A VARIATIONAL ANALYSIS METHOD FOR RETRIEVAL OF 3-DIMENSIONAL WIND-FIELD FROM SINGLE DOPPLER RADAR DATA

A variational method for retrieval of the three-dimensional wind field from single-Doppler radar observations is developed and tested. The m ethod uses the conservation equation for reflectivity and the continui ty equation as a constraining model. Weak and strong constraint formal isms in data analysis are reviewed and compared using a one-dimensiona l advection equation for reflectivity considered as a passive tracer. The authors show that a model equation should be used as a weak constr aint when the model does not predict exactly the evolution of the obse rvations (such as the conservation equation for reflectivity). Consequ ently, the variational method presented here combines both formalisms: the conservation equation for reflectivity is used as a weak constrai nt, while the continuity equation is used as a strong constraint. The method is applied to retrieve detailed three-dimensional wind field of a microburst observed by two C-band Doppler radars during the Phoenix II Convective Boundary Layer Experiment. Retrieved wind fields are co mpared with dual-Doppler wind analysis. Results of experiments show th at the cost function has multiple minima, and consequently retrievals are sensitive to the initial guess. To find the true minimum the retri eval is performed from large to small scale. The results are very enco uraging.