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Let $U(x)$ and $\Delta (x)$ denote the characteristic vertical speed and width. Integrating the result of part (a), with $b(x)=B{x}^{-1/5}$, gives the scalingThe boundary-layer scaling in the momentum equation balances vertical inertia against transverse viscosity:Substituting this into the momentum-flux relation givesand thereforeReturning to the viscous-inertial balance then givesThese are the similarity scaling of a two-dimensional laminar plume.