1. Tropical Instability Waves and Ocean-Atmosphere Feedback; Coupled Modeling Study Hyodae Seo, Art Miller, John Roads (Scripps Institution of Oceanography) Markus Jochum (National Center for Atmospheric Research) Raghu Murtugudde (ESSIC, Univ. Maryland) Hyodae Seo, Art Miller, John Roads (Scripps Institution of Oceanography) Markus Jochum (National Center for Atmospheric Research) Raghu Murtugudde (ESSIC, Univ. Maryland) ROMS/TOMS User Workshop October 24-26, 2005 La Jolla, CA

2. Outline SCOAR Model Research ; TIWs and Air-Sea Interaction 1 Atmospheric Response to TIWs - Stability adjustment of ABL  Thermal and dynamic response 2. Effect of Atmospheric Feedback on TIWs - Modifications of Amplitude and Wavenumber- Frequency Characteristics of the TIWs Summary SCOAR Model Research ; TIWs and Air-Sea Interaction 1 Atmospheric Response to TIWs - Stability adjustment of ABL  Thermal and dynamic response 2. Effect of Atmospheric Feedback on TIWs - Modifications of Amplitude and Wavenumber- Frequency Characteristics of the TIWs Summary

3. SCOAR Model

4. Scripps Coupled Ocean-Atmosphere (SCOAR) Model Sequential Coupling Coupling Frequency  3 hourly coupling  Daily coupling Bulk Formula in ABL Winds Relative to Ocean IC and Lateral BC: NCEP/DOE Reanalysis SST Boundary Layer Variables Ocean Atmosphere COARE Bulk Formula Plus Winds relative to ocean currents Regional Spectral Model (RSM) Lateral BC: Ocean Analysis (JPL/ECCO) or Climatology Regional Ocean Modeling System (ROMS) Seo et al., 2005 (submitted to J. Climate)

5. Tropical Instability Waves in the Pacific; Evolving SSTs and Wind-stress SST and Wind-stress vector in 1999 Tehuantepec Papagayo Panama Galapagos Is. 50 km ROMS + 45 km RSM 20 km ROMS + 30 km RSM  We are interested in response of atmospheric boundary layer to TIWs and subsequent feedback on to TIWs.

6. Response of ABL to SST by TIWs

7. Stability Adjustment of ABL by TIWs Weaker stratification of ABL over warm phase of TIWs.  Stronger surface winds over warmer Weaker stratification of ABL over warm phase of TIWs.  Stronger surface winds over warmer Atmospheric Temperature Ocean Temperature U-Wind Ocean Temp. Profile Stronger shear Weaker shear

8. Warm (Cold) SST enhances (reduces) surface winds; in-phase relationship; CEOF 1 of SST and WS Vector Temporal/Spatial Associations: Combined EOFs of SST and Wind-stress CEOF 1 of SST and WSM PC 1

9. Response from thermal state of ABL; Combined EOFs of SST and Latent Heat-flux Latent heating flux (and sensible heat flux) appear to dampen the growth of TIWs; negative feedback by heat- flux (Xie et al. 2004, Chelton et al., 2001, Liu et al., 2000). CEOF 1 of SST and LH Latent Heat Flux (W/ m 2) ) SST (  C): Jul31-Aug2 1999 PC 1 and 2 (W/ m 2)

10. Dynamic Response of ABL to TIWs Chelton, 2005 OBSERVATION Chelton, 2001 WSD (N/m 2 per 10 4 km) WSC (N/m 2 per 10 4 km) WSC/WSD according to the alignment of wind-vector and isotherm. What would be the dynamic feedback on to TIWs; positive? negative? COUPLED MODEL WSD (N/m 2 per 10 4 km) WSC (N/m 2 per 10 4 km)

11. Atmospheric Feedback to Mesoscale Stability Question still remains; What are the effects of atmospheric FEEDBACK on to TIWs? Additional Experiments: 1999-2001 1. CPL: Coupled Wind-stress + Coupled Heat-flux 2. DYNM: Coupled Wind-stress + Climatological heat-flux 3. THERM: Climatological Wind-stress + Coupled Heat-flux  Climatological Flux: Mean Flux from CPL runs (1999-2003). Question still remains; What are the effects of atmospheric FEEDBACK on to TIWs? Additional Experiments: 1999-2001 1. CPL: Coupled Wind-stress + Coupled Heat-flux 2. DYNM: Coupled Wind-stress + Climatological heat-flux 3. THERM: Climatological Wind-stress + Coupled Heat-flux  Climatological Flux: Mean Flux from CPL runs (1999-2003).

