A two-step variational method for three-dimensional wind retrieval from single Doppler radar

A two-step variational method is developed to retrieve the three-dimension wind field from single-Doppler radar observation for operational applications. The first step produces a proxy background wind field, and the second step retrieves the detailed wind structures in data dense areas on a high-resolution grid. The background field is called proxy because it is obtained in the first step by a spectral analysis of the same radial-wind observations that will be used in the second step and thus the background is not independent of the observations. In the second step, the wind retrieval is constrained by the proxy background and the advection equation of liquid water content in the cost function. Tested with a dataset collected during Meiyu front heavy rainfall on 22 July 2002 in China, the two-step approach is shown to yield the best performance in comparison with a single-step approach that uses either only the proxy background field or the retrieval without the proxy background.