Exploring a lower‐resolution physics grid in CAM‐SE‐CSLAM

This paper describes the implementation of a coarser‐resolution physics grid into the Community Atmosphere Model (CAM), containing urn:x-wiley:jame:media:jame20916:jame20916-math-0001 fewer grid columns than the dynamics grid. The dry dynamics is represented by the spectral element dynamical core, and tracer transport is computed using the Conservative Semi‐Lagrangian Finite Volume Method (CAM‐SE‐CSLAM). Algorithms are presented that map fields between the dynamics and physics grids while maintaining numerical properties ideal for atmospheric simulations such as mass conservation and mixing ratio shape and linear‐correlation preservation. The results of experiments using the lower‐resolution physics grid are compared to the conventional method in which the physics and dynamical grids coincide. The lower‐resolution physics grid provides a volume mean state to the physics computed from an equal sampling of the different types of nodal solutions arising in the spectral‐element method and effectively mitigates grid imprinting in regions with steep topography. The impact of the coarser‐resolution physics grid on the resolved scales of motion is analyzed in an aquaplanet configuration, across a range of dynamical core grid resolutions. The results suggest that the effective resolution of the model is not degraded through the use of a coarser‐resolution physics grid. Since the physics makes up about half the computational cost of the conventional CAM‐SE‐CSLAM configuration, the coarser physics grid may allow for significant cost savings with little to no downside.