The Origin of Bubble-like Structures in Midlatitudes during Geomagnetic Storms

Abstract:

Plasma density structures that resemble the plasma bubbles found in equatorial regions have been detected away from the equatorial region during geomagnetic storms. The source of these bubble-like structures in midlatitudes, which we call ‘midlatitude bubbles’, are often understood in terms of the development of anomalously large equatorial plasma bubbles; equatorial bubbles can be detected in midlatitudes when they grow to the altitude of several thousand kilometers. However, solid observational evidence of the origin of midlatitude bubbles has not yet been provided. This study investigates the association of midlatitude bubbles with the ionospheric fountain process. The fountain effect transports equatorial bubbles to higher latitudes in addition to the development of large equatorial bubbles. Previous studies did not consider the effect of the meridional transport. In addition, the geometry of a bubble should also be taken account to properly interpret the midlatitude bubble phenomenon. We conduct event-based case studies of midlatitude bubbles by analyzing various coincident observational data. SAMI3 model simulations are conducted to identify the effect of the fountain process on the generation of equatorial bubbles and their transport.