Impacts

ESMF interpolation technique improves representation of ocean transport in the Community Climate System Model (CCSM)

The above figure shows the latitudinal structure of the interpolation noise in the derivative of the zonal wind stress (dTAUx/dy). This derivative is closely related to the curl of the wind stress, which drives the upper ocean circulation and is therefore important to represent accurately in climate simulations. The wind stress was mapped from the T62 (2-degree) Community Atmospheric Model (CAM) grid to the gx1v5 (384x320 irregularly spaced) Parallel Ocean Program (POP) grid, using three different interpolation methods. The black line is the current CCSM bilinear method; the red line is an early version of the ESMF higher-order patch interpolation method (v3.1.1); and the green line is a recently improved version of the ESMF higher-order method (v4.0.0). The noise is calculated as the deviation of a point's value from the average of its own value plus the four surrounding points' values. The latest version of the ESMF higher-order method reduces the noise globally by 33% compared to the current CCSM approach. This is a significant improvement in the representation of transport processes in the model.

Image courtesy of Markus Jochem, CGD/NCAR.