Ionospheric effect of earthquakes as determined from ground based TEC measurement and satellite data

Abstract

63-70Total electron content (TEC) measurements have been carried out at Agra (geographic lattitude 27°N, longitude 78°E), India using a dual frequency GPS receiver since 24 June 2006. Similarly, DEMETER satellite data of electron density and VLF/ULF electromagnetic emission data are available since its launch on 29 June 2004. The effect of earthquake on GPS-TEC and electron density (Ne) data, obtained from DEMETER satellite, has been investigated in the present paper. GPS-TEC and Ne data for seven months, during 01 December 2006-30 June 2007, has been investigated. Two large magnitude earthquakes occurred during this period: one on 08 January 2007 (M=6.0, depth=16 km) and other on 05 May 2007 (M=6.2, depth=09 km) at a distance of 1587 and 887 km, respectively from the observation station at Agra. The results show anomalous enhancements in TEC and Ne 1-4 days before and 1-2 days after the occurrence of these earthquakes. The calculated percentage deviations of TEC and Ne from their monthly mean values are found to vary between 40 and 80% during anomalous enhancements. The observed effect is interpreted in terms of generation of electric fields between the ionosphere and quasi-neutral ion clusters which are formed at troposphere heights by radon gas emanation from seismic region and followed by triggering of these clusters by green house gases. The electric fields so generated penetrate the ionosphere and bring out structural and dynamical changes in ionospheric parameters