Equatorial Plasma Drifts during the Magnetic Storm on 7-11 November 2004: Identifications of the Roles of Penetration and Disturbance Dynamo Electric Fields with Multi-Instrumental Measurements

Penetration electric fields and disturbance dynamo electric fields are the two major disturbance electric fields in the equatorial ionosphere during geomagnetic storms. In this study, we analyze equatorial ion drifts measured by radar and satellites during the geomagnetic storm on 7-11 November 2004. The magnetic storm had two main phases, with minimum Dst values of -373 and -289 nT, respectively. The equatorial vertical ion drifts in the dusk-evening sector were continuously enhanced in the upward direction for 13 hours on 7-8 November, including 7 hours of the first main phase and 6 hours of the early stage of the recovery phase. On 10 November, the equatorial vertical ion drifts were continuously enhanced in the upward direction for ~10 hours, including ~9 hours of the second main phase and ~1.5 hours of the early stage of the recovery phase. Enhanced thermospheric nitric oxide 5.3 m emission and westward disturbance winds were measured in the equatorial region during the two main phases of the magnetic storm, indicating occurrence of disturbance dynamo electric fields. The observations show that penetration electric fields are the dominant electric fields in the equatorial ionosphere for 13 and 10 hours with continuous southward IMF even if disturbance winds already occur. Very large westward ion drifts are generated in the dusk-evening equatorial region during the magnetic storm, and it is suggested that the westward drifts are caused by penetration of electric fields associated with subauroral polarization streams.