A Systematic Study of GCM Sensitivity to Latitudinal Changes in Solar Radiation

Benjamin Felzer Department of Geological Sciences, Brown University, Providence, Rhode Island

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Robert J. Oglesby Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana

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Hong Shao Department of Geological Sciences, Brown University, Providence, Rhode Island

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Thompson Webb III Department of Geological Sciences, Brown University, Providence, Rhode Island

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Dena E. Hyman Department of Geological Sciences, Brown University, Providence, Rhode Island

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Warren L. Prell Department of Geological Sciences, Brown University, Providence, Rhode Island

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John E. Kutzbach Center for Climatic Research, University of Wisconsin-Madison, Madison, Wisconsin

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Abstract

Paleoclimatic data and climate model simulations have demonstrated that orbitally forced changes in solar radiation can have a pronounced effect on global climate. Key questions remain, however, about the spatial patterns in the climatic sensitivity to these changes in solar radiation. The authors use GCM simulations of Kutzbach and Guetter and Prell and Kutzbach that were made with the NCAR Community Climate Model (CCM), version CCM0. The results of these simulations are employed to compute linear equilibrium sensitivity coefficients and jackknife uncertainties relating the response of key climate variables to orbitally forced changes in solar radiation. The spatial distributions of the sensitivities and the corresponding uncertainties reveal the synoptic patterns of climate response for these climate variables and identify areas of high and low sensitivity.

The sensitivity of CCM0 to solar radiation changes such as those experienced during the Quaternary is large and predominately linear for many climatic variables. The climatic response is always greatest in the summer hemisphere, because the orbitally induced radiation changes are more pronounced during the summer. The larger landmasses also show a greater climatic response than the smaller ones, due to both the larger heat capacity of the land relative to the oceans, and to the effects of the fixed SSTs. The land surface temperature always increases with increased radiative heating. The surface pressure generally decreases with increasing solar insulation over the landmasses, which were heated, with corresponding increases over the oceans. The net change in moisture (precipitation - evaporation) to increasing solar radiation is greatest over the summer hemisphere Tropics. All three of these variables combine to produce stronger summer monsoons with increasing solar radiation.

Abstract

Paleoclimatic data and climate model simulations have demonstrated that orbitally forced changes in solar radiation can have a pronounced effect on global climate. Key questions remain, however, about the spatial patterns in the climatic sensitivity to these changes in solar radiation. The authors use GCM simulations of Kutzbach and Guetter and Prell and Kutzbach that were made with the NCAR Community Climate Model (CCM), version CCM0. The results of these simulations are employed to compute linear equilibrium sensitivity coefficients and jackknife uncertainties relating the response of key climate variables to orbitally forced changes in solar radiation. The spatial distributions of the sensitivities and the corresponding uncertainties reveal the synoptic patterns of climate response for these climate variables and identify areas of high and low sensitivity.

The sensitivity of CCM0 to solar radiation changes such as those experienced during the Quaternary is large and predominately linear for many climatic variables. The climatic response is always greatest in the summer hemisphere, because the orbitally induced radiation changes are more pronounced during the summer. The larger landmasses also show a greater climatic response than the smaller ones, due to both the larger heat capacity of the land relative to the oceans, and to the effects of the fixed SSTs. The land surface temperature always increases with increased radiative heating. The surface pressure generally decreases with increasing solar insulation over the landmasses, which were heated, with corresponding increases over the oceans. The net change in moisture (precipitation - evaporation) to increasing solar radiation is greatest over the summer hemisphere Tropics. All three of these variables combine to produce stronger summer monsoons with increasing solar radiation.

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