Checkerboard patterns in E3SMv2 and E3SM-MMFv2

An unphysical checkerboard pattern is identified in E3SMv2 and E3SM-MMF that is detectable across a wide range of timescales, from instantaneous snapshots to multi-year averages. A detection method is developed to quantify characteristics of the checkerboard signal by cataloguing all possible configurations of the eight adjacent neighbors for each cell on the model's cubed sphere grid using daily mean data. The checkerboard pattern is only found in cloud-related quantities, such as precipitation and liquid water path. Instances of pure and partial checkerboard are found to occur more often in E3SMv2 and E3SM-MMF when compared to satellite data regridded to the model grid. Continuous periods of partial checkerboard state are found to be more persistent in both models compared to satellite data, with E3SM-MMF exhibiting more persistence than E3SMv2. The checkerboard signal in E3SMv2 is found to be a direct consequence of the recently added deep convective trigger condition based on dynamically generated CAPE (DCAPE). In E3SM-MMF the checkerboard signal is found to be associated with the trapping of cloud-scale fluctuations within the embedded cloud-resolving model. Solutions to remedy this issue are discussed.

Automated summary

An unphysical checkerboard pattern has been identified in E3SMv2 and E3SM-MMF models, primarily in cloud-related quantities. This pattern is more prevalent and persistent in the models compared to satellite data. In E3SMv2, the checkerboard signal is a direct result of the recently added deep convective trigger condition based on dynamically generated convective available potential energy. In E3SM-MMF, the checkerboard signal is associated with the trapping of cloud-scale fluctuations within the embedded cloud-resolving model.