Q-GCM Results

1. Decadal Variability of the Wind-Driven Gyres

Eddy-resolving quasigeostrophic simulations of wind-driven circulation in a large ocean basin produce ocean gyres. These gyres vary on decadal scales when eddies are explicitly included. The figure below shows the first 3 EOFs (colour scale) for ocean circulation with a mean flow shown by the black lines. The spectra on the bottom right shows a clear decadal signal for EOF 1. This mode represents a shifting and strengthening of the jet, and has been called the Turbulent Oscillator.

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2. Intrinsic Variability of the Southern Ocean

The intrinsic variability of the Antarctic Circumpolar Current is investigated using Q-GCM three quasigeostrophic layers, with steady wind stress forcing, and no diabatic effects (see figure). The model shows how inclusion of turbulence can lead to enhanced low frequency (decadal) variability in this system.

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3. Southern Ocean response to variable wind forcing

Analysis of satellite altimeter data reveals anomalously high Eddy Kinetic Energy (EKE) in the Antarctic Circumpolar Current (ACC) during the period 2000-2002. Around 2-3 years earlier (1998), the circumpolar eastward wind stress (as quantified by the Southern Annular Mode; SAM) showed a significant positive peak, and we have shown previously that the ACC peaked around 1998 in response. An eddy-resolving ocean model is used to investigate the delay between wind forcing and the eddy response, and demonstrates that the lag is due to the time taken to influence the deep circulation of the ACC. Winds over the Southern Ocean have shown a strong climatic increase over the past few decades. If this increase in winds is also reflected as an increase in eddy activity (as our analysis suggests it might), then the increased poleward heat flux may have played a significant role in the observed warming of the Southern Ocean.

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