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.

Poloidal monochromatic pulsations in the Pc4-Pc5 range observed in the Earth magnetosphere ит от Figure 3. The comparison of the magnetic field variation (he-component) on GOES-IO spacecraft (MLT=UT-4) with the fluxes o f energetic electrons (left-hand panel) and protons (right-hand panel) in various energy channels on LANL-1994 spacecraft (MLT=UT-3.5). Before the onset of Pc5 waves on the GOES-IO, the increase of the magnetospheric electron density has been detected by the LANL-1994 spacecraft (Fig. 4). We suppose that this cloud of energetic electrons may be responsible for the pulsation excitation. Approximately 1 hour after the appearance of Pc5 pulsations, a substantial increase of the magnetospheric electron temperature Те has been observed by LANL-1994 (Fig. 4). This temperature growth may be associated with the electron heating by enhanced Pc5 waves. 3.5. THEMIS observations. The poloidal pulsations in the morning sector have been also detected by THEMIS-E, -B, and -C spacecraft (Fig. 5). According to time delay between signals on different probes, we find that these Pc5 waves propagate in the sunward direction, i.e. in the same direction as drifting electrons. The pulsation phase velocity in XY plane is -100 km/s, i.e. much smaller than the typical Alfven speed VA. The time delay between THB-THC-THE probes gives the azimuthal wave number /и-24.6. Thus, these pulsations are indeed small-scale disturbances in the azimuthal direction. The frequency of the poloidal pulsations on THE is lower f~4.5 mHz, than that at GOES-10, f~5.4 mHz. Because THE probe is located on a larger L-shell than GOES-IO does (see Fig. 1), this frequency difference may indicate on resonant properties of these pulsations, i.e. a frequency decrease with an increase of L-shell. The magnetometer (GOES-IO) and particle detector (LANL-1994) are shifted azimuthally by -0.5 h MLT. As a result the phase difference of small-scale magnetic pulsations and periodic particle oscillations is not steady and cannot be reliably measured. The cross-phase between the azimuthal Ey electric component (Fig. 5) and radial magnetic component Bx is close to 90°. So, these oscillations are standing AlfVen waves along a field line. 4. Discussion The poloidal Pc5 pulsations under examination are quite similar to Pg pulsations: both have a very monochromatic waveforms, and are excited during low geomagnetic activity. However, contrary to Pg pulsations, the observed poloidal pulsations cannot be seen by ground-based magnetometers. This distinction may be caused by a higher value of m -value of the poloidal Pc5 waves as compared with typical Pg pulsations (m~15) [Takahashi et al., 2011]. It may be supposed that the observed poloidal pulsations are generated by a kinetic instability of the ‘hot’ electrons. However, such instabilities require a finite value of parameter /? for their effective excitation. According to LANL-1994 and GOES-IO data, during the considered event pe is very low, -0.015. Therefore, these poloidal pulsations can hardly be generated due to development of kinetic instabilities. We suggest that generation of these waves by energetic electrons may occur in a non-resonant way, via the "ship waves" mechanism [Mager and Klimushkin, 2008]. The poloidal Alfven wave is supposed to be emitted by a non-steady electric current created by a 61