2002 Annual

Wednesday, 16 January 2002: 2:45 PM
Forced and Free Intra-Seasonal Variability Over the South Asian Monsoon Region Simulated by 10 AGCMs
Man Li C. Wu, NASA/GSFC, Greenbelt, MD; and S. D. Schubert, I. S. Kang, and D. Waliser
In this study, we examine the intra-seasonal variability of the South Asian monsoon region in 10 different atmospheric general circulation models (AGCMs). For each model, ensembles of 10 two-year (1997/98) simulations forced by the observed weekly sea surface temperature (SST) were produced. We partition the intra-seasonal variability into forced (the variability of the ensemble mean) and free (the intra-ensemble variability that is uncorrelated with the SST) fluctuations. The results are compared with NCEP/NCAR reanalysis data and observed precipitation.

The results show considerable variation among the models in the representation of intraseasonal variability ranging from much weaker too much stronger than the observed. We find that the models produce a significant forced response to the SST on intraseasonal time scales. The partition of the forced and free components also varies between the models.

Further results will be presented from the model simulations from a case study of a strong intra-seasonal oscillation (ISO) event, as well as, from a composite analysis of ISO variability and its links to SST in 17 years of observations.

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