Description of the MITgcm Atmospheric Physics (Fizhi): Algorithm and Simulated Climate

This report is a description of the MITgcm in its ‘high end’ atmospheric configuration, focusing on the details of the physics package. Included are implementation and algorithmic details, and the results of a 10-year simulation forced with climatological sea surface temperatures. The atmospheric physics package is derived from the NASA Goddard GEOS-3 package, and is implemented in the MITgcm using the newly developed GridAlt interface.

The seasonal mean climate is evaluated against multi-year climatologies computed from available satellite-based and reanalysis fields. The seasonal mean climate of the MITgcm simulation generally agrees well with the observational estimates. The largest differences between MITgcm and observations are in the cloud cover and cloud effects, and indicate an MITgcm climate with excessive cloud cover in the extratropics and tropical clouds which are too low in altitude. Other biases include strong mid-latitude zonal jets and a cold tropical tropopause, which exist in many other GCM simulations. Recommendations are included to address the major climate bias, which involve improvements in the parameterization of clouds and convection.