Numerical study and remote sensing of the convection, restratification and mesoscale processes in the Labrador Sea and their implications on the subpolar North Atlantic warming.

摘要

This dissertation focuses on quantifying the physical processes in the Labrador Sea, such as wintertime deep convections, subsequent restratification, and the mesoscale eddy activities. The Labrador Sea is one of the areas where deep ocean is warming since 1998, so it has an implication on the recent global surface warming slow-down, which is also termed the global warming "hiatus". The restratification after the 2008 deep convection is studied using regional ocean model. The modeled mixed layer depth during wintertime resembles the ARGO observed mixed layer very well, and the lateral heat flux during the subsequent restratification is in line with observations. The Irminger Rings (IRs) are reproduced with fresher caps, and they are identified and tracked automatically. The model underestimates both the number of IRs into the convection area and the heat they carry. The underestimation is most likely caused by the errors in the direction of the West Greenland currents (WGC) in the model, which causes more IRs propagating westward. Yet, the model still observed three eddies propagating into the convection area during restratification phase in 2008, and they contribute from 1 to 4% of the total heat regain during central Labrador Sea restratification. Then a merged along track altimeter dataset is used to study the variability of eddy kinetic energy (EKE) in the Labrador Sea from 1993 to 2012. The WGC EKE propagates far into the central Labrador Sea during occasional years, and its annual cycle magnitude declines. The decreasing annual cycle is related to the central basin convections, while the WGC EKE strengths is controlled by a low frequency variation of the wind stress curl, which is related to the subpolar gyre (SPG) circulation. Finally, the subpolar North Atlantic (SPNA) warming during the recent global warming slow-down is studied by separately investigating the subsurface warming of the eastern and western SPNA. Temperature decompositions indicate buoyancy domination in the west, and wind stress forcing domination in the east prior hiatus period, and the contrary during the hiatus period. Atlantic Multidecadal Oscillation only shows shallow influence in the west SPNA.