Large scale patterns of auroral ionospheric convection observed with the Chatanika Radar

Abstract

Ionospheric convection at auroral latitudes has been examined during a series of long duration experiments with the Chatanika, Alaska, incoherent scatter radar. These experiments have been carefully designed to obtain maximum latitudinal coverage (56°Λ–75°Λ) while maintaining a temporal resolution of 30 min in order to resolve the effects of individual substorms on the convection pattern. Design criteria for the experiments are described together with presentation of observational data acquired during 400 hr of radar operations during various levels of geophysical disturbance. The data accentuate the repeatability of the gross features of the auroral convection and its basic conformity to the two‐cell pattern predicted from the large‐scale magnetospheric circulation. For moderate to active geomagnetic conditions uniform sunward convection with velocities of 800–1200 m/s spans the 62°Λ to 72°Λ latitude band at both dawn and dusk. In quieter circumstances the sunward convection continues in this region, but has smaller speeds and is centered at higher latitudes. Little evidence of a ‘throat’ in the dayside convection pattern is seen at latitudes below 75°Λ except in very disturbed circumstances. During several experiments coordinated operation of the Chatanika and Millstone Hill, Massachusetts, radars permitted the simultaneous observation of the auroral convection pattern at two different local times. Substorms affect the convection at all local times and appear to generally enhance the rate of convection without seriously changing its direction. Near midnight, latitudinal displacements and expansions of the convection pattern during substorms may result in a local rotation or reversal of the direction of convection, while near dawn and dusk, convection velocities are enhanced and the region of sunward flow expands to lower latitudes.