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Simulating Equatorial Pacific SST, Wind Stress and Surface Fluxes

Paper Reviewed
Solomon, A. 2014. Using initialized hindcasts to assess simulations of 1970-2009 equatorial Pacific SST, zonal wind stress, and surface flux trends. Journal of Climate 27: 7385-7393.

In the report of her recent study of the ability of CMIP5 models to simulate Pacific Ocean sea surface temperature, zonal wind stress and surface flux trends, Solomon (2014) used decadal hindcasts archived in the CMIP5 database (Taylor et al. 2012) that were initialized yearly from 1960 to 2009 and run ten times with perturbed initial conditions for each start date, in order to be able to assess simulations of 1970-2009 equatorial Pacific SST, zonal wind stress and surface flux trends that take account of changes in external forcings such as greenhouse gases, solar activity, stratospheric aerosols associated with volcanic eruptions and anthropogenic aerosols. And what did this arduous effort reveal?

Solomon reports that the decadal hindcasts (1) "do not produce an unambiguous weakening or strengthening of the Walker circulation over the 1970-2009 period," that they (2,3) forecast "ocean mixed layer and net surface heat flux trends with an opposite sign to air-sea datasets," that they (4) "do not produce an unambiguous zonal SST gradient response to an increase in external forcing," that (5) "year-1 forecasts produce a positive shortwave feedback on decadal time scales," whereas (6) "year 6-10 forecasts produce a negative or statistically insignificant shortwave flux feedback on decadal time scales," and that (7) "in the cold-tongue region, all three initialized ensembles forecast a positive net radiative flux trend even though the shortwave flux trend is negative."

Once again, as in the case of the study of Tiwari et al. (2014), we thus have another set of "seven sins" running rampant throughout the climate modeling enterprise, which all continue to cry out for significant redemptive actions.

Taylor, K.E., Stouffer, R.J. and Meehl, G.A. 2012. An overview of CMIP5 and the experiment design. Bulletin of the American Meteorological Society 93: 485-498.

Tiwari, P.R., Kar, S.C., Mohanty, U.C., Kumari, S., Sinha, P., Nair, A. and Dey, S. 2014. Skill of precipitation prediction with GCMs over north India during winter season. International Journal of Climatology 34: 3440-3455.

Posted 10 February 2015