Storm and Substorm Driven by Magnetic Reconnection in the Plasma Sheet

J. R. Kan

Geophysical Institute, University of Alaska Fairbanks

The magnetic storm and substorm are both driven by convection enhanced by magnetic reconnection in the plasma sheet. Substorm growth phase is driven by the MDXL (mid-to-distant X-line) beyond ~30 Re radial distance. Substorm expansion phase is driven by the NEXL (near-Earth-X-line) within ~ 30 Re. Cowling current intensifies by the blockage of the northward Hall current due to lack of azimuthal pressure gradient in the midnight sector in the near-Earth plasma sheet. Interaction of intensified Cowling current loop with the near-Earth plasma sheet causes dipolarization. Dipolarization-induced thinning, tailward of the dipolarizing region, can cause the NEXL formation to drive the substorm expansion phase. Further intensifications of the westward Cowling current in the substorm current wedge, tailward expansion of the dipolarizing region and the expansion of the auroral bulge are all driven by the NEXL during the expansion phase. A ring current injection conjecture is proposed to order the storm intensity based on the X-line location. Ring current intensifies by convection driven by the NEXL during the substorm expansion phase to produce major and super storms. On the other hand, ring current intensifies by the MDXL in the absence of substorms to produce moderate and small storms. Results obtained previously with the Rice Convection Model coupled to an equilibrium magnetic-field solver indicate that the entropy function PV5/3 must be non-adiabatically reduced if plasma-sheet flux tubes are to be injected into the heart of the storm-time ring current. Magnetic reconnection in the plasma sheet reduces the entropy function, and the effect is stronger if the X-line is closer to the Earth. It is estimated that an X-line must form within ~25 RE of Earth in order for the reconnected flux tubes to penetrate deep into the heart of the ring current to produce major storms.