Field-aligned currents (FACs) play an important role in the energy, momentum, and mass coupling between magnetosphere and ionosphere. This study investigates the statistical characteristics of polar ionospheric FACs during substorms by using high resolution magnetic field measurements on board CHAMP. Obvious daynight and dusk-dawn asymmetries emerge in both FACs density and location. It shows: (1) FACs densities are related to AL index, with larger AL for larger current density. FACs densities during substorm are 5 times of that during quiet period. The duskside and nightside FACs densities correlate well with AL, while the dawnside and dayside FACs densities are not well correlated with AL; (2) the locations of peak FACs densities do not correlate with AL. The dusk FACs are located equatorward of the dawn, and the nightside FACs are located equatorward of the dayside.

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Wang, H.; Mao, D.-D.; Ma, S.-Y.; Lühr, H. (2010): Substorm time ionospheric field-aligned currents as observed by CHAMP. Chinese Journal of Geophysics-Chinese Edition, 53, 6, 1256-1262.