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Observational evidence for propagation of decadal spiciness anomalies in the North Pacific

Observational evidence for propagation of decadal spiciness anomalies in the North Pacific. Yoshi N. Sasaki , N. Schneider , N. Maximenko, and K. Lebedev International Pacific Research Center, University of Hawaii. Subduction of water mass.

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Observational evidence for propagation of decadal spiciness anomalies in the North Pacific

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  1. Observational evidence for propagation of decadal spiciness anomalies in the North Pacific Yoshi N. Sasaki, N. Schneider, N. Maximenko, and K. Lebedev International Pacific Research Center, University of Hawaii

  2. Subduction of water mass • In the subtropical region, the mixed layer water in winter is subducted into the main thermocline • Subduction plays an important role in the freshwater cycle Qiu and Huang (1995)

  3. Decadal salinity variability • Spiciness (density compensated) anomaly • Sa (x, y, ,t) = S (x, y, ,t) – Sclm (x, y,) • warm/salty or cool/fresh • passive advection by current • Subsurface spiciness signals show substantial decadal fluctuations Lukas et al. [2008] from the Hawaii Ocean Time-series (HOT) [PSS-78]

  4. Subduction of spiciness anomaly  = 25.5 kg m-3 • Several modeling studies showed propagation of spiciness signals from the subtropics to the equator • It is difficult to identify basin-wide propagation of spiciness signals from observations due to the sparseness of salinity observations Yeager and Large [2004]

  5. Argo • Argo observations provide a lot of T-S profiles with nearly global coverage from the early 2000s  suitable for examining propagation of spiciness signals

  6. Purpose • To show observational evidence for basin-wide propagation of spiciness anomalies in the North Pacific • propagation speed? • decay timescale?

  7. Data • The Argo profile data are obtained from the US Argo Data Assembly Center • The each Argo profile is linearly interpolated to isopycnal surfaces, and the variables are averaged into 3  3 bins for each month • We also employ a spatially interpolated dataset using the Variational Interpolation algorithm Number of profiles on 25–25.5

  8. outcrop line Depth [m] Long-term mean on 25–25.5 Montgomery

  9. Salinity anomaly 2003 2004 2005 2006 [10 PSS-78] 2007 2008

  10. Salinity anomaly 2003 2004 2005 2006 [10 PSS-78] 2007 2008

  11. Salinity anomaly 2003 2004 2005 2006 [10 PSS-78] 2007 2008

  12. Salinity anomaly 2003 2004 2005 2006 [10 PSS-78] 2007 2008

  13. Hovmoller diagram [103 km] [10 PSS-78]

  14. Trajectory of particles • Fifteen parcels are released around the cool/fresh spiciness anomaly positions in 2008, and their backward trajectories are calculated using the mean velocity field

  15. Trajectory of particles

  16. Trajectory of particles

  17. Trajectory of particles

  18. Trajectory of particles

  19. Trajectory of particles

  20. Trajectory of particles 2004 2003 2005 2006 The propagation path and speed show good agreement with advection by the mean geostrophic current 2007 2008

  21. Hovmoller diagram [103 km] [10 PSS-78]

  22. Hovmoller diagram [103 km] [10 PSS-78]

  23. Spiciness on streamline coordinate • The amplitude of the salinity anomaly of the spiciness signal decreases by about 80% from -0.15 in 2004 to -0.03 in 2008 • The anomalies are diffused in the course of propagation

  24. Summary • Argo observations provide an evidence for propagation of the spiciness anomalies from the eastern subtropics to western tropics • The propagation path and speed of the spiciness signals are good agreement with advection by the mean geostrophic current Sasaki, Y. N., N. Schneider, N. Maximenko and K. Lebedev, 2010: Observational evidence for propagation of decadal spiciness anomalies in the North Pacific. GRL, 37, L07708, doi:10.1029/2010GL042716.

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