Observing and Modelling the East Australian Current and its Eddies using IMOS data and Bluelink models

David Griffin, Madeleine Cahill and Peter Oke

CSIRO Marine and Atmospheric Research

What is the East Aust Current doing now? Bluelink and IMOS can help

• OceanMAPS is the Bluelink global ocean model, run by BoM. Has 4 parallel members, updated in turn, each producing a 7-day forecast.

• OceanMAPS analysis cycle assimilates altimetry, SST and Argo into MOM using multivariate ensemble optimal interpolation. Initialises the forecast.

• ROAM is the Bluelink Relocatable Ocean-Atmosphere Model. Nested within OceanMAPS, it provides higher resolution, adds tides and assimilates additional data. Runs at CSIRO and RAN.

• IMOS has a new sub-project Ocean Current with a similar broad objective, but different focus and approach.

• SynTS is the Ocean Current 3-D ocean analysis. Uses gridded sea level anomaly from altimetry, and SST anomaly (from AVHRR) to adjust climatology.

National view of Sea Surface Temperature:Warm in the west and south, cool in the east

Gridded sea level & Sea Surface Temperature

Start tour of ocean at surface on 20 Jan 2012:OM, OC, ROAM 20 Jan SST, SSV.

Back 1day:OM, OC, ROAM 19 Jan SST, SSV.

Back 1day:OM, OC, ROAM 18 Jan SST, SSV.

Back 1day:OM, OC, ROAM 17 Jan SST, SSV.

Back 1day:OM, OC, ROAM 16 Jan SST, SSV.

Back 1day:OM, OC, ROAM 15 Jan SST, SSV.

Go down to 250m:OM, OC, ROAM 15 Jan T_250, V_250

Altimeter view:OM, OC 15 Jan SSH

Forward 1day:OM, OC 16 Jan SSH

Forward 1day: OM, OC 17 Jan SSH

Forward 1day: OM, OC 18 Jan SSH

Next OceanMAPS member:OM(b), OC 18 Jan SSH

Next OceanMAPS member: OM(c), OC 18 Jan SSH

Back to 250m:OM(c), OC 18 Jan T_250, V_250

Back up to surface:OM(c), OC 18 Jan SST, SSV

Forward 1day (NB result of assimilation):OM(c), OC 19 Jan SST, SSV

Forward 1day:OM(c), OC 20 Jan SST, SSV

Back to start:OM(a), OC 20 Jan SST, SSV

Main points

• Ocean nowcasting is here. The GODAE dream has eventuated.• Error estimation is difficult. Observations are sparse. • Ensemble approach, and size of assimilation shocks, expose

uncertainties.• Three analyses yield same picture: a weak warm core eddy is

mostly detached from the EAC at depth but additional warm surface water is occasionally flooding over the eddy and being advected around its perimeter.

• A low-energy version of the situation last year:

• Compare to last year (when the sea level anomaly broke the record)

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Conclusion

• Can we ‘monitor’, let alone forecast, the EAC as precisely as we want to?

• That depends on how demanding you are.• Present-day products are definitely worth using. Ask any

Sydney-Hobart competitor.• But still plenty of scope for improvement. Observations are too

few and/or the assimilation is not sufficiently optimal, to constrain the model trajectory to the truth.

• Also need to improve the accessibility of information, while containing user expectations.

Thankyou

• … to the many people and agencies (ESA, EuMetSat, CNES, NASA, NOAA, Argo, Drifter program) for the data shown here.

• … to all members of the (BoM and CSIRO) Bluelink and (many) IMOS teams and communities

• … RAN and DIISRTE for continued support

• Bluelink forecast: www.bom.gov.au/oceanography/forecasts.index.shtml

• OceanCurrent: imos.aodn.org.au/oceancurrent

• Plug: www.altimetry2012.org Abstracts due 15 Feb.

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