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

Abstract 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.