Report 56: Dynamical Seasonal Predictability of the Asian
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.
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.