The Spectral Width on the Nightside and the CPS/BPS Boundary:

Wave Contribution

R. ANDRE (1), M.P. FREEMAN (2)

(1) LPCE/CNRS, France

(2) British Antarctic Survey, UK

We show that the latitudinal gradient in HF coherent radar spectral width across the CPS/BPS boundary can be explained by low-frequency wave activity. This conclusion is based on a study of POLAR electric field and Halley HF radar measurement during a favourable magnetic conjunction in the southern hemisphere. The electric field observed at POLAR altitude is projected to the F-region ionosphere using certain assumptions. The projected electric field is then used as an input to a radar simulator to predict the spectral width behaviour. This behaviour is shown to agree well with the actual radar observations. The assumptions underlying the proposed physical mechanism are discussed, as well as the ability of the radar spectral width to map magnetospheric boundaries.

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