Results of VLF campaigns in Summer and Winter in Indian subcontinent

VLF propagation effects can be understood using the earth-ionosphere waveguide. However due to emergence of the new fields such as VLF Astronomy where the ionosphere is treated as a giant detector for extraterrestrial energetic phenomena and the seismo-electromagnetism where the disturbances of this giant detector is influenced by terrestrial events, especially earthquakes and other seismic activities. In order to interpret observed data correctly, we need to have the basic propagation characteristics throughout India. In this paper, we concentrate on the results of the VLF campaigns we conducted using over a dozen receiving stations in Summer and in Winter. We observe the well-known asymmetry in East to West and West to East propagation. From the signal amplitude characteristics, we divide the sub-continent in four zones as far as the VTX transmitter is concerned.