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East Australia Current and Tasman Sea surface drifter experiment, 2007

East Australia Current and Tasman Sea surface drifter experiment, 2007 . Brassington*, Summons* # , Simmonds # , Dexter*, Ball*, Cowen*, Jarrot* *Bureau of Meteorology, # University of Melbourne. Objectives:. Lagrangian properties of the EAC and Tasman Sea

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East Australia Current and Tasman Sea surface drifter experiment, 2007

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  1. East Australia Current and Tasman Sea surface drifter experiment, 2007 Brassington*, Summons*#, Simmonds#, Dexter*, Ball*, Cowen*, Jarrot* *Bureau of Meteorology, #University of Melbourne

  2. Objectives: • Lagrangian properties of the EAC and Tasman Sea • Validation of a total surface current product • Validation of BLUElink> surface currents • Pilot project for a linkage grant proposal for a three year observing program • Assimilation of surface drifter observations

  3. Experiment (2007) • NOAA providing 8 SVP drifting buoys. • Deployment from VOS (the PX30 line) • Two ships available, Capitaine Tasman and Forum Samoa II • Managed by OEB/Bureau out of Melbourne • Four deployments at fortnight intervals • Each deployment will be a drifter pair 5 minutes apart (1-2km)

  4. PX30 line

  5. Experiment design tools • Data products • BLUElink ReANalysis1, u, v, du/dz, dv/dz • ECMWF wind stress • Lagrangian trajectory model • De Vries and Doos (2001) • Synthetic drifter model • Niiler et al., (1995) • Advected tracer model • QUICK

  6. Experiment design questions • Where along PX30 will deployments drift with the EAC? • Where along PX30 will deployments have the longest lifetime? • How long will a close pair remain close? • Is a fortnightly deployment a close pair in time? • What is the residence time in the Tasman Sea (communication costs)? • What is the distribution in the Tasman Sea (pressure sensors)?

  7. Initial Results: March 2002 (365 days)

  8. Initial Results: March 2003 (365 days)

  9. Initial Results: March 2004 (365 days)

  10. Initial Results: 365 day final positions

  11. Conclusion • Deployment at 155-155.5E based on this limited study offers a reasonable return against the objectives • VOS is convenient and low cost but limited temporally and spatially. Is this on balance a good strategy? • Errors: BRAN1 currents (error and spectrum), synthetic drag model not applied yet, no wave-induced currents • Idealised: no account of failures at deployment, tether breakage and instrument faults • Continuing to gather evidence ahead of first deployment ~15 Jan 2007 • Pilot project ahead of a linkage grant for a multi-year experiment

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