Welcome to the UW Isentropic Analysis and Modeling Group home page.
Our group specializes in the use of isentropic coordinates for the
analysis
and modeling of atmospheric circulation on regional to global scales.
Emphasis
is on investigation of the atmosphere's hydologic cycle, atmospheric
heating,
and regional entropy and energy balance.

Global Climate Simulation with the University of Wisconsin Global Hybrid Isentropic Coordinate Model (J. Climate, 2004, ~1 Mb)

An additional objective is to examine the accuracy and theoretical limits of global climate predictability which are imposed by the inherent limitations of simulating trace constituent transport and the hydrologic processes of condensation, precipitation and cloud life cycles. This objective involves a diagnostic comparison of results from the hybrid isentropic and sigma models described above as well as other "state of the art" general circulation models. Results from a series of numerical experiments indicate that sigma coordinate models fail to simulate the transport of dry and moist entropy with appropriate conservation under reversible moist adiabatic processes as accurately as the UW hybrid model.

Trace
constituent
experiments

Conservation of Equivalent Potential Temperature

Model
Simulations

In a follow on study entitled "Entropy, the Lorenz Energy Cycle and Climate" Johnson (1998) reconciled the theoretical concepts of available potential energy with the classical thermodynamic concepts of thermodynamic efficiency, the Carnot cycle, and verified that a climate model atmosphere must become cold, thus becoming more efficient in order to simulate a climate state without drift in the presence of spurious positive definite sources of entropy. Globally, an aphysical source of entropy from numerical diffusion/dispersion and other inadequacies of parameterization equivalent to 4% of the entropy source from kinetic energy dissipation corresponds with a biased temperature error of 10C, thus limiting the accuracy of climate model simulations. Increasing the accuracy of climate model simulations through reducing aphysical sources of entropy and cold temperature biases is exceedingly difficult to realize. Theory substantiates that a major source of the positive definite source of entropy comes from the numerical diffusion of water substances and the spurious mixing of moist static energy.

Johnson, D. R., 1999: Entropy, the Lorenz Energy Cycle and
Climate.
In “General Circulation Model Development: Past, Present and Future”

(D. A. Randall, ed.), Academic Press, pp. 659-720..

Johnson, D. R., 1997: On the "General Coldness of Climate Models"
and
the Second Law: Implications for Modeling the Earth System. __J.
Climate__,10,
2826-2846.

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