Validation of a Thermodynamic Retrieval Technique by Application to a Simulated Squall Line with Trailing Stratiform Precipitation

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  • 1 Department of atmospheric Sciences, University of Washington, Seattle, Washington
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Abstract

A thermodynamic retrieval technique, which uses the equation of motion in conjunction with the thermodynamic equation, is validated in a two-dimensional numerical model simulation of a squall line with a trailing stratiform region. Model wind and reflectivity output are used as input to the retrieval. The availability of model thermodynamic output allows us to examine the performance of the retrieval. The computational technique involved is found to be valid. When the retrieval is applied to the time-averaged model wind fields, reasonably accurate results are obtained for the stratiform region, but errors arise for the convective region because of the neglect of eddy correlations of the temporally fluctuating wind components. Application of the retrieval to instantaneous model wind fields demonstrates that very high lime resolution is needed in the wind data (< about 2 min) to obtain reliable results where time changes are large and nonlinear.

Abstract

A thermodynamic retrieval technique, which uses the equation of motion in conjunction with the thermodynamic equation, is validated in a two-dimensional numerical model simulation of a squall line with a trailing stratiform region. Model wind and reflectivity output are used as input to the retrieval. The availability of model thermodynamic output allows us to examine the performance of the retrieval. The computational technique involved is found to be valid. When the retrieval is applied to the time-averaged model wind fields, reasonably accurate results are obtained for the stratiform region, but errors arise for the convective region because of the neglect of eddy correlations of the temporally fluctuating wind components. Application of the retrieval to instantaneous model wind fields demonstrates that very high lime resolution is needed in the wind data (< about 2 min) to obtain reliable results where time changes are large and nonlinear.

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