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

• Published in: Annales geophysicae (1988) Vol. 18; no. 4; pp. 436 - 444
• Main Authors: MILAN, S. E, LESTER, M, COWLEY, S. W. H, BRITTNACHER, M
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau European Geophysical Society 2000; European Geosciences Union; Copernicus Publications
• Subjects: Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Ocean, Atmosphere; Physics of the magnetosphere; Plasma motion, convection, circulation. Plasma instabilities; Sciences of the Universe; Northern Hemisphere; Interplanetary magnetic field; Auroral oval; Image analysis; Vacuum ultraviolet radiation; Convection flow; Ionosphere magnetosphere coupling; Satellite observation; Magnetosphere; Auroral activity
• ISSN: 0992-7689; 1432-0576; 1432-0576
• DOI: 10.1007/s00585-000-0436-9

We investigate the dayside auroral dynamics and ionospheric convection during an interval when the interplanetary magnetic field (IMF) had predominantly a positive Bz component (northward IMF) but varying By. Polar UVI observations of the Northern Hemisphere auroral emission indicate the existence of a region of luminosity near local noon at latitudes poleward of the dayside auroral oval, which we interpret as the ionospheric footprint of a high-latitude reconnection site. The large field-of-view afforded by the satellite-borne imager allows an unprecedented determination of the dynamics of this region, which has not previously been possible with ground-based observations. The location of the emission in latitude and magnetic local time varies in response to changes in the orientation of the IMF; the cusp MLT and the IMF By component are especially well correlated, the emission being located in the pre- or post-noon sectors for By < 0 nT or By > 0 nT, respectively. Simultaneous ground-based observations of the ionospheric plasma drift are provided by the CUTLASS Finland HF coherent radar. For an interval of IMF By \\approx 0 nT, these convection flow measurements suggest the presence of a clockwise-rotating lobe cell contained within the pre-noon dayside polar cap, with a flow reversal closely co-located with the high-latitude luminosity region. This pattern is largely consistent with recent theoretical predictions of the convection flow during northward IMF. We believe that this represents the first direct measurement of the convection flow at the imaged location of the footprint of the high-latitude reconnection site.Key words: Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; plasma convection)