The Role of Storm-Time Electrodynamics in the Dawn and Dusk Sectors Across Equatorial and Low-Latitude Ionosphere During December 19-21, 2015

We present the distinct responses of the nighttime ionosphere due to an intense and long lasting geomagnetic storm of December 19-21, 2015 using a chain of ionosondes from magnetic equator to anomaly crest region over India. The observations exhibited unique features throughout the night including dawn and dusk sectors. The results showed twin episodes of pre-reversal enhancement (PRE) in dusk sector associated with oscillatory vertical plasma drift due to shielding electric field that produced briefly post-sunset equatorial spread F (ESF) irregularities. Accordingly, relative dominance of interplanetary magnetic field (IMF) and auroral electrojet (AE) related electric field fluctuations in vertical and zonal drifts at different times are investigated throughout the night. Also the application of wavelet/wavelet coherence analysis on interplanetary and geomagnetic conditions and ionospheric data showed distinct relationships. The results showed that vertical drift is in phase with interplanetary electric fields (IEFy) with period of similar to 30 min at similar to 18:30 IST (13:00 UT) that drives first PRE whereas similar to 60 min period in AE which is in phase with vertical drifts drives second PRE at similar to 20:30 IST (15:00 UT). However, other short term periods in vertical drifts are in phase with IEFy and AE at other times suggesting that both are contributing to the drift variations. The simultaneous upliftment of F layer at all stations producing fresh ESF irregularities in the dawn sector is attributed to the unique electrodynamical response of the Indian low latitude stations to the eastward disturbance dynamo electric fields (DDEFs). These results are also in concomitant with satellite observations and thermospheric ionospheric electrodynamics general circulation model (TIE-GCM) drifts.