Chromospheric models of a solar flare including velocity fields

We study the chromospheric structure of a small flare, before, during and after the rst hard X-ray spike. We construct 5 semiempirical models for dierent times, which will reproduce the proles of the H ,C a II Ka nd Si I 3905 lines during the flare evolution. In order to reproduce the intensity and the main characteristics of the line asymmetry, we introduce the velocity elds in the prole calculations. We nd that the whole chromosphere undergoes a strong upward motion within 1 s of the maximum of the rst hard X-ray spike, when the temperature and the density begin to rapidly increase. This seems the rst chromospheric response to the energy deposition and/or release. Only 6 s after the hard X-ray peak, a strong downflow begins in the low chromosphere and its velocity continues to increase even during the cooling phase.