Dynamical roles of mixed layer in regulating the meridional mass/heat fluxes

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C05036, doi:10.1029/2006JC004046.The mixed layer is an important component of the oceanic circulation system. Recent progress in energetics of the oceanic circulation suggests that the amount of external mechanical energy available for mixing is directly linked to the strength of the meridional overturning circulation. Using an analytical two-dimensional model and a three-dimensional numerical model, it is shown that the meridional distribution of mixed layer depth plays an important role in regulating the meridional overturning circulation and poleward heat flux. In fact, if the mixed layer at low and middle latitudes is deeper because of increase in mechanical energy input to the turbulence in the upper ocean, the meridional overturning circulation and poleward heat flux are enhanced in a steady circulation system, and at the same time, it may take less mechanical energy to support the subsurface diapycnal mixing.RXH was supported by the National Oceanic and Atmospheric Administration through CICOR Cooperative Agreement NA17RJ1223, CJH was supported by the National Key Basic Research Program of China through grant 2006CB403605, andWWwas supported by the National Natural Science Foundation of China through grant 40476010. This study is also supported through the Chinese 111 Project under Contract B07036