Vorticity Balance of the Antarctic Circumpolar Current in Drake Passage

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• Dr. Yvonne Firing, National Oceaongraphy Centre Southampton
• Wednesday 03 December 2014, 14:00-15:00
• British Antarctic Survey, Room 330B.

If you have a question about this talk, please contact Dr Alexander Brearley.

If you are external to BAS, please email the seminar organiser to arrange access

The nonlinear vorticity balance of the Antarctic Circumpolar Current in Drake Passage is examined using observations and the eddy-permitting Southern Ocean State Estimate (SOSE). Four years of near-bottom currents, bottom pressures, and bottom-surface round-trip sound travel time were collected by Current and Pressure-recording Inverted Echo Sounders (CPIES) deployed in a line across Drake Passage and in a two-dimensional array in the Polar Frontal Zone (PFZ) downstream of the Shackleton Fracture Zone (SFZ) as part of the cDrake experiment. Empirical relationships based on historical hydrography are used to convert travel time data to baroclinic streamfunction, which can be referenced by measured bottom pressures and currents.

Nonlinear relative vorticity advection dominates the observed time-varying and mean PFZ vorticity budgets, and approximately one third of the time-averaged relative vorticity advection in this region is attributable to transient eddies. In the model time-mean vorticity budget terms dependent on model grid resolution, including parameterized eddy diffusivity, are significant, and at spatial scales of 100s of km planetary vorticity advection becomes first order. Depth-integrated relative vorticity advection in the cDrake array in the PFZ is negatively correlated with the observed bottom pressure torque, which is driven by strong near-bottom currents. Much larger and highly time-variable bottom pressure torques inferred over the northern and southern continental slopes are produced by moderate currents flowing slightly across steep topographic slopes. SOSE also exhibits strong bottom pressure torques over these topographic features, positively correlated with depth-integrated relative vorticity advection and balanced by depth-integrated planetary vorticity advection and model grid resolution terms.

This talk is part of the British Antarctic Survey - Polar Oceans seminar series series.

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