SABRE observations of E-region vertical velocity structures

Abstract

The variation of backscatter intensity with slant range for the Wick radar of the SABRE system consistently exhibits a minimum at approximately 800 km. Theoretical modelling of the antenna characteristics indicates that this is due to a null in the vertical polar diagram due to interference from ground reflections (Lloyd's mirror effect). By means of this “null” feature, the vertical velocity distribution within the scattering layer can be examined. A sharp discontinuity often exists in the variation of the Doppler velocity with range across the backscatter minimum. These observations can be accounted for in terms of an increase in the drift velocity of about 200 m s −1 with height across the 10 km range of the scattering layer. These results are consistent with the theoretical predictions of St.-Maurice and Schlegel based on the assumption of a two-stream instability.