LARGE-SCALE IMAGING OF HIGH-LATITUDE CONVECTION WITH SUPER DUAL AURORAL RADAR NETWORK HF RADAR OBSERVATIONS

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) prov ide measurements of the E x B drift of ionospheric plasma over extende d regions of the high-latitude ionosphere. With the recent augmentatio n of the northern hemisphere component to six radars, a sizable fracti on of the entire convection zone (approximately one-third) can be imag ed nearly instantaneously (similar to 2 min). To date, the two-dimensi onal convection velocity has been mapped by combining line-of-sight ve locity measurements obtained from pairs of radars within common-volume areas. We describe a new method of deriving large-scale convection ma ps based on all the available velocity data. The measurements are used to determine a solution for the distribution of electrostatic potenti al, Phi, expressed as a series expansion in spherical harmonics. The a ddition of data from a statistical model constrains the solution in re gions of no data coverage. For low-order expansions the results provid e a gross characterization of the global convection. We discuss the pr ocessing of the radar velocity data, the factors that condition the fi tting, and the reliability of the results. We present examples of imag ing that demonstrate the response of the global convection to variatio ns in the interplanetary magnetic field (IMF). In the case of a sudden polarity change from northward to southward IMF, the convection is se en to reconfigure globally on very short (<6 min) timescales.