A Variational Analysis Method for Retrieval of Three-Dimensional Wind Field from Single-Doppler Radar Data

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  • 1 Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, Québec, Canada
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Abstract

A variational method for retrieval of the three-dimensional wind field from single-Doppler radar observations is developed and tested. The method uses the conservation equation for reflectivity and the continuity equation as a constraining model. Weak and strong constraint formalisms in data analysis am reviewed and compared using a one-dimensional advection equation for reflectivity considered as a passive tracer. The authors show that a model equation should be used as a weak constraint when the model does not predict exactly the evolution of the observations (such as the conservation equation for reflectivity). Consequently, the variational method presented here combines both formalisms: the conservation equation for reflectivity is used as a weak constraint, 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 compared with dual-Doppler wind analysis. Results of experiments show that the cost function has multiple minima, and consequently retrievals are sensitive to the initial guess. To find the true minimum the retrieval is performed from large to small scale. The results are very encouraging.

Abstract

A variational method for retrieval of the three-dimensional wind field from single-Doppler radar observations is developed and tested. The method uses the conservation equation for reflectivity and the continuity equation as a constraining model. Weak and strong constraint formalisms in data analysis am reviewed and compared using a one-dimensional advection equation for reflectivity considered as a passive tracer. The authors show that a model equation should be used as a weak constraint when the model does not predict exactly the evolution of the observations (such as the conservation equation for reflectivity). Consequently, the variational method presented here combines both formalisms: the conservation equation for reflectivity is used as a weak constraint, 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 compared with dual-Doppler wind analysis. Results of experiments show that the cost function has multiple minima, and consequently retrievals are sensitive to the initial guess. To find the true minimum the retrieval is performed from large to small scale. The results are very encouraging.

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