R. P. Patel*, S. Singh, A. K. Singh and R. P.
Singh1
Atmospheric Research Laboratory, Department of Physics, Banaras Hindu
University,
Varanasi 221 005, India
1 Vice-chancellor, V.K.S. University, Ara, Bihar, India
Abstract. The disturbances on the solar surface lead to the enhanced injec- tion of energetic charged particles into the inner magnetosphere, which modifies the electrodynamic features of ionosphere and magnetosphere. The electrody- namic properties control the generation and propagation characteristics of VLF waves. At Varanasi station, which is one of the low latitude stations in India, we have recorded VLF waves from 1990 onwards. The source of VLF wave is natural lightning discharges. Whistler activity varies with latitude having maximum around 50 geomagnetic latitude. The occurrence rate is low at low latitudes and also depends on the solar and geomagnetic conditions. In this pa- per, we report the results derived from the statistical analysis of whistler waves recorded at Varanasi during the period January 1990 December 1999. The monthly occurrence rate shows maximum during January to March. Seasonal variations of the occurrence rate are also studied. In order to study the role of geomagnetic disturbances on the occurrence rate, we have used Kp index and its variation. It is observed that the occurrence probability monotonically in- creases with Kp values. Detailed result of occurrence of whistler waves during the main phase and recovery phase of geomagnetic storms is also presented.
Keywords: whistler waves - ducted mode propagation - geomagnetic storms