Horizontal Electrojet Associated with the Sun-Aligned Arcs
Journal of Atmospheric and Solar-Terrestrial Physics
Analysis of two strong sun-aligned arcs over the Canadian Eureka Observatory (89° CGM) near the north magnetic pole and accompanying related ground magnetometer measurements has identified an electrojet current of not, vert, similar1×104 A flowing within the arcs in a sunward direction. The electrojet current was carried by low energy electrons created by impacting precipitation drifting at E×B/B2 velocity within the arcs, where E is the dawn-to-dusk electric field. One of the arcs moved rapidly in a dawn to dusk direction. The measured arc velocity was 365 m/s. This agrees well with the velocity of 380 m/s inferred from the magnetic field signature of the electrojet current. This study suggests that such an electrojet is present whenever a polar arc is set up. However, a few conditions are required to observe clear ground magnetic signatures of the electrojet: (1) quiet local magnetic conditions; (2) a single sun aligned arc near or moving across zenith; and (3) arc excitation by ≥1 keV electrons.
Zhang, Y., D. J. McEwen, N. Kong, J. J. Sojka, and L. Zhu, Horizontal electrojet associated with the sun-aligned arcs, J. Atmos. Solar-Terr. Phys. 61, 1249-1257, 1999.