Post substorm convection and auroral arc currents determined from multiple ionospheric, magnetic, and electric field observations

Abstract

Field, particle, and optical observations from rocket‐borne probes, magnetic data from a meridian chain of stations, and data from three scanning photometers were used for analyses of auroral current systems during the recovery phase of a substorm. The rockets were launched southeastward over several discrete arcs from Ft. Churchill, Canada, on January 15, 1972. Current models were determined independently from the magnetic field observations and from the electric field and ionospheric observations. The electric fields were measured by a rocket‐borne electrostatic analyzer while the ionospheric model was determined from plasma probe measurements and also calculated from the energetic particle observations. Broad westward current systems were encountered on the initial and final segments of the trajectory and were determined from Ohm’s law and compared with those calculated from magnetic observations obtained along the rocket trajectory and from the meridian chain of stations. Auroral arc currents under the apogee segment of the trajectory were calculated from the electric field observations and a model ionosphere and were eastward. Field‐aligned currents were estimated from the divergence of the meridian current and added to these electrojets. The model was iterated to obtain a reasonable fit to both the ground‐based and the rocket‐borne observations. A very active region poleward of the arcs was much more structured than that indicated from the analysis of the ground‐based magnetic data. It consisted of both eastward and westward currents, which may have been remnants of the substorm. Intense field‐aligned currents flowed inward on the poleward edge of the electrojets and outward near the arcs, at the Harang discontinuity, and between the electrojets. These field‐aligned currents appeared to be located at the boundaries of cells that contained the convection, active remnant region, and auroral arc current systems.