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Article
Article Type:
Research Article

SST–Wind Interaction in Coastal Upwelling: Oceanic Simulation with Empirical Coupling

Xin Jin Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Changming Dong Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Jaison Kurian Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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James C. McWilliams Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Dudley B. Chelton College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

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Zhijin Li NASA Jet Propulsion Laboratory, Pasadena, California

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Print Publication:
01 Nov 2009
DOI:
https://doi.org/10.1175/2009JPO4205.1
Page(s):
2957–2970
Restricted access

Abstract

Observations, primarily from satellites, have shown a statistical relationship between the surface wind stress and underlying sea surface temperature (SST) on intermediate space and time scales, in many regions inclusive of eastern boundary upwelling current systems. In this paper, this empirical SST–wind stress relationship is utilized to provide a simple representation of mesoscale air–sea coupling for an oceanic model forced by surface winds, namely, the Regional Oceanic Modeling System (ROMS). This model formulation is applied to an idealized upwelling problem with prevailing equatorward winds to determine the coupling consequences on flow, SST, stratification, and wind evolutions. The initially uniform wind field adjusts through coupling to a cross-shore profile with weaker nearshore winds, similar to realistic ones. The modified wind stress weakens the nearshore upwelling circulation and increases SST in the coastal zone. The SST-induced wind stress curl strengthens offshore upwelling through Ekman suction. The total curl-driven upwelling exceeds the coastal upwelling. The SST-induced changes in the nearshore wind stress field also strengthen and broaden the poleward undercurrent. The coupling also shows significant impact on the developing mesoscale eddies by damaging cyclonic eddies more than anticyclonic eddies, which leads to dominance by the latter. Dynamically, this is a consequence of cyclones with stronger SST gradients that induce stronger wind perturbations in this particular upwelling problem and that are therefore generally more susceptible to disruption than anticyclones at finite Rossby number. The net effect is a weakening of eddy kinetic energy.

Corresponding author address: Dr. Xin Jin, IGPP, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1567. Email: xjin@ucla.edu

Abstract

Observations, primarily from satellites, have shown a statistical relationship between the surface wind stress and underlying sea surface temperature (SST) on intermediate space and time scales, in many regions inclusive of eastern boundary upwelling current systems. In this paper, this empirical SST–wind stress relationship is utilized to provide a simple representation of mesoscale air–sea coupling for an oceanic model forced by surface winds, namely, the Regional Oceanic Modeling System (ROMS). This model formulation is applied to an idealized upwelling problem with prevailing equatorward winds to determine the coupling consequences on flow, SST, stratification, and wind evolutions. The initially uniform wind field adjusts through coupling to a cross-shore profile with weaker nearshore winds, similar to realistic ones. The modified wind stress weakens the nearshore upwelling circulation and increases SST in the coastal zone. The SST-induced wind stress curl strengthens offshore upwelling through Ekman suction. The total curl-driven upwelling exceeds the coastal upwelling. The SST-induced changes in the nearshore wind stress field also strengthen and broaden the poleward undercurrent. The coupling also shows significant impact on the developing mesoscale eddies by damaging cyclonic eddies more than anticyclonic eddies, which leads to dominance by the latter. Dynamically, this is a consequence of cyclones with stronger SST gradients that induce stronger wind perturbations in this particular upwelling problem and that are therefore generally more susceptible to disruption than anticyclones at finite Rossby number. The net effect is a weakening of eddy kinetic energy.

Corresponding author address: Dr. Xin Jin, IGPP, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1567. Email: xjin@ucla.edu

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