Impulsive phase heating by uni-directional current systems in solar flares

The possibility of producing rapid heating of a substantial coronal volume by current dissipation, driven by a tearing instability associated with a single unidirectional current system, is investigated. For the fast tearing mode, it is found that, for initial growth rates gamma(f) equal or less than 0.3/s, the electron heating is offset by convective losses, resulting in a very slow temperature rise, and hard X-ray emitting temperatures are never realized. For the larger growth rates, heating from 10 to the 7th to 10 to the 8th K can be achieved in a few seconds; however, in this regime, the maximum volume heated is some three to five orders of magnitude less than the volume of heated material that is inferred from hard X-ray emission measures. The results suggest that to achieve the required heating for the fast tearing mode, a more complicated geometry involving multiple small-scale, oppositely directed current channels may be necessary.