Polar region Birkeland current, convection, and aurora for northward interplanetary magnetic field

Abstract

Viking magnetic field, electric field, and image data have been used to assess polar region phenomena for steady state northward interplanetary magnetic field (IMF) conditions. Regions of polar Birkeland current (NBZ currents) and convection and their extent from the vicinity of the magnetic pole are determined. Also discussed are mechanisms that could produce polar aurora in general; two suggestions are (1) converging electric fields from convection patterns alone and (2) the bifurcation of the magnetotail with its associated plasma transport and convection patterns. Macroscopic (> 1° latitude) systems of Birkeland currents and convection in the polar regions have been established for a case on April 9,1986, from Viking spacecraft data. The current systems were confined to the highest latitudes of the polar regions and occurred during strongly northward IMF with a significantly negative Bx. An arc extends across the polar region within the dawn cell of Birkeland current. The arc is located at a sunward to antisunward convection reversal that corresponds to a converging electric field. A converging electric field (▽ · E < 0) alone is suggested as the cause of this polar arc. The signature of both transverse disturbance vectors indicates that the polar region dawn NBZ Birkeland current does not connect to the dayside auroral region. It is inferred that the dawn polar region convection cell associated with this Birkeland current is also limited in the sunward direction and does not connect to the dayside auroral region convection.