Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...394..299v&link_type=abstract
Astronomy and Astrophysics, v.394, p.299-310 (2002)
Astronomy and Astrophysics
Astrophysics
55
Shock Waves, Sun: Flares, Sun: Corona, Sun: Chromosphere
Scientific paper
Three traveling disturbances recorded in the absorption line of Helium I at 10 830 Å, (He I), analogous to Hα Moreton waves, are analyzed. The morphology and kinematics of the wavefronts are described in detail. The He I wave appears as an expanding arc of increased absorption roughly corresponding to the Hα disturbance, although not as sharply defined. He I perturbations consist of a relatively uniform diffuse component and a patchy one that appears as enhanced absorption in He I mottles. It leads the Hα front by some 20 Mm and can be followed to considerably larger distances than in Hα observations. Behind the front stationary areas of reduced He I absorption develop, resembling EUV coronal dimming. The observed He I as well as the Hα disturbances show a deceleration of the order of 100-1000 m s-2. Moreover, in the event where Hα , He I, and EUV wavefronts are observed, all of them follow closely related kinematical curves, indicating that they are a consequence of a common disturbance. The analysis of spatial perturbation profiles indicates that He I disturbances consist of a forerunner and a main dip, the latter being cospatial with the Hα disturbance. The properties and behavior of the wavefronts can be comprehended as a consequence of a fast-mode MHD coronal shock whose front is weakly inclined to the solar surface. The Hα disturbance and the main He I dip are a consequence of the pressure jump in the corona behind the shock front. The He I forerunner might be caused by thermal conduction from the oblique shock segments ahead of the shock-chromosphere intersection, or by electron beams accelerated in the quasi-perpendicular section of the shock.
Brajsa Roman
Hanslmeier Arnold
Vrsnak Bojan
Warmuth Alexander
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