The Formation Mechanism of Merged EIA During a Storm on 4 November 2021

In this study, we conduct an in-depth analysis of Whole Atmosphere Community Climate Model-eXtended simulations to examine physical mechanisms of the formation and evolution of an equatorial ionization anomaly (EIA) merging phenomenon during a storm on 4 November 2021. A quantitative analysis reveals that the rapid decay of the EIA crests at their poleward sides at altitudes of ∼200–250 km plays a crucial role in the EIA merging during that day. This rapid decay is due to the fast recombination at low altitudes (∼200–250 km) as the plasma are transported downward by the westward disturbance dynamo electric field and poleward neutral winds during the storm. The results suggested EIA-merging is not merely northern and southern EIA crests moving together, but it involves a crucial rapid decay of the EIA crests at their poleward sides that descended to low altitudes (rapid recombination, ∼200–250 km), driven by regional electric fields and neutral winds. This study plays a crucial role in our understanding of the evolution and formation of the merged EIA on 4 November 2021 during the storm.