It is well-known that equatorial plasma bubbles (EPBs) are highly; correlated to the post-sunset rise of the ionosphere on a climatological; basis. However, when proceeding to the daily EPB development, what; controls the day-to-day/longitudinal variability of EPBs remains a; puzzle. In this study, we investigate the underlying physics responsible; for the day-to-day/longitudinal variability of EPBs using the Sami3 is A; Model of the Ionosphere (SAMI3) and the Whole Atmosphere Community; Climate Model with thermosphere-ionosphere eXtension (WACCM-X).; Simulation results on October 20, 22, and 24, 2020 were presented.; SAMI3/WACCM-X self-consistently generated midnight EPBs on October 20; and 24, displaying irregular and regular spatial distributions,; respectively. However, EPBs are absent on October 22. We investigate the; role of gravity waves on upwelling growth and EPB development and; discuss how gravity waves contribute to the distributions of EPBs. Of; particular significance is that we found the westward wind associated; with solar terminator waves and gravity waves causes midnight vertical; drift enhancement and collisional shear instability, which provides; conditions favorable for upwelling growth and EPB development. The; converging and diverging winds associated with solar terminator waves; and midnight temperature maximum also affect the longitudinal; distribution of EPBs. The absence of EPBs on October 22 is related to; the weak upward drift induced by weak westward wind associated with; solar terminator waves.