Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

A. G. Yahnin et al. belonged to the first group. As already mentioned, these REP events are related to scattering the particles into the loss cone due to violation of the adiabatic motion of particles in the stretched magnetic field in the night side magnetosphere (e.g., Sergeev and Tsyganenko, 1982). Events, which we refer as belonged to group 2 and 3, are similar to spikes of the precipitation studied by Imhofet al. (1986). In particular, our Fig. 2 showing the MLT/Latitude distribution of the REP events is similar to their Fig. 9. The distribution of Imhof et al. has, however, significant gaps, which are due to the worse, in comparison to our study, coverage of MLTs. It is worth to note that duration of REP events studied by Imhof et al. (1986) (<10 s) is less than that in our study (4-32 s). Nakamura et al. (2000) compared the morphology of precipitation bursts with a timescale <10 s and <30 s on the basis of SAMPEX data and demonstrated that distributions in L-shell and MLT of these two subsets of events is similar. Most of events are seen between L=4 and 6, and they more often occur in the premidnight sector like it is shown in the present study. Thus, one may conclude that independently on the duration the REP events studied here and those studied by Imhof et al. and Nakamura et al. have the same nature. Since REP events of our groups 2 and 3 are well within the trapped population, they cannot be associated with scattering in the stretched magnetic field, but can relate to some wave-particle interaction mechanism. Scattering of the relativistic electrons can be provoked by interaction with whistler mode chorus, hiss emissions, equatorial magnetosonic waves, electromagnetic ion-cyclotron (EMIC) waves (see, Milan and Thorne, 2007; Thorne, 2010, and references therein). Sklyar and Kliem (2006) argued that electrostatic waves near the upper hybrid resonance (UHR) frequency are capable to effectively precipitate ~1 MeV electrons. Occurrence of whistler mode chorus is maximal at large distances (L>5) in the dawn-noon sector (e.g. Meredith et al., 2013). Thus, it is hardly possible that chorus emissions are responsible for a significant portion of the REP events seen by NOAA POES within the trapping zone. In fact, the similarity of the morphology as well as direct comparisons leads to suggestion that chorus emissions are responsible for relativistic electron microbursts (e.g., Lorentzen et al., 2001), which are not a subject of this paper. The equatorial magnetosonic emission occurrence and largest amplitudes have been also found in the dawn-noon sector (e.g., Ma et al., 2013) where REP on NOAA POES have the minimal occurrence. The plasmaspheric hiss locates, statistically, on the day-aftemoon side during quiet intervals and tends to expand to the night sector during disturbed intervals ( Meridith et al., 2004). Also, the plasmaspheric hiss tends to intensify within the plasmaspheric plume and plume structures ( Summers et al., 2008; Chen et al., 2012). The UHR waves are observed at all MLTs ( Kurth et al., 1979). Thus, the plasmaspheric hiss and UHR waves could be responsible for significant part of REP events observed by NOAA POES. The plasmaspheric plume is the region where both relativistic electrons and energetic protons might be scattered by EMIC waves (e.g., Thorne and Kennel, 1971; Meredith et al., 2003). Coincidence of energetic proton and relativistic electron precipitation is often considered as evidence of REP as result of the interaction with EMIC waves (e.g., Carson et al., 2012 and references there). However, all REP events of our third group (REP associated with precipitating protons) also coincide with the precipitation of energetic electrons. The presence of simultaneous precipitation of energetic (>30 keV) electrons means that some other waves (besides EMIC waves) exist in the same place. Perhaps, just these waves scatter relativistic electrons. Closely spaced precipitation of energetic protons and electrons can be generated within a small-scale plasmaspheric plume structure due to interaction with EMIC waves and ELF-VLF waves, respectively. This has been suggested by Yahnin et al. (2006) and demonstrated by Yuan et al. (2012, 2013). In the case of sufficiently small cold plasma inhomogeneity the precipitation related to different waves should nearly coincide. Thus, the coincidence of the energetic proton and relativistic electron precipitation cannot be considered as undoubted evidence of the interaction with EMIC waves. Acknowledgments. The work was partly supported by the basic research programs of RAS #22 and #4. References Carson, B.R., CJ. Rodger, and M.A. Clilverd (2012), POES satellite observations of EMIC-wave driven relativistic electron precipitation during 1998-2010, J. Geophys. Res. Space Physics, 118, 232-243, doi:10.1029/2012JA017998. Chen, L., RM. Thome, and R.B. Horne (2009), Simulation of EMIC wave excitation in a model magnetosphere including structured high-density plumes, J. Geophys. Res., 114, A07221, doi:10.1029/2009JA014204. Chen, L., R.M. Thome, W. Li, J. Bortnik, D. Turner, and V. Angelopoulos (2012), Modulation of plasmaspheric hiss intensity by thermal plasma density structure, Geophys. Res. Lett., 39, L14103, doi:10.1029/2012GL052308. Evans, D.S., and M.S. Greer (2004), Polar Orbiting Environmental Satellite Space Environment Monitor-2 Instrument Descriptions and Archive Data Documentation, NOAA Tech. Mem. 1.4, Space Environ. Lab., Boulder, Colorado. Home, R.B., M.M. Lam, and J.C. 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