Adjoint-Method Retrievals of Low-Altitude Wind Fields from Single-Doppler Wind Data

Abstract

The simple adjoint method of Qiu and Xu is extended and used to retrieve the low-altitude horizontal wind field from single-Doppler radial wind data measured during the Phoenix II field experiment. Since the extended method uses only the radial momentum equation on a low-altitude horizontal plane with a weak nondivergence constraint for the horizontal winds, the pressure gradient and vertical advection are treated as an unknown residual forcing. The test results show that (i) the method can retrieve the low-altitude time-mean (or running mean) horizontal winds (averaged over a period of several sequential radar scans) from single-Doppler radial wind data; (ii) retrieving the time-mean part of the unknown residual forcing term improves the wind retrieval; (iii) the detailed data treatments and proper settings of the weights considered in Xu et at. remain useful for improving the retrieval.