Joint RAP/MMM Seminar

Radar Data Assimilation with a Cloud-Resolving Model as a Weak Constraint

by

Alain Caya
McGill University, Montreal, Canada
NCAR, Boulder, Colorado

Wednesday, 5 September 2001
Foothills Lab, Building 2, Auditorium Room 1022,
3:30 p.m.

Abstract

Reflectivity, single-Doppler velocity, and near-surface refractivity index are assimilated into a non-hydrostatic fully compressible atmospheric model coupled with a warm microphysics scheme. The model is used as a weak constraint; i.e. the model error is explicit in the 4D-Var cost function. To provide a full domain analysis required for model initialization, a linear wind analysis in a moving frame is performed situ single-Doppler velocity measurements over a given assimilation window, which is then used as the background for the high-resolution analysis. The background-, observation- and model-error variances are adaptively tuned by matching them with the reduced cost function residuals. The method is able to fit the data over a short assimilation period while keeping model-error residuals small. Experiments with synthetic data from model outputs show that the method is also able to retrieve non-observed variables.

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