On the ionospheric and thermospheric response of solar flare events of 19 January 2005: An investigation using radio and optical techniques

Abstract

This study presents optical signatures of thermospheric OI 630.0-nm dayglow variability over a geomagnetic dip equatorial station Trivandrum (8.5°N, 77°E, 0.5° dip latitude), India, in response to solar flares of different ranks that occurred on 19 January 2005. It is found that over equator, the response of thermospheric dayglow to solar flares can be either prompt or delayed depending upon rank of the flare and dominant neutral/electrodynamical processes prevailing in the emission altitudes. This is strikingly in contrast to the earlier results, where prompt response of equatorial OI 630.0-nm dayglow to solar flares has been noticed. In addition, the flare-induced changes at the E and F regions of the equatorial ionosphere are studied using high-cadence measurements of the equatorial electrojet (EEJ) and total electron content (TEC) obtained from the ground-based magnetometers and GPS receivers, respectively. The Hall/Pedersen conductivity measurements as inferred using the magnetometers over the EEJ station and an off-EEJ station showed concomitant changes during these flares. Although, the GPS-measured TEC showed prompt enhancement associated with these flares, the evolution of the equatorial ionization anomaly, as seen in the TEC did not show any flare-induced changes. The plausible mechanisms explaining these observations are adduced in context of the present understanding of the equatorial electrodynamics and its imprint on these dayglow features. ©2014. American Geophysical Union. All Rights Reserved.