USGS Open-File Report 94-588
Modeling of mid-Pliocene climate with the NCAR Genesis GCM
- Lisa C. Sloan
- Institute of Marine Sciences, University of California, Santa Cruz
A climate modeling study was carried out which used boundary conditions
created by the USGS PRISM group. The model used for this study is the
National Center for Atmospheric Research (NCAR) Genesis model. Genesis is
an atmospheric general circulation model (GCM) that is coupled to a land-
surface model and contains submodels for snow, sea-ice, and soil.
Boundary conditions incorporated into the model were (1) present day
continental configuration, with a 35 m sea-level increase over present;
(2) present day elevations, (3) Pliocene vegetation cover, (4) Pliocene
sea-surface temperatures (SSTs) for 12 months. Present day orbital
configuration and pCO2 were specified. The model was run at 4.5° latitude
by 7.5° longitude spatial resolution, with the full annual cycle, for 7
years. It is important to note that the SST's are prescribed in the
model and as such the climate that the model produced is (by definition)
in equilibrium with those SST's and is greatly influenced by the SST
values.
The greatest influence of the warm SST's upon the resulting climate was
the result of warmer and moister high-latitudes. Additionally, global
mean surface temperature was 3.6°C warmer than the present day control
case, and global mean precipitation increased by 8.4 cm/yr over the
control case. Zonal winds weakened in the Pliocene case but jet stream
and Hadley Cell locations were unchanged. High latitude clouds increased
in response to the imposed SST's and low latitude clouds decreased. An
interesting result that is somewhat supported by marine data was that the
mean annual intertropical convergence zone latitudinal location was
located northward of its present position in the Pliocene case.
Comparison of these model results with results from the GISS study and
various data from the paleoclimate record show the importance of
validating these model results, as well as the need for iterative studies
to understand the nature of the Pliocene warm interval. The results
suggest certain regions of the globe where we might try to test the model
predictions, as well as give a clear indication of where additional data
are needed to improve the boundary conditions used in this type of study.
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