Determination of field-aligned currents using the Super Dual Auroral Radar Network and the UVI ultraviolet imager

Field-aligned currents (FACs) derived from the divergence of horizontal current estimates are presented. The technique for determining the currents is discussed and then example observations are presented. The horizontal currents were estimated from the product of the ionospheric conductance and the convection electric field. The ionospheric conductance was estimated from auroral ultraviolet luminosity observations from the ultraviolet imager instrument on the Polar satellite combined with an empirical model of the solar ultraviolet produced ionization. The convection electric field was estimated from plasma drift observations from the Super Dual Auroral Radar Network. The general features of the statistical FAC pattern [Iijima and Potemra, 1976] are found in the observations. In addition, transient currents in the vicinity of the magnetospheric cusp are observed and are found to be the most intense currents within the field of view. An example of FACs during the development of a magnetospheric substorm is presented. Conductance gradients are found to play an important role in determining the currents on both the dayside and nightside.