Generation and characteristics of equatorial spread F plasma bubbles during intense magnetic storms

Magnetic storms represent very large disturbances in the magnetosphere and ionosphere. Equatorial spread F (ESF) is a process that causes plasma density irregularities in the equatorial F region. However, it is not well understood how magnetic storms affect the generation of ESF plasma bubbles. We will present the measurements of the evening equatorial ion density and velocity by the Defense Meteorological Satellite Program (DMSP) satellites and the Jicamarca incoherent scatter radar during twenty-three intense magnetic storms with minimum Dst value of smaller than ­-100 nT. The radar measurements show that penetration electric field during southward interplanetary magnetic field (IMF) is eastward in the evening sector and lifts the equatorial F region there. The DMSP measurements show that deep equatorial ion density depletions (ESF plasma bubbles) are generated after the IMF turns southward. The time delay between the IMF southward turning and the first DMSP detection of ion density depletions becomes shorter when the interplanetary electric field during southward IMF, correspondingly an eastward penetration electric field in the evening equatorial ionosphere, is larger. The results of this study provide strong evidence that enhanced magnetic activity increases the generation of ESF plasma bubbles during the main phase of magnetic storms. We will also present the observations of a case in which the plasma density depletions occurred at middle magnetic latitudes, as well as at equatorial latitudes. The depletions at middle latitudes (20-46 deg) were identified as the extension of depleted flux tubes into these latitudes. It implies that the plasma bubbles might have reached the altitude of 6800 km over the magnetic equator. The observations may represent the highest altitude/latitude of plasma bubbles that has ever been reported in the literature.