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 D ual Auroral Radar Network (SuperDARN) HF radar network have been analy zed to study the two-dimensional structure and dynamics of dayside hig h-latitude ionospheric convection under northward interplanetary magne tic field (IMF) conditions. A period extending from 1600 to 2030 UT (s imilar to 0900-1330 MLT) on January 10, 1994, was examined, During thi s interval, magnetic field data were available from the LMP 8 satellit e and indicated moderately stable northward IMF conditions. For the fi rst few hours of observation the B-y component of the IMF was positive , reasonably steady, and approximately twice the magnitude of B-z. Dur ing this interval, the high-latitude convection images obtained with t he SuperDARN radars were very similar to the distorted two-cell convec tion 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 incre ase in B-z, led to an extended period with B-y approximate to B-z. Dur ing this second interval the convection patterns were highly variable and even chaotic. Finally, a sharp decrease in the B-y component at 19 14 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. Dur ing this third interval, the high latitude convection pattern was agai n stable and exhibited a single counterclockwise rotating vortex consi stent 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 ar ea within two radar scans (200 s) and appeared to proceed via an equat orward incursion of the vortex into the previous convection configurat ion. Once this polar cap merging cell was formed, it remained stable f or the remainder of the period (similar to 40 min) that B-y remained s mall. Sunward convection was also observed in the polar cap of the con jugate hemisphere at 1932 UT by the DMSP F11 satellite, confirming tha t both magnetopause and internal reconnection sites were active at tha t time.