Event Fluences of Energetic 3He and 4He: Different Behavior During the Rise and the Maximum of Solar Cycle 23

Details Event Fluences of Energetic 3He and 4He: Different Behavior During the Rise and the Maximum of Solar Cycle 23 Event Fluences of Energetic 3He and 4He: Different Behavior During the Rise and the Maximum of Solar Cycle 23

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsh11a..06h&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SH11A-06

Physics

2114 Energetic Particles, Heliospheric (7514), 7514 Energetic Particles (2114)

Scientific paper

The ACE/ULEIS instrument allows us to study the behavior of the 3He/4He ratio at low energies (0.4-2.0 MeV/nuc) in a large number of solar particle events (SEPs). We had previously investigated 27 3He-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 ˜30 for both 3He and 4He. They showed a reasonable correlation so that F(3He)/F(4He) lay predominantly within the range 0.1<3He/4He<1.0. We have now added 57 more events for the years 2000-2002. F(3He) still varied by a factor of ˜30, but F(4He) now varied by ˜300. Remarkably, in the lower range of F(4He), the correlation with F(3He) 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<3He/4He<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 4He events appeared during the maximum of solar activity that was not, however, accompanied by correspondingly larger 3He events. As to why the upper range of F(/3He) is limited, we note that most of the events are short-lived ( ˜10-20 hours) whereas the scatter-free transit time to 1 AU for these ions is ˜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 3He ions in this energy range that can be released in an SEP event.

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