User's guide to the Penn State/NCAR Mesoscale Modeling System

An updated version of the Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Modeling system (the MM4 system) is presented. The standard MM4 modeling package employs a Cressman multi-scan isobaric and surface analysis, with a hydrostatic predictive component using a leap frog integration of the flux form of the primitive equations on sigma coordinates. An experimental version has expanded the data ingest routines to allow hybrid isentropic-isobaric + surface analyses. Experimental versions of the model allow split-explicit time integration, several cumulus parameterizations coupled with an explicit moisture scheme, multiple levels of movable nests, relaxation of the hydrostatic assumptions, additional planetary boundary layer schemes, and microphysical packages. Due to the developmental nature of the modeling system, periodic upgrades in documentation are required to keep the manuals in accord with the programs. The document supersedes Penn State/NCAR Mesoscale Model User's Manual--Ver 8.