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Modelling the Asian Summer Monsoon: Another Revealing Analysis

Sperber, K.R., Annamalai, H., Kang, I.-S., Kitoh, A., Moise, A., Turner, A., Wang, B. and Zhou, T. 2013. The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century. Climate Dynamics 41: 2711-2744.
In the woreds of Sperber et al. (2013), "nearly half of the world's population is dependent on monsoon rainfall for food and energy security," and "the vagaries of its timing, duration and intensity are of major concern, especially over semi-arid regions where agriculture is the primary source of food." Therefore, the team of researchers evaluated how well the boreal summer Asian monsoon is represented by 25 Coupled Model Intercomparison Project-5 (CMIP5) and 22 CMIP3 climate models. And what did they find as a result of this exercise?

The eight researchers report (1) "the onset of the monsoon over India is typically too late in the models," (2) "the extension of the monsoon over eastern China, Korea, and Japan is under-estimated," while (3) "it is over-estimated over the subtropical western/central Pacific Ocean." They also note (4) "the anti-correlation between anomalies of all-India rainfall and Niño3.4 sea surface temperature is overly strong in CMIP3 and (5) typically too weak in CMIP5," adding, (6) "for both the ENSO-monsoon teleconnection and the East Asian zonal wind-rainfall teleconnection, the MMM [multi-model mean] inter-annual rainfall anomalies are weak compared to observations," and (7) "simulation of intra-seasonal variability remains problematic."

In commenting on their several findings, Sperber et al. say "the most important take away message is that in terms of the MMM, the CMIP5 models outperform the CMIP3 models for all of the diagnostics," which does indeed represent some degree of progress. But "even so," as they continue, they say "there are systematic errors that are consistent between the two vintages of models." And these common errors, which are enumerated above, constitute important inadequacies of the CMIP3 and CMIP5 climate models that remain to be adequately addressed. In light of such, the scientists who developed the 47 CMIP models with which they worked state, "given the multitude of physical processes and interactions that influence the monsoon, it is no wonder that simulation and prediction of the monsoon remain grand challenge problems," which one can only hope will someday be solved.

Archived 5 February 2014