Report 23:   Intercomparison of the Spectral Characteristics of 200 hPa Kinetic Energy in AMIP GCM Simulations

Boyle, James S.
August 1995, 39 pp. 

---

The 200 hPa kinetic energy budget terms are represented by means of their spherical harmonic components for a number of AMIP simulations. The data used are the monthly mean wind fields for 1979 to 1988 decadal simulations. The budget terms are decomposed into the divergent and rotational components. The comparison is limited to the lower wavenumbers so as to be within the nominal limits imposed by the models with the coarsest spatial resolution.

The results show considerable differences among the models. The comparison is best for the rotational wind and degrades for the divergent components, especially the conversion term. There is some ambiguity among the models as to the sign of some terms at certain wavenumbers. The models tend to overestimate the Walker-type (east-west) divergent circulations compared to the Hadley-type (north-south), as indicated by recent NMC and ECMWF operational analyses.

The intermodel differences are substantial when viewed in light of the differences in the oservational analyses and ensemble differences for the ECMWF model. However, the median values of all the models taken together are usually in fair agreement with observational values.

There is no obvious, systematic pattern of errors which can be consistently attributed to specifics of the individual model horizontal and vertical resolution, numerics or physical parameterizations (pdf file).

UCRL-MI-123395