Understanding the Causes of the Excessive Cold Tongue in the National Center for Atmospheric Research Community Climate System Model (NCAR CCSM)

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The equatorial Pacific cold-tongue plays a fundamental role in the heat and carbon balance of the coupled ocean-atmosphere system. The processes and feedbacks that control the cold tongue are not well understood and coupled climate models, e.g., the Community Climate System Model (CCSM), do not properly simulate it. The PI has hypothesized that the tendency for the coupled GCMs to develop an excessive cold-tongue in the equatorial Pacific is at least in part due to a weak regulating effect from the model atmosphere on SST changes in that region. More specifically, the net atmospheric feedback (radiative plus dynamical feedbacks) in the coupled models is less negative than in the observations. The corresponding weaker constraining effect on the SST change by the surface heating then results in an "over-expression" of the effect of ocean dynamics, leading to the development of an excessive cold-tongue in the coupled model. The PI will conduct a pilot project to test his hypothesis by checking whether other (than CCSM) major coupled models that suffer from an excessive cold-tongue also lack a sufficiently strong regulating effect from their corresponding model atmosphere over the equatorial Pacific. This first step will be achieved by the PI extending his feedback analysis to all the atmospheric models participating with the Atmospheric Model Intercomparison Project (AMIP) and by examining their corresponding coupled runs submitted to the Coupled Model Intercomparison Project (CMIP). The broader impacts expected from this project include, contributions to the learning, education, and training of interested citizens as well as future scientists and improvements in climate prediction models, which would be of value to society.