Responses of the Daytime Low and Equatorial Ionosphere and Thermosphere Over the Indian Region During the Geomagnetic Storm of April 2023

Abstract

Study of the response of Thermosphere–Ionosphere (TI) system over the Indian longitude sector during the geomagnetic storm of April 23–24, 2023, is presented. The ionosonde observations at the dip equatorial station, Trivandrum (8.52°N, 77°E, dip lat. = 1.96°N), are found to have unusually high F2 peak plasma density (foF2), with three maxima during the daytime on April 24. The Total Electron Content (TEC) observations from different latitudes showed enhancements temporally progressing from north to south. These features are identified as Traveling Ionospheric Disturbances (TIDs) with speeds ∼400 to 750 m/s. Two major enhancements in TEC observed over Trivandrum were concurrent to the first and third maxima in foF2. Simulations of meridional wind and temperature for this storm were carried out using the Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIEGCM) that was driven with high-latitude inputs derived from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique. Simulations show the signatures of Traveling Atmospheric Disturbances (TADs) in ionospheric F-region, which conform with the TID observations. The second foF2 peak is found to be simultaneous to the modulation in Prompt Penetration Electric Field (PPEF), which is also observed in the drift of the E-region ionospheric plasma irregularities using an HF radar and the Equatorial Electrojet (EEJ) strength measured by ground-based magnetometer. Simultaneously increasing electric field and foF2 implies the presence of storm-time equatorward wind, inhibiting the plasma fountain. This is the first report comparing comprehensive observations and AMIE-TIEGCM modeling studies of daytime responses of low and equatorial TI during a geomagnetic storm.