A SYSTEMATIC STUDY OF GCM SENSITIVITY TO LATITUDINAL CHANGES IN SOLAR-RADIATION

Paleoclimatic data and climate model simulations have demonstrated tha t orbitally forced changes in solar radiation can have a pronounced ef fect on global climate. Key questions remain, however, about the spati al patterns in the climatic sensitivity to these changes in solar radi ation. The authors use GCM simulations of Kutzbach and Guetter and Pre ll and Kutzbach that were made with the NCAR Community Climate Model ( CCM), version CCM0. The results of these simulations are employed to c ompute linear equilibrium sensitivity coefficients and jackknife uncer tainties relating the response of key climate variables to orbitally f orced changes in solar radiation. The spatial distributions of the sen sitivities and the corresponding uncertainties reveal the synoptic pat terns of climate response for these climate variables and identify are as of high and low sensitivity. The sensitivity of CCM0 to solar radia tion changes such as those experienced during the Quaternary is large and predominately linear for many climatic variables. The climatic res ponse is always greatest in the summer hemisphere, because the orbital ly induced radiation changes are more pronounced during the summer. Th e larger landmasses also show a greater climatic response than the sma ller ones, due to both the larger heat capacity of the land relative t o the oceans, and to the effects of the fixed SSTs. The land surface t emperature always increases with increased radiative heating. The surf ace pressure generally decreases with increasing solar insolation over the landmasses, which were heated, with corresponding increases over the oceans. The net change in moisture (precipitation - evaporation) t o increasing solar radiation is greatest over the summer hemisphere Tr opics. All three of these variables combine to produce stronger summer monsoons with increasing solar radiation.