Kunkel, K.E., X-Z. Liang, and participating CMIP2+ modeling groups, 2004:
GCM simulations of the climate in the central United States,
Illinois State Water Survey Report, Champaign, Illinois, USA, 44 pp.


A diagnostic analysis of relationships between surface climate characteristics and various flow and scalar fields was used to evaluate 9 global coupled ocean-atmosphere general circulation models (CGCMs) participating in the Coupled Model Intercomparison Project (CMIP).  In order to facilitate identification of physical mechanisms causing biases, data from 21 models participating in the Atmospheric Model Intercomparison Project (AMIP) were also used for certain key analyses. 

Most models reproduce basic features of the circulation, temperature, and precipitation patterns in the central U.S., including the pronounced seasonal cycles that are characteristic of this region and the general flow patterns, although no model exhibits small differences from observations for all characteristics in all seasons.  Similar to the findings of other investigators performing global analyses, model ensemble means generally produce better agreement with observations than any single model.  No single model is unambiguously superior to all other models.

A fall precipitation deficiency, found in all AMIP and CMIP models except HadCM3, appears to be related in part to slight biases in the flow on the western flank of the Atlantic subtropical ridge.  In the model mean, the ridge at 850 hPa is displaced slightly to the north and to the west, resulting in weaker southern flow into the central U.S.

The CMIP doubled-CO2 transient runs show warming for all models and seasons, ranging from 2-7 degrees C in summer to 6-9 degrees C in winter with respect to their control simulations.  These changes are larger than the natural variations that are observed in the 20th Century and the model variations in the control simulations.  Precipitation changes with respect to the control simulations are mostly upward, but the magnitudes of changes are mostly less than the natural variations that are observed in the 20th Century and less than the model variations in the control simulations.

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