Modeling of Regional Ocean-Atmosphere Feedback in the Eastern Equatorial Pacific;

Tropical Instability Waves

Modeling of Regional Ocean-Atmosphere Feedback in the Eastern Equatorial Pacific;

Tropical Instability Waves

Hyodae Seo, Art Miller and John Roads

Scripps Institution of Oceanography

Hyodae Seo, Art Miller and John Roads

Scripps Institution of Oceanography

Annual AMS Meeting

February 2, 2006

Annual AMS Meeting

February 2, 2006

OutlineOutline

• Introduce the regional coupled model

• Discuss the stability adjustment of the atmospheric boundary layer (ABL) due to undulating SST front by TIWs.

Altering heat flux

Coupling with wind stress

• Work in progress and summary

• Introduce the regional coupled model

• Discuss the stability adjustment of the atmospheric boundary layer (ABL) due to undulating SST front by TIWs.

Altering heat flux

Coupling with wind stress

• Work in progress and summary

Regional coupled modelRegional coupled model

Scripps Coupled Ocean-Atmosphere Regional (SCOAR) ModelScripps Coupled Ocean-Atmosphere Regional (SCOAR) Model

• Sequential coupling

• Purpose: Investigate the air-sea coupling process of ocean eddy scale

• Bulk formula or non-local RSM physics in the ABL

• Wind relative to ocean currentIC and Lateral BC:

NCEP/DOE Reanalysis

SST

Boundary Layer Variables

Ocean Atmosphere

Bulk Formula or RSM BL

Physics

Regional Spectral Model (RSM)

Lateral BC: Ocean Analysis (JPL/ECCO) or Climatology

Regional Ocean Modeling System

(ROMS)

SCOAR Model

Seo, Miller and Roads (submitted to J. Climate, 2005)

Regional Coupled Model (2)Regional Coupled Model (2)

TIWs contribute to heat balance in the mixed layer and thus meridional SST gradient, to which the ITCZ is sensitive.

Hypothesis: Resolving oceanic mesoscale feature such as TIWs and details of coastal upwelling will improve the simulation of SST and marine ITCZ in the Tropical Atlantic.

TIWs contribute to heat balance in the mixed layer and thus meridional SST gradient, to which the ITCZ is sensitive.

Hypothesis: Resolving oceanic mesoscale feature such as TIWs and details of coastal upwelling will improve the simulation of SST and marine ITCZ in the Tropical Atlantic.

H: 1/4 ROMS + 1 RSM L: 1 ROMS + 1 RSM

S. America

Western Africa

It is being used to investigate the importance in ocean mesoscale to the tropical Atlantic climate. Here is an example...

Regional Coupled Model (3)Regional Coupled Model (3)Central America: Gap Winds, Costa Rica Dome, and ITCZ (Xie et al., 2005)

US. West coast : SST-induced Ekman Pumping (Chelton et al., 2006) Bering Sea: Sea-Ice-Atmosphere Coupling

It is also being used in various regions from the tropics to high-latitude oceans for various purposes.

Tehuantepec

C. Mendocino

Pt. Conception

Papagayo

Bering Sea

Russia

Alaska

Evolving SST and wind-stress vector in 1999-2000

45 km ROMS + 50 km RSM

Coupled system

ITCZ / Eastern Pacific Warm Pool

Cross-equatorial trade winds

Gap Winds

Tropical Depressions and Hurricanes

Coastal Upwelling and Equatorial front

Tropical Instability Waves

Eastern equatorial Pacific domain;Review of ocean-atmoshere systemEastern equatorial Pacific domain;Review of ocean-atmoshere system

Tehuantepec

Papagayo

Changes in stability of ABLdue to evolving SST

Changes in stability of ABLdue to evolving SST

Modeled stability changes in ABL due to SSTModeled stability changes in ABL due to SST

17(15) warm(cold) phases during 2-4 Sep. 1999

Atmospheric Temperature

Ocean TemperatureZonal Wind

Stronger shear

Weaker shear

Stronger stratification

Weaker stratification

Virtual Potential Temperature

• Warm (Cold) SST enhances (reduces) surface winds; in-phase relationship; • So.. what’s the implication?

