"xlsc0" (surface mixing length scale constant)

For the Generic Length Scale (GLS) turbulence closure (Umlauf and Burchard, 2003) in SCHISM, the mixing length ($l$) near the free surface is determined as

$l=\kappa d_s$ (Zhang and Baptista, 2008),

where

$\kappa=0.4$ is the von Karman's constant;

$d_s$ = xlsc0 $\cdot$ surface layer thinkness.

As a scale constant, xlsc0 should take a value between 0 and 1. Note that the spatially varying option (xlsc.gr3) is disabled in the latest SCHISM version.

If wind wave module is invoked, the surface layer thickness is taken as 0.6$H_s$ (significant wave height) following Terray et al. (1996); otherwise, it is taken as the distance between the top two vertical layers.

References:

Terray, E.A., Donelan, M.A., Agrawal, Y.C., Drennan, W.M., Kahma, K.K., Williams, A.J., Hwang, P.A. and Kitaigorodskii, S.A., 1996. Estimates of kinetic energy dissipation under breaking waves. Journal of Physical Oceanography, 26(5), pp.792-807.

Umlauf, L. and Burchard, H., 2003. A generic length-scale equation for geophysical turbulence models. Journal of Marine Research, 61(2), pp.235-265.

Zhang, Y. and Baptista, A.M., 2008. SELFE: a semi-implicit Eulerian–Lagrangian finite-element model for cross-scale ocean circulation. Ocean modelling, 21(3-4), pp.71-96.