Doppler spectrum statistics obtained from three different-frequency radar auroral experiments

Three coherent radar systems, Halley (PACE), SABRE and COSCAT are employed to investigate the properties of auroral plasma irregularities. Each radar is sensitive to a different irregularity wavelength. Halley typically observes irregularities of 10.7 m wavelength, SABRE observes 1 m wavelength and COSCAT 16 cm wavelength. A comparison is made between the irregularity characteristics at the different wavelengths. In order to account for the variations between the different data sets it is important to consider each radar's observing geometry in addition to the differences in irregularity wavelength. A special investigation is conducted on the width of the backscatter spectrum, a measure of the coherence of the backscattered signal. The variation of the frequency spectral width with irregularity wave number is found to follow a k 1 dependence. Relationships between the width and irregularity phase speed and the width and backscatter power are identified. Type-I coherent scatter, typical of the Wick and COSCAT observations, exhibit minima in spectral width at phase speeds of the order of the ion-acoustic speed and the mean scattered power decreases as the spectral width increases. In contrast, type-II spectra as observed by the Halley radar have minimum widths at phase speeds near 0 m s −1 and there is an increase in power as the width increases