Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctic Circumpolar Current (ACC) and Future Changes Under Warming Scenarios – Representation in CMIP5 Climate Models

According to Meijers et al. in the 5^th Coupled Models Comparison Project (CMIP5) the representation of the Antarctic Circumpolar Current (ACC) is in general improved over that in the CMIP3. In the historical (1976-2000) scenario the range of transports that were modelled is reduced (90-264 Sv) compared to CMIP3 (33-337 Sv) with a mean of 155 ± 51 Sv). Significant differences in the density structure of the ACC are associated with the large intermodal range. There is accurate representation of the ACC position at most longitudes, with a small (1.27^o) standard deviation in mean latitude. On average the westerly wind jet that drives the ACC is biased too strongly and too far to the north. There is no correlation between the modelled ACC latitude and the westerly wind jet, which differs from the situation in the CMIP3. Meijers et al. say that under forcing scenarios in the future (2070-2099 mean) the modelled ACC transport changes by between -26 to +17 Sv and the ACC shifts toward the pole in models in which transport increases and where the transport decreases the ACC shifts towards the equator. Meijers et al. say there is no significant correlation between the changed position of the ACC and the position of the westerly wind jet, which shifts towards the pole and strengthens. The change in the area of the subpolar gyre varies between models, and the subtropical gyres strengthen, and expand southwards. A decrease in ACC transport and a shift towards the equator of the position of the ACC corresponds with an increase in the area of the subpolar gyre, and vice versa for a contraction of the area of the gyre. In the upper 1,000 m there is a general decrease of density, in particular equatorwards of the core of the ACC.

Sources & Further reading

1. Meijers, A. J. S., E. Shuckburgh, N. Bruneau, J. B. Sallee, T. J. Bracegirdle and Z. Wang (2012). "Representation of the Antarctic Circumpolar Current in the CMIP5 climate models and future changes under warming scenarios." Journal of Geophysical Research: Oceans 117(C12): C12008.