June 2017: New publication, ‘Model under-representation of decadal Pacific trade wind trends and its link to tropical Atlantic bias’

A new study led by SMURPHS researcher Jules Kajtar, published in Climate Dynamics, concludes that the variability of decadal trends in Pacific wind stress is under-represented in CMIP5 coupled models.

Variability of Pacific zonal wind stress in CMIP5 models and observations, over the period 1900-2014. (a) Equatorial mean of the standard deviation of annual zonal wind stress across the Pacific Ocean. (b) Equatorial mean of the standard deviation of running 10-year zonal wind stress trends. (c) The range of 10-year trends in central Pacific zonal wind stress, averaged over the region indicated by the vertical lines in (a) and (b). MMM denotes the CMIP5 multi-model mean. MME denotes the range of the multi-model ensemble. NOAA-20CR and ERA-20C denote the two observation/reanalysis products. The figure illustrates that models tend to under-represent Pacific wind stress variability.

The strengthening of the Pacific trade winds in recent decades has been unmatched in the observational record stretching back to the early twentieth century. This wind strengthening has been connected with numerous climate-related phenomena, including the recent global warming hiatus. Here we show that models in the Coupled Model Intercomparison Project, phase 5 (CMIP5), underestimate the decadal trends in the Pacific trade winds. Analysis of observational data suggests that tropical Atlantic SST contributes considerably to the Pacific trade wind trends, whereas the Atlantic feedback in coupled models is muted. Biases in Atlantic sea surface temperature appear to be the source of the weaker Atlantic-Pacific decadal connection in models.

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