Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland

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 (~0900-1330 MLT) on January 10, 1994, was examined. During this interval, magnetic field data were available from the IMP 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 ~ 1840 UT, a decrease in B_y in association with an increase in B_z, led to an extended period with B_y » 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 << 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 (~ 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.

J. Geophys. Res., 100, No. A10, 19661-19674, Oct. 1995