ИСТИНА

On June 20, 2013, very long IPDP (Intervals of Pulsations of Diminishing Period) with frequencies varying from 0.3 to 1.5 Hz were observed at ground-based observatories Lovozero, Barentzburg, and Novaya Zhizn at 16-21 UT. Immediately after IPDP, in the interval of 21-23 UT, Pc1 pulsations were observed with a rather high frequency of 2.5-4.0 Hz. To compare the characteristics of the observed IPDP and Pc1 pulsations with the dynamics of localized precipitation of energetic (>30 keV) protons (LPEP) and relativistic electron precipitation (REP), we use energetic particle flux data from low-orbiting POES satellites (NOAA and MetOp). During the IPDP, clear LPEP events were detected in the energy ranges <20 keV and 30-80 keV, indicating possible magnetospheric sources of these pulsations. Those events coincided in the invariant latitudes (61.5–65° CGMlat) with the location of RBSP-B spacecraft that observed EMIC waves in the equatorial magnetosphere in the interval of 19:30–20:30 UT. During the same time RBSP-B recorded an increase in the cold plasma density up to 800 cm–3 indicating its entrance into the plasmasphere. The EMIC wave growth rate calculated by using the energetic proton distribution measured by RBSB-B showed an increase in the time-frequency domain corresponding well to the EMIC waves. Therefore, we assume that RBSP-B crossed the IPDP generation region during the EMIC wave observation. The IPDP frequency increase was accompanied by equatorward shift in the LPEP latitudes. This favors the mechanism of IPDP formation related to the inward drift of energetic protons generating the EMIC waves. Unlike IPDP, the sources of higher-frequency Pc1 pulsations were localized from local enhancements in the fluxes of trapped protons only. Such enhancements indicate the presence of weak pitch-angle diffusion insufficient for causing precipitation. Comparison of the equatorial gyrofrequencies of He+ fHe+ ions and protons fH+, estimated from the invariant latitude of the assumed wave sources, with the Pc1 frequencies showed that the IPDP detected in this event was generated in the helium band (f< fHe+), while the higher-frequency Pc1 were generated in the proton band (fHe+ < f < fH+). Precipitation of relativistic electrons was observed simultaneously with local enhancements in the fluxes of trapped protons, which mark the region of the Pc1 pulsation source.