Multi-instrument probing of the polar ionosphere under steady northward IMF

Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identi®ed. A steep latitudinal density gradient at the equatorward edge of the precipitation identi®es the general location of an adiaroic boundary, separating the open ®eld lines of polar lobe cells from the closed ®eld of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being recon®gured as it is thrust against the boundary by the antisunward ̄ow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the di€erent experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere.