二维振荡流动中污染云团的收缩*

当垂向扩散时间尺度与流动的周期相当时,在转流过程中,污染云团将会出现收缩.这时水平剪切分散导数将会出现负值奇性.本文根据作者两维延迟扩散方程7]: 其中u(t),v (t)为深度平均水平速度.导出X(t,τ),Y(t,τ)坐标位移,D_ij(t,τ)为剪切扩散导数的方程.一般情况下,?D_ij(t,τ)/?τ是正的.不存在奇异性.但在转流的初期.记忆函数D_ij(t,τ)就有可能是负的.本文给出了D_ij和X、Y的解析表示式.

Contaminant Contraction in Two-dimensional Oscillatory Flows

If the vertically-mixing time is comparable with that of period of oscillator)' current, the contaminant contraction may occur. The coefficient of shear dispersion is negative (singulurity). According io the two-dimensional delay-diffusion equation derived by the author. where u(O. t;(<) are verticay-averaged velocities, the equations for X(i ,r)t Y( t, T), central displacements, dispersion tensor, had been derived. D,, is positive when r is small. If the r is large, the memory functions may be negative. Also the expressions for and X ,Y had been obtained.