Horizontal electrojet associated with the sun-aligned arcs

Analysis of two strong sun-aligned arcs over the Canadian Eureka Observatory (89 degrees CGM) near the north magnetic pole and accompanying related ground magnetometer measurements has identified an electrojet current of similar to 1 x 10(4) 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 x B/B-2 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 are 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 are 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 are near or moving across zenith; and (3) are excitation by greater than or equal to 1 keV electrons. (C) 2000 Elsevier Science Ltd. All rights reserved.