Review and intercomparison of operational methods for the determination ofthe mixing height

The height of the atmospheric boundary layer (ABL) or the mixing height (MH ) is a fundamental parameter characterising the structure of the lower trop osphere. Two basic possibilities for the practical determination of the MH are its derivation from profile data (measurements or numerical model outpu t) and its parameterisation using simple equations or models (which only ne ed a few measured input values). Different methods suggested in the literat ure are reviewed in this paper. The most important methods have been tested on data sets from three different sites in Europe (Cabauw - NL, Payerne - CH, Melpitz - D). Parcel and Richardson number methods applied to radiosond e profiles and the analysis of sodar and wind profiler data have been