Regional Ocean-Atmosphere Interactions in the Eastern Pacific:

TIW’s, Mesoscale Eddies and Gap Winds

Regional Ocean-Atmosphere Interactions in the Eastern Pacific:

TIW’s, Mesoscale Eddies and Gap Winds

Woods Hole Oceanographic InstitutionOcean Engineering Seminar Series

April 26, 2006

Woods Hole Oceanographic InstitutionOcean Engineering Seminar Series

April 26, 2006

Arthur J. MillerScripps Institution of OceanographyUniversity of California, San Diego

Based on the Ph.D. Dissertation ofMr. Hyodae Seo (SIO)

Including collaboration with John Roads (SIO)

Ragu Murtugudde (Maryland)Markus Jochum (NCAR)

OutlineOutline• Background

• Regional Ocean-Atmosphere Coupled Model

• Research Topics

TIWs and Air-Sea InteractionAtmospheric Response to TIWs

- Stability adjustment of ABL Thermal and dynamic response

Effect of Atmospheric Feedback on TIWs frequency-wavenumber

California Current Eddies and Air-Sea Interaction Gap Winds and Air-Sea Interaction

Wind-induced forcing Thermocline doming Suppression of atmospheric deep convection

• Summary

• Background

• Regional Ocean-Atmosphere Coupled Model

• Research Topics

TIWs and Air-Sea InteractionAtmospheric Response to TIWs

- Stability adjustment of ABL Thermal and dynamic response

Effect of Atmospheric Feedback on TIWs frequency-wavenumber

California Current Eddies and Air-Sea Interaction Gap Winds and Air-Sea Interaction

Wind-induced forcing Thermocline doming Suppression of atmospheric deep convection

• Summary

BackgroundBackground

• Important component of large-scale atmospheric and oceanic circulation

• Atmospheric deep convection over the eastern Pacific warm pool and Equatorial Current system

• Coastal upwelling and equatorial cold tongue

• Equatorial SST front and TIWs• Influence by land and coastline• Different cloud response to SSTs All involve interactions among air, sea

and land. Studying the nature of such coupling is important for regional climate, and large-scale climate as well.

• Important component of large-scale atmospheric and oceanic circulation

• Atmospheric deep convection over the eastern Pacific warm pool and Equatorial Current system

• Coastal upwelling and equatorial cold tongue

• Equatorial SST front and TIWs• Influence by land and coastline• Different cloud response to SSTs All involve interactions among air, sea

and land. Studying the nature of such coupling is important for regional climate, and large-scale climate as well.

• Air-sea interaction in the Eastern Pacific

Consider a new high-resolution regional coupled model….

Latitude

Deep CumulusShallow Stratocumulus

Scripps Coupled Ocean-Atmosphere Regional (SCOAR) ModelScripps Coupled Ocean-Atmosphere Regional (SCOAR) Model

• Sequential Coupling 3 hourly or daily coupling

• Bulk formulae or RSM physics in ABL for momentum, heat and fresh-water fluxes

• Wind stress relative to ocean currents:

IC and Lateral BC: NCEP/DOE Reanalysis

SST

Boundary Layer Variables

Ocean Atmosphere

Bulk Formulaeor RSM BL

physics

Regional Spectral Model (RSM)

Lateral BC: Ocean Analysis (JPL/ECCO) or Climatology

Regional Ocean Modeling System

(ROMS)

Schematic of Ocean-Atmosphere Coupled Model

Seo, Miller and Roads (2006) J. Climate, sub judice

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

Equatorial and Coastal Upwelling

Tropical Instability Waves

Eastern equatorial Pacific domain exampleEastern equatorial Pacific domain example

Tehuantepec

Papagayo

Model domains in the eastern Pacific sector

Model domains in the eastern Pacific sector

(a) Eastern Tropical Pacific: TIW’s

(b) California Current System: Eddies

(c) Central American Coast: Gap Winds

(a) Eastern Tropical Pacific: TIW’s

(b) California Current System: Eddies

(c) Central American Coast: Gap Winds

Tropical Instability Waves:How do Feedbacks Between SST and

the Atmospheric Boundary LayerAffect TIW stability characteristics?

Tropical Instability Waves:How do Feedbacks Between SST and

the Atmospheric Boundary LayerAffect TIW stability characteristics?

TIW Domain in the Eastern Tropical PacificTIW Domain in the Eastern Tropical Pacific

Tropical Instability Waves 20 km ROMS + 30 km RSM

Galapagos Is.

RSM: 28 layers (6 below 900mb)ROMS: 30 layers (9 in top 100m)

EOF analysis of SSTEOF analysis of SST

• 1st and 2nd EOFs and PCs are paired and directly related to TIWs, explaining more than 60% of the total variance.

• 1st and 2nd EOFs and PCs are paired and directly related to TIWs, explaining more than 60% of the total variance.

CLM EOF 1; 34.2%

CLM EOF 2; 30.5%

CLM EOF 3; 9.3%

CLM EOF 4; 6.6%

PC 1

PC 2

PC 3

PC 4

EOF from September to December, 1999 over 1S-6N, 130W-100W.

