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CdB: $C_{dB}$

If the roughness at the bottom is zero (i.e. $z_{0B}$=0) then the drag coefficient at the bottom is given by this constant, otherwise the drag coefficient is calculated with the rough wall relationship. Use of no-slip boundary conditions for the bottom cell is specified by setting CdB=-1.

C_{dB} = \left[\ln\left(\frac{1}{2}\frac{\Delta z_{bot}}{z_{0B}}\right)\right]^{-2} ,

where $\Delta z_{top}$ is the thickness of the bottom cell (in meters) and $\kappa=0.4$ is the von Karman constant.