Spectral analysis and atmospheric models of microflares

By use of the high-resolution spectral data obtained with THEMIS on 2002 September 5, the spectra and characteristics of five well-observed microflares have been analyzed. Our results indicate that some of them are located near the longitudinal magnetic polarity inversion lines. All the microflares are accompanied by mass motions. The most obvious characteristic of the H alpha microflare spectra is the emission at the center of both H alpha and Call 8542 angstrom lines. For the first time both thermal and non-thermal semi-empirical atmospheric models for the conspicuous and faint microflares are computed. In computing the non-thermal models, we assume that the electron beam resulting from magnetic reconnection is produced in the chromosphere, because it requires lower energies for the injected particles. It is found there is obvious heating in the low chromosphere. The temperature enhancement is about 1000-2200 K in the thermal models. If the non-thermal effects are included, then the required temperature increase can be reduced by 100-150 K. These imply that the H alpha microflares can probably be produced by magnetic reconnection in the solar lower atmosphere. The radiative and kinetic energies of the Ha microflares are estimated and the total energy is found to be 10(27) - 4 x 10(28) erg.