Dependence of the AGCM climatology on the method of prescribing surface boundary conditions and its climatological implication

By using IAP 9L, AGCM, two sets of long-term climatological integration hav e been performed with the two different interpolation procedures for genera ting the daily surface boundary conditions. One interpolation procedure is the so-called " traditional" scheme, for which the daily surface boundary c onditions are obtained by linearly interpolating between the observed month ly mean values, however the observed monthly means cannot be preserved afte r interpolation. The other one is the " new" scheme, for which the daily su rface boundary conditions are obtained by linearly interpolating between th e " artificial" monthly mean values which are based on, but are different f rom the observed ones, after interpolating with this new scheme, not only t he observed monthly mean values are preserved, the time series of the new g enerated daily values is also more consistent with the observation. Compari son of the model results shows that the differences of the globally or zona lly averaged fields between these two integrations are quite small, and thi s is due to the compensating effect between the different regions. However, the differences of the two patterns (the global or regional geographical d istributions), are quite significant, for example, the magnitude of the dif ference in the JJA mean rainfall between these two integrations can exceed 2 mm/ day over Asian monsoon regions, and the difference in DJF mean surfac e air temperature can also exceed 2 degrees C over this region. The fact that the model climatology depends quite strongly on the method of prescribing the daily surface boundary conditions suggests that in order t o validate the climate model or to predict the short-term climate anomalies , either the " new" interpolation scheme or the high frequency surface boun dary conditions (e.g., daily or weekly data instead of the monthly data) sh ould be introduced. Meanwhile, as for the coupled model, the daily coupling scheme between the different component climate models (e.g., atmospheric a nd oceanic general circulation models) is preferred in order to partly elim inate the " climate drift" problem which may appear during the course of di rect coupling.