Solar Extreme Events of 2003:
Fundamental Science and Applied Aspects

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Chertok I. M., Grechnev V. V.,

Based on the SOHO/EIT imaging data, we analyze large-scale disturbances associated with extremely powerful flares and coronal mass ejections (CMEs) occurred in October-November 2003 during two passages across the disk of a grandiose complex of three active regions. In particular, we study dimmings (i.e. transient coronal holes or regions of temporary depressions of EUV emission) and coronal waves (propagating emitting fronts) by derotated fixed-difference heliograms, i.e., difference images in which the solar rotation is preliminary compensated and the same base frame before the event is subtracted from all heliograms. Such a method allows us to consider both the 12-min interval heliograms at 195 and images observed in different-temperature lines of 171, 195, 284, and 304 with intervals of 6 or 12 hours. The running-difference images, emphasizing changes of the brightness, location, and structure of various features between two subsequent heliograms, are used as a subsidiary tool. The analysis has revealed, in particular, that in practically all the eruptive events during the both rotations, the CME-associated disturbances had a global character and covered the entire south hemisphere, while the north hemisphere, where a large coronal hole was present, was almost not affected by the disturbances. The predominating dimmings were observed as narrow dark channels basically stretching between three main remote active regions as well as an extending longitudinal structure in the south polar sector. The homology of the dimmings is apparent in the sense that the same structures were involved in the dimmings in different events. The analysis of dimmings using four EUV lines shows that, along with dimmings that coincide entirely or partially in those lines, there exist dimmings which appear different, mainly, in the transition-region line of 304 and in the highest-temperature coronal line of 284 . This suggests that not only partial opening of the magnetic structures resulting in the depletion of stuff density and the decrease of the emission is important. Besides, temperature variations can work in the formation of some dimming structures. This also means that these processes involve not only the solar corona, but also cooler plasma of the transition region.

Skobeltsyn Institute of Nuclear Physics, Moscow State University, 2004