A fast model for mean and turbulent wind characteristics over terrain with mixed surface roughness

The real-time near-range atmospheric model chain in RODOS already includes the fast spectral LINCOM code, which was originally developed by Rise for modelling the mean wind fields over hilly, but otherwise homogeneous, terrain. Its output is used as a wind field driver for the dispersion model RIMPUFF also included in the near-range model chain. An extension of the LINCOM wind model is described, which enables it also to respond to the effects of a heterogeneous or non-constant surface roughness distribution. This is of importance in the RODOS framework for: (1) prediction of the time of arrival of radioactive clouds traversing, for instance, a land/water/land surface, and (2) for calculation of the turbulent shear stress, and thereby the scaling parameters, over mixed terrain.