• We are interested in....1) from EOFs, changes in

amplitude and wavelength of zonal temperature fluctuations by TIWs.

2) from PCs, changes in frequency of TIWs.

• We are interested in....1) from EOFs, changes in

amplitude and wavelength of zonal temperature fluctuations by TIWs.

2) from PCs, changes in frequency of TIWs.

Stability Changes in ABL due to SSTStability Changes in ABL due to SST

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

17(15) warm(cold) phases during 2-4 Sep. 1999

Modification of heat and momentum fluxModification of heat and momentum flux

• Turbulent heat flux damps the SST; a negative feedback• Feedback from wind stress perturbation remains largely unknown• Turbulent heat flux damps the SST; a negative feedback• Feedback from wind stress perturbation remains largely unknown

CEOF 1 of SST and Latent Heat Flux

WSC

WSD

Coupling of SST and Wind stress

LH anomaly : 20W / m2

Div and curl anomaly : 2N/m2 per 100km

Change in thermal state

Change in dynamic state

Observed: -40-50 W/m2/K

Comparable to observed values

Effects of atmospheric feedbacks on TIW’sEffects of atmospheric feedbacks on TIW’s

How do the perturbation heat fluxes and wind stresses affect the characteristics of TIW’s?

Additional experiments: sensitivity test for the year of 1999

How do the perturbation heat fluxes and wind stresses affect the characteristics of TIW’s?

Additional experiments: sensitivity test for the year of 1999

wind stress heat flux

CPL coupled coupled fully coupled

DYNM coupled smoothed* CPLdynamically

coupled

THERM smoothed CPL coupledthermally

coupled

CLM smoothed CPL smoothed CPL uncoupled

* : temporally smoothed using 120-day moving mean

• Analysis using the first two EOFs and PCs of ocean temperature • We are interested in....1) EOFs: changes in wavelength of zonal temperature fluctuations by TIWs.2) PCs: changes in frequency of the TIWs.

• Analysis using the first two EOFs and PCs of ocean temperature • We are interested in....1) EOFs: changes in wavelength of zonal temperature fluctuations by TIWs.2) PCs: changes in frequency of the TIWs.

Changes in amplitude of SST fluctuationsChanges in amplitude of SST fluctuations

• TIWs occur under climatological forcing.

• Heat flux coupling damps the fluctuations of SST by TIWs.

• Wind coupling yields a stronger damping; also increases wavelength. (cf. Pezzi et al., 2002)

• Full-coupling results in weakest fluctuations of SST over the TIW region.

• TIWs occur under climatological forcing.

• Heat flux coupling damps the fluctuations of SST by TIWs.

• Wind coupling yields a stronger damping; also increases wavelength. (cf. Pezzi et al., 2002)

• Full-coupling results in weakest fluctuations of SST over the TIW region.

std of SST (C)

Reduction wrt CLM (%)

CPL 1.1 35

DYNM 1.3 23

THERM 1.5 11

CLM 1.7 -

mean of 1st and 2nd modesCPL EOF-1 37% (2nd: 26%, Total 63%)

DYNM EOF-1 31% (2nd 19%, Total 50%)

THERM EOF-1 37% (2nd 30%, Total 67%)

CLM EOF-1 34% (2nd 30%, Total 64%)

Longitude

Latit

ude

EOF from September to December, 1999 over 1S-6N, 130W-100W.

Changes in vertical distributionChanges in vertical distribution

• Heat flux coupling : thermal damping increases baroclinicity in the mixed layer

• Wind coupling: damping + increase in wavelength.

• Full-coupling: mixture of effects from wind and heat feedback

• Heat flux coupling : thermal damping increases baroclinicity in the mixed layer

• Wind coupling: damping + increase in wavelength.

• Full-coupling: mixture of effects from wind and heat feedback

CLM EOF-1 41% (2nd 35%, Total 76%)

Longitude

THERM EOF-1 40% (2nd 37%, Total 77%)

DYNM EOF-1 32% (2nd 28%, Total 60%)

CPL EOF-1 40% (2nd 31%,Total 71%)Zonal STD of temperature

Dep

th (

m)

De

pth

(m

)

Zonal STD of temperature (C)

Average over 1N-6N

Changes in wavenumber and frequency characteristicsChanges in wavenumber and frequency characteristics

wavelength ( long.)

period (day)

phase speed (m s-1)

CPL 12 36 0.4

DYNM 18 36 0.6

THERM 12 36 0.4

CLM 12 27 0.5

Coupling increases the period of waves.

Dynamic coupling increases the wavelength of the wave.

Frequency spectra

Spe

ctra

l den

sity

[(

C)2

/cp

d]

~ 0.04 cycle / day

~ 0.03 cycle / day

Frequency (cycle per day)

Average of 1st and 2nd PCsAverage of 1N-6N

Wavenumber (cycle per long.)

Spe

ctra

l den

sity

[(

C2//c

p

long

.]

~ 0.1 cycle / long.

~0.07cycle / long.

