Ion Acceleration and Transport in Impulsive and Gradual Solar Flares

One of the most curious phenomena occuring during impulsive solar flares is the enrichment of the accelerated particle flux by some ion species. The most striking example is the ³He to ⁴He ratio that can increase by a factor of 10⁴. Relative abandances of the heavy elements such as O, Si, and Fe also increase though less dramatically. Some gradual flares are characterized by unusually high Fe abundances at the initial stage as well. The observational situation in the field has significantly improved with the launch of the ACE satellite that has on board several instruments, most importantly SEPICA, measuring the spectra and composition of solar particles. This proposal is to request funding for a three-year program of research on the elemental and isotopic abundances and spectra of ions in impulsive and some gradual flares. Combined with the data from ULEIS, SIS, and CELIAS STOF on SOHO, the SEPICA data are ideally suited for testing the existing models for ion acceleration in flares as well as for developing more advanced theories. The extreme selectivity of the acceleration mechanism suggests that its understanding could provide significant insights into flare physics. The proposed projects include:

• developing models for and testing them against the data on the spectrum of ³He in impulsive flares, which results from a balance between the processes of resonant acceleration by the electromagnetic ion-cyclotron waves, Coulomb energy losses, particle escape from the acceleration region, and subsequent propagation in interplanetary space;
• investigating the effect of the Coulomb energy losses during the preacceleration in reconnecting current sheets on the formation of anomalous abundances of the heavy ions, both in impulsive and at the initial stage of hybrid flares that appear to be intermediate between the impulsive and gradual flares, thus extending the convential two-class picture.

The study will emphasize analytical methods as well as comparisons between theoretical predictions and observations. Overall, the work is intended to be a step towards a unified modeling of global magnetic energy release and charged particle acceleration in flares.

• Principal Investigator: Martin A. Lee, Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824-3525.
  • Tel: (603)862-3509, FAX: (603)862-1915. marty.lee@unh.edu
• Co-Investigator: Yuri E. Litvinenko, Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824-3525,
  • Tel: (603)862-4710, FAX: (603)862-1915. yuri.litvinenko@unh.edu

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