The Occurrence Feature of Plasma Bubbles in the Equatorial to Midlatitude Ionosphere During Geomagnetic Storms Using Long‐Term GNSS‐TEC Data

Abstract

AbstractWe performed a superposed epoch analysis of solar wind, interplanetary magnetic field, geomagnetic index, and the rate of total electron content (TEC) index (ROTI) derived from global navigation satellite system‐TEC data during 652 geomagnetic storm events (minimum SYM‐H < −40 nT), to clarify the occurrence features and causes of storm‐time plasma bubbles in the equatorial to mid‐latitude ionosphere. In this analysis, we defined the time of the SYM‐H minimum as the zero epoch. As a result, the ROTI enhancement started at the duskside magnetic equator and expanded to higher latitudes during the main phase. Approximately 1 h after the onset of the recovery phase, the ROTI values at the magnetic equator in the dusk‐to‐midnight sectors decreased while those in the dawn sector increased. This situation persisted for at least 12 h. The ratio of the ROTI during the main phase to that during the quiet period in the dusk sector is the largest in May–July. The ratio of the ROTI during the recovery phase decreased during dusk with increasing solar activity. Considering the requirement of the Rayleigh‐Taylor instability, the difference in the magnetic local time of the ROTI signature, between the main and recovery phases, can be explained by a local time distribution of storm‐time electric fields associated with a prompt penetration electric field and disturbance dynamo. This implies that the occurrence feature of the plasma bubble is different from that during quiet times when the input of solar wind energy to the magnetosphere and ionosphere increases significantly.