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= Turbulence closure =

One of the main challenges in LES modeling is the turbulence closure. The filtering process yields four SGS covariance terms (see Eqs.~\ref{eq:nse}\ref{eq:1hss}) that cannot be explicitly calculated. In PALM, these SGS terms are parametrized using a 1.5-order closure after [#deardorff Deardorff (1980)]. PALM uses the modified version of [#moeng Moeng and Wyngaard (1988)] and [#saiki Saiki et al. (2000)]. The closure is based on the assumption that the energy transport by SGS eddies is proportional to the local gradients of the mean quantities and reads





== References ==
* [=#deardorff]'''Deardorff JW.''' 1980. Stratocumulus-capped mixed layers derived from a three-dimensional model. Bound.-Lay. Meteorol. 18: 495–527.

* [=#moeng]'''Moeng CH, Wyngaard JC.''' 1988. Spectral analysis of large-eddy simulations of the convective boundary layer. J. Atmos. Sci. 45: 3573–3587.

* [=#saiki]'''Saiki EM, Moeng CH, Sullivan PP.''' 2000. Large-eddy simulation of the stably stratified planetary boundary layer. Bound.-Lay. Meteorol. 95: 1–30.