Investigating Asia's Low-Latitude Ionosphere's Pulse During the Spectacular September 2017 Solar Storms

Abstract

This research examines fluctuations in Total Electron Content (TEC) variations in the ionosphere along the Asian longitude, focusing on the impact pertaining to solar flares and geomagnetic storms that occurred from September 6 to 9, 2017, in the geographical regions of India, Beijing, Dhaka, Islamabad, Thimphu, and Kathmandu. The investigation explores the impacts of solar flares in isolation and the compounded impact when both solar flares and geomagnetic storms coincide. On 6 September, two noteworthy X-class solar flares, specifically X2.2 at 08:57 UT and X9.3 at 11:53 UT, were observed during a period of calm geomagnetic conditions. The extreme ultraviolet (EUV)/X-ray intensity associated with the X9.3 flare was documented., with both flares exhibiting a slower recovery phase compared to their impulsive phase. This decelerated recovery in extreme ultraviolet (EUV)/X-ray intensity manifests as a delayed Total Electron Content (TEC) reaction. The observation of nearly an 10% greater crest-to-trough TEC variation on the day of the flare compared to the day before the flare indicates an intensified equatorial electrojet. The relatively subdued Total Electron Content (TEC) response to the X9.3 solar flare is ascribed to the shift in solar flare occurring from the disk centre towards the west limb. The solar flares on September 7-8 aligned with geomagnetic storms, leading to substantial TEC increments. These observed changes are attributed not only to the solar flares but also to the rapid penetration electric field and an elevated extent of thermosphere compositional alterations. On 9 September, 10 September, an escalation in the TEC was observed in solar flares of the M class under the joint influence of solar flares and a destroyed Dynamo electric field.