| Summary: | The Antarctic Circumpolar Current (ACC) is shaped by westerly winds, a meridional density gradient, topography and mesoscale activity. Ekman-driven isopycnal sloping is counterbalanced by eddy mixing. Many global climate models deal with a Southern Ocean (SO) warm bias and bottom water formation issues. Eddy processes are often parameterized in absence of sufficient resolution. Increasingly frequent, ocean grids at 1/4˚–1/12˚ are applied allowing for some representation of the mesoscale and eddy parameterization is thus turned off. We use FOCI, a global climate model based on ECHAM and NEMO atmosphere and ocean models with the capability of two-way nesting in the ocean to discuss related effects. Grid refinement south of 28˚S from 1/2˚ to 1/10˚ enables a realistic representation of mesoscale dynamics in the latitude band of the ACC, whereas standard GM-parameterization is applied to the non-eddying model. In both model configurations the deep, dense water layer is eroding over the first 50 years of the simulation after starting from observation-based initial fields. ACC strength declines from initially 165 Sv to 110–120 Sv. In the nested, eddying simulation the dense water layer recovers until model year 100 and ACC strength resumes to about 150 Sv. In contrast, ACC strength keeps declining in the eddy-parameterized run, which also starts to form a significant SO warm bias (see contribution presented by M. Ödalen in this session). We shed light on the mechanisms leading to the recovery of the ACC on multi-decadal timescale and the role of mesoscale dynamics therein.
|
|---|