Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> The 2D morphology of coherent HF radar and optical cusp aurora has been studied for conditions of predominantly southward IMF conditions, which favours low-latitude boundary layer reconnection. Despite the variability in shape of radar cusp Doppler spectra, the spectral width criterion of <u>></u> 220 m s<sup>â1</sup> proves to be a robust cusp discriminator. For extended periods of well-developed radar backscatter echoes, the equatorward boundary of the <u>></u> 220 m s<sup>â1</sup> spectral width enhancement lines up remarkably well with the equatorward boundary of the optical cusp aurora. The spectral width boundary is however poorly determined during development and fading of radar cusp backscatter. Closer inspection of radar Doppler profile characteristics suggests that a combination of spectral width and shape may advance boundary layer identification by HF radar. For the two December days studied the onset of radar cusp backscatter occurred within pre-existing 630.0 nm cusp auroral activity and appear to be initiated by sunrise, i.e. favourable radio wave propagation conditions had to develop. Better methods are put forward for analysing optical data, and for physical interpretation of HF radar data, and for combining these data, as applied to detection, tracking, and better understanding of dayside aurora. The broader motivation of this work is to develop wider use by the scientific community, of results of these techniques, to accelerate understanding of dynamic high-latitude boundary-processes. The contributions in this work are: (1) improved techniques of analysis of observational data, yielding meaningfully enhanced accuracy for deduced cusp locations; (2) a correspondingly more pronounced validation of correlation of boundary locations derived from the observational data set; and (3) a firmer physical rationale as to why the good correlation observed should theoretically be expected.<br><br><b>Key words:</b> Ionosphere (ionospheric irregularities; polar ionosphere)
Highlights
All-sky cameras and SuperDARN HF radars with large ®elds-of-view, constitute powerful tools to study temporal and spatial behaviour of large-scale auroral and polar cap dynamics, and both techniques have proven potential for identi®cation of magnetospheric boundary layers. Baker et al (1990, 1995) combined PACE HF radar observations with DMSP particle data, and identi®ed broad multi-component Doppler spectra to be a feature characteristic of coherent HF radar cusp backscatter
A detailed study on the correlation between radar and optical cusp auroral morphology has been accomplished in a 2D perspective
The study is based on two December days of red-dominated type 1 cusp auroral activity associated with strong radar backscatter seen by the CUTLASS Finland HF radar above Svalbard
Summary
All-sky cameras and SuperDARN HF radars with large ®elds-of-view, constitute powerful tools to study temporal and spatial behaviour of large-scale auroral and polar cap dynamics, and both techniques have proven potential for identi®cation of magnetospheric boundary layers. Baker et al (1990, 1995) combined PACE HF radar observations with DMSP particle data, and identi®ed broad multi-component Doppler spectra to be a feature characteristic of coherent HF radar cusp backscatter. Baker et al (1990, 1995) combined PACE HF radar observations with DMSP particle data, and identi®ed broad multi-component Doppler spectra to be a feature characteristic of coherent HF radar cusp backscatter. The occurrence distribution of spectral widths peaked at 220 m s) in the cusp and 60 m s) in the LLBL. Rodger et al (1995) employed wide spectral widths as a radar cusp identi®er. For the other case of unknown IMF conditions, the radar cusp boundary was either embedded within or located near the poleward edge of the auroral luminosity. Yeoman et al (1997) demonstrated a near collocation of strong HF backscatter power, poleward moving auroral forms, and energy dispersed ions for a DMSP snapshot through the winter cusp above Svalbard. For the other case of unknown IMF conditions, the radar cusp boundary was either embedded within or located near the poleward edge of the auroral luminosity. Yeoman et al (1997) demonstrated a near collocation of strong HF backscatter power, poleward moving auroral forms, and energy dispersed ions for a DMSP snapshot through the winter cusp above Svalbard. Milan et al (1999) demonstrated a good correlation between CUTLASS HF backscatter and dayside 630.0 nm aurora along the meridian swept by the scanning
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