= Near-neutral log-linear surface-layer profiles
{title2=$K_{M,B}=u_*z f_{M,B}(z/\ell)$}
If the similarity functions of a <turbulent boundary layer> are differentiable at zero and have finite positive neutral values, expanding $f=a+d z/\ell+O((z/\ell)^2)$ gives a shear proportional to $1/z-d/(a\ell)$. Integration yields a logarithmic term plus a linear correction. Dimensional reasoning alone does not fix the coefficients or guarantee this regular neutral limit. The <gradient Richardson number> is of order $z/\ell$, so $|z/\ell|\ll1$ is a shear-dominated, nearly neutral regime on either side of stability.
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