IMF driving of dayside convection and the cusp

Recent measurements from ground based facilities, sounding rockets and the Polar satellite have been combined to investigate the influence of the IMF on dayside convection patterns. Detailed comparisons of the IMF measurements by the Wind satellite with ionospheric electric field data from the sounding rockets provide conclusive evidence that signals interacted with the magnetosphere on time scales significantly different, both shorter and longer, than nominal advection lag times. For example, under IMF Bz north conditions, rocket measurements are consistent with Northern Hemisphere convection being stirred by merging with closed field lines in the Southern Hemisphere. This adds open flux to both polar caps. Under Bz south and positive By conditions, we detected evidence for Southern Hemisphere merging directly driving the variable westward flows observed by the rocket. The data supports the antiparallel merging hypothesis of Crooker (1979). These measurements show that variations in the solar wind couple to the magnetosphere and ionosphere through anti-parallel merging more directly than has been previously observed. Implications for understanding and interpreting Cluster data are discussed.