Preflare chromospheric and photospheric line-of-sight velocities

Abstract

The preflare plage spectra were obtained with the ATsU-26 solar telescope mounted at the Peak Terskol. The spectra were acquired from 1 h to 20 min before the flare onset. The most prominent peculiarity of all the observed events are the tilted $H_{\alpha}$-emission details which appear less than 40 min before the flare. This result may testify to spiral structure of the ascending $H_{\alpha}$ loops. The ascending velocities in the chromosphere attain more than 10 km/s. Two crossing $H_{\alpha}$ loops were observed to interact before 1n flare. As a result of their interaction, the redistribution of velocities occurs in the both chromosphere and photosphere. This can be a consequence of the preflare reconnection at the lower atmospheric layers. As the flare onset approaches the ascend of photospheric material start to dominate. The preflare line-of-sight velocities exceed considerably those in the neighbouring unperturbed regions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html