Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

0.1. Yagodkina at al. One can see from Figure 3 and Figure 4 the displacement of the boundaries to lower latitudes and the zone broadening increases with the geomagnetic activity growth. During the magnetic storms the width o f the DAZ precipitation in the evening sector (18-21 MLT) does not change significantly while the width of these precipitation in the morning sectors (03-06, 06-09 MLT) increase up to -5° of latitude. The AOP region displays the opposite pattern: weaker widening o f the precipitation in the morning sector than in the evening. In the evening sector about 10° expansion o f the structured precipitation is observed. Figures 2, 3 and 4 demonstrate the differences in dawn- dusk widening (i.e., asymmetry) of the DAZ and AOP zones during magnetic storms. Discussion and conclusions The present study presents the model pattern of the global auroral precipitation during magnetic storms driven by magnetic clouds. The auroral boundary positions in the morning and in the evening MLT sectors were studied in detail for two different auroral regions: the diffuse auroral zone (DAZ) and the structured auroral oval precipitation (AOP). It is shown that there is a significant shift of the auroral boundaries in both sectors depending on the storm intensity. For the strong magnetic storm on July 15-16, 2000 the DAZ boundary was located at 40° CGL and for the weak storm on 10-11 January 1997 it was located at about 60° CGL. It is shown that the width of DAZ did not change in the evening sector and it extended up to 10° in the morning one. It is found different expanding o f the AOP region in both sectors for the different intensity storms. For the moderate and the strong storms the expansion the AOP region was observed in both sectors and for the weak storm the significant expansion was only in the evening sector. The dawn-dusk widening (asymmetry) of the auroral precipitation regions was found during the main and the recovery phases of the magnetic storms under investigation. The most significant widening o f the precipitation zones occurred during the moderate and strong magnetic storms. Newell et al. (1998) explained such asymmetry by changes in the configuration of the geomagnetic tail under storm conditions. They showed that magnetic field inclination (the extent to which the magnetotail is stretched) strongly controls the b2i latitude and that the magnetic field is more depressed and stretched at dusk than at dawn, and asymmetry increases with increasing magnetotail stretching. This asymmetry is consistent with the rotation of the symmetry line o f the b2i (MLT) curve toward premidnight hours and suggests the growth of a so-called “partial ring current” system with increasing activity. In the studies of Vorobjev and Yagodkina (2003, 2005), a simultaneous displacement to the equator of the DAZeq, AOPeq and the isotropization boundary (b2i) in the nightside sector, which is dependent on the AL and Dst indices, was demonstrated. Judging by a significant displacement o f these boundaries during the storms under investigation we can suggest an enhanced magnetotail stretching and development o f the dawn-dusk asymmetry. A cknow ledg em en ts. The paper was supported by the RFBR Grants 09-05-00818 and Program No. 4 o f the Russian Academy of Science. The study is part of a joint Russian -Bulgaria project “The influence o f solar activity and solar wind streams on the magnetospheric disturbances, particle precipitations and auroral emissions” of PGI RAS and STIL-BAS under the program for fundamental space research between RAS and BAS. References Hardy, D.A., Gussenhoven, M.S., Holeman, E., 1985. A statistical model of auroral electron precipitation. 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