Toward resolving small-scale structures in ionospheric convection from SuperDARN

The combination of radial velocities measured by a pair of Super Dual Auror al Radar Network (SuperDARN) HF coherent radars gives, in their common fiel d of view, the velocity vectors in a plane perpendicular to the magnetic he ld. The standard merging is based on a natural grid defined by the beam int ersections, which provides a resolution varying between 90 and 180 km (depe nding upon the distance to the radars). This allows the description of stru ctures with a typical scale size (L) of the order of 500 km. The present st udy is devoted to a merging method which takes advantage of individual rada r grids to enhance the resolution (L approximate to 200 km). After a brief description of the standard merging method, we define the high-resolution g rid and discuss the potential problems which have to be overcome. The first problem concerns the localization of the scattering volume, whereas the se cond one deals with the independence of the velocity vectors. These two lim itations have been addressed in previous studies [Andre et al., 1997; Barth es et al., 1998]. In the method proposed here, several velocity vectors are determined at each grid point, from which the selection is made by using t he hypothesis of minimization of the divergence magnitude. The selected map is the one which minimizes the divergence. The performances are tested and compared to the standard merging algorithm through simulated double vortic es. Finally, we apply this method to real data, and show, through two examp les, its ability to describe small-scale structures (L approximate to 200 k m).