What Determines the Properties of the Prompt Penetration Electric Fields? -- A Case Study of April 17, 2002, Storm Event

During geomagnetic storms, the prompt penetration to lower latitudes of the convection electric fields has often been observed. The mechanism involves interactions of the solar wind, magnetosphere, and ionosphere. One of the major causes is a sudden change in the cross polar cap potential drop, which represents a change in the region-1 field-aligned currents and is controlled by the interaction between the solar wind and magnetosphere. The pressure in the plasma sheet is redistributed by the convection electric field. Another contribution is from the reconfiguration of the storm-time magnetic fields. The resultant pressure gradients from inner edge of the plasma sheet generate the region-2 field-aligned currents which tend to shield the region earthward of it from the convection electric fields. The typical time scale of the penetration electric field is less than one hour, before shielding is established. During some time periods, a strong correlation has been observed between the interplanetary electric field and the penetration fields in the equatorial ionosphere [e.g., Nishida, 1968; Kelley et al., 2003]. The main goal of our study is to explore the impact of the various solar wind and IMF parameters on the correlation between the interplanetary and equatorial ionospheric electric fields, such as reported in Kelley et al. [2003]. Utilizing the Rice Convection Model (RCM) and altering the various input parameters, we investigate the temporal variation of the penetration electric field. Our previous results demonstrate that the penetration electric field can modify the ionospheric dynamo by changing the conductivity and neutral wind, preferentially at night. We will address the feedback of the time-dependent conductivity and neutral wind on the penetration electric field. Furthermore, we will discuss our results in relation to global latitudinal-chain observations of the ionospheric electric field during the April 17, 2002, storm event.