Regional climate changes as simulated in time-slice experiments

Three 30 year long simulations have been performed with a T42 atmosphere model, in which the sea-surface temperature (SST) and sea-ice distribution has been taken from a transient climate change experiment with a T21 global coupled ocean-atmosphere model. In this so-called time-slice experiment, the SST values (and the greenhouse gas concentration) were taken at present time CO_2 level, at the time of CO_2 doubling and tripling. The annual cycle of temperature and precipitation has been studied over the IPCC regions and has been compared with observations. Additionally the combination of temperature and precipitation change has been analysed. Further parameters investigated include the difference between daily minimum and maximum temperature, the rainfall intensity and the length of droughts. While the regional simulation of the annual cycle of the near surface temperature is quite realistic with deviations rarely exceeding 3K, the precipitation is reproduced to a much smaller degree of accuracy. The temperature changes nonlinearly in response to the enhanced greenhouse forcing. This is connected with the cold start of the transient simulation. The changes in temperature at the time of CO_2 doubling amount to only 30%-40% of those at the 3"*CO_2 level and show hardly any seasonal variation, contrary to the 3"*CO_2 experiment. Due to the delay in warming, the 3"*CO_2 experiment can be compared to the CO_2 doubling studies performed with mixed-layer models. The precipitation change does not display a clear signal. However, an increase of the rain intensity and of longer dry periods is simulated in many regions of the globe. The changes in these parameters as well as the combination of temperature- and precipitation change and the changes in the daily temperature range give valuable hints, in which regions observational studies should be intensified and under which aspects the observational data should be evaluated. (orig.)Available from TIB Hannover: RR 1347(153) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman