Possible impact of subsurface biases in coupled models
The CMIP-5 models develop internal warm and saline biases between a depth range of ~100 and ~800m in long term simulations. These internal biases are found to have implications in large scale ocean dynamics via their linkage through baroclinicity of the ocean. The role of internal biases in the ensuing dynamics is quantified via relations between Brunt Vaisala frequency (N2) and baroclinic wave speeds using both Sturm-Loiuville theorem and WKBJ approximation. The CMIP-5 models are found to have a higher baroclinic speed compared to that of observations (figure). The study suggests that faster wave propagation in climate models due to subsurface biases has potential to change lifecycle and periodicity of simulated planetary scale events. A corollary being a cautionary outlook on climate projections made by coupled models as long as the biases are persistent.