Characteristics of Large-Scale Birkeland Currents in the Cusp and Polar Regions

Abstract

Particle observations from satellites acquired over a decade ago confirmed the presence of the dayside cusp regions (Heikkila and Winningham, 1971; Frank, 1971). Later studies showed that a wide variety of phenomena was associated with the cusps, including auroral emissions (Meng 1981), kilometric radiation (Alexander and Kaiser, 1977), ULF-ELF noise (Gurnett and Frank, 1978), ionospheric disturbances (Greenwald 1982). and Birkeland currents (Iijima and Potemra, 1976a). The fact that large scale Birkeland currents flow into and away from the cusps has been confirmed by several satellite experiments. Their locations, intensities, and flow directions are closely related to the orientation and magnitude of the interplanetary magnetic field (IMF). The characteristics of cusp-region Birkeland currents and their relationships to the IMF, polar convection, ionospheric currents, and ULF-VLF waves are reviewed here. The characteristics of a new large-scale Birkeland current system (referred to as the “NBZ” system) in the dayside polar region which intensifies during periods of strongly northward IMF are also reviewed.