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

We report here a collection of complementary measurements near local magnetic 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 magnetic 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 riometer 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, which propagates poleward over the magnetometers and radar field of view. For the cases presented the interplanetary B-z is strongly negative, while the ionospheric variations are associated with the low-frequency component of variations in the interplanetary B-y component. In contrast to the previously discovered traveling convection vortices, these features exhibit a poleward phase motion rather than one along lines of invariant latitude. The propagation velocity is slower (approximate to 0.5-1.0 km/s) and the structures cover 2 to 3 hours of local time. We interpret the observations as a poleward propagation of the DPY current system intensification associated with enhancements in the IMF B-y component. Our observations indicate that the DPY field-aligned current system is propagating poleward and may be moving independent of the convection motion of the plasma and associated field lines.