Simultaneous conjugate observations of dynamic variations in high-latitude dayside convection due to changes in IMFBy
Two conjugate HF radars are currently operating at Goose Bay, Labrador, and Halley Station, Antarctica, and are providing continuous, high temporal resolution measurements of plasma convection over large areas of the high‐latitude ionosphere. In this paper, data from these radars for a single 45‐min period about local noon on 22 April 1988 are examined to study near‐instantaneous, conjugate, two‐dimensional patterns of plasma convection in the vicinity of the cusp and their response to changes in the By component of the interplanetary magnetic field (IMF). Our observations indicate that under quasi‐stationary IMF conditions, the conjugate convection patterns are quite similar to the synthesized patterns of Heppner and Maynard [1987]. The patterns respond rapidly to changes in the IMF By component. The average response time was 8 min between an IMF transition at the IMP‐8 satellite and the beginning of a convection reconfiguration in the ionosphere. Typically, the newly reconfigured convection pattern filled the radar field of view (10° to 15° of invariant latitude and 2.5 h of local time) within 6 min of reconfiguration onset. For the examples studied, the reconfiguration onsets began over an extended local time sector in the invariant latitude range from 73° to 75° and proceeded by means of a poleward expansion of the reconfigured pattern into a region containing fossil convection associated with the prior IMF state. We interpret the onset region in the ionosphere as being associated with cusp field lines and the poleward region as being associated with open field lines in the plasma mantle and tail lobe.