Predictability of the Asian Summer Monsoon in a coupled general circulation model

The hypothesis that the dynamical predictability of the Asian Summer Monsoon is limited either by the chaotic intraseasonal variability or by the poor representation of the mean monsoon in climate models is tested with a long-run (~100 years) of a coupled general circulation model (CGCM). The CGCM we analyse, ECHAM4/HOPE (ECHO-G), has a realistic simulation of mean monsoon precipitation and the various components of the boreal summer intraseasonal variability associated with the 30-50 day mode are reasonably well represented. Following Sperber et al. (2000), we study the relationship between intraseasonal and interannual variability of the Asian Summer Monsoon through analysis of the dominant modes of variability in precipitation and low-level winds. We test if the statistical properties of intraseasonal variability are modulated on interannual time-scales in a systematic and therefore predictable manner. We also examine if the predictability is enhanced due to the proper representation of the mean monsoon precipitation and a better ENSO-monsoon correlation in the coupled model. The CGCM results are validated against the 40- year ECMWF Reanalysis products.

Sperber, K. R., J. M. Slingo, and H. Annamalai, 2000: Predictability and the relationship between subseasonal and interannual variability during the Asian summer monsoon. Quart. J. Roy. Meteorol. Soc., 126, 2545-2574.