Surface fluxes and boundary layer scaling : models and applications

This study deals with applied modelling of some Atmospheric Boundary Layer (ABL) features. We use scaling techniques for the description of the turbulent structure in the ABL. A review is given on the different properties of the scaling techniques in stable and unstable conditions. The essential role of the surface fluxes of heat and momentum for the structure in the ABL is discussed.

Schemes are proposed for the estimation of the surface fluxes from routine weather data over land. Both for day- and nighttime, hourly values of the surface fluxes are modelled with the aid of the surface radiation and energy balance. Models and parameterizations for the individual components of these balances are compared with observations. During nighttime also the temperature profile up to 80 m is simulated with the modelled surface fluxes. The output of the surface flux schemes can be used for stability determination of the ABL.

Subsequently, diabatic wind profiles along the 200 m Cabauw tower are analysed in terms of surface layer similarity. For stable conditions an extension of the profile functions to strong stability is evaluated. Besides, the turning of wind with height up to 200 m is analysed. Together with the flux schemes, the wind speed profile can be estimated from near surface weather data only. It is shown that the agreement between estimates and observations is very good up to at least -100 m in generally level terrain. The methods are applied to simulate the wind frequency distribution and the reversed diurnal variation of the wind at 80 m.

Finally, a method for calculating the dispersion of non-buoyant plumes in the ABL is presented. The method is based on the scaling techniques of the ABL. Models are suggested for ground level concentrations of pollutants dispersed from continuous point sources. These models are evaluated with independent tracer experiments over land. The overall agreement between observations and predictions is very good and shown to be better than the skill of the traditional Gaussian plume model.

The proposed models and methods are intended for applications in meteorology and hydrology, for wind energy assessment methods and for air pollution dispersion studies.