simulated sea surface salinity variability in the tropical pacific xiaochun wang yi chao jpl/caltech...
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Simulated Sea Surface Salinity Variability in the Tropical Pacific
Xiaochun Wang Yi Chao
JPL/CaltechTerrain-Following Ocean Models User Workshop
Seattle , Aug. 4-6Acknowledgement: Discussions with J. McWilliams, P. Marchesiello, A. Shchepetkin , T. Song, Y. Golubev about the use of ROMS model. Computations were performed on computers of JPL and NASA Ames Research Center.
Scientific Issues
• What is the Sea Surface Salinity (SSS) structure associated with the ENSO phenomenon?
• What are the detailed features of SSS seasonal cycle?
• Are there any salinity signatures associated with the Tropical Instability Waves (TIWs)?
Motivation
• The effect of salinity on dynamics is gradually realized, e.g. barrier layer, influence on SSH, … However, salinity has very sparse observation.
• Aquarius mission, measure monthly SSS with accuracy of 0.2 psu with horizontal resolution of 100km
Pacific ROMS (Regional Ocean Modeling System)• Horizontal resolution, 50km, 45S-65N, 99E-70W• 20 S-coordinate levels • KPP scheme• Open boundary condition • 1990-2001 NCEP-NCAR Daily Forcing (Wind
stress, heatflux, precipitation and evaporation)• 5-day (pentad) average
Validation of Model Simulation
• TAO Data• 5-day • 99% Sig.
SSS Change on InterannualTimescale
• 1-yr lowpassed• Freshening
during ENSO
Spatial Pattern Associated with ENSO
• EOF Analysis• Consistent with Ob.• Variance (24.9%)
Seasonal Cycle of SSS
• EOF Analysis• Variance (66.0%)• ITCZ
Annual Mean
SSS Features Associated with TIWsSSS SST and Current
50day Highpassed
• Westward Propagation
• Seasonal Change
• Intreannual Change
• 50day Highpassed
SSS Features of TIWs
Spatial Features of TIWs
.Fresh
.Warm
.Upward
.Southward
.Eastward
TIWs SSS Variability is along EQ
Why TIWs SSS Variability is along EQ?
Meridional Advection !
SSS Variability on Different Timescales
Total
Interannual
Seasonal
Intraseasonal(<50day)
Summary• The western tropical Pacific is a region of large
variability on different timescales, interannual, seasonal, and intraseasonal.
• Though ENSO events show up as a freshening of the whole equatorial Pacific, the eastern equatorial Pacific is not a center of SSS variability on interannual timescale.
• On timescale shorter than 50days, besides the variability center in the western tropical Pacific, there is a variability center along the equator in the eastern equatorial Pacific associated with the TIWs.