12. Non-local wave adjustment and non-linear processes in the the ocean (Xie, 2004) and the coupling make it harder to understand what’s happening in reality (fully coupling). Dynamic feedback also suppress the growth of TIWs; Negative Feedback; (71%) Heat-flux dampens TIWs; Negative Feedback; weaker TIWs (68%). TIWs begins earlier and lasts longer. Atmospheric Feedback to Mesoscale Stability; Meridional Surface Current (m/s) CPL EOF1 Variance =16% DYNM EOF1 Variance =13% THERM EOF1 Variance = 15% CPL PC1 (m/s) DYNM PC1 (m/s)THERM PC1 (m/s)

13. Changes in wavenumber-frequency Characteristics  Wind-forcing changes mostly wavelength (wavenumber).  Heat-flux changes mostly period (frequency). Period (day) Wavelength (  longitude) CPL32 (30)14 (9) DYNM32 (30) 9 (11) THERM27 (23)14 (9) Frequency Domain Frequency (cycle per day) Spectral density [(m/s) 2 /cpd] ~ 0.03 cycle / day Wavenumber Domain Wavenumber (cycle per 0.18  ) Spectral density [(m/s) 2 /cpdx] ~ 0.08 cycle / 0.18 

14. Summary Coupled model captures an observed association between undulating SST by TIWs and ABL. 1. Warm SST produces weak stratification within the ABL, enhancing vertical turbulent mixing of momentum and moisture, and thus increase surface winds (Wallace et al.), Sc cloudiness (Deser et al.), and turbulent flux (Thum et al., Small et al, Liu et al); THERMAL FEEDBACK. 2. Effect of SST on wind-stress derivatives changes according to the alignment of isotherms and wind vectors. Winds-stress divergence (curl) is closely related to the downwind (crosswind) component of the SST gradient (Chelton et al., 2001); DYNAMIC FEEDBACK.  Questions;  How does thermal coupling due to TIWs contribute to heat budget in the equatorial Pacific? (Jochum et al., 2005) Coupled model captures an observed association between undulating SST by TIWs and ABL. 1. Warm SST produces weak stratification within the ABL, enhancing vertical turbulent mixing of momentum and moisture, and thus increase surface winds (Wallace et al.), Sc cloudiness (Deser et al.), and turbulent flux (Thum et al., Small et al, Liu et al); THERMAL FEEDBACK. 2. Effect of SST on wind-stress derivatives changes according to the alignment of isotherms and wind vectors. Winds-stress divergence (curl) is closely related to the downwind (crosswind) component of the SST gradient (Chelton et al., 2001); DYNAMIC FEEDBACK.  Questions;  How does thermal coupling due to TIWs contribute to heat budget in the equatorial Pacific? (Jochum et al., 2005)

15. Air-Sea Coupling in S. California Coastal Ocean WSDLH WSC Over Cold Filaments: 2-3 days SST & WS Over Warm Eddies: ~ 100km, 4 months mean SST & WS WSC WSD LH Similar coupling of SST with dynamics and thermodynamics of ABL is also seen in CCS region over various spatial and temporal scales.

16. Summary (cont.) Similar coupling patterns are observed wherever strong SST gradient is associated with oceanic front, meander of the currents and mesoscale eddy in both tropics and extra-tropics. Both thermal feedback and dynamic feedback suppress the amplitude of the TIWs; both negative feedback (cf. Pezzi et al. 2004) Non-local and non-linear process in the ocean (Xie, 2004) and air-sea coupling make it harder to understand process in the reality (fully- coupled cases) at this moment; details are now under investigations. Different modes of feedback by atmosphere leads to different wavenumber-frequency characteristics of TIWs. Questions; 1. Why does dynamic feedback suppress the TIWs? 2. Can we use this feedback mechanism to understand stability property of the ocean current and eddy? Similar coupling patterns are observed wherever strong SST gradient is associated with oceanic front, meander of the currents and mesoscale eddy in both tropics and extra-tropics. Both thermal feedback and dynamic feedback suppress the amplitude of the TIWs; both negative feedback (cf. Pezzi et al. 2004) Non-local and non-linear process in the ocean (Xie, 2004) and air-sea coupling make it harder to understand process in the reality (fully- coupled cases) at this moment; details are now under investigations. Different modes of feedback by atmosphere leads to different wavenumber-frequency characteristics of TIWs. Questions; 1. Why does dynamic feedback suppress the TIWs? 2. Can we use this feedback mechanism to understand stability property of the ocean current and eddy?

17. Thanks!