Southern Ocean Eddy Heat Flux and Eddy-Mean Flow Interactions in Drake Passage
The Antarctic Circumpolar Current (ACC) is a complex current system composed of multiple jets that is both unique to the world's oceans and relatively under observed compared with other current systems. Observations taken by current- and pressure-recording inverted echo sounders (CPIES) over fo...
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DigitalCommons@URI
2017
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| Online Access: | https://digitalcommons.uri.edu/oa_diss/624 https://doi.org/10.23860/diss-foppert-annie-2017 https://digitalcommons.uri.edu/context/oa_diss/article/1642/viewcontent/Foppert_uri_0186A_11757.pdf |
| Summary: | The Antarctic Circumpolar Current (ACC) is a complex current system composed of multiple jets that is both unique to the world's oceans and relatively under observed compared with other current systems. Observations taken by current- and pressure-recording inverted echo sounders (CPIES) over four years, from November 2007 to November 2011, quantify the mean structure of one of the main jets of the ACC - the Polar Front - in a composite-mean sense. While the array of CPIES deployed in Drake Passage included a 3 x 7 local dynamics array, analysis of the Polar Front makes use of the line of CPIES that spanned the width of Drake Passage (C-Line). The Polar Front tends to prefer one of two locations, separated along the C-Line by 1_ of latitude, with the core of the jet centered on corresponding geopotential height contours (with a 17 cm difference between the northern and southern jets). Potential vorticity fields suggest that the Polar Front is susceptible to baroclinic instability, regardless of whether it is found upstream (farther south along the C-Line) or downstream (farther north along the C-Line) of the Shackleton Fracture Zone (SFZ), yet the core of the jet remains a barrier to smaller-scale mixing, as inferred from estimated mixing lengths. Within the local dynamics array of CPIES, the observed offset between eddy heat flux (EHF) and eddy kinetic energy (EKE) and the alignment of EHF with sea surface height (SSH) standard deviation motivates a proxy for depth-integrated EHF that can be estimated from available satellite SSH data. An eddy-resolving numerical model develops the statistics of a logarithmic fit between SSH standard deviation and cross-frontal EHF that is applied to the ACC in a circumglobal sense. We find 1.06 PW enters the ACC from the north and 0.02 PW exits towards Antarctica. The magnitude of the estimated EHF, along with contemporaneous estimates of the mean heat flux, suggests that the air-sea heat flux south of the PF is an overestimate. Long-term trends in EHF are calculated from ... |
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