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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