The Dawn-Dusk Asymmetrical Distribution of Earthward Poynting Flux in the Dayside Polar Cap From DMSP

We investigated the dawn-dusk asymmetrical distribution of quasi-dc earthward Poynting flux (EPF) in the dayside polar cap of the Northern Hemisphere based on 3 years of observations at similar to 850 km made by the Defense Meteorological Satellite Program (DMSP) F17. The satellite data have been sorted by low (Kp <= 2) and high (Kp > 2) geomagnetic activity, as well as the orientation and strength of interplanetary magnetic field (IMF) By and Bz components, binned by magnetic latitude, and magnetic local time. Statistical results show that the enhanced convection electric field favors the asymmetrical EPF distribution. Asymmetrical distribution characteristics are summarized as (a) there are mainly two enhanced EPF regions, near dawn and cusp and the mean EPF is 28% larger on the dawn than on the dusk for all IMF and Kp conditions. (b) The mean EPF for high Kp is 3 times greater than that for low Kp in the dayside polar cap. The enhanced EPF shifted from near the dawn for low Kp to near the cusp for high Kp. The EPF is also larger on the dawn than on the dusk for high Kp. (c) The EPF of the dayside polar cap is significantly enhanced as the IMF strength increases. Under IMF By+, EPF is greater on the dawn than on the dusk. The opposite is true under IMF By-. The IMF Bz- favors enhanced EPF and the EPF on the dawn (dusk) reaches its maximum for IMF By+ and Bz- (IMF By- and Bz-).