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The Beijing Normal University Earth System Model (BNU-ESM)

Paper Reviewed
Ji, D., Wang, L., Feng, J., Wu, Q., Cheng, H., Zhang, Q., Yang, J., Dong, W., Dai, Y.., Gong, D., Zhang, R.-H., Wang, X., Liu, J., Moore, J.C., Chen, D. and Zhou, M. 2014. Description and basic evaluation of Beijing Normal University Earth System Model (BNU-ESM) version 1. Geoscientific Model Development 7: 2039-2064.

Cutting right to the chase, Ji et al. (2014) write that the new model -- which is "used to study mechanisms of ocean-atmosphere interactions, natural climate variability and carbon-climate feedbacks at inter-annual to inter-decadal time scales" -- has a number of "important biases with regard to observations ... including [1] warm SST discrepancies in the major upwelling regions, [2] equatorward drift of mid-latitude westerly wind bands, and [3] tropical precipitation bias over the ocean that is related to [4] the double Inter-Tropical Convergence Zone (ITCZ)."

More specifically, the sixteen scientists say that with (5) "the annual temperature underestimated and [6] the annual precipitation overestimated over global land areas excluding Antarctica," the model (7) "has a tendency to have excessive ice extent during winter seasons," that (8) "the Madden-Julian Oscillation signal in large scale circulation is not as well simulated as it is in convection (precipitation)," that (9,10) "the northward and eastward propagating motions are both weaker than observed," that "BNU-ESM has significant biases that need to be improved, such as [11] tropical precipitation bias over oceans related to the double ITCZ," which they say "has long been a problem among many climate models," citing Lin (2007) and stating that (12) "further parameterization improvements are certainly required," while noting that (13) "land surface-air temperature simulated for the last few decades of the 20th century exhibit a mean bias greater than 2°C over significant regions compared with observations," that (14) "modeled temperatures increase significantly during the last few years of the historical simulation relative to observations," that (15) "this is very likely related to the lack of indirect aerosol effects in the atmospheric component (e.g., Gent et al., 2011)," that (16) there are "positive SST biases prevailing at major coastal up-welling regions," that (17) there are "cold biases in mean SST along the equator in the Pacific Ocean," that (18) "the negative SST bias in the southern ocean and excessive sea ice extent in the Antarctic suggest a need to correct the wind stress field to ensure sufficient southern ocean heat transport and proper ocean gyre boundaries," that (19,20) "BNU-ESM underestimates both the positive Bjerkness and the negative heat flux feedbacks by about 45 and 50% respectively,"

Yet in spite of all of these deficiencies, Ji et al. write that the BNU-ESM model "is being actively used by many researchers in prognostic simulations for both anthropogenic and geo-engineering forcing scenarios." All we can say is ... Go figure!

Gent, P.R., Danabasoglu, G., Donner, L.J., Holland, M.M., Hunke, E.C., Jayne, S.R., Lawrence, D.M., Neale, R.B., Rasch, P.J., Vertenstein, M., Worley, P.H., Yang, Z.-L. and Zhang, M. 2011. The Community Climate System Model Version 4. Journal of Climate 24: 4973-4991.

Lin, J.-L. 2007. The Double-ITCZ Problem in IPCC AR4 Coupled GCMs: Ocean-Atmosphere Feedback Analysis. Journal of Climate 20: 4497-4525.

Posted 7 April 2015