In climate simulations, the impacts of the subgrid scales on the resolved scales are conventionally represented using deterministic closure schemes, which assume that the impacts are uniquely determined by the resolved scales. Stochastic parameterization relaxes this assumption, by sampling the subgrid variability in a computationally inexpensive manner. This study shows that the simulated climatological state of the ocean is improved in many respects by implementing a simple stochastic parameterization of ocean eddies into a coupled atmosphere-ocean general circulation model. Simulations from a highresolution, eddy-permitting ocean model are used to calculate the eddy statistics needed to inject realistic stochastic noise into a low-resolution, non-eddy-permitting version of the same model. A suite of four stochastic experiments is then run to test the sensitivity of the simulated climate to the noise definition by varying the noise amplitude and decorrelation time within reasonable limits. The addition of zero-mean noise to the ocean temperature tendency is found to have a nonzero effect on the mean climate. Specifically, in terms of the ocean temperature and salinity fields both at the surface and at depth, the noise reduces many of the biases in the low-resolution model and causes it to more closely resemble the highresolution model. The variability of the strength of the global ocean thermohaline circulation is also improved. It is concluded that stochastic ocean perturbations can yield reductions in climate model error that are comparable to those obtained by refining the resolution, but without the increased computational cost. Therefore, stochastic parameterizations of ocean eddies have the potential to significantly improve climate simulations.
Global air-sea heat and freshwater flux data, constrained by World Ocean Circulation Experiment (WOCE) hydrographic section transports, is used to construct a new global density flux climatology. Global transformations calculated using this density flux dataset show two regimes: surface waters with density less than ;1023.3 kg m 23 are transformed to lighter density classes with a maximum rate of 130 Sv (1 Sv [ 10 6 m 3 s 21 ) at s ; 1021.6 kg m 23 , and surface waters with density greater than 1023.3 kg m 23 are transformed to denser density classes with a maximum rate of 100 Sv at s 5 1025.4 kg m 23 . At higher density (s 5 1027 kg m 23 ) the net transformation rates vanish, reflecting heat loss in the Northern Hemisphere balanced by Southern Hemisphere freshening. This results in a kink in the global transformation rate, which is attributed to the presence of Drake Passage. Further analysis of the control run of the third Hadley Centre global climate model, HadCM3, suggests this feature to be robust and to reflect the ''channel'' geometry of the Southern Ocean and the ''basin'' geometry of the Northern Hemisphere.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.