Tropical Sea Surface Temperature Biases in CMIP 3 & 5 Models
Li, G. and Xie, S.-P. 2012. Origins of tropical-wide SST biases in CMIP multi-model ensembles. Geophysical Research Letters 39: 10.1029/2012GL053777.
The two researchers state that the SST biases they studied were of two types: "one with a broad meridional structure and of the same sign across all basins that is highly correlated with the tropical mean; and one with large inter-model variability in the cold tongues of the equatorial Pacific and Atlantic." They report that "the first type can be traced back to biases in atmospheric simulations of cloud cover, with cloudy models biasing low in tropical-wide SST," while they indicate that "the second type originates from the diversity among models in representing the thermocline depth," such that "models with a deep thermocline feature a warm cold tongue on the equator."
Given that Li and Xie note that the errors they studied "have persisted in several generations of models for more than a decade [italics and bold added]," one can only hope that someone will eventually get around to determining how to eliminate or at least significantly reduce them.
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