Physics of auroral phenomena : proceedings of the 34th Annual seminar, Apatity, 01 - 04 March, 2011 / [ed.: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 231 с. : ил.

AG. Yahninetal. The proton aurora observations were provided by the Spectrographic Imager (SI) detector of the FUV instrument onboard the IMAGE spacecraft, which was designed to select the Doppler shifted Lyman H-alpha line at 121.82 nm in the ultraviolet part of the optical spectrum and to reject the non-Doppler shifted Lyman H-alpha from the geocorona at 121.567 nm (see, Mende et al., 2000, for details). The ground observations of geomagnetic pulsations were performed with induction coil magnetometer at the geomagnetic observatory Lovozero (67.97°N, 35.02°E; Corrected Geomagnetic latitude (CGLat) is 64.3°; MLT = UT + 3) of Polar Geophysical Institute. The plasmapause model is the Kp-depended model based on the Lemaire’s theory of plasmapause formation (see, e.g., Lemaire and Gringauz, 1998). The model satisfactorily reproduces the plasmapause and some plasmaspheric structures (Pierrard and Lemaire, 2004; Pierrard and Cabrera, 2005; Pierrard et al., 2007; Pierrard and Stegen, 2008). The model is freely available at http://www.spaceweather.eu. For each of 25 selected events the plasmapause was modeled. Often, it is difficult to determine the poleward edge of the proton aurora flash since it merges with the proton oval. Therefore we will characterize the location of the proton aurora flash by its equatward edge. Suggesting the dipole magnetic field, the equatorial boundary of each proton aurora flash was mapped onto equatorial plane and compared with location of plasmapause. Results Figure 1 presents difference between the L-shall of the equatorial projection of the proton aurora flash boundary (Leq) and location of the modeled plasmapause (Цр) for all 25 events under consideration (black dots). In Figure 1 the events are ordered according to the value of this difference. Negative values mean that the flash projection onto the equatorial plane and plasmapause overlap. The dots within shaded area correspond to events when the near- Earth edge of the proton aurora projection was within 1REfrom plasmapause. Event Number Figure 1. Distance between locations of the equatorwad edge of the proton aurora flash (Leq) and modeled plasmapause (Lpp) for 25 selected events (black dots). From Figure 1 it is clear that in most cases the equatorward edge of proton aurora flashes maps outside plasmasphere. Even in the cases when Leq-Lpp is negative, the overlap of the flash projection and plasmasphere is less than 1 RE. All such cases correspond to flashes, which are wide in latitude (up to ~10 degrees). Thus, the greater part of the proton luminosity region maps outside plasmasphere. This means that cold plasma density is not a rrwin factor in generation of the proton flash. Olson and Lee (1983) argued that increase in anisotropy o f hot protons is a primary cause of the IC instability development under compression. They showed that the compression-related enhancement of the anisotropy is maximal in the outer magnetosphere on the dayside, and it decreases toward the Earth. The anisotropy change at a given point is larger when the compression is stronger. The latter means that stronger compression should produce proton auroras, whose equatorward edge is closer to the Earth. However, this is not exactly true. Figure 2 (on the left) shows dependences of Leq and Leq-Lpp on A(SYM-H), which is the value of the SYM-H index enhancement occurred during compression. Linear approximations are shown with straight lines. Surprisingly, the correlation coefficients are very low (0.32 for dependence of Lcq and 0.37 for dependence of Leq-Lpp). The rest of Figure 2 shows dependencies o f equatorial location of the mapped proton flash on geomagnetic activity indices. These dependencies demonstrate much larger correlations. Correlation coefficients for dependence on (SYM-H)b which is the value of SYM-H taken just before the compression, are 0.67 and 0.57, respectively. Mean Kp (Kp averaged for two days before the compression) shows similar correlations, while correlation coefficients for dependence on mean AE index (also averaged for two days) are even higher (0.74 and 0.68). Both Leqand Leq-Lppvalues tend to decrease when preceding geomagnetic activity increases. 58