Impact of wind-surface current covariability on the Tropical Instability Waves
Impact of wind-surface current covariability on the Tropical Instability Waves
Tropical Atlantic MeetingParis, FranceOctober 18, 2006
Tropical Atlantic MeetingParis, FranceOctober 18, 2006
Hyodae SeoScripps Institution of
OceanographyUniversity of California San
Diego
Markus Jochum (NCAR)Ragu Murtugudde (Maryland)
Arthur J. Miller (SIO)
OutlineOutline
• Model Description; the SCOAR Model;
• Air-Sea Coupling due to TIWs• In the Tropical Pacific Ocean; Atmospheric Wind Response to SST
• In the Tropical Atlantic Ocean; Effect of Wind and Surface Current Covariability
on to Ocean
• Summary
• Model Description; the SCOAR Model;
• Air-Sea Coupling due to TIWs• In the Tropical Pacific Ocean; Atmospheric Wind Response to SST
• In the Tropical Atlantic Ocean; Effect of Wind and Surface Current Covariability
on to Ocean
• Summary
Model Description and Some Examples;Model Description and Some Examples;
Scripps Coupled Ocean-Atmosphere Regional (SCOAR) ModelScripps Coupled Ocean-Atmosphere Regional (SCOAR) Model
SCOAR Model (1)SCOAR Model (1)
• Various coupling frequency (3hrs, 1-day, 5-days..)
• Bulk formula or RSM physics in ABL for momentum, heat and fresh-water fluxes
• Wind stress relative to ocean currents:
Seo, Miller and Roads (2006) J. Climate, in press
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IC and Lateral BC: NCEP/DOE Reanalysis
OceanAtmos
Flux-SST Coupler
Regional Spectral Model
(RSM)
Lateral BC: Ocean analysis / climatology
Regional Ocean
Modeling System
(ROMS)
SST
Flux
Purpose: Examine air-sea coupled feedback arising in the presence of ocean mesoscale eddies, fronts, and filaments.
It is now being used in various regions in the world ocean. Here are some examples…It is now being used in various regions in the world ocean. Here are some examples…
Central America
US. West coast
SCOAR Model (2)SCOAR Model (2)
Eastern Tropical Pacific Ocean
Tropical Atlantic Ocean
Seo et al. 2006 GRL
In the Eastern Tropical Pacific Ocean...Wind Response to TIW-induced SST
In the Eastern Tropical Pacific Ocean...Wind Response to TIW-induced SST
Coupled System
Gap Winds
Tropical Depressions and Hurricanes
Tropical Instability Waves
Evolving SST and wind-stress vector in 1999-200045 km ROMS + 50 km RSM
Eastern Equatorial Pacific Ocean DomainEastern Equatorial Pacific Ocean Domain
Atmospheric Stability Adjustment to the SSTAtmospheric Stability Adjustment to the SST
Weaker stratification of ABL over warm phase of TIWs.
Stronger wind near surface
Weaker stratification of ABL over warm phase of TIWs.
Stronger wind near surface
Combined EOF 1 of SST and WS Vector
Stronger shear
Weaker shear
Atmospheric Feedback?Atmospheric Feedback?
In the Atlantic Ocean...Effect of Correlation of Wind and Surface Current
on the TIWs
In the Atlantic Ocean...Effect of Correlation of Wind and Surface Current
on the TIWs
Pezzi et al. (2002, GRL) : wind-SST coupling reduces variability of TIWs; but why?
TIWsSST´
Usfc´
´
?
Coupling of Wind and Current...Coupling of Wind and Current...
1/4 ROMS + 1/4 RSM
6-year simulations 1999-2004;
Effect of correlation of wind and current
1/4 ROMS + 1/4 RSM
6-year simulations 1999-2004;
Effect of correlation of wind and current
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rU ⋅
r ∇r K e + ′
r u ⋅
r ∇r K e = −
r ∇ ⋅( ′
r u ′ p ) − g ′ ρ ′ w + ρ o(− ′
r u ⋅(− ′
r u ⋅
r ∇r
U ))
+ρ oAh ′ r u ⋅∇ 2 ′
r u + ρ o ′
r u ⋅(Av ′
r u z )zMasina et al. 1999;
Jochum et al. 2004;
€
+ ′ r
u ⋅r ′ τ z
EKE Equation
SST, Surface Current and Wind Stress associated with TIWs.SST, Surface Current and Wind Stress associated with TIWs.
• Cyclonic surface current driven by TIWs and overlying cross-front wind stress
• Cyclonic surface current driven by TIWs and overlying cross-front wind stress
Meridional Wind and Current over TIW Eddies...Meridional Wind and Current over TIW Eddies...
