Low latitude sub-ionospheric VLF signal behaviour during the two recent solar eclipses: Observation and simulation

We present the VLF observational data from the VTX (18.2 kHz) and NWC (19.8 kHz) transmitters during the solar eclipses of July 22, 2009 and January 15, 2010. The data were collected at several receiving stations in India and the corresponding VLF amplitudes show all possible behaviour with respect to different propagation conditions. We simulate the observed behaviour of the VLF signals using the most-well known Long Wave Propagation Capability (LWPC) code and find the corresponding ionospheric parameters during the solar eclipses. We also show that the VLF radio data during solar eclipses incorporate the effects of short-period (~min to hrs) atmospheric gravity waves. Dominant wave periods ranging from 10 minutes to 1 hour around the time of maximum eclipse phase have been found. We also present the anomalies in the topside ionosphere during these two solar eclipses. Measurements of the densities and temperatures of the thermal electrons and ions were provided by the DEMETER satellite, which flew near India during the time of partial solar obscuration. We find decrease in plasma density, electron and ion temperatures along the orbit by several unit.