Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh42a09c&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SH42A-09
Physics
7507 Chromosphere, 7509 Corona, 7513 Coronal Mass Ejections, 7519 Flares
Scientific paper
Solar flares convert large amounts of magnetic energy into thermal and bulk plasma motions. Such large changes in the magnetic field and plasma properties excite the available wave modes. Not all modes are equally excited of course and, in principle, this can be used to probe the flare mechanism. In practice however we are still at the stage of identifying the different modes we see. The initial breakthrough in this regard occurred in the early 1970s when Uchida (Uchida 1968) identified the previously observed Moreton waves (Moreton and Ramsey 1960) as the skirt of a fast mode shock propagating in the Corona. This picture has remained essentially unchanged since. In the 1990s the regular observation of the sun in EUV wavelengths revealed the existence of a new blast related wave: the EIT wave. The most distinctive difference between the behavior of the two types of waves is their different velocities, with the Moreton wave being about twice as fast as the EIT wave. Where the two waves are similar however is in the fact that they can both propagate almost isotropically. For the Moreton wave this is expected as the Moreton wave is a fast mode disturbance. For the EIT wave the isotropic behavior suggests that the information is also being carried by the fast mode. We suggest that the difference between the two types of modes is not in the way the information is being carried, but rather in the information content of the two different types of waves. The Moreton wave conveys the information of the sharp, rapid energy release associated with the impulsive phase of the flare. The EIT wave conveys information as to the ejection of excess mass and energy from the system via the slow mode. Unlike the simple spiked structure which characterizes the impulsive phase, the time-scale associated with the energy release is determined by the bulk mass motion along the magnetic field lines - typically the slow mode velocity.. It will be shown that this variation in the `source term' of the EIT disturbance gives rise to an apparent velocity consistent with the EIT observations.
Cameron Robert
Uchida Yoshiharu
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