기후모델내의 기후내부변동 및 부정확성 이해

Abstract

Internal Climate Variability(ICV) which is climate phenomena caused by earth system contains various regions and time scales (e.g. seasonal to decadal). Although there are lots of arguments and studies, their definite process and mechanism are complicate and extensive. For this reason, ICV causes the uncertainty and the nonlinear precess in the view point of global scale climate. The ensemble differences in the Community Earth System Model Large Ensemble data, which is the climate simulation uses same model and same forcing and only describes different initial conditions each 30 ensembles, for simulating uncertainty. El Nino–Southern Oscillation(ENSO) is one of the well known interannual ICVs in the tropical Pacific, and it is associated with not only the Pacific ocean but also the Indian, Atlantic ocean and middle latitude climate. Because of the important of ENSO, changes in the central and eastern Pacific have been investigated by several studies. According to the CESM-LE analysis, although the ensemble mean of ENSO amplitude basically shows positive trend in both historical and warming scenario, the future trend of ENSO amplitude in warming scenario will be changed by ENSO amplitude in present climate. ICV is large in historical scenario, the amplitude trend shows small change or even small reduction. In contrast, ENSO amplitude change due to external forcing is large under the condition that ICV is small in the historical scenario. This suggests that ICV simulation of the climate model is important to investigate the variabilities of future climate in global warming scenario. On the other hand, the earth surface temperature differences between the ensembles in CESM-LE data analysis has association with the sea ice of Polar region. It can be considered that the ice fraction difference is a kind of model uncertainty. The uncertainty of the sea ice fraction in CESM-LE is mainly caused by the ICV of simulated climate system. This study suggests that the uncertainty caused by ICV also drives it in middle latitude climate again. If the sea ice is melted down under the global warming scenario, the uncertainty of global climate will be reduced.