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

€

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