Abstract
The representation of the Antarctic Circumpolar Current (ACC) in the fifth Coupled Models Intercomparison Project (CMIP5) is generally improved over CMIP3. The range of modeled transports in the historical (1976–2006) scenario is reduced (90–264 Sv) compared with CMIP3 (33–337 Sv) with a mean of 155 ± 51 Sv. The large intermodel range is associated with significant differences in the ACC density structure. The ACC position is accurately represented at most longitudes, with a small (1.27°) standard deviation in mean latitude. The westerly wind jet driving the ACC is biased too strong and too far north on average. Unlike CMIP3 there is no correlation between modeled ACC latitude and the position of the westerly wind jet. Under future climate forcing scenarios (2070–2099 mean) the modeled ACC transport changes by between −26 to +17 Sv and the ACC shifts polewards (equatorwards) in models where the transport increases (decreases). There is no significant correlation between the ACC position change and that of the westerly wind jet, which shifts polewards and strengthens. The subtropical gyres strengthen and expand southwards, while the change in subpolar gyre area varies between models. An increase in subpolar gyre area corresponds with a decreases in ACC transport and an equatorward shift in the ACC position, and vice versa for a contraction of the gyre area. There is a general decrease in density in the upper 1000 m, particularly equatorwards of the ACC core.
Highlights
[2] The Antarctic Circumpolar Current (ACC) and the southern limb of the MOC are intimately linked, and are driven by a combination of wind and buoyancy forcing [Marshall and Radko, 2003; Marshall and Speer, 2012]
[4] Modeling studies [e.g., Hallberg and Gnanadesikan, 2006; Farneti et al, 2010; Morrison et al, 2011; Meredith et al, 2012] have shown that the ACC is sensitive to the strength of buoyancy forcing and the strength and latitude of the zonal wind stress, but its characteristics are strongly influenced by the underlying bathymetry, internal mixing, vertical stratification, the subtropical and subpolar gyre positions and mesoscale eddies
[16] The westerly wind jet has been shown in Coupled Model Intercomparison Project phase 3 (CMIP3) to be strongly correlated with both the latitude of the ACC core and its strength [Russell et al, 2006; Sen Gupta et al, 2009]
Summary
[2] The Antarctic Circumpolar Current (ACC) and the southern limb of the MOC are intimately linked, and are driven by a combination of wind and buoyancy forcing [Marshall and Radko, 2003; Marshall and Speer, 2012]. North of the ACC Roemmich et al [2007] showed that the Pacific subtropical gyre has increased in strength since 1993, probably due to increased wind stress curl over this basin, while to the south possible changes to the subpolar gyre waters have been observed [Rintoul, 2007]. [4] Modeling studies [e.g., Hallberg and Gnanadesikan, 2006; Farneti et al, 2010; Morrison et al, 2011; Meredith et al, 2012] have shown that the ACC is sensitive to the strength of buoyancy forcing and the strength and latitude of the zonal wind stress, but its characteristics are strongly influenced by the underlying bathymetry, internal mixing, vertical stratification, the subtropical and subpolar gyre positions and mesoscale eddies. The change in the ACC transport, was extremely varied between models, with some increasing by up to 27 Sv, while others decreased by over 29 Sv. Wang et al [2011] attributed this variability to differing responses of the subtropical and the subpolar gyres between models, which acted to change the area of eastward ACC flow
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
