Dayside convection and auroral morphology during an interval of northward interplanetary magnetic field

We investigate the dayside auroral dynamics and ionospheric convection duri ng an interval when the interplanetary magnetic field (IMF) had predominant ly a positive B-z component (northward IMF) but varying B-y. Polar UVI obse rvations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the day side auroral oval, which we interpret as the ionospheric footprint of a hig h-latitude reconnection site. The large field-of-view afforded by the satel lite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based obser vations. The location of the emission in latitude and magnetic local time v aries in response to changes in the orientation of the IMF; the cusp MLT an d the IMF B-y component are especially well correlated, the emission being located in the pre- or post-noon sectors for B-y. < 0 nT or B-y> 0 nT, resp ectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interva l of IMF B-y approximate to 0 nT, these convection flow measurements sugges t the presence of a clockwise-rotating lobe cell contained within the pre-n oon dayside polar cap, with a flow reversal closely co-located with the hig h-latitude luminosity region. This pattern is largely consistent with recen t theoretical predictions of the convection how during northward IMF. We be lieve that this represents the first direct measurement of the convection f low at the imaged location of the footprint of the high-latitude reconnecti on site.