Coherent-Scatter Radar Studies of the Dayside Cusp

Abstract

It is now commonly accepted that in the cusp regions the entry of magnetosheath particles into the magnetosphere, and ultimately, the ionosphere is most direct [1]. Furthermore, magnetic reconnection at the magnetopause between the interplanetary magnetic field (IMF) and Earth’s magnetic field, as proposed by Dungey [2], facilitates mass, momentum and energy transfer from the solar wind into the magnetosphere and ionosphere. This coupling process at the magnetopause leads to large-scale convective flows in the magnetosphere-ionosphere system. The time variation of these flows is most clearly observed in the cusp region and hence study of the ionospheric footprint of the cusp gives direct information on the dynamics of the magnetopause. Many recent in situ, ground based and theoretical studies of the cusp have been reviewed by Smith and Lockwood [3]. It is not the purpose of this paper to revisit that material, rather to consider observations of the ionospheric footprint of the cusp that can be made by coherent scatter radars such as those that form the network of HF radars termed SuperDARN [4]. It is pertinent, however, to ask what coherent radars can provide which are important for studies of the cusp. The key element is the spatial coverage obtained by the radars which can be achieved at relatively high spatial and temporal resolution, typically 45 km and 2 minutes respectively, although these can be improved. The extended coverage of such radars can then provide measurements over a large part of the polar cap, especially when combined in the manner of the SuperDARN network.