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Beatriz Pe ña -Molino, Terry M. Joyce and John M. Toole AMOC Meeting, Miami, June 7, 2010

Recent changes in the circulation and water mass structure of the Deep Western Boundary Current southeast of Cape Cod. Beatriz Pe ña -Molino, Terry M. Joyce and John M. Toole AMOC Meeting, Miami, June 7, 2010.

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Beatriz Pe ña -Molino, Terry M. Joyce and John M. Toole AMOC Meeting, Miami, June 7, 2010

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  1. Recent changes in the circulation and water mass structure of the Deep Western Boundary Current southeast of Cape Cod Beatriz Peña-Molino, Terry M. Joyce and John M. Toole AMOC Meeting, Miami, June 7, 2010

  2. In Stommel’s classical theory for the abyssal circulation dense water is exported southward along the Deep Western Boundary Current (DWBC). Dense water formation

  3. The distribution of Potential Vorticity suggests the LSW spreads southward mostly along the western boundary Planetary Potential Vorticity (Talley and McCartney, 1982)

  4. Without dense water formation there is no DWBC reduced forcing strong forcing (Gerdes and Koberle, 1995)

  5. W3 The Line W Program: monitoring the North Atlantic Deep Western Boundary Current http://www.whoi.edu/science/PO/linew/about/index.htm

  6. (Toole et al, accepted in Deep-Sea Research)

  7. Cross-stream (v>0) Downstream (u>0) In the rotated coordinate system, downstream velocities are normal to array (along-isobath direction)

  8. Integrated KE wavelet amplitude for the 15-60day at the bottom

  9. The combined effect of rings and meanders reduces the southwestward flow

  10. Leading joint-EOF (ring/meanders excluded)

  11. The leading mode EOF of (normalized) PPV at W3 Upward migration of the PPV MINIMUM (anomaly).

  12. Changes at Line W follow changes in the Labrador Sea (6-8 years later) (Yashayaev, 2007)

  13. Leading joint-EOF (ring/meanders excluded)

  14. dLSW ISOW DSOW

  15. DSOW dominated dLSW dominated • The flow reorganizes around the upper and bottom velocity cores. • The Gulf Stream axis move north.

  16. In a few words… • The PPV distribution along the North Atlantic DWBC suggests that the export of recently ventilated dLSW and DSOW have opposite phase. • Enhanced DWBC transports are associated with low (lower than the mean) PPV in the uLSW and DSOW depth ranges.

  17. Floats vs. Eulerian view: • The export of LSW is an advective-diffusive process. The diffusive part pulls the water away from the boundary. • The LSW core deepens as we move away from the Labrador Sea • The LSW exported southward changes density (depth) from year to year. (Bower et al, 2009)

  18. GS-PC2 Line W-PC1 The abrupt change of the Gulf Stream is captured by the second mode EOF of the Gulf Stream position

  19. Leading EOF of the surface geostrophic velocity correspond to domain-wide shifts in the latitude of the Gulf Stream

  20. Filtering rings and meanders

  21. A ring/meander index based on temperature and velocity anomaly extrema 0.1 = 1oC * 10cm/s change

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