€
y
€
′ y
€
′ v
€
′ v
COLDWARM
€
′ y
BACKGROUND • Wind stress are in opposition of phase with current.
TIW meridional currents are slowed down by wind.
• Wind stress are in opposition of phase with current.
TIW meridional currents are slowed down by wind.
€
′ y€
′ v
Zonal Wind and Current over TIW Eddies...Zonal Wind and Current over TIW Eddies...
WARM COLD
€
x
€
′ x
€
′ x
€
′ u €
′ u
€
′ u €
′ u BACKGROUND North: opposite
(-) CORR
South: aligned (+) CORR
North: opposite (-) CORR
South: aligned (+) CORR
€
′ u
€
′ x
Correlation of Wind and Current (95%)Correlation of Wind and Current (95%)
• Wind and current are negatively correlated over TIW region.
• Wind-current covariability energy sink to the TIWs.
• Wind and current are negatively correlated over TIW region.
• Wind-current covariability energy sink to the TIWs.
Correlation of vsfc and y Correlation of usfc and x
€
+ ′ r
u ⋅r ′ τ z < 0
Estimate of energy conversion rate- Barotropic conversion rate of zonal flow- Local wind-current coupling
Estimate of energy conversion rate- Barotropic conversion rate of zonal flow- Local wind-current coupling
€
rU ⋅
r ∇r K e + ′
r u ⋅
r ∇r
K e = −r
∇⋅( ′ r u ′ p )− g ′ ρ ′ w + ρ o(− ′
r u ⋅(− ′
r u ⋅
r ∇r
U ))
+ρ oAh ′ r u ⋅∇2 ′
r u + ρ o ′
r u ⋅(Av ′
r u z )z + ′
r u ⋅
r ′ τ z
Masina et al. 1999; Jochum et al. 2004;
Estimated Energy via Coupling of Wind and CurrentEstimated Energy via Coupling of Wind and Current
• At ~2°N, wind contribution to the TIWs amounts to roughly ~40% of the barotropic convergent rate term...
• Integrated over TIW region (2S-5N), contribution can be roughly ~10% .
• At ~2°N, wind contribution to the TIWs amounts to roughly ~40% of the barotropic convergent rate term...
• Integrated over TIW region (2S-5N), contribution can be roughly ~10% .
€
rU ⋅
r ∇r K e + ′
r u ⋅
r ∇r K e = −
r ∇ ⋅( ′
r u ′ p ) − g ′ ρ ′ w + ρ o(− ′
r u ⋅(− ′
r u ⋅
r ∇r
U ))
+ρ oAh ′ r u ⋅∇ 2 ′
r u + ρ o ′
r u ⋅(Av ′
r u z )z + ′
r u ⋅
r ′ τ z
Latitude
Averages over 30W-10W for 6 years.
barotropic conversion rate
Wind-Current Coupling
Masina et al. 1999; Jochum et al. 2004;
Seo et al. 2006 submitted to J. Climate
Conclusion; Coupling due to TIWsConclusion; Coupling due to TIWs
2. Wind stress anomaly generated by SST of TIWs slows down the TIW currents; a negative correlation indicates that coupling of wind and current acts as an EKE sink to the TIWs ( ≈ Pezzi et al. 2002). Over 2S-5N, the energy sink amounts to ~10% of the barotropic conversion rate.
2. Wind stress anomaly generated by SST of TIWs slows down the TIW currents; a negative correlation indicates that coupling of wind and current acts as an EKE sink to the TIWs ( ≈ Pezzi et al. 2002). Over 2S-5N, the energy sink amounts to ~10% of the barotropic conversion rate.
1. Stability adjustment of the ABL due to SST changes vertical turbulent mixing of momentum, thus changes near-surface wind.
• This generates perturbation wind stress (and heat flux and ) in phase with SST.
• It thus implies further feedback to TIWs in terms of wind stress (and heat flux).
1. Stability adjustment of the ABL due to SST changes vertical turbulent mixing of momentum, thus changes near-surface wind.
• This generates perturbation wind stress (and heat flux and ) in phase with SST.
• It thus implies further feedback to TIWs in terms of wind stress (and heat flux).
• Coupled model well captures observed associations between undulating SST front and ABL.
• Coupled model well captures observed associations between undulating SST front and ABL.
Questions or Comments? Thanks!Questions or Comments? Thanks!
Observed: -40~-50 W/m2/K
Latent Heat Flux and SST
Sensible Heat Flux and SST
Coupling of SST and turbulent heat fluxCoupling of SST and turbulent heat flux
zonally high-pass filtered SST and heat flux from 1999-2003Evolving SST generates perturbations in
turbulent heat flux (and also radiation flux).
Coupling of SST and wind stressCoupling of SST and wind stress MODEL
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Chelton et al. 2005