Observation and simulation of the development of equatorial plasma bubbles: Post‐sunset rise or upwelling growth?

This study investigates the underlying physics of equatorial plasma bubbles (EPBs) on 11 December 2019, under solar minimum conditions. The Global-scale Observations of the Limb and Disk (GOLD) ultraviolet nightglow images exhibit a periodic distribution of reduced emissions related to EPBs. Remarkably, FORMOSAT-7/COSMIC-2 (F7/C2) observes a significant altitudinal difference of similar to 45 km in the bottomside ionosphere between two nearly collocated electron density profiles before the onset of EPBs, indicating the presence of an upwelling. Distinct ionospheric perturbations are also observed in F7/C2 and ground-based Global Positioning System observations, suggesting that gravity waves may contribute to the upwelling. Simulations with SAMI3/ESF are further carried out to evaluate the upwelling growth and pre-reversal enhancement (PRE) effect on EPB development. Simulations reveal that the crests of upwellings show a localized uplift of similar to 50 km, and EPBs only develop from the crest of upwellings. The uplift altitude of upwellings is comparable to the F7/C2 observations and the post-sunset rise in moderate solar conditions. The polarization electric field (E-p) developed within the upwellings can drive vertical E-p x B drifts of similar to 32-35 m/s, which are comparable to the PRE vertical E x B drifts. We find that the PRE alone cannot drive EPBs without upwelling growth, but it can facilitate the upwelling growth. Observations and simulations allow us to conclude that upwelling growth could play a vital role in the formation of EPBs.