Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

Precipitation o fprotons related to EMIC waves on the dayside In particular, the precipitation is observed in the range of 64°-76° CGLat. Median value is 69.13° and first and third quartiles are -68° and 71°, respectively. Fig. 3d presents intensity of the proton fluxes in WPEP. Finally, Fig. 3e shows the number o f orbits of NOAA satellites with registration of WPEP for every day during the whole interval under study. The data presented in Fig. 3 demonstrate that the large-size precipitation of protons within the anisotropy zone is, indeed, a typical dayside phenomenon. The occurrence rate, which is defined as the ratio of the number of satellite orbits with registration of WPEP to the number of all orbits crossing the dayside, is about 25%. A spatial distribution of the WPEP occurrence in coordinates MLT-CGLat is shown in Fig. 4. The occurrence in percent is presented in bins with resolution of 1 h in MLT and 1° in latitude. The occurrence is defined as the ratio of the number of orbits with WPEP registration within the bin to the number of all orbits crossing the bin. The occurrence is maximal (7-9%) in the afternoon sector at CGLat=68°-70° and decreases to both dawn and dusk. In general, this WPEP occurrence distribution is consistent with the results of statistical studies of EMIC waves. The occurrence distribution in Fig. 4 mapped onto the equatorial plane resembles that found, for example, by Usanova et al. (2012). Similar to the EMIC wave statistics, the probability to observe WPEP maximizes outside the geosynchronous orbit and is small in the near Earth magnetosphere. \M LT CGLat\ 6-7 7-8 8-9 9-10 10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-18 74-75 0 0 0 0.27 1.56 1.38 0.54 0.66 0 0 0 0 73-74 0 0.61 0 2.63 2.02 1.79 1.63 0.5 0 0 0 0 72-73 0.29 1.8 2.12 0.59 2.03 2.95 2 2.67 1.49 1.04 0 0 71-72 1.25 0.4 0 3.24 3.41 2.86 3.32 2.51 1.84 1.19 0 70-71 69-70 68-69 67-68 66-67 0.74 1.81 0.7 2.39 1.25 1.27 3.17 3.89 3.17 2.21 2.88 3.45 1.36 2.07 1.95 1.82 0 1.72 3.28 3.18 4.22 2.12 2.6 ; 2.02 0.98 2.98 M 7 3.12 2.76 0 6.24 8 53 Ш Ш 6.72 6.33 7.86 6.72 1 0.76 2.52 3.64 1.23 0 1.39 0.99 2.23 2.6 65-66 0.94 1.22 0 1.52 0 0.27 0.54 1.64 0.38 1.25 1.52 0.8 Fig. 4 4. Discussion and conclusion Using the THEMIS data, Wang et al. (2013) studied spatial distributions of the ion pitch-angle anisotropy at different energies (from 0.05 to 600 keV). For ions with the energy of a few tens of keV, they found well-defined transverse anisotropy (Т|>Тц) in the outer magnetosphere (at r > 5 RE) on the dayside. The most convenient mechanisms of the transverse anisotropy of energetic ions on the dayside are the drift shell splitting ( Roederer, 1967) and drift orbit bifurcation ( Shabansky , 1971). Both mechanisms are the result of the interaction of the magnetosphere with the permanently flowing solar wind producing day-night asymmetry of the magnetospheric magnetic field, which is compressed on the dayside and stretched on the night side. The stronger compression the larger dayside anisotropy resulting from the two mentioned mechanisms ( McCollough et al., 2012). This anisotropy should permanently exist on the dayside. The transverse anisotropy of ions is a favorable condition for growth of EMIC waves and related scattering of ions into the loss cone. Thus, on the dayside there exists a permanent source of precipitation of protons. The solar wind-magnetosphere interaction and magnetospheric processes producing the energetic protons in the day sector rule spatial scale and structure of the source region as well as intensity of the precipitation. Note, that characteristics of EMIC waves on the dayside demonstrate clear dependence on both solar wind dynamic pressure and geomagnetic activity (e.g. Usanova et al., 2012). The dependence of WPEP on solar wind and geomagnetic activity are not discussed here (this will be a subject of future investigations). Nevertheless, the case study illustrated by Figs. 1, 2 and occurrence statistics ( Fig. 4) show that WPEP events within the region of anisotropic fluxes of energetic protons are the particle counterpart of EMIC waves in the outer magnetosphere on the dayside. A cknow ledgem en ts. This study was performed in frames of scientific programs of the Presidium of RAS ## 22 and 4. The work of TAY was supported by the RFBR grant #11-02-00397. 83