Observation and simulation of upwelling growth and equatorial plasma bubbles with FORMOSAT-7/COSMIC2, GOLD, and SAMI3/ESF

In this study, we report the observations of upwelling and equatorial plasma bubbles (EPBs) under solar minimum conditions using the FORMOSAT 7/COSMIC 2 (F7/C2) and Global scale Observations of the Limb and Disk (GOLD) observations. The GOLD ultraviolet nightglow images exhibit a periodic distribution of reduced emissions related to EPBs. Remarkably, the nearly collocated F7/C2 electron density profiles show a significant altitudinal difference of ~45 km in the bottomside ionosphere before the onset of EPBs, indicating the presence of an upwelling. Distinct ionospheric perturbations are also observed in the F7/C2 and ground-based Global Positioning System observations, suggesting that gravity waves may contribute to the formation of upwelling and EPBs. Interestingly, GOLD and F7/C2 observed EPBs every night in December 2019, despite the pre-reversal enhancement (PRE) being weak from the F7/C2 and Jicamarca radar observations, contrary to our current understanding that PRE should be the primary driver to trigger EPBs. Simulations with SAMI3/ESF are further carried out to understand the relative significance of upwelling growth and the PRE. Simulations reveal that upwelling growth is independent of the PRE. The crest of upwelling can rise to an altitude of ~50 km that is comparable to the F7/C2 observations and post-sunset rise due to the PRE in moderate solar conditions. We found that PRE along cannot drive EPBs without upwelling growth. Observations and simulations allow us to conclude that upwelling growth could play a vital role in the formation of EPBs.