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CMIP5 Simulations of the North American Monsoon System

Paper Reviewed
Geil, K.L., Serra, Y.L. and Zeng, X. 2013. Assessment of CMIP5 model simulations of the North American monsoon system. Journal of Climate 26: 8787-8801.

The North American Monsoon System (NAMS) covers an area that includes much of the Mexican Plateau and the Desert Southwest of the United States; and its behavior has been modeled by both CMIP3 and 5 participants. In a recent study of the NAMS, Geil et al. (2013) examined precipitation, geopotential height and wind fields from 21 models that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5) in order to determine "how well this generation of general circulation models represents the NAMS."

Among their top ten findings, the three researchers report that (1) "there has been no improvement in the magnitude (rms error and bias) of the mean annual cycle of monthly precipitation over the core NAMS region since CMIP3," that (2) "a few models do not have a recognizable monsoon signal at all," that (3) "the multimodel mean annual cycle is biased wet," that it (4) "exhibits the common problem of late monsoon termination," that (5) "the multimodel mean onset and retreat dates are 23 days early and 9 days late, respectively," that (6) "yearly model retreat variability is much greater than what is seen in the observations," that (7) "even the best models poorly represent monsoon retreat," that (8) there is a "prevailing wet bias in model precipitation," that (9) "neither the composite of best models nor the composite of worst models realistically captures the retreat of the NAMS because of an extended connection to tropical moisture that causes excessive fall and winter precipitation," and that (10) "even the highest resolution model examined is still too coarse to capture small-scale topographically-influenced processes."

It would appear that essentially all of the CMIP5 models studied by Geil et al. continue to exhibit several of the Top Ten Shortcomings they discovered in their analyses of the models' abilities to simulate the defining characteristics of the North American Monsoon System.

Posted 17 October 2014