On the ionospheric and reconnection potentials of the earth: Results from global MHD simulations

The reconnection potential along the reconnection line provides a quantitative description of magnetic reconnection that dominates the solar wind‐magnetosphere coupling. To properly determine the reconnection potential is a first and crucial step in deeply understanding magnetospheric processes. This paper proposes three methods to calculate the reconnection potential based on data obtained by global magnetohydrodynamic simulations of the Earth’s magnetosphere‐ionosphere system. The simulations are limited to the due southward interplanetary magnetic field (IMF) case for simplicity. The three methods are all based on the line integration of electric field and differ in the choice of integration path, radial rays in the equatorial plane for method 1, last closed magnetic field lines for method 2, and IMF lines nearby the reconnection line for method 3. The effect of numerical diffusion of the algorithm is included approximately by an equivalent uniform resistivity. For a properly selected numerical resistivity, the three methods give answers of the reconnection potential, which are reasonably close to each other. The reconnection voltage is found to be larger than the transpolar potential, and the ratio between them increases with increasing ionospheric conductance. The fact that method 2 also gives reasonable answers means that the appearance of parallel electric field along the last closed magnetic field lines is responsible for the difference between the ionospheric and the reconnection potentials and between the transpolar potential and the reconnection voltage as well. We suggest that similar methods may be applicable to general cases with arbitrary IMF orientations.