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第 90 回 大気海洋圏物理系セミナー のおしらせ
日 時：2000年 11月 30日(木) 午前 9:30 − 12:00
場 所：地球環境科学研究科 2F講堂
発表者：W.R. Young (Scripps Institution of Oceanography)
題 目：Temperature and salinity compensation in the ocean mixed layer
発表者：P. Cessi (Scripps Institution of Oceanography)
題 目：Low-frequency variability in simple models of ocean/atmosphere
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Temperature and salinity compensation in the ocean mixed layer (W.R. Young) 発表要旨 :
Recent high resolution measurements of temperature (T) and salinity (S) in the northeast Pacific show that in the mixed layer these two components virtually cancel in their joint effect on density. This density compensation is observed on horizontal length scales between 20 meters and 10 kilometers. Below the mixed layer, in the thermocline, there is only partial compensation between T and S gradients. I will argue that compensation can be explained by density-driven shear dispersion: random thermohaline forcing creates non-compensated T-S gradients, but then the resulting density gradients drive vertically sheared currents. The transport associated with these currents then quickly remove the density gradients. This dynamics suggests a diffusive parameterization in which the flux of T and S is in the direction of the density gradient, and proportional to the third power of the gradient. I will discuss model results using this nonlinear parameterization.
Low-frequency variability in simple models of ocean/atmosphere (P. Cessi) 発表要旨 :
A model of the large scale interaction between the troposphere and the upper ocean, wind-driven circulation is formulated. Simplified parametrizations, built upon the conservation of global heat and momentum, relate the atmospheric eddy heat and momentum fluxes to the zonally averaged oceanic and atmospheric temperatures. The formulation shows that the wind-driven circulation influences the winds by controlling the strength of the oceanic northward heat transport, and thus the atmospheric northward heat transport and temperature distribution. Because the ocean takes decades to adjust to changes in the winds, the coupled system equilibrates into a state which is periodic in time, rather than steady. The period is linearly proportional to the transit time of long Rossby waves across the basin, and thus is of the order of decades for large scale basins.
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