variable $\sg$: = - \_0\^z dz, Note, that $\sg$ is just an auxiliary variable. All the final results will be given in terms of the original variables: $\rho$ and $z$. Condition (\[vp3\]) is satisfied on $\mit{R}$ only. As $\sg$ is a function of $z$ only, we can simplify the diffusion equations below. In the right hand side of (\[vp5\]) we have: f\_[1,0]{} &=& a + b\_1 ,\
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a &=& (z) (- 1 ) ( 1+ / ),\
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b\_1 &=& -2 1[+1]{}, and $$f_{2,0} = - \frac{r_i}2 \rho \left(\rho^2-1\right) \: \left( 1+ \ln \rho \: / \ln \: \eta \right).$$ The relation between $a$ and $b_1$ defines the properties of the phase portrait on $(\th,
\th^{\pr})$ phase plane. If | b\_1 | &gt; | a |, \[vpc4b\] the phase portrait looks like the one shown in Fig. 1a. If (\[vpc4b\]) does not hold, the phase portrait looks like the one shown in Fig. 1b. Note, that $a=0$ at $\la z = \pi/2$ and $\la z =
3\pi/2$ (where $\cos(\la z) = 0$). Therefore, while in the center of the mixing region condition (\[vpc4b\]) may be either satisfied or not, there are always zones near the edges of the mixing 