Modeling the Post-Midnight Equatorial Plasma Bubbles With SAMI3/SD-WACCM-X: Large-Scale Wave Structure

This study investigates the relative significance of gravity wave and gravity dynamo effects in large-scale wave structure (LSWS) development using the coupled Sami3 is Also a Model of the Ionosphere (SAMI3) and Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCM-X). Simulations show significant vertical E × B drift perturbations associated with gravity waves in the F region after ∼1700 LT, leading to LSWS near midnight. Notably, LSWS can occur independently of gravity-driven dynamo current, emphasizing the significance of the gravity wave wind dynamo mechanism. However, LSWS exhibits more pronounced vertical E × B drift perturbations, indicating the involvement of background wind fields. Both gravity wave and background wind dynamo effects cause LSWS to grow vertically by ∼20 km and extend to ±10° in latitude. Gravity-driven Pedersen current, therefore, plays a role in amplifying the upwelling growth and equatorial plasma bubble development. Furthermore, simulations demonstrate the emergence of predawn ionospheric irregularities in the bottomside F layer, even without gravity-driven currents, attributed to concentric gravity waves over the magnetic equator. A comparison between FORMOSAT-7/COSMIC2 and SAMI3 ion density is also conducted. These findings emphasize the significant influence of gravity waves and background wind fields on the formation of LSWS and irregularities.