High-time resolution conjugate SuperDARN radar observations of the daysideconvection response to changes in IMF B-y

We present data from conjugate SuperDARN radars describing the high-latitud e ionosphere's response to changes in the direction of IMF B-y during a per iod of steady IMF B-z southward and B-x positive. During this interval, the radars were operating in a special mode which gave high-time resolution da ta (30 s sampling period) on three adjacent beams with a full scan every 3 min. The location of the radars around magnetic local noon at the time of t he event allowed detailed observations of the variations in the ionospheric convection patterns close to the cusp region as IMF B-y varied. A signific ant time delay was observed in the ionospheric response to the IMF B-y chan ges between the two hemispheres. This is explained as being partially a con sequence of the location of the dominant merging region on the magnetopause , which is similar to 8-12R(E) closer to the northern ionosphere than to th e southern ionosphere (along the magnetic field line) due to the dipole til t of the magnetosphere and the orientation of the IMF. This interpretation supports the anti-parallel merging hypothesis and highlights the importance of the IMF B-x component in solar wind-magnetosphere coupling.