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Abstract

Magnetic storms cause significant disturbances in the middle- and low-latitude ionosphere through penetration electric fields, disturbance dynamo electric fields, and neutral winds and composition changes. Understanding the interplay of different processes is critical for understanding storm-time ionospheric electrodynamics. In this study, we analyze ionospheric data measured by multiple satellites and ionospheric radars during intense magnetic storms and address the following important issues in ionospheric dynamics. (1) Long-lasting penetration electric fields are identified. The eastward penetration electric field is dominant in the equatorial ionosphere for 10-14 hours during continuous southward interplanetary magnetic field (IMF) and cause increase of 100-200 m/s in the equatorial vertical ion drift. (2) Strong subauroral polarization streams (SAPS) occur in the dusk-evening sector during the main and recovery phases of the magnetic storm and penetrate to equatorial latitudes without obvious time delay, leading to the generation of large westward plasma drifts of 200-300 m/s at all middle and low latitudes. (3) The topside ion density measured by the DMSP satellites is increased by a factor of 5-10, and these density enhancements last for 12 hours or longer, indicating the enhanced equatorial fountain effects caused by penetration electric fields. (4) A new type of ionospheric ion density oscillations with a period of ~6 hours is identified, which is different from travelling ionospheric disturbances and longitudinal wave-4 structure. This study provides new insight into storm-time ionospheric electrodynamics at middle and low latitudes.