Some aspects of Doppler radar measurements of the mean and fluctuating components of the wind field in the upper middle atmosphere

The basic assumptions made when a Doppler radar is used to measure the mean and fluctuating components of the wind field in the middle atmosphere with various beam configurations are examined. Particular reference is made to the measurement of the various components of the Reynolds stress tensor associated with short period internal gravity waves. It is shown that it is not generally possible to measure the upward flux of horizontal momentum with the conventional Doppler radar beam configuration in the upper middle atmosphere and that an optimum beam configuration is that in which beams are directed at + theta and - theta to the zenith in both the zonal and meridional planes. This allows five of the six components of the Reynolds stress tensor to be obtained directly from the mean square radial velocities. In addition, the mean wind components and, in principle, the horizontal divergence and stretching deformations may be obtained.