The Relation between Dayside Local Poynting Flux Enhancement and Cusp Reconnection

The Defense Meteorological Satellite Program (DMSP) F15 satellite frequently observes an unusually high level of local Poynting flux when the IMF is northward but also has a large y component. We use the OpenGGCM coupled magnetosphere-ionosphere-thermosphere code to study several events where, under such conditions, unusually large earthward Poynting flux has been observed. We find that the Joule heating rate in the model agrees well with the observed Poynting flux. Analysis of the model results shows that the strong Poynting flux hot spots are physically linked with magnetic reconnection at the high-latitude cusps. The movement of the newly opened field lines created by cusp reconnection produces a Pedersen current, which consequently generates an intense Joule heating region, and a pair of adjacent and opposite FACs connecting to the magnetopause currents forming a closed circuit. The distribution, scale, and magnitude of this Joule heating region and corresponding FACs in the polar regions are mainly controlled by IMF clock angle, IMF magnitude, and solar wind dynamic pressure. Our simulation results show that the large earthward Poynting flux is likely to be the main energy source that causes the unusual thermospheric upwelling and neutral density enhancements observed by CHAMP satellite during such events.