Dynamic Processes Associated With Prominent Ionospheric Variations in a Narrow Longitudinal Zone Near the EIA Crest Region as Revealed by ICON Satellite and Ground Beidou Receiver Observations Over South Asia

Neutral winds and plasma motions from the Ionospheric Connection Explorer mission were used to investigate dynamic processes associated with large regional total electron content (TEC) differences in a narrow longitudinal zone exceeding similar to 45 TECU obtained from dense Beidou geostationary receivers at low latitudes over South Asia. The TEC east-west asymmetry was defined to quantify this difference, which exceeded similar to 5 TECU per 1 degrees longitude distance and occurred around the equatorial ionization anomaly (EIA) crest on 31 March 2021 under geomagnetically quiescent conditions. Moreover, the magnetic meridional ion velocity exhibited a large longitude difference around the EIA crest during periods with strong ionospheric east-west asymmetry. Furthermore, the longitude difference variation was consistent with the TEC east-west asymmetry variation during 11-21 March 2020 and 27 March-4 April 2021. No significant correlations between TEC east-west asymmetry and longitude differences under conditions with neutral winds and magnetic zonal ion drifts were observed in either case. The different vertical plasma drifts could contribute to ionospheric changes with a zonal range of a few hundred kilometers. Recently, a sharp regional ionospheric longitudinal change over a few degrees was observed, and the regional ionospheric change in a narrow longitudinal zone (similar to 45 TECU) was much greater than the global variation (similar to 2-4 TECU) in the longitudinal wave-4 patterns. The physical processes that cause such strong regional ionospheric change are poorly understood. Here, neutral wind and plasma drift data from Ionospheric Connection Explorer, along with observations from dense Beidou geostationary receivers over South Asia, were used to explore ionospheric dynamic processes associated with large regional total electron content (TEC) variations. The different vertical plasma drifts driven by zonal electric fields may be a key factor in the formation of strong ionospheric variation, as indicated by the significant correlation between the TEC east-west asymmetry and longitude differences in magnetic meridional ion velocity in both the case study and statistical results. Neutral winds also greatly control the equatorial ionization anomaly (EIA) morphology; however, their longitude differences are not directly correlated with strong local ionospheric changes. This study provides an important view to understand the sharp ionospheric changes in a narrow longitudinal zone. The strong east-west asymmetry in total electron content (TEC) exceeded similar to 5 TECU per 1 degrees longitude is detected at the northern equatorial ionization anomaly (EIA) crestPlasma drift and neutral wind observations were used to explore dynamic processes associated with regional TEC changes in the EIA regionDifferent vertical plasma drifts driven by zonal electric fields could contribute to regional TEC changes around the EIA crest