In 27 October 2012 the ULF wave in Pc4 range being Alfv'en wave was observed with Van Allen Probe A. In the event the parallel Poynting flux of the wave was directed towards the Northern ionosphere. Assuming that this may be caused by the asymmetry of ionospheric conductivity between the Northern and Southern hemispheres, its effect on the standing structure of the Alfv'en wave was investigated in this paper. For this purpose the analytical model with straight magnetic field lines was used. As a result the method for estimation of the Northern and Southern ionospheric conductivity was developed. It allows us to reconstruct the parallel structure of Alfv'en waves under various conditions of the ionospheric conductivity. With the method developed, the ionospheric conductivity for the October 27, 2012 event was evaluated and compared with ionosphere model IRI-2016.

In the paper a unique phenomenon - the resonant generation of ultra-low frequency (ULF) wave by energetic electrons in the magnetosphere - is presented. On 27 October 2012 in the morning side of the magnetosphere Van Allen Probe A registered an ULF wave with period of 100 s and an amplitude of 0.7 nT. A cloud of energetic electrons was observed simultaneously with the wave. It is established that the electron cloud was injected into the magnetosphere as a result of a substorm. Electron fluxes in several energy channels were modulated with the frequency of the observed wave. It is shown that these flux modulations are caused by the drift resonance of 38 keV electrons and the wave being a fundamental harmonic of an Alfven mode with an azimuthal wavenumber m~ 110-115 propagating to the east, and generated through the gradient instability due to steep earthward density gradient of the resonant electrons.