Monitoring the transport through Drake Passage. Mike Meredith Chris Hughes Phil Woodworth. South Atlantic Workshop, May 2007. Overview:-. Why? Drake Passage transport variability on a range of timescales:- 1) subseasonal 2) seasonal 3) interannual 4) secular (briefly)
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Monitoring the transport through Drake Passage
South Atlantic Workshop, May 2007
=> Therefore important to know what variability the oceanic circumpolar transport exhibits on a range of timescales, and how it interacts with lower latitudes.
Large quantities of mass, heat, salt etc moved around Southern Ocean, with links to lower latitudes.
Divergence between chokepoints requires knowledge of the chokepoint transports.
How do these change?
How do we monitor the transport variability?
(Hughes, Meredith & Heywood, JPO, 1999)
BPRs deployed from ship; depths typically 1000-3000m
Deployments typically of 1-2 years duration – main use is for subseasonal and seasonal variability.
(Hughes et al., GRL, 2003;
see also Aoki, GRL, 2002)
850-hPa height regressed on SAM index
So what is the forcing for the northern Drake BPRs …?
Equatorial/tropical Pacific winds, rather than circumpolar SAM.
Related to waves propagating along shelf and slope of South America.
Evidence of baroclinicity in wave structure
=> choice of deployment depth is critical (unlike south Drake)
(Hughes and Meredith, 2006)
North Drake BPR data also shows strong correlation with transport of Malvinas Current at ~40˚S.
Lag is approximately 2 weeks – a different mode?
(Vivier, Provost and Meredith, JPO, 2001).
(Meredith et al., GRL, 2004)
(Meredith et al., 2004)
(Meredith and Hughes, GRL, 2005)
Why does the ACC vary so little on interannual timescales?
(Meredith & Hogg, GRL, 2006)
(Fyfe & Saenko, 2005)
UK CTD + BPR (WOCE SR1b)