CEOF 1 of SST and WS Vector

Temporal and spatial associations: Combined EOFs of SST and wind stressTemporal and spatial associations: Combined EOFs of SST and wind stress

CEOF 1 of SST and WS

PC 1

1999

Modification of heat fluxModification of heat flux

Modeled changes in heat flux due to SSTModeled changes in heat flux due to SST

• Heat flux suppresses the the growth of TIWs; both turbulent flux and radiative flux provide negative feedback to SST by TIWs. • Observations suggest cooling of ~0.6°C / month from Deser et al. (1993), and Zhang and McPhaden (1995).

CEOF 1 of SST & LH CEOF1 of SST & CIWV (kg/m2)

Principal Component 1kg/m2

Coupling of SST and wind stress and synchronous westward propagation

Coupling of SST and wind stress and synchronous westward propagation

Coupling of wind stress and SSTCoupling of wind stress and SST

Chelton, 2005

ObservationsMODEL

WSC

WSD

€

∇T • τ^

= ∇T cosθ

€

∇T ×τ^

• k^

= ∇T sinθ

∆

WSD ~ Downwind SST gradient WSC ~ Crosswind SST gradient

Westward Propagation in the modelWestward Propagation in the modelSST and Wind stress from July-December, 1999 from model along 2°N

SST WS & SST WSD & DdT WSC & CdT

WSD & DdT

WSC & CdT

4S-4N, 130W-90W

• Co-propagation of SST and wind stress

• Weaker coupling coefficient in the model than in the observations (e.g. Chelton et al., 2001)

• Co-propagation of SST and wind stress

• Weaker coupling coefficient in the model than in the observations (e.g. Chelton et al., 2001)

Work in progressWork in progress

• Intensity of wind stress derivatives and its co-propagation with SST gradient suggest that there must be a dynamic feedback from the perturbations wind stress derivatives to energetics and dynamics to TIWs. The nature of this feedback still remains uncertain.

• Impact of such additional feedback from the perturbed thermal and dynamic forcing from the atmosphere back on the amplitude and wavenumber-frequency characteristics of the TIWs.

• Intensity of wind stress derivatives and its co-propagation with SST gradient suggest that there must be a dynamic feedback from the perturbations wind stress derivatives to energetics and dynamics to TIWs. The nature of this feedback still remains uncertain.

• Impact of such additional feedback from the perturbed thermal and dynamic forcing from the atmosphere back on the amplitude and wavenumber-frequency characteristics of the TIWs.

SummarySummary

• A high-resolution coupled model has been developed and used in the various regions.

• Main purpose is to investigate the ocean-atmosphere feedback on ocean mesoscale spatial and time scales.

• Evolving SST front perturbed by the TIWs alters vertical stratification of ABL. This leads to responses from ...

the turbulent and radiative (implied from the model) heat flux, thus changing thermal component of the atmospheric forcing; a negative feedback.

wind stress and its derivative fields, thus induces dynamic feedback from the atmosphere forcing; This feedback effect still remains uncertain.

• A high-resolution coupled model has been developed and used in the various regions.

• Main purpose is to investigate the ocean-atmosphere feedback on ocean mesoscale spatial and time scales.

• Evolving SST front perturbed by the TIWs alters vertical stratification of ABL. This leads to responses from ...

the turbulent and radiative (implied from the model) heat flux, thus changing thermal component of the atmospheric forcing; a negative feedback.

wind stress and its derivative fields, thus induces dynamic feedback from the atmosphere forcing; This feedback effect still remains uncertain.

Comments or questions?

Thanks!

Comments or questions?

Thanks!

Dependence of wind stress derivatives on the alignmentDependence of wind stress derivatives on the alignment

€

∇T • τ^

= ∇T cosθ

€

∇T ×τ^

• k^

= ∇T sinθ WSD ~ Downwind SST gradient è

WSC ~ Crosswind SST gradient èObservations WSD & Angle

WSC & Angle

WSD & Angle

WSC & Angle

Model

Air-sea coupling in California coastal oceanAir-sea coupling in California coastal oceanOver Cold Filaments: 5 days

WSC Over Warm Eddies: ~ 100km, 4 months Mean

• Similar coupling of SST with dynamics and thermodynamics of ABL is also seen in CCS region over various spatial and temporal scales.

SST & WS

LHWSD

WSCSST & WS

LHWSD