Parallelization of a Subgrid Orographic Precipitation Scheme in an MM based Regional Climate Model

Regional Climate Models RCMs are practical downscaling tools to yield regional climate information for assessing the impacts of climate variability and change The Paci c Northwest National Labora tory PNNL RCM based on the Penn State NCAR Mesoscale Model MM features a novel subgrid treatment of orographic precipitation for coupling climate hydrologic and ecologic processes at the watershed scale The parameterization aggregates subgrid variations of surface to pography into a nite number of surface elevation bands An air ow model and a thermodynamic model are used to parameterize the oro graphic uplift descent as air parcels cross over mountain barriers or val leys The parameterization has signi cant performance advantages over nesting to achieve comparable resolution of climate information how ever previous implementations of the subgrid scheme required signi cant modi cation to the host MM model prohibiting its incorporation within the NCAR supported community version of MM With this ef fort software engineering challenges have been addressed to incorporate parallelize and load balance the PNNL subgrid scheme with minimum changes to MM The result is an e cient maintainable tool for regional climate simulation and a step forward in the development of an MM based community regional climate model