Role of Equatorial Fountain for the Delayed Response of Thermosphere O1D 630.0 nm Dayglow Over the Dip Equator During an X‐Class Flare

Abstract

AbstractThis paper reports, for the “first time,” the delayed response of O1D 630.0 nm dayglow emissions over Trivandrum (8.5°N, 77°E, 0.5°N dip lat.), a geomagnetic dip equatorial station in India, to the noontime X‐class solar flare event of July 30, 2005. The dayglow measurements were made using a unique dayglow photometer operating at three wavelengths. The Equatorial Electrojet induced magnetic field, measured using a proton precession magnetometer, showed a magnetic spike having ∼90 nT enhancement during this flare with a time delay of ∼7.2 min. A noteworthy observation is that unlike to the conventional belief, the O1D 630.0 nm dayglow over the dip equator exhibited a fourfold enhancement during the noontime flare after a time delay of ∼45 min. Analysis of satellite measured electron density and modeling simulations indicate that the thermospheric O1D 630.0 nm dayglow emission over the dip equatorial region during a solar flare is primarily driven by the electrodynamics, rather than the direct solar control. This finding is new, unique and very important for the studies related to plasma‐neutral coupling and also for modeling studies on the equatorial thermosphere‐ionosphere region is concerned.