Investigating the Initial Errors that Cause Predictability Barriers for Indian Ocean Dipole Events Using CMIP5 Model Outputs

摘要

By analyzing the outputs of the pre-industrial control runs of four models within phase 5 of the Coupled Model Intercomparison Project,the effects of initial sea temperature errors on the predictability of Indian Ocean Dipole events were identified.The initial errors cause a significant winter predictability barrier (WPB) or summer predictability barrier (SPB).The WPB is closely related with the initial errors in the tropical Indian Ocean,where two types of WPB-related initial errors display opposite patterns and a west-east dipole.In contrast,the occurrence of the SPB is mainly caused by initial errors in the tropical Pacific Ocean,where two types of SPB-related initial errors exhibit opposite patterns,with one pole in the subsurface western Pacific Ocean and the other in the upper eastern Pacific Ocean.Both of the WPB-related initial errors grow the fastest in winter,because the coupled system is at its weakest,and finally cause a significant WPB.The SPB-related initial errors develop into a La Ni(n)a-like mode in the Pacific Ocean.The negative SST errors in the Pacific Ocean induce westerly wind anomalies in the Indian Ocean by modulating the Walker circulation in the tropical oceans.The westerly wind anomalies first cool the sea surface water in the eastern Indian Ocean.When the climatological wind direction reverses in summer,the wind anomalies in turn warm the sea surface water,finally causing a significant SPB.Therefore,in addition to the spatial patterns of the initial errors,the climatological conditions also play an important role in causing a significant predictability barrier.