Comparison of gravity wave momentum fluxes estimated by different methods using mesosphere-stratosphere-troposphere radar

Mesosphere-stratosphere-troposphere radar measurements have been used to estimate momentum flux of gravity waves in a 2–6 hour period in the lower atmosphere over Gadanki (13.5°N, 79.2°E), a tropical station. Different methods have been adopted to compute momentum flux profiles, and a comparative study shows that momentum flux estimates produced by a hybrid method (Worthington and Thomas, 1996) which measures the vertical wind with a vertical beam and the horizontal wind with a pair of radial beams and those obtained by direct computation of spatial covariances ($\overline{u\prime w\prime }\ {\rm and},\overline{v\prime w\prime }$) show satisfactory agreement. The symmetric beam radar method of Vincent and Reid (1983) has the unique advantage since it does not require vertical beam measurement, and it is found to produce momentum flux estimates compatible with other methods except in high wind shear zones. It is observed that the result of momentum flux obtained by the symmetric beam method shows excellent matching with other methods when the average of vertical winds derived from E-W and N-S beams is used in the formula for both zonal and meridional fluxes.