18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Monday, 30 July 2001
A finite-volume “shaving” method for interfacing NASA/DAO’s Physical Space Statistical Analysis System to the finite-volume GCM with a Lagrangian control-volume vertical coordinate
Shian-Jiann Lin, NASA/GSFC, Greenbelt, MD; and A. M. da Silva
Toward the development of a finite-volume Data Assimilation System (fvDAS), a consistent finite-volume methodology is developed for interfacing the NASA/DAO’s Physical Space Statistical Analysis System (PSAS) to the joint NASA/NCAR finite-volume CCM3 (fvCCM3). To take advantage of the Lagrangian control-volume vertical coordinate of the fvCCM3, a novel “shaving” method is applied to the lowest few model layers to reflect the surface pressure changes as implied by the final analysis. Analysis increments (from PSAS) to the upper air variables are then consistently put onto the Lagrangian layers as adjustments to the volume-mean quantities during the analysis cycle. This approach is demonstrated to be superior to the conventional method of using independently computed “tendency terms” for surface pressure and upper air prognostic variables.

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