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Estimating the Meridional Overturning Circulation (MOC) in the Atlantic

Estimating the Meridional Overturning Circulation (MOC) in the Atlantic. Greg Pinkel Mentor: Dimitris Menemenlis Comentor: Michael Schodlok. Outline. MOC: Meridional Overturning Circulation

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Estimating the Meridional Overturning Circulation (MOC) in the Atlantic

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  1. Estimating the Meridional Overturning Circulation (MOC) in the Atlantic Greg Pinkel Mentor: Dimitris Menemenlis Comentor: Michael Schodlok

  2. Outline • MOC: Meridional Overturning Circulation • Observations: RAPID Array • Model: ECCO2 Model • Results: Comparisons

  3. MOC:Meridional Overturning Circulation • North Atlantic MOC: • northward movement of near surface warm waters • southward movement of deeper, colder waters • Warm water emerges from Florida Strait as the Gulf Stream • Water sinks down at higher latitudes • begins to move southward at a depth of 2km

  4. Surface winds and density gradients create northward flow • Warmer, saltier, lighter at low latitudes Colder, fresher, denser water and higher latitudes - Max of 25% of the global heat flux (at 24.5 degrees N) - Northwest parts of Europe to enjoy a mild climate despite the high latitude - 2007: Intergovernmental Panel on Climate Change (IPCC) reported clear evidence that climate change is happening now

  5. Two things can slow this process • Ocean surface warming • Decreased Salinity • Freshwater runoff from melting glaciers and the Greenland Ice Sheet ------> • Controversially suggested that MOC has slowed by 30% since 1957 • 20% decrease in northward heat transport ACIA (Arctic Climate Impact Assessment)

  6. Determining The MOC • Surface: zonal (east-west) stress from winds cause Ekman transport • Perpendicular to the direction of the wind • Usually occurs within the top 50m • Major component of the short-term variability in the MOC • Wind measurements used to calculate the contribution of the Ekman transport to the MOC

  7. Measure the density of the water at different depths • With densities, currents can be estimated at different depths • Ekman transport and density transport gives a rough estimate of the meridional velocity • Density-induced transport (light blue arrows)

  8. RAPID/MOCHA Array • Natural Environment Research Council (NERC) in the UK • Rapid Climate Change/Meridional Overturning Circulation and Heat Flux Array (RAPID/MOCHA) • Deployed in March 2004 to monitor MOC at 26 degrees N • 19 Moorings measure variations in pressure, temperature, and salinity • Determine density at different depths

  9. ECCO2:Estimating the Circulation and Climate of the Ocean, Phase II • High resolution global-ocean and sea-ice data synthesis • ECCO2 is a project from collaboration between JPL, MIT, and SIO (Scripps Institution of Oceanography) • The estimates are derived from a least-squares fit (or regression) of the MIT-gcm model (MIT general circulation model) to observations • Cubed-Sphere model • ¼ degree grid • 50 depth levels • 1 cube per month

  10. Rapid/ECCO2 Cube78 Comparisons

  11. Summary/Outlook • Model and In-situ Temperature data agree well for East and West Boundaries • Model and In-situ Salinity data correspond well for Western Boundary • Meridional velocities correlate to depths of ~1000m • Zonal velocities don't agree but have similar trends

  12. Grid spacing, differences in depth spacing, interpolation, and large averages may account for some differences • ECCO2 could be improved by using the RAPID data to further constrain the model

  13. Acknowledgments • Mentor: Dimitris Menemenlis • Comentor: Michael Schodlok • Robin McCandliss (BODC) • The British Oceanographic Data Centre (BODC) • JPL • Caltech

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