High latitude convection based on long-term incoherent scatter radar observations in North America

Abstract

High latitude ionospheric convection patterns and models are obtained based on a composite analysis of incoherent scatter radar (ISR) observations in the North America sector at Millstone Hill and Sondrestrom (MHS). These observations span a combined latitude range of 55 ∘ ⩽ Λ ⩽ 82 ∘ over time periods starting from 1978 for Millstone Hill and from 1995 for Sondrestrom. These models, regional to the America sector, represent average and steady patterns of the convection as driven by the interplanetary magnetic field (IMF) By and Bz or by Kp and the By direction, and update the existing MHS models. This paper describes the ISR and IMF data processing and modeling technique and discusses convection changes under a variety of conditions. In particular, we have examined By and Bz effects on the electrostatic potential at dawn and dusk, the location of the cells, and the shape of the cells; we also present the convection change in response to magnetic activity. This long-term data set has enabled us to study seasonal variations of the convection. The cross polar cap potential is on average higher in equinox than in solstice. With the advance of season from winter to summer, the convection cells appear to move antisunward, and the axis across the two cells rotates toward earlier local times; meanwhile, for By negative, the crescent-shaped dawn cell and circular dusk cell become well defined with a reduced cross polar cap potential, while for By positive, the cross polar cap potential tends to be higher. The dusk–dawn cell similarity in summer is found to be high for By negative and low for By positive, supportive of the theory of lobe cell generation in summer. Because of the asymmetry of the convection response to By negative and positive, and of seasonal differences in the convection, it is speculated that there exist perceptible hemispheric differences in the cross polar cap potential drop.