Report 56: Dynamical Seasonal Predictability of the Asian Summer Monsoon

Sperber, K. R., C. Brankovic, M. Déqué, C. S. Frederiksen, R. Graham, A. Kitoh, C. Kobayashi, T. Palmer, K. Puri, W. Tennant, and E. Volodin
July 2000, 62 pp. 

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Ensembles of hindcasts from seven models are analyzed to evaluate dynamical seasonal predictability of the Asian summer monsoon (ASM) during 1987, 1988, and 1993. These integrations were performed using observed sea surface temperatures and from observed initial conditions. The experiments were performed at the behest of the CLIVAR Working Group on Seasonal to Interannual Prediction as part of the Seasonal prediction Model Intercomparison Project (SMIP). Integrations from the European Union PROVOST (PRediction of climate Variations on Seasonal to interannual Timescales) experiment are also evaluated. The National Centers for Environmental Prediction/National Center for Atmospheric Research and European Centre for Medium-Range Weather Forecasts reanalyses and observed pentad rainfall form the baseline against which predictability is judged. The time-mean state and the interannual and subseasonal variability are evaluated. It is demonstrated that to varying degree the models can simulate the hirarchy of modes that are important for controlling the subseasonal variability of the 850hPa flow during the ASM. In many cases the models represent the strong link between the 850hPa flow and rainfall observed on subseasonal timescales. However, deficiencies in the simulation of the subseasonal modes contribute directly to poor seasonal predictability and are related to systematic error of the mean state. With regard to dynamical seasonal predictability, in most instances the models fail to properly project the subseasonal modes onto the interannual variability with result that hindcasts of ASM are poor. In cases where the observed modes are known to be related to the boundary forcing, the failure of the models to properly project the modes onto the interannual variability indicates that the models are not setting up observed teleconnection patterns. (pdf file)

UCRL-MI-123395