1. 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

2. Outline 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

3. Regional coupled model

4. Scripps 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 current IC 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)

5. 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...

6. 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 Alask a

7. 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 system Tehuantepec Papagayo

8. Changes in stability of ABL due to evolving SST

9. Modeled stability changes in ABL due to SST 17(15) warm(cold) phases during 2-4 Sep. 1999 Atmospheric Temperature Ocean Temperature Zonal Wind Stronger shear Weaker shear Stronger stratification Weaker stratification Virtual Potential Temperature

10. 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 stress CEOF 1 of SST and WS PC 1 1999

11. Modification of heat flux

12. Modeled 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/m 2 ) Principal Component 1 kg/m 2

13. Coupling of SST and wind stress and synchronous westward propagation

14. Coupling of wind stress and SST Chelton, 2005 Observations MODEL WSC WSD   ∆∆  WSD ~ Downwind SST gradient   WSC ~ Crosswind SST gradient 

15. Westward Propagation in the model SST and Wind stress from July-December, 1999 from model along 2°N SST WS & SSTWSD & DdT WSC & CdT WSD & DdT WSC & CdT 4  S-4  N, 130  W-90  W 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)

16. Work 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.

17. Summary 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.

18. Comments or questions? Thanks!

19. Dependence of wind stress derivatives on the alignment  WSD ~ Downwind SST gradient è  WSC ~ Crosswind SST gradient è Observations WSD & Angle WSC & Angle WSD & Angle WSC & Angle Model

20. Air-sea coupling in California coastal ocean Over 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