Modeling the Low-Frequency Sea Surface Temperature Variability in the North Pacific

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  • 1 Max-Planck-Institut.für Meteorologie, Hamburg, Federal Republic of Germany
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Abstract

The question of whether the large-scale low-frequency sea surface temperature (SST) variability in the North Pacific can be interpreted as a response to large-scale wind anomalies is studied by an ocean general circulation model coupled to an advective model for the air temperature. Forced with observed monthly mean winds, the model is successful in reproducing the main space and time characteristics of the large-scale low-frequency SST variability. In winter also the simulated and observed SSTs are highly correlated.

The dominant process in producing wintertime SST tendencies is the anomalous turbulent beat exchange with the atmosphere that is parameterized by the bulk aerodynamic formula and takes into account the simulated air temperature, the simulated SST, and the observed winds. The oceanic response to turbulent momentum fluxes is much smaller. The horizontal scale of the simulated air temperature is induced by advective transports with the observed winds and transferred to the ocean by anomalous turbulent latent and sensible heat fluxes. The ocean response is lagging the atmospheric forcing by about one month and persists over much longer time than the atmospheric anomalies, particularly in winter.

Part of the observed low-frequency SST variance can be explained by teleconnection. A wind field that is directly related to the tropical El Niño–Southern Oscillation (ENSO) phenomenon produces SST anomalies with an ENSO-related variance of more than 50% instead of 10% to 30% as observed.

Abstract

The question of whether the large-scale low-frequency sea surface temperature (SST) variability in the North Pacific can be interpreted as a response to large-scale wind anomalies is studied by an ocean general circulation model coupled to an advective model for the air temperature. Forced with observed monthly mean winds, the model is successful in reproducing the main space and time characteristics of the large-scale low-frequency SST variability. In winter also the simulated and observed SSTs are highly correlated.

The dominant process in producing wintertime SST tendencies is the anomalous turbulent beat exchange with the atmosphere that is parameterized by the bulk aerodynamic formula and takes into account the simulated air temperature, the simulated SST, and the observed winds. The oceanic response to turbulent momentum fluxes is much smaller. The horizontal scale of the simulated air temperature is induced by advective transports with the observed winds and transferred to the ocean by anomalous turbulent latent and sensible heat fluxes. The ocean response is lagging the atmospheric forcing by about one month and persists over much longer time than the atmospheric anomalies, particularly in winter.

Part of the observed low-frequency SST variance can be explained by teleconnection. A wind field that is directly related to the tropical El Niño–Southern Oscillation (ENSO) phenomenon produces SST anomalies with an ENSO-related variance of more than 50% instead of 10% to 30% as observed.

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