Wavenumber spectra

Air-Sea Coupling in the California Current RegionAir-Sea Coupling in the California Current Region

WSD

LHSST & WS

WSC

• Similar coupling of SST with dynamics and thermodynamics of ABL is also seen in CCS region over various spatial and temporal scales.•But model coupling strength in midlatitudes is 3 - 5 times weaker than observed

RSM: 16 km

ROMS: 7 km

RSM: 16 km

ROMS: 7 km

• Gap Winds produce cold tongues due to evaporative cooling and entrainment, plus windstress curl forcing. • Affect the atmospheric deep convection and precipitation.

• Gap winds are driven by pressure gradient across narrow gaps or by intrinsic variability of the trades.

AVHRR Satellite SST Image; Jan 1999

Tehuantepec

Papagayo

Panama

OBS; Chelton et al., 2000

Gap Winds and Air-Sea InteractionsGap Winds and Air-Sea Interactions

Wind Stress and Ekman Pumping VelocityWind Stress and Ekman Pumping Velocity

• Wind-induced vorticity forcing leads to dynamic response in the ocean thermocline.

• Low-level wind jets through mountain gaps

• Ekman Pumping Velocity Unit :10-6m/s

Xie et al., 2005

Winter

Summer

OBSERVATION

Winter

MODEL: 1999-2003

95W 85W

95W 85W

Summer

RSM: 27 km ROMS: 25 km

Thermocline Doming by Ekman Forcing; Costa Rica DomeThermocline Doming by Ekman Forcing; Costa Rica Dome

OBSERVATION MODEL: 1999-2003

Along 8.5°N

Along 90°W

Costa Rica

DomeAlong 90°W

Along 8.5°N

• Ekman pumping (above) causes thermocline shoaling (left), which further cools SST and supports a productive ecosystem.• MLD is ~10 m and thermocline is ~30 m deep over Costa Rica Dome, both in obs and model.

95W 85W

SST: Response to Gap WindsSST: Response to Gap Winds

• Cold tongues off the major mountain gaps (due to wind-induced mixing, evaporative cooling, and Ekman pumping)

OBSERVATION

Winter

Winter

MODEL: 1999-2003

Summer

Costa Rica

Dome

Cold bias in CRD

Rainfall: Suppression of Precipitation by EddiesRainfall: Suppression of Precipitation by Eddies

• Costa Rica Dome and cold tongues by gap winds suppress atmospheric deep convection and precipitation, shifting the ITCZ southward (Xu et al., 2005)

OBSERVATION

Xie et al., 2005

Summer

WinterMODEL

Summer

Region of rain deficit

within ITCZ

Winter

Summary of TIW feedbacksSummary of TIW feedbacks

• Coupled model simulates the observed atmospheric response to TIWs - Evolving SST induces ABL stability adjustment and changes in heat flux and wind stress.

• Coupled model simulates the observed atmospheric response to TIWs - Evolving SST induces ABL stability adjustment and changes in heat flux and wind stress.

• Series of fully coupled, partially coupled, and uncoupled experiment show that ...

• 1) as expected, heat flux feedback suppresses amplitude of SST fluctuation by TIWs; a negative feedback

• 2) dynamic feedback provides even stronger damping to SST fluctuation (cf. Pezzi et al., 2002)

• 3) surface damping of temperature by heat flux results in stronger baroclinicity of zonal temperature fluctuation.

• 4) dynamic feedback also increases the wavelength of TIW

• Series of fully coupled, partially coupled, and uncoupled experiment show that ...

• 1) as expected, heat flux feedback suppresses amplitude of SST fluctuation by TIWs; a negative feedback

• 2) dynamic feedback provides even stronger damping to SST fluctuation (cf. Pezzi et al., 2002)

• 3) surface damping of temperature by heat flux results in stronger baroclinicity of zonal temperature fluctuation.

• 4) dynamic feedback also increases the wavelength of TIW

Summary of Gap Winds FeedbacksSummary of Gap Winds Feedbacks

• Coupled model simulates observed mean structure and seasonal variability of gap winds and their influences on upper ocean hydrography (Xie et al. 2005).

• Shoaling of thermocline and colder SST over Costa Rica Dome results in suppression and displacement of atmospheric deep convection and rainfall (Xie et al. 2005; Xu et al. 2005).

• Coupled model simulates observed mean structure and seasonal variability of gap winds and their influences on upper ocean hydrography (Xie et al. 2005).

• Shoaling of thermocline and colder SST over Costa Rica Dome results in suppression and displacement of atmospheric deep convection and rainfall (Xie et al. 2005; Xu et al. 2005).

Future work…. Future work….

1) Bering Sea- Add Sea Ice- Bering Ecosystem Study (BEST)

2) VOCALS - Peru-Humboldt Upwelling – SST - Stratocumulus

3) North Pacific Decadal Variability- KOE – Aleutian Low feedbacks 1948-2005

1) Bering Sea- Add Sea Ice- Bering Ecosystem Study (BEST)

2) VOCALS - Peru-Humboldt Upwelling – SST - Stratocumulus

3) North Pacific Decadal Variability- KOE – Aleutian Low feedbacks 1948-2005

Thanks!Thanks!