ИСТИНА

Energetic proton precipitation equatorward of the boundary of isotropic fluxes (EPPEBIF) is the consequence of the ion-cyclotron instability (ICI) developing in the vicinity of the equatorial plane of the magnetosphere. Thus, the precipitation can be used for statistical studies of the EMIC wave occurrence. The global distribution of the occurrence rate of EPPEBIF is constructed on the basis of the data from four POES satellites that operated during July-December of 2005. The distribution exhibits the maximal occurrence on the dayside at distances behind the geostationary orbit. This agrees with the EMIC waves occurrence in the magnetosphere. It is also shown that maximal occurrence rate of the precipitations increases with the increase in the solar wind dynamic pressure independently of the geomagnetic activity level. We demonstrate that the maximal occurrence rate on the dayside increases when the geomagnetic activity changes from low to moderate, and it decreases during the higher activity. Such behavior can be explained by the effect of the two competitive processes, both of them are due to the nightside injections of energetic protons. On the one hand, the injections lead to growth of particle flux, which, in turn, causes the increase of ICI increment. On the other hand, the injections lead to the decrease of the radial gradient of the particle flux on the nightside. This results in the decrease of transverse anisotropy of energetic protons on the dayside and diminishes the ICI increment.