Wind and Thermodynamic Retrieval from Single-Doppler Measurements of a Gust Front Observed during Phoenix II

Abstract

The adjoint method to retrieve the three-dimensional wind and thermodynamic fields is applied to single-Doppler observations of a gust front measured during the Phoenix II experiment. This method uses a fluid dynamics model and its adjoint, and combines the retrieval with data assimilation into the prediction model. The wind and thermodynamic variables are determined by minimizing the difference between the model solution and the observations. Experiments are conducted first with radial velocity alone and then with both radial velocity and reflectivity to examine the quality of the retrieval with respect to radar location, boundary conditions, length of assimilation, data filtering, smoothing enforced by penalty functions, and model accuracy. Verification of these experiments is provided by a dual-Doppler analysis. Test results show that the adjoint method is able to retrieve the wind and thermodynamic fields of the gust front. The retrieved horizontal wind agrees very well with the dual-Doppler analysis. This study also demonstrates that the adjoint method has the ability to resolve finescale features along the loading edge of the gust front.