Hemispheric responses of ionosphere-thermosphere to intense geomagnetic storms over the East Asian-Australian sector

Abstract

The irregularities of huge geomagnetic storms impact the satellite communication by enforcing large delays in ray path. This work investigates the hemispheric asymmetries in ionosphere-thermosphere responses to three large geomagnetic storms (Dst ∼−170 nT), occurring in different seasons and storm phases beginning in different local times, over the middle and low latitudes of East Asian-Australian longitude sector. The variations have been studied by critical frequency of F2 layer (foF2) and multi-satellites observables at ±60° conjugate latitudes along ∼115° E. The enhanced equatorial ionization anomaly (EIA) is associated to the strong eastward electric fields, trigger significant part in main phases of the December 2015 and August 2018 storms during dayside. The main phase covering the night side during March 2023 storm, exhibited no significant total electron content (TEC)/foF2 variations except small-scale ionospheric irregularities. The unexpected ionospheric-thermospheric asymmetry on 26 August 2018 is mainly influenced by the northward neutral winds as opposed to the seasonal winds. Moreover, the recovery phases of the December 2015 and March 2023 commenced around morning hours activate a classic seasonal response at middle latitudes along with disturbance dynamo effect at low latitudes. On contrary, the ionospheric responses at the recovery phase during August 2018 storm is not dominated by expected seasonal flow and disturbance dynamo. At different phases of the three storms, E region electric fields, thermospheric composition and neutral winds played a major role for ionospheric disturbances.