ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Springer Verlag Göttingen, Germany 10.1007/s00585-000-0782-7 Dayside ionospheric response to changes in IMF polarity: optical and plasma-flow observations Pryse S. E. 2 1 3 Smith A. M. 2 1 3 Kersley L. 2 1 3 Department of Physics, University of Wales, Aberystwyth, SY23 3BZ, UK e-mail: lek@aber.ac.uk <i>Correspondence to:</i> L. Kersley 31 07 2000 18 7 782 788 Copyright: © 2000 S. E. Pryse et al. 2000 © European Geosciences Union 2000 This article is available from https://angeo.copernicus.org/articles/18/782/2000/angeo-18-782-2000.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/18/782/2000/angeo-18-782-2000.pdf

The response of the dayside ionosphere to changes in polarity of the interplanetary magnetic field was observed by two independent techniques. The signatures were seen in the 630.0 nm red-line emission, measured by a meridian scanning photometer at Ny-Ålesund on Svalbard, and also in the line-of-sight plasma velocities monitored by the Finland CUTLASS SuperDARN radar. A time difference of some 6 to 8 min occurred between the responses of the two techniques, with the flows being first to respond. In the present case study, the longer delay in the optics suggests that ion precipitation controls the auroral emission.<br><br><b>Key words: </b>Ionosphere (ionosphere-magnetosphere interactions) · Magnetospheric physics (magnetosphere-ionosphere interactions; polar cap phenomena)