Generation mechanism for VLF chorus emissions observed at a low-latitude ground station

Abstract. A detailed spectral analysis of VLF chorus emissions observed at the low-latitude ground station Gulmarg (geomag. lat., 24° 26' N, geomag. long., 147° 9' E, L=1.28) during the strong magnetic activity on 7-8 March 1986 have been carried out, which shows that each chorus element originates from the upper edge of the underlying hiss band. To explain various temporal and spectral features of these emissions, a possible generation mechanism has been presented based on the backward wave oscillator regime of the magnetospheric cyclotron maser. On the basis of this model, we have computed various chorus parameters as well as some magnetospheric parameters affecting the generation process. A comparison of the observed chorus characteristics with the proposed generation mechanism shows a good agreement.