SUPER DUAL AURORAL RADAR NETWORK RADAR IMAGING OF DAYSIDE HIGH-LATITUDE CONVECTION UNDER NORTHWARD INTERPLANETARY MAGNETIC-FIELD - TOWARD RESOLVING THE DISTORTED 2-CELL VERSUS MULTICELL CONTROVERSY

Data from the Kapuskasing and Saskatoon radars of the evolving Super Dual Auroral Radar Network (SuperDARN) HF radar network have been analyzed to study the two-dimensional structure and dynamics of dayside high-latitude ionospheric convection under northward interplanetary magnetic field (IMF) conditions. A period extending from 1600 to 2030 UT (similar to 0900-1330 MLT) on January 10, 1994, was examined, During this interval, magnetic field data were available from the LMP 8 satellite and indicated moderately stable northward IMF conditions. For the first few hours of observation the B-y component of the IMF was positive, reasonably steady, and approximately twice the magnitude of B-z. During this interval, the high-latitude convection images obtained with the SuperDARN radars were very similar to the distorted two-cell convection maps for positive B-y as presented by Heppner and Maynard (1987). At similar to 1840 UT, a decrease in B-y in association with an increase in B-z, led to an extended period with B-y approximate to B-z. During this second interval the convection patterns were highly variable and even chaotic. Finally, a sharp decrease in the B-y component at 1914 UT, probably in association with a rotational discontinuity in the solar wind, led to an extended period with B-y much less than B-z. During this third interval, the high latitude convection pattern was again stable and exhibited a single counterclockwise rotating vortex consistent with one of the polar cap merging cells proposed by Dungey (1963), Burke et al. (1979), and Reiff and Heelis (1994). The transition to the counterclockwise rotating vortex occurred over a large spatial area within two radar scans (200 s) and appeared to proceed via an equatorward incursion of the vortex into the previous convection configuration. Once this polar cap merging cell was formed, it remained stable for the remainder of the period (similar to 40 min) that B-y remained small. Sunward convection was also observed in the polar cap of the conjugate hemisphere at 1932 UT by the DMSP F11 satellite, confirming that both magnetopause and internal reconnection sites were active at that time.