HR: 16:30h
AN: SM52F-03    [PDF]
TI: The Effects of High Frequency ULF Wave Activity on the Spectral Characteristics of Coherent HF Radar Returns
AU: * Wright, D M
EM: darren.wright@ion.le.ac.uk
AF: Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH United Kingdom
AU: Yeoman, T K
EM: tim.yeoman@ion.le.ac.uk
AF: Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH United Kingdom
AU: Woodfield, E E
AF: NCAR, P.O. Box 3000, Boulder, CO 80307-3000 United States
AB: It is now a common practice to employ ground-based radars in order to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromso, Norway ($66\deg$ N geomagnetic). On this occasion, a series of transient regions of radar backscatter exhibiting large spectral widths are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band. These observations would then, seem to support the possibility that high frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the cusp and polar cap ionospheres.
DE: 2736 Magnetosphere/ionosphere interactions
DE: 2772 Plasma waves and instabilities
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting