OBSERVATIONS OF A SOLAR-WIND-DRIVEN MODULATION OF THE DAYSIDE IONOSPHERIC DPY CURRENT SYSTEM

We report here a collection of complementary measurements near local m agnetic noon of a unique ionospheric convection variation observed by the Sondrestrom radar which is related to a nearly periodic variation (approximate to 25-30 min period) in the interplanetary magnetic field B-y component. We observe also a poleward phase propagation of magnet ic pulsations over a region limited in longitude and latitude near the dayside polar cusp. A series of poleward propagating radio absorption enhancements are observed in the Greenland and South Pole imaging rio meter data. The pulsations and absorption enhancements are associated with a latitudinally narrow and longitudinally limited intensification of the westward convection and associated eastward Hall current, whic h propagates poleward over the magnetometers and radar field of view. For the cases presented the interplanetary B-z is strongly negative, w hile the ionospheric variations are associated with the low-frequency component of variations in the interplanetary B-y component. In contra st to the previously discovered traveling convection vortices, these f eatures exhibit a poleward phase motion rather than one along lines of invariant latitude. The propagation velocity is slower (approximate t o 0.5-1.0 km/s) and the structures cover 2 to 3 hours of local time. W e interpret the observations as a poleward propagation of the DPY curr ent system intensification associated with enhancements in the IMF B-y component. Our observations indicate that the DPY field-aligned curre nt system is propagating poleward and may be moving independent of the convection motion of the plasma and associated field lines.