Development of an Atmospheric Mesoscale Model on a CRAY — Experiences with Vectorization and Input/Output

Some concepts and experiences are discussed from the present development of a three-dimensional model for atmospheric flows in the mesoscale (typical lengthscale L ≤ 250 km) on the CRAY-1/S computer of the DFVLR. After an introduction to the range of physical problems and adequate numerical schemes to tackle them two more technical aspects are dealt with. First, an integration algorithm, which minimizes input/output operations, is introduced together with figures that show the capabilities of different software and hardware components for input/output. Then, the emphasis goes to the pressure solution as an important subtask, the vectorization capabilities of existing software and gains due to its restructuration. Calculations involving the entire code (dealing with the Taylor-Green vortex in a 64×36×64 grid) and a discussion of the technical aspects’ impact on three dimensional Navier-Stokes codes conclude the paper.