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Impact of wind-surface current covariability on the Tropical Instability Waves

Impact of wind-surface current covariability on the Tropical Instability Waves. Hyodae Seo Scripps Institution of Oceanography University of California San Diego Markus Jochum ( NCAR ) Ragu Murtugudde ( Maryland ) Arthur J. Miller ( SIO ). Tropical Atlantic Meeting Paris, France

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Impact of wind-surface current covariability on the Tropical Instability Waves

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  1. Impact of wind-surface current covariability on the Tropical Instability Waves Hyodae Seo Scripps Institution of Oceanography University of California San Diego Markus Jochum (NCAR) Ragu Murtugudde (Maryland) Arthur J. Miller (SIO) Tropical Atlantic Meeting Paris, France October 18, 2006

  2. Outline • 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

  3. Model Description and Some Examples; Scripps Coupled Ocean-Atmosphere Regional (SCOAR) Model

  4. Bulk formula or RSM physics in ABL for momentum, heat and fresh-water fluxes • Wind stress relative to ocean currents: Regional Ocean Modeling System (ROMS) Regional Spectral Model (RSM) • Various coupling frequency (3hrs, 1-day, 5-days..) Seo, Miller and Roads (2006) J. Climate, in press SCOAR Model (1) ` Atmos Ocean  Flux  Flux-SST Coupler   SST Lateral BC: Ocean analysis / climatology IC and Lateral BC: NCEP/DOE Reanalysis Purpose: Examine air-sea coupled feedback arising in the presence of ocean mesoscale eddies, fronts, and filaments.

  5. Tropical Atlantic Ocean Seo et al. 2006 GRL SCOAR Model (2) It is now being used in various regions in the world ocean. Here are some examples… Central America Eastern Tropical Pacific Ocean US. West coast

  6. In the Eastern Tropical Pacific Ocean...Wind Response to TIW-induced SST

  7. Eastern Equatorial Pacific Ocean Domain Evolving SST and wind-stress vector in 1999-2000 45 km ROMS + 50 km RSM • Coupled System • Gap Winds • Tropical Depressions and Hurricanes • Tropical Instability Waves

  8. Combined EOF 1 of SST and WS Vector Atmospheric Stability Adjustment to the SST Weaker stratification of ABL over warm phase of TIWs.  Stronger wind near surface Stronger shear Weaker shear

  9. Atmospheric Feedback?

  10. ´ SST´ TIWs Usfc´ ? Pezzi et al. (2002, GRL) : wind-SST coupling reduces variability of TIWs; but why? In the Atlantic Ocean...Effect of Correlation of Wind and Surface Current on the TIWs

  11. Coupling of Wind and Current... 1/4 ROMS + 1/4 RSM 6-year simulations 1999-2004; Effect of correlation of wind and current EKE Equation Masina et al. 1999; Jochum et al. 2004;

  12. SST, Surface Current and Wind Stress associated with TIWs. • Cyclonic surface current driven by TIWs and overlying cross-front wind stress

  13. Meridional Wind and Current over TIW Eddies... • Wind stress are in opposition of phase with current.  TIW meridional currents are slowed down by wind. COLD WARM BACKGROUND

  14. Zonal Wind and Current over TIW Eddies... WARM COLD BACKGROUND North: opposite  (-) CORR South: aligned  (+) CORR

  15. Correlation of Wind and Current (95%) Correlation of usfc and x Correlation of vsfc and y • Wind and current are negatively correlated over TIW region. • Wind-current covariability energy sink to the TIWs.

  16. Estimate of energy conversion rate- Barotropic conversion rate of zonal flow- Local wind-current coupling Masina et al. 1999; Jochum et al. 2004;

  17. Estimated Energy via Coupling of Wind and Current Averages over 30W-10W for 6 years. barotropic conversion rate • At ~2°N, wind contribution to the TIWs amounts to roughly ~40% of the barotropic convergent rate term... • Integrated over TIW region (2S-5N), contribution can be roughly ~10% . Wind-Current Coupling Latitude Seo et al. 2006 submitted to J. Climate Masina et al. 1999; Jochum et al. 2004;

  18. Conclusion; Coupling due to TIWs • Coupled model well captures observed associations between undulating SST front and ABL. 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). 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 2S-5N, the energy sink amounts to ~10% of the barotropic conversion rate.

  19. Questions or Comments? Thanks!

  20. Coupling of SST and turbulent heat flux Latent Heat Flux and SST Sensible Heat Flux and SST Observed: -40~-50 W/m2/K zonally high-pass filtered SST and heat flux from 1999-2003 Evolving SST generates perturbations in turbulent heat flux (and also radiation flux).

  21. Coupling of SST and wind stress MODEL Chelton et al. 2005 `

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