Effective local roughness length was determined from averaging the land-use-grid related roughness length over a square area of 4000 x 4000 m2.
Due to change of turbulence from step M to M+1 (either by change of stability class or by change of roughness length) the sigma parameters of a puff can only increase, never decrease. This increase was applied both to the sigma parameters at puff head and puff end.