Documentation of Scalable Incremental MM5v3 4D-VAR System

摘要

This report documents the changes made to the Penn State University/ National Center for Atmospheric Research third revision of the Fifth Generation Mesoscale Model (MM5v3) four dimensional variational (4D-Var) analysis system to allow the execution of incremental driver for the system. The incremental driver allows the user to select resolution or choice of physics that are used in the minimization of the cost function that are different than those used to describe the basic state. In practice, this would mean either a coarser resolution model grid or less computationally intensive physics routines would be chosen for the cost function minimization while a finer resolution model grid or more computationally intensive phyiscs for the basic state. The effect would be to significantly reduce the computations needed to complete the analysis. This report presents examples of the use of the incremental driver for the Hurricane Isaac case and compares the results to the original driver that uses consistent resolution and physics for the minimization and basic state computations. The results show that with the use of less computationally complex physics, the minimization does not reduce the accuracy of the analysis or time to convergence. Using coarser resolution in the minimization does not reduce the accuracy of the analysis but does appear to increase the time to convergence.