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       森羅万象/地球環境大気海洋専攻(eoas セミナー)ジョイントセミナー

                   http://www.ep.sci.hokudai.ac.jp/~sinra/

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                  時 ：  11 月 30 日 (月) 9:30 〜 12:00
                 場所：  地球環境 2 階講堂

             W.R. Young (Scripps Institution of Oceanography)

    『Temperature and salinity compensation in the ocean mixed layer』

    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.


            P. Cessi (Scripps Institution of Oceanography)

    『Low-frequency variability in simple models of ocean/atmosphere』

    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.

世話人：林 祥介

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セミナー幹事：倉本　圭