ANALYSIS OF IONOSPHERIC VARIABILITY ASSOCIATED WITH A SEISMIC EVENT AND A SPACE WEATHER EVENT

This paper focuses on the ionospheric variability observed in the F region during a seismic event and space weather event in the low latitude region. A strong earthquake of magnitude M = 7.7 hit the Bhuj region of Gujarat, India in the morning hours (0825 IST). The epicenter of the seismic activity was located around 220 km west of Ahmedabad (23°N, 72.4°E). Five days prior to the earthquake, strong negative deviation (as high as 70%) in the foF2 values is observed. The magnitude of the negative deviation increases as the moment of earthquake approaches. This negative deviation persists even four days after the seismic event. This observed ionospheric variability is compared with a space weather event. The foF2 data used for study is of a storm, which occurred on 11-13/04/01. The Dst value reached as high as-271 nT. The foF2 values have been studied for the low latitude stations Ahmedabad (23°N, 72.4°E) and Delhi (28.6N, 77.2E). The most striking feature is the dramatic collapse of F region ionization when main phase of storm is in progress (up to 40%). However the magnitude of negative deviation associated with the seismic event is found to be larger than that observed during the geomagnetic storm event