The effect of equatorial fountain on the evolution of equatorial plasma bubbles

This study presents new observational results that can make a significant contribution to the ICON mission. Equatorial plasma bubbles are thought of as nighttime phenomena because they are understood to develop at night and disappear after sunrise. Little attention has been paid to the evolution of these "fossil" bubbles during daytime. However, our preliminary study using ROCSAT-1, CHAMP, and SWARM satellites shows that bubbles are not solely a nighttime phenomenon because a significant portion of nighttime bubbles survive into the daytime. These fossils (early morning bubbles) are difficult to detect because the lower altitude portion of the bubble has been filled in by solar ionization and much, if not all, of the turbulence that produces an RF scintillation signature has disappeared. We note the more frequent occurrence of fossil bubbles at the anomaly region than near the magnetic equator. We interpret that this phenomenon is related to the latitudinal redistribution of fossil bubbles by the fountain effect; fossil bubbles concentrated at the magnetic equator at night are transported to higher latitudes by the fountain effect. We expect to identify tidal signatures from the observations of daytime irregularities because the intensity of the fountain effect is affected by tidal forcing. We investigate the origin of daytime irregularities by tracing the history of daytime irregularities and validate the effect of tidal forcing on the evolution of bubbles by investigating the temporal, longitudinal, and seasonal distributions of daytime irregularities. We discuss the application of our results to ICON observations.