HF RADAR SIGNATURES OF THE CUSP AND LOW-LATITUDE BOUNDARY-LAYER

Continuous ground-based observations of ionospheric and magnetospheric regions are critical to the Geospace Environment Modeling (GEM) progr am. It is therefore important to establish clear intercalibrations bet ween different ground-based instruments and satellites in order to cle arly place the ground-based observations in context with the correspon ding in situ satellite measurements, HF-radars operating at high latit udes are capable of observing very large spatial regions of the ionosp here on a nearly continuous basis. In this paper we report on an inter calibration study made using the Polar Anglo-American Conjugate Radar Experiment radars located at Goose Bay, Labrador, and Halley Station, Antarctica, and the Defense Meteorological Satellite Program (DMSP) sa tellites. The DMSP satellite data are used to provide clear identifica tions of the ionospheric cusp and the low-latitude boundary layer (LLB L). The radar data for eight cusp events and eight LLBL events have be en examined in order to determine a radar signature of these ionospher ic regions. This intercalibration indicates that the cusp is always ch aracterized by wide, complex Doppler power spectra, whereas the LLBL i s usually found to have spectra dominated by a single component. The d istribution of spectral widths in the cusp is of a generally Gaussian form with a peak at about 220 m/s. The distribution of spectral widths in the LLBL is more like an exponential distribution, with the peak o f the distribution occurring at about 50 m/s. There are a few cases in the LLBL where the Doppler power spectra are strikingly similar to th ose observed in the cusp.