Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001kfnt...17...99p&link_type=abstract
Kinematika i Fizika Nebesnykh Tel, vol. 17, no. 2, p. 99-112
Astronomy and Astrophysics
Astronomy
Scientific paper
The changes in the line-of-sight velocity and in the direction of the motions of chromospheric and photospheric matter in an active region before and during the flare of September 4, 1990 and in an active plage are analysed. The spectrograms were obtained at Terskol Peak (h = 3100 m) with the large horizontal solar telescope ATsU-26 of the Main Astronomical Observatory, NAS of Ukraine. The spectral region lambdalambda 654.4-659.4 nm chosen for the investigation includes the chromospheric line H_alpha and 10 Fraunhofer lines formed in different photospheric layers (from 41 km to 416 km in the quiet photosphere). Two hours before the flare the matter moved downwards in the active plage photosphere and upwardws in the chromosphere. A downflow was observed in the photosphere and the chromosphere during the flare. In the chromosphere there were the largest velocity variations of up to 3.6 km/s. The line-of-sight velocities increased during the first flare phase in the upper and middle photospheric layers. The velocity reached its maximum about flare the H_alpha-maximum. The velocity of downflows was constant over approximately 7 minutes at the main flare phase, and then it gradually decreased by the end of the flare. There was a middle photospheric layer (h<240 km) with particularly large velocity changes of up to 2 km/s. During the flare the velocity increased in the lower photospheric layers and reached the lowest layer (h = 41 km) 7 minutes after the flare H_alpha-maximum. The flare disturbance propagated from the upper to the lower layers and had a wave character. The observed line-of-sight velocity changes in the photosphere and chromosphere layers of the active region may be caused by the passage of a chromospheric condensation and by the waves formed during the flare.
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