Modeling Equatorial Plasma Bubbles with SAMI3/SD-WACCM-X: Large-Scale Wave Structure

Large-scale wave structure (LSWS) in the bottomside F layer is pivotal in developing equatorial plasma bubbles (EPBs), potentially serving as a precursor of EPBs. Gravity waves, hypothesized to contribute through the wind dynamo mechanism, face experimental challenges. This study, utilizing the coupled SAMI3 and SD-WACCM-X models, investigates the role of gravity wave wind dynamo effect and gravity in LSWS development. We found that the gravity waves originating from the lower atmosphere induce vertical E×B drift perturbations in the nighttime ionosphere. Notably, LSWS can manifest independently of gravity, emphasizing the dominance of the gravity wave wind dynamo mechanism. However, LSWS exhibits more pronounced vertical E×B drift perturbations, indicating an additional eastward Pedersen current driven by equatorial winds (i.e., downward wind) via the gradient drift instability. Gravity-driven Pedersen current, therefore, plays a role in amplifying the LSWS and EPB development. Simulations also show the emergence of pre-dawn turbulent bubble-like irregularities in the bottomside ionosphere even without gravity, attributed to concentric gravity waves over the magnetic equator. Our findings underscore the significant influence of gravity waves on the formation of LSWS and ionospheric irregularities.