Background Regional Ocean-Atmosphere Coupled Model


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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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