Regional Ocean-Atmosphere Interactions in the Eastern Pacific: TIW’s, Mesoscale Eddies and Gap Winds Woods Hole Oceanographic Institution Ocean Engineering Seminar Series April 26, 2006 Woods Hole Oceanographic Institution Ocean Engineering Seminar Series April 26, 2006 Arthur J. Miller Scripps Institution of Oceanography University of California, San Diego Based on the Ph.D. Dissertation of Mr. Hyodae Seo (SIO) Including collaboration with John Roads (SIO) Ragu Murtugudde (Maryland) Markus Jochum (NCAR)

Outline Background Regional Ocean-Atmosphere Coupled Model Research Topics TIWs and Air-Sea Interaction Atmospheric 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 Interaction Atmospheric 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 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 Cumulus Shallow Stratocumulus

Scripps 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 Formulae or 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 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 example Tehuantepec Papagayo

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 Layer Affect TIW stability characteristics?

TIW 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 SST 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 1  S-6  N, 130  W- 100  W. 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 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 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 / m 2 Div and curl anomaly :  2N/m 2 per 100km Change in thermal state Change in dynamic state

Observed: W/m2/K Comparable to observed values

Effects 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 stressheat flux CPL coupled fully coupled DYNM coupledsmoothed * CPL dynamically coupled THER M smoothed CPLcoupled thermally coupled CLM 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 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 DYNM THERM CLM 1.7- mean of 1st and 2nd modes CPL 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 Latitude EOF from September to December, 1999 over 1  S-6  N, 130  W-100  W.

Changes 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 Depth (m) Zonal STD of temperature (  C) Average over 1  N-6  N

Changes in wavenumber and frequency characteristics wavelengt h (  long.) perio d (day) phase speed (m s - 1 ) CPL DYNM THERM CLM  Coupling increases the period of waves.  Dynamic coupling increases the wavelength of the wave. Frequency spectra Spectral density [(  C )2/cpd] ~ 0.04 cycle / day ~ 0.03 cycle / day Frequency (cycle per day) Average of 1st and 2nd PCs Average of 1  N-6  N Wavenumber (cycle per  long.) Spectral density [(  C 2 / / cp  long. ] ~ 0.1 cycle /  long. ~0.07cycle /  long. Wavenumber spectra

Air-Sea Coupling in the California Current Region WSD LH SST & 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 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 Interactions

Wind 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 : m/s Xie et al., 2005 Winter Summer OBSERVATION Winter MODEL: W 85W Summer RSM: 27 km ROMS: 25 km

Thermocline Doming by Ekman Forcing; Costa Rica Dome OBSERVATIONMODEL: Along 8.5°NAlong 90°W Costa Rica Dome Along 90°WAlong 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 Winds Cold tongues off the major mountain gaps (due to wind- induced mixing, evaporative cooling, and Ekman pumping) OBSERVATION Winter MODEL: Summer Costa Rica Dome Cold bias in CRD

Rainfall: 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 Winter MODEL Summer Region of rain deficit within ITCZ Winter

Summary 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. 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 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…. 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 )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

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