Background Regional Ocean-Atmosphere Coupled Model

Regional Ocean-Atmosphere Interactions in the Eastern Pacific: TIW’s, Mesoscale Eddies and Gap Winds

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

• 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.

Scripps Coupled Ocean-Atmosphere Regional (SCOAR) Model

Eastern equatorial Pacific domain example

Model domains in the eastern Pacific sector

• (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

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.

Stability Changes in ABL due to SST

•  Weaker stratification of ABL over warm phase of TIWs.

• 

• Stronger surface winds over warmer

Modification of heat and momentum flux

• Turbulent heat flux damps the SST; a negative feedback

• Feedback from wind stress perturbation remains largely unknown

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.

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

Air-Sea Coupling in the California Current Region

Wind Stress and Ekman Pumping Velocity

Thermocline Doming by Ekman Forcing; Costa Rica Dome

SST: Response to Gap Winds

Rainfall: Suppression of Precipitation by Eddies

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

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).

Future work….

Thanks!

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