FAS Abstracts 2004 Meeting Page

Joint Meeting: Engineering & Physics and Space Sciences B (PSS): PSS-10

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Variation of elemental abundances in the solar corona as inferred from ACE and WIND measurements of solar energetic particles. M. Al-Dayeh, J. DWYER, and H. Rassoul.  Florida Institute of Technology, Dept. of Physics and Space Sciences, Melbourne., FL, 32901.  Solar energetic particles (SEPs) can be used to probe the composition of the solar corona, independent of spectroscopic or solar wind measurements. However, previous studies have shown that SEPs elemental abundances in large gradual events can vary considerably (by factors of >10) from event to event, which must be taken into account when using SEP measurements to deduce the coronal composition. Unfortunately, the causes of these variations are still not known, and may be produced either by acceleration/transport effects or variations in the source abundances, the later of which might be expected to show up as the solar cycle dependence in abundance ratios.  Using the Ultra Low Energy Isotope Spectrometer (ULEIS) onboard the Advanced Composition Explorer (ACE) and the STEP instruments onboard the WIND spacecraft, we have measured the fluxes of the iron (Fe) and the averaged C-N-O at high and low energies ranging between 0.02-2 MeV/nucleon.  In this study, we report measurements of the compositional changes for 30 gradual events between 1994 and 2003. Although our preliminary analysis of these events reveal that the Fe to C-N-O ratios vary drastically from event to event, no dependence has been found on the solar cycle.