data
appear as if an additional component of larger $^{4}$He events appeared during the maximum of solar activity that was not,
however, accompanied by correspondingly larger $^{3}$He events. As to why the upper range of F(/$^{3}$He) is limited, we
note that most of the events are short-lived ($\sim$10-20 hours) whereas the scatter-free transit time to 1 AU for these ions
is $\sim$5 hours. Thus the fluence is approximately proportional to the total number of ions released onto the field line
to Earth. This suggests to us that there is a limit to the total number of $^{3}$He ions in this energy range that can be
released in an SEP event.
DE: 2114 Energetic particles, heliospheric (7514)
DE: 7514 Energetic particles (2114)
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting