Rong-Hua Zhang Funded partly by NASA PO Program , ….

1. Applications of Remotely Sensed High-resolution SST Data to Representing Tropical Instability Wave (TIW)-Induced Surface Wind Response Rong-Hua Zhang Funded partly by NASA PO Program, …. University of Maryland, College Park, Maryland, USA

2. Outline • Introduction • Representing TIW-induced wind forcing & feedback • A hybrid coupled ocean-atmosphere model (HCMOGCM ) Atmosphere: Wind stress: SVD-based; Ocean: The Cane-Gent OGCM • Ocean model experiments: with and without TIW wind forcing • Coupled ocean-atmos experiments: TIW wind feedback • Summary τTIW = aTIW Svd ( SSTTIW ) aTIW=0.0 aTIW=2.0

3. Tropical Instability Waves (TIWs)

4. Effects of TIWs on the Tropical Pacific Climate & Marine Ecosystem • Heat and momentum budget & balance • Mean ocean and atmosphere states • Seasonal modulation • Interannual variations e.g., as a stochastic forcing to modulate ENSO ? • ……. High resolution modeling evidence: Model improvements,biases, … => TIW effects

5. Challenges:TIW-induced wind forcing and feedback • Resolving TIW wind signals: high resolution • Studies mostly on diagnostic analyses, less on solutions • Uncertainty in representing TIW wind forcing in observations & data products • TIW wind forcing not adequately represented in ocean and coupled modeling • Mechanisms for atmos wind responses: still in debate e.g.: vertical mixing vs pressure gradients • Poor understanding of interactions between TIWs and large-scale processes • A clean & clear assessment of TIW-induced wind forcing & feedback => still lacking …. • …..

6. IPCC AR4 climate models & ENSO forecast models TIW-induced wind feedbackNOT taken into account

7. Different ways TIW-induced wind forcing is represented in the Atmos for ocean-related modeling τTIW • ocean models • Not resolved at low resolution e.g.: global climate models; atmos re-analysis climate products => Biases • High resolution wind data (e.g.,: directly from satellite obs. ) e.g.: prescribed wind data : A forced ocean modeling without feedback from the ocean to the atmos => Biases • TIW resolving coupled air-sea models at TIW scales Regional models: Scripps; IPRC => regional !! Global climate model => expensive; not affordable now !! Biases can be introduced by TIW-induced wind forcing

8. This work Taking into account TIW-induced wind forcing & feedback • Using satellite data to explore statistical modeling for TIW wind => another application of satellite data to climate modeling; • A simple parameterization for TIW winds; • A modeling tool for interactions between TIWs and large-scale processes; • A clean assessment for the effects of TIW wind forcing & feedback on ocean & coupled modeling; • Understanding basic processes involved, the role in biases of SST simulation; …. • Improving climate simulations & prediction;

9. An empirical mpdel for τTIW τTIW = aTIW Svd ( SSTTIW ) • TMI SST & QuikSCAT winds • Daily data during 2000-2007; • Filtered for TIW signals • SVD analyses: dominant modes • Relationship between SSTTIW &τTIW • Given SSTTIW => τTIWfields

10. An SVD-based Empirical Model for τTIW τTIW = aTIW Svd ( SSTTIW )

11. Svd ( SSTTIW )=τTIW

12. Svd ( SSTTIW ) = τTIW Year 1999

14. Representing Tropical Instability Waves (TIWs)-induced Wind Forcing & Feedback in Climate Models

15. Assessing TIW-induced wind forcing/feedback effects in ocean and coupled models • Not clearly examined; mostly diagnostic analyses; • Difficulty in representing/isolating TIW wind forcing part: e.g.: satellite data contaminated by non-TIW wind signals • High resolution models: include everything, not clean & clear A simple, clean, clear way to do this: add-on/off approach An empirical model for TIW wind part: τ = τclim + τTIW τTIW = 0.0 τTIW = observed wind directly from satellite obs. τTIW = aTIW Svd ( )

16. SST differences at (140W,0): τTIW= aTIW Svd (SSTTIW)

18. Hybrid Coupled Model at ESSIC/UMD • The Gent-Cane ocean model A sigma-layer, reduced-gravity OGCM with (1) A hybrid mixing scheme Chen, Rothstein & Busalacchi (1995) (2) Coupling to an advective atmos mixed layer model (Murtugudde, Seager & Busalacchi 1995) (3) Model specifications: Tropical Pacific domain: 25N-25S; 31-layers; Resolution: 1 deg in longitude and 0.5 deg in latitude • An empirical atmospheric wind stress anomaly model (SVD-based)

19. TIW-induced wind forcing & feedback experiments

22. Effects induced in ocean & coupled ocean-atmos models • Ocean modeling: Cooling effects on SST; However: over-cooling in ocean modeling directly forced by atmos wind without TIW feedback • Interannual variabilityin coupled ocean-atmos models Enhanced ENSO amplitude Shortened oscillation periods How to adequately represent the TIW wind feedabck

23. Using satellite SST data to represent tropical instability wave (TIW)-induced surface wind forcing • An empirical modeling approach: can be used to adequately represent TIW-induced wind feedback for climate modeling Critical to SST data: resolution, error, …. τTIW = aTIW Svd ( SSTTIW ) • Observations • Simulations

24. Sensitivity to spatial resolution of SSTTIW: SSTTIW variance along 3N

25. Concluding remarks • An empirical model for TIW-induced wind forcing; • Large effects identified on ocean and coupled simulations e.g.: cooling effects; Modulation of ENSO ; => Importance of TIW wind forcing but significant uncertainties in representing it in climate models & reanalysis data; • Aclearfeedbackinduced by TIW wind forcing: Processes identified…. • A clear source for biases; thisforcing component adequately be taken into account for better climate simulation & prediction • A new way to use satellite data for climate modeling: physical parameterizationsdata assimilation • ……

27. Interactions between TIWs and large-scale processes Tropical Instability Waves (TIWs)

28. Interactions between TIWs and large-scale processes Atmospheric response Tropical Instability Waves (TIWs)

29. Interactions between TIWs and large-scale processes Feedback Atmospheric response Tropical Instability Waves (TIWs)