SIMULATIONS OF TROPOSPHERIC JOINT DISTRIBUTIONS IN THE UW THETA-SIGMAMODEL AND CCM2

Results are presented for experiments which examine the ability of the University of Wisconsin (UW) hybrid isentropic-sigma (theta-sigma) an d sigma (sigma) coordinate models and the NCAR Community Climate Model 2 (CCM2) to transport and conserve the joint distributions of potenti al temperature (theta) or equivalent potential temperature (theta(e)) and a source-free inert trace constituent identical to the respective initial distribution (t theta or t theta(e)). Under the idealized isen tropic conditions of these experiments, the governing equations for th e atmospheric continuum require that the joint distributions (theta, t theta or theta(e), t theta(e)) be conserved throughout the integratio n. Deviation in the paired values is an objective measure of a model's skill to conserve the joint distributions. Results show that conserva tion remains higher in the UW theta-sigma model than in the other mode ls, even near the interface between isentropic and sigma model domains .