Regional stretched grid generation and its application to the NCAR RegCM

A method for the generation and application of a regional variable resolution stretched grid system is developed. In the modeling domain, a stretched grid buffer zone surrounds the central uniform grid region. To be comparable with current nesting methods, two integers are specifically considered in the design of the grid system. The first integer is the total stretching rate, which is the ratio of the maximum grid distance to the minimum grid distance, and the other integer is the ratio of the width of the buffer zone to the maximum grid distance. The grid distance is uniformly reduced from the outer lateral boundary of the model domain to the edge of the central uniform grid region. The final purpose of this grid is to facilitate the two-way interaction between global and regional models. However, the primary objective of this paper is to present the theoretical framework of the stretched grid system and its implementation within the NCAR regional climate model (RegCM). We provide an example of the performance of the stretched grid model configuration by applying it to an adiabatic version of the RegCM and completing a 3-day simulation over a domain encompassing the continental United States, The stretched grid version of the model produces results comparable to a control run with uniform resolution. The computational cost of running the stretched grid system is about 40% lower than that of the uniform grid system because of the smaller number of grid points in the lateral buffer area. These preliminary numerical tests with the RegCM illustrate the robustness of our new regional stretched grid method.