COMPARISON BETWEEN DOUBLED CO2 TIME-SLICE AND COUPLED EXPERIMENTS

The production of climate simulations using global coupled ocean-atmos phere models at high resolution is currently limited by computational expense and the long periods of integration that are necessary. A meth od of increasing the number of experiments that can be performed is th e so-called time-slice technique. Using the Arpege-climat atmospheric model three 5-yr integrations of this type were run: a control and two integrations forced with sea surface temperatures derived from couple d model simulations of the transient response to increasing carbon dio xide. These coupled models are the ECHAM1 model of the Max-Planck Inst itute (Hamburg, Germany) and the U.K. Meteorological Office model of t he Hadley Centre. The sensitivity of the response to the oceanic forci ng is studied. The results are compared with the 10-yr mean atmospheri c response of the coupled models at the time of the doubling of CO2. G lobal warmings ranging from 1.3 K to 1.9 K are obtained. Special atten tion is given to the modifications that occur in the hydrological cycl e and their sensitivity to the SSTs. Climatic signals related to ocean ic forcing, such as the modification of the ITCZ maximum of precipitat ion, are separated from signals due to the internal feedbacks and phys ical parameterizations of the models.