Publication Abstracts
Seager 1990
Seager, R., 1990: Modeling Sea Surface Temperature and Low-Level Winds in the Tropics. Ph.D. thesis. Columbia University.
Some steps towards development of a coupled, reduced physics, model of the tropical atmosphere and ocean climatology are presented. The work divides into three parts–a model of the tropical Pacific sea surface temperature (SST) climatology, a study of the interannual variability of SST using this model and a model of the low level wind field in the tropics.
The first part describes a model of the climatological SST of the tropical Pacific ocean. The upper ocean response is computed using a time dependant, linear, reduced gravity model with the addition of a constant depth frictional surface layer. The three dimensional temperature equation and a surface heat flux parameterization that requires specification of only wind speed and total cloud cover are used to evaluate the SST. The model simulates the major features of the observed SST and their seasonal evolution. Analysis demonstrates the control the ocean has over the surface heat flux from ocean to atmosphere and the crucial role that dynamics play in determining the SST in the equatorial Pacific.
We then compute the SST of the tropical Pacific for the period between January 1970 and September 1987, using observed winds as forcing. Variability with periods longer than one year, including each El Nino event in the time interval, is well represented in the model. El Nino related SST anomalies develop as follows. In the east Pacific Kelvin waves, excited by variations in trade wind strength, increase the SST via depression of the thermocline. Here the surface heat flux is a negative feedback on the SST anomaly. In the central Pacific weakened trades both reinforce heating through suppression of the latent heat loss and force Rossby waves that advect warm water from the west while anomalous cooling by entrainment is a negative feedback on the SST anomaly.
Finally a simple model of the low level wind field in the entire tropics is presented. The dynamics are linear, steady state, contained within a single baroclinic mode and damped by Rayleigh friction. Convective heating is computed with reference to buoyancy criteria and the cloud model of Yanai et al. (1973). Radiative cooling is represented by a Newtonian cooling to an equilibrium lapse rate. When forced by surface temperature and humidity a qualitatively correct representation of the climatological flow is achieved but the model is unable to reproduce the intensity and limited spatial scale of the convergence zones. Conclusions as regards the essential physics operating in the tropical atmosphere and suggestions for future work are presented.
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BibTeX Citation
@phdthesis{se03100m,
author={Seager, R.},
title={Modeling Sea Surface Temperature and Low-Level Winds in the Tropics},
year={1990},
school={Columbia University},
address={New York, N.Y.},
}
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RIS Citation
TY - THES ID - se03100m AU - Seager, R. PY - 1990 BT - Modeling Sea Surface Temperature and Low-Level Winds in the Tropics PB - Columbia University CY - New York, N.Y. ER -
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