Response of the Southern Ocean overturning circulation to extreme
Southern Annular Mode conditions
Abstract
The positive trend of the Southern Annular Mode (SAM) will impact the
Southern Ocean’s role in Earth’s climate, however the details of the
Southern Ocean’s response remain uncertain. We introduce a methodology
to examine the influence of SAM on the Southern Ocean, and apply this
method to a global ocean–sea-ice model run at three resolutions
(1$^{\circ}$, 1/4$^{\circ}$
and 1/10$^{\circ}$). Our methodology drives
perturbation simulations with realistic atmospheric forcing of extreme
SAM conditions. The thermal response agrees with previous studies;
positive SAM perturbations warm the upper ocean north of the windspeed
maximum and cool it to the south, with the opposite response for
negative SAM. The overturning circulation exhibits a rapid response that
increases/decreases for positive/negative SAM perturbations and is
insensitive to model resolution. The longer term adjustment of the
overturning circulation, however, depends on the representation of
eddies, and is faster at higher resolutions.