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: 1. Lagrangian properties of the EAC and Tasman Sea 2. Validation of a total surface current product 3. Validation of BLUElink> surface currents 4. Pilot project for a linkage grant proposal for a three year observing program 5. Assimilation of surface drifter observations

3. Experiment (2007) 1. NOAA providing 8 SVP drifting buoys. 2. Deployment from VOS (the PX30 line) 3. Two ships available, Capitaine Tasman and Forum Samoa II 4. Managed by OEB/Bureau out of Melbourne 5. Four deployments at fortnight intervals 6. Each deployment will be a drifter pair 5 minutes apart (1-2km)

4. PX30 line

5. Experiment design tools 1. Data products 1.BLUElink ReANalysis1, u, v, du/dz, dv/dz 1.ECMWF wind stress 2. Lagrangian trajectory model 1.De Vries and Doos (2001) 3. Synthetic drifter model 1.Niiler et al., (1995) 4. Advected tracer model 1.QUICK

6. Experiment design questions 1. Where along PX30 will deployments drift with the EAC? 2. Where along PX30 will deployments have the longest lifetime? 3. How long will a close pair remain close? 4. Is a fortnightly deployment a close pair in time? 5. What is the residence time in the Tasman Sea (communication costs)? 6. 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 1. Deployment at 155-155.5E based on this limited study offers a reasonable return against the objectives 2. VOS is convenient and low cost but limited temporally and spatially. Is this on balance a good strategy? 3. Errors: BRAN1 currents (error and spectrum), synthetic drag model not applied yet, no wave-induced currents 4. Idealised: no account of failures at deployment, tether breakage and instrument faults 5. Continuing to gather evidence ahead of first deployment ~15 Jan 2007 6. Pilot project ahead of a linkage grant for a multi-year experiment