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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. - PowerPoint PPT Presentation
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Observational evidence for Observational evidence for
propagation of decadal propagation of decadal
spiciness anomalies in the spiciness anomalies in the
North PacificNorth Pacific
Yoshi N. Sasaki, N. Schneider, N. Maximenko, and K. Lebedev
International Pacific Research Center, University of Hawaii
Subduction of water massSubduction 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)
Decadal salinity variabilityDecadal 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]
Subduction of spiciness Subduction of spiciness anomalyanomaly
• 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]
= 25.5 kg m-3
ArgoArgo
• Argo observations provide a lot of T-S profiles with nearly global coverage from the early 2000s
suitable for examining propagation of spiciness signals
PurposePurpose
• To show observational evidence for basin-wide propagation of spiciness anomalies in the North Pacific
– propagation speed?
– decay timescale?
DataData• 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
Trajectory of particles 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
Trajectory of particlesTrajectory of particles
2003 2004
2005 2006
2007 2008
The propagation path and speed show good agreement with advection by the
mean geostrophic current
Spiciness on streamline Spiciness on streamline coordinatecoordinate
• 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
SummarySummary
• Argo observations provide an evidence for propagation of the spici
ness anomalies from the eastern subtropics to western tropics
• The propagation path and speed of the spiciness signals are good a
greement with advection by the mean geostrophic current
Sasaki, Y. N., N. Schneider, N. Maximenko and K. Lebedev, 2010: Observational e
vidence for propagation of decadal spiciness anomalies in the North Pacific. GR
L, 37, L07708, doi:10.1029/2010GL042716.