The chromospheric line-of-sight velocity changes in a solar microflare
The variation of the chromospheric line-of-sight velocity in the active region NOAA 11024 on 4 July 2009 before, during, and after a solar microflare is studied. The spectral observations were carried out by E.V. Khomenko with the French-Italian THEMIS telescope of the Instituto de Astrofisica de Canarias. We used high resolution Hα spectra obtained over 21 min. Spatial resolution was below 1′′. The time interval between the spectra was 2.84 s. Doppler velocities were measured in five cuts in the microflare location and its surroundings using the wavelength shift of the local minimum of the line profiles. We revealed strong line-of-sight velocity temporal variations in the chromosphere. During 12 min at the beginning of the observations the upflows were in all cuts of the plage before the microflare. The velocities were in the range from -25 км/s to -4 km/s. Then during 3 min the upflow velocities in the plage were decreasing in time from -14 km/s to about 0 km/s. Before the flare the direction of the motion changed and the downflows in the center of the flare region with the velocity up to 5 km/s continued till the flare maximum. The upflows were observed in the chromosphere after the flare.
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