Suzanne Dickinson and Kathryn A. Kelly Applied Physics Lab University of Washington, Seattle
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Transcript of Suzanne Dickinson and Kathryn A. Kelly Applied Physics Lab University of Washington, Seattle
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Using High Quality SST Productsto determine Physical ProcessesContributing to SST Anomalies
A First Step
Suzanne Dickinson and Kathryn A. KellyApplied Physics Lab
University of Washington, SeattleNovember 8, 2010
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MethodologyGoal: to determine which physical processes are
important in controlling SST in different areas of the North Atlantic.
First step: How much influence does surface forcing have on interannual SST anomalies?
Run 1-d vertical ocean model• Surface forcing of heat, freshwater and stress• Include horizontal geostrophic and Ekman advection
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Model Domain
• North Atlantic ocean• 1 degree grid • Daily fields• 1500 m deep
March mean SST from Observations
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Price, Weller, Pinkel1-d Ocean Model
Temperatureprofile
Salinityprofile
Density profile
Climatology
Price, et al. 1986
1500 m
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Price, Weller, Pinkel1-d Ocean Model
Temperatureprofile
Salinityprofile
Density profile
SST obs
1500 m
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Price, Weller, Pinkel1-d Ocean Model
Turbulent heat flux
Temperatureprofile
Salinityprofile
Density profile
SST obs
Short and longwavefluxes Freshwater (P-E)
flux
1500 m
Stress
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Price, Weller, Pinkel1-d Ocean Model
Freshwater (P-E) flux
Turbulent heat flux
Temperatureprofile
Salinityprofile
Density profile
SST obsVertical mixing:
• static instability
1500 m
Short and longwavefluxes
Stress
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Price, Weller, Pinkel1-d Ocean Model
Freshwater (P-E) flux
Turbulent heat flux
Temperatureprofile
Salinityprofile
Density profile
SST obsVertical mixing:
• static instability• wind mixing
1500 m
Short and longwavefluxes
Stress
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Price, Weller, Pinkel1-d Ocean Model
Freshwater (salt) flux
Turbulent heat flux
Temperatureprofile
Salinityprofile
Density profile
SST obsVertical mixing:
• static instability• wind mixing• vertical advection• vertical diffusion1500 m
Short and longwavefluxes
Stress
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Data Sets
• Temperature, Salinity profiles - WOA 2009• SST - NOAA OI with microwave• Wind stress, Curl - QuikSCAT winds• Turbulent heat flux - OAFlux• Radiant heat flux - ISCCP• Freshwater flux– Precipitation - GPCP– Evaporation - OAFlux
Time Period of data overlap: 2003 - 2007
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Experiments
• Climatological runs– 1 year– climatological fields
• Continual run– 5 years– actual data fields– relax to monthly climatological temperature and salinity
profiles, temperature profile modified by observed SST
Surface forcing only, no advection
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Climatological RunBaseline
Gulf Stream:missing temperature advection
Labrador Current: missing salinity advection
Southeast: lacking some of both temperature and salinity advection
RMS SST Error
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Calculate heat deficit
Heat = S [(Tmod – Tclim)* dh]*r*cp/time W/m2
ObservationsModel
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Calculate heat deficit
ObservationsModel
Missing heat
Heat = S [(Tmod – Tclim)* dh]*r*cp/time W/m2
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Calculate heat deficit
ObservationsModel
Missing heat
Excess heat
Adjust heat flux: + 171 W/m2
Heat = S [(Tmod – Tclim)* dh]*r*cp/time W/m2
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Calculate freshwater deficit
Freshwater = S[(1-Smod/Sclim)*dh]/time cm/yr
ObservationsModel
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Calculate freshwater deficit
ObservationsModel
Missing freshwater
Freshwater = S[(1-Smod/Sclim)*dh]/time cm/yr
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Calculate freshwater deficit
ObservationsModel
Missing freshwater
Excess freshwater
Adjust freshwater flux: + 16 cm/yr
Freshwater = S[(1-Smod/Sclim)*dh]/time cm/yr
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Heat flux Freshwater flux
Deficit flux
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Heat flux Freshwater flux
- Deficit flux
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Heat flux Freshwater flux
- Deficit flux
Annual Mean: Advection balances surface flux
Annual Mean
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RMS SST Error for Climatological Runs
Run 5 cases: adjust the surface heat and/or freshwater.½ Heat, ½ Freshwater½ Heat
¾ Freshwater¾ Heat
½ Freshwater
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Which correction gives the smallest SST Error?
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Which correction gives the smallest SST Error?
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RMS Error in SST for best case
Errors still large in the Gulf Stream and the Labrador Current
RMS SST Error for Baseline run
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Five year run, 2003-2007
• Daily forcing fields as input
• Adjust surface fluxes with best deficit estimate of heat and/or freshwater.
• Relaxing to climatological profiles 1/month.
• Monthly means
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Monthly SST time series show two types of errors
ObservationsModel
1. Drift
2. Seasonal bias
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Removed seasonal signal and the trend
SST Anomalies: observed (blue), modeled (red)
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Skill = 1- (error/std dev)2
How well does surface forcing onlypredict interannual SST anomlies?
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Conclusions
Skill of model in predicting observations indicates that interannual anomalies in SST are not controlled by surface forcing alone.
Ocean circulation must play a part.
Mean heat flux important in subtropical gyre and Gulf Stream.
Mean freshwater flux important in subpolar gyre.
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What’s next?
• Develop profiles of currents • Develop profiles of gradT and gradS• Apply advection• Go to longer runs with inferior (?) fields
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Bottom Topography, Smith and Sandwell
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Mean surface currents, AVISO