The Impact of Vertical Plasma Motion on the Evolution of Predawn Equatorial Plasma Bubbles on the Dayside

This study investigates the impact of vertical ionospheric drift during daytime on the evolution of predawn equatorial plasma bubbles by conducting model simulations using “Sami3 is Another Model of the Ionosphere.” The upward drift of the ionosphere transports bubbles to higher altitudes, where their lifetime is set by the atomic oxygen photoionization rate. While the bubbles generated at predawn persist into dayside, the bubbles generated shortly after sunset diminish before sunrise. Therefore, post‐sunset bubbles do not contribute to daytime electron density irregularities. Bubbles maintain their field‐aligned characteristics throughout the daytime regardless of the vertical ionospheric drift. This property allows bubbles to exist near the magnetic equator despite poleward plasma transport by the fountain process. The shift of irregularity concentration to higher latitudes over time in satellite observations is explained by the combined effect of transport of bubbles to higher altitudes and rapid refilling of depletions near the magnetic equator. Plain Language Summary The Earth's equatorial ionosphere becomes turbulent at night, manifested in the phenomenon known as equatorial spread F (ESF). During ESF large‐scale electron density depletions (often referred to as “bubbles”) develop and low‐density plasma is transported to higher altitudes. While bubbles are primarily nighttime phenomena, some persist longer and evolve into sources of electron density irregularities on the dayside. Bubbles are concentrated near the magnetic equator at night in satellite observations, but during the daytime, their peak occurrence frequency shifts to higher latitudes over time. This phenomenon is attributed to the latitudinal redistribution of bubbles in association with the vertical motion of the ionosphere. We assess this hypothesis by conducting numerical simulations. The simulation results reveal that the field‐aligned characteristics of bubbles are maintained during the plasma redistribution process. This property provides a valuable tool for understanding the daytime behavior of bubbles as observed by satellites. Key Points Evolution of predawn equatorial plasma bubbles on the dayside is investigated using Sami3 is Another Model of the Ionosphere Bubbles generated at predawn persist into the dayside, and their transport to higher altitudes by vertical motion prolongs their lifetime Bubbles maintain their field‐aligned characteristics during their evolution on the d