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Solar Cycle Variation of Suprathermal Heavy Ion Composition and Spectra during Quiet Times near 1 AU during Solar Cycles 23 and 24

Presentation #201.04 in the session Suprathermal Particles and their Importance to Understanding Energetic Particles.

Published onOct 20, 2022
Solar Cycle Variation of Suprathermal Heavy Ion Composition and Spectra during Quiet Times near 1 AU during Solar Cycles 23 and 24

We report on the annual variation of quiet-time suprathermal ion composition and spectral properties for C through Fe using Advanced Composition Explorer (ACE)/Ultra-Low Energy Isotope Spectrometer (ULEIS) over the energy range 0.3 MeV/nuc to 1.28 MeV/nuc from 1998 through 2020, covering solar cycle 23’s rising phase through Solar Cycle 24’s declining phase. Our novel findings are (1) quiet time suprathermal abundances resemble CIRs during solar minima and a 70% gradual solar energetic particle (GSEP) + 30% impulsive solar energetic particle (ISEP) abundance during solar maxima; and(2) suprathermals are M/Q fractionated in a manner that is consistent with M/Q fractionation in large solar energetic particle events (LSEP). Given this 70% GSEP + 30% ISEP abundance matches typical LSEP abundances and suprathermal M/Q fractionation matches LSEP fractionation, we infer that LSEP events must accelerate a pre-existing suprathermal pool. Coincident with these results, we also unexpectedly show that Su behaves like a low FIP ion in the suprathermal regime and therefore drawn from low FIP solar sources.

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