Investigation of gravity wave characteristics in the equatorial ionosphere during the passage of the 15 January 2010 solar eclipse over Tirunelveli

Abstract

Solar eclipses are known to produce gravity wave disturbances in the atmosphere-ionosphere system in addition to density reduction due to temporary changes in solar radiation. The magnetic equator is ideally located to investigate these waves and their coupling to the equatorial ionosphere due to its unique geometry. Accordingly, the response of the equatorial ionosphere to a rare Annular Solar Eclipse (ASE) observed on 15 January 2010 is investigated using high-resolution observations from Canadian Advanced Digital Ionosonde (CADI) located at Tirunelveli which is a magnetic equator and on the eclipse totality path in India. In addition, simultaneous observations of GPS TEC from Tirunelveli, electron density profiles from Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC), and Equatorial Electrojet (EEJ) strength were analysed. The real height analysis has been performed on the ionosonde data using POLynomial ANalysis (POLAN). The isoheight/isofrequency analysis has been performed using real height on eclipse and control days. The results indicate a reduction of ∼33% in the lower ionosphere whereas no change has been noticed close to the F layer peak on the eclipse day. The isoheight analysis further indicates the presence of gravity waves with dominant periods in the range of 5-30 minutes. Further analyses have been performed on the altitude variation of dominant waves and their amplitudes/phases using ionosonde to identify whether they are generated in-situ or propagated from below. The altitude variation of group and phase velocities showed opposite propagation indicating that they were propagated from the below. In addition, the simultaneous presence of gravity waves in the fmin, TEC, and EEJ strength on eclipse day supports our finding that these waves were propagated from the lower atmosphere.