Tropical Instability Waves and Ocean-Atmosphere Feedback;

Coupled Modeling Study

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

OutlineOutline

• 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

SCOAR ModelSCOAR Model

Scripps Coupled Ocean-Atmosphere (SCOAR) ModelScripps 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)

Tropical Instability Waves in the Pacific; Evolving SSTs and Wind-stress

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.

Response of ABL to SST by TIWsResponse of ABL to SST by TIWs

Stability Adjustment of ABL by TIWsStability 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

• 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-stressTemporal/Spatial Associations: Combined EOFs of SST and Wind-stress

CEOF 1 of SST and WSM

PC 1

Response from thermal state of ABL; Combined EOFs of SST and Latent Heat-fluxResponse 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/ m2) )

SST (C): Jul31-Aug2 1999

PC 1 and 2 (W/ m2)

Dynamic Response of ABL to TIWsDynamic Response of ABL to TIWs

Chelton, 2005

OBSERVATION

Chelton, 2001

WSD (N/m2 per 104km)

WSC (N/m2 per 104km)

• WSC/WSD according to the alignment of wind-vector and isotherm.• What would be the dynamic feedback on to TIWs; positive? negative?

COUPLED MODELWSD (N/m2 per 104km)

WSC (N/m2 per 104km)

Atmospheric Feedback to Mesoscale StabilityAtmospheric 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).

• 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).

• 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%)

• 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.

• 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)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)

Changes in wavenumber-frequency CharacteristicsChanges in wavenumber-frequency Characteristics

Wind-forcing changes mostly wavelength (wavenumber).

Heat-flux changes mostly period (frequency).

Period(day)

Wavelength( longitude)

CPL 32 (30) 14 (9)

DYNM 32 (30) 9 (11)

THERM 27 (23) 14 (9)

Frequency Domain

Frequency (cycle per day)

Sp

ectr

al d

ensi

ty

[(m

/s)2

/cp

d]

~ 0.03 cycle / day

Wavenumber Domain

Wavenumber (cycle per 0.18)

Sp

ectr

al d

ensi

ty [

(m/s

)2/c

pd

x]

~ 0.08 cycle / 0.18

SummarySummary

• 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)

Air-Sea Coupling in S. California Coastal OceanAir-Sea Coupling in S. California Coastal Ocean

WSD LH

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.

Summary (cont.)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?

Thanks!