Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

Mapping theproton aurora spots into the magnetosphere map within 0.5 RE into the vicinity of the modeled plasmapause like those shown in Fig. 1 a,b. Three spots map inside the plasmapause at distances larger than 0.5 RE(as in Fig. 1 c), and other three spots map well outside the plasmapause (as in Fig. 1 d). 3. Discussion According to Table 1, some 65% of the considered events (11 of 17) map into the vicinity (within 0.5 RE) of the modeled plasmapause. This is consistent with the results of simultaneous space observations of the EM1C waves and plasmapause. For example, Erlandson et al. (1992; 1996) used Viking satellite measurements and observed the EMIC waves in the pre-noon sector just inside the plasmapause. Usanova et al. (2008, 2010) using, respectively, THEMIS and Cluster spacecraft data have found the EMIC waves in He+ band just inside the plasmapause near noon. With the Polar spacecraft, Mursula et al. (2001) observed the EMIC waves in the pre-noon sector in the He+ band at the inner plasmapause, while the waves in H+ band were observed both at the plasmapause and just outside it. Fraser et al. (1996) observed the EMIC waves on CRRES near the plasmapause in the afternoon and night sectors. Anderson et al. (1992) and Fraser and Nguyen (2001) argued that the EMIC waves are most probably observed outside the plasmapause. In the statistical study based on the EMIC wave and cold plasma density measurements onboard the CRRES spacecraft, Fraser and Nguyen (2001) found less than 50% of wave events in the plasmapause vicinity (AL<1 RE). In contrast, we found 65% proton aurora spot events in a narrowed vicinity (AL<0.5 RE) of the modeled plasmapause. The apparent contradiction is, obviously, due to the fact that the proton aurora spots relate to the specific type of the EMIC waves seen on the ground as quasi-monochromatic pulsations Pci, while observations by Anderson et al. (1992) and Fraser and Nguyen (2001) included the EMIC waves of different types. Some of the waves are generated on the dayside as a result of increase of the hot proton temperature anisotropy during magnetosphere compressions. These waves are not necessarily related to the high density of the cold plasma and can be observed well above the plasmapause. A large amount of the events considered by Anderson et al. (1992) and Fraser and Nguyen (2001) are found at high L in the afternoon-evening sector. These events, evidently, relate to the plasmaspheric plume. The morphology of these waves and their ground counterparts (Pci bursts, 1PDP) significantly differs from that of monochromatic Pci. This suggests different source characteristics. Respectively, sub-oval proton auroras related to these waves (dayside proton aurora flashes, evening side proton aurora arcs) demonstrate very different characteristics in comparison to the proton aurora spots (e.g. Yahnina et al., 2008; Yahnin et al., 2009; Spasojevid and Fuselier, 2009). In particular, co-rotation of a spot (in contrast to dayside flashes and evening arcs) and its location at the same latitude during a long time can be easily explained by connection with plasmapause (Frey et al., 2004; Yahnin et al., 2007). At the same time, projections of three of the proton aurora spots are found deeper in the plasmasphere, at distances up to ~1 RE from the modeled plasmapause. For one of such events, 26 November 2001, the comparison with real plasmapause observed with IMAGE EUV instrument showed that in this case the source region (the proton aurora spot projection) is in the cold plasma gradient inside the plasmapause. One may suggest that this holds true for other two similar events. Non-monotonic, sometimes step-wise, decrease of the cold plasma density (multiple plasmapause) is often observed (e.g., Horwitz et al., 1984). Data presented by Mursula et al. (2001) and Usanova et al. (2010) show that multiple sources of Pci can be observed in connection with such plasmapause structures. Location of the proton aurora spot projection well inside the modeled plasmapause can be related with such plasmapause structure, which can hardly be reproduced by the model used in this study. As to those events in which the spots mapped well outside plasmapause, they can relate to the cold plasma structures detached from the plasmasphere. All the three events were observed in the pre-noon sector in accordance with Chappell (1974), who found detached cold plasma structures in the pre-noon sector to be well separated from the plasmasphere. Indirect confirmation of the above statement is the fact that sub-oval proton aurora spot events, independently of their latitudinal position, correlate well with long-term quasi-monochromatic pulsations Pci, which are, typically, below the equatorial He+ hyrofrequency (Yahnin et al., 2007). This means rather high percentage of He+that reveals the presence of the plasmaspheric material in the source location. 4. Conclusion In this report, we have compared locations of 17 sub-oval proton aurora spots mapped onto the equatorial plane with the plasmapause position obtained using the numerical model based on the quasi-interchange instability mechanism. -Joe Fig. 1. 51