Longitudinal Dependence of the Apex Altitude of Ionospheric Bubbles

Over the past decades, significant progress has been done toward understanding the physics of ionospheric bubbles/irregularities that cause the rapid amplitude and phase fluctuations of radio signals that traverse through it. However, characterization of the global ionospheric irregularities as a function of local time, longitude, altitude, and magnetic activities is still a challenge for the modeling community. In this paper, we investigate the longitudinal dependence of the bubbles penetration to higher altitudes (or apex altitudes longitudinal difference). Different driving mechanisms have been suggested for the occurrence of apex altitude longitudinal dependences. One of the mechanisms is the equatorial vertical drift which is associated to the neutral wind amplitude and direction. Thus, to understand the physics behind longitudinal dependence of apex altitude, we will utilize multi-instrument observations onboard COSMIC-2, ICON, GOLD, and SWARM satellites. While IVM in-situ density onboard COSMIC and ICON, as well as GOLD UV imager, provide the latitudinal distributions of ionospheric bubbles, the MIGHTI instrument onboard ICON provides the horizontal wind magnitude and direction at different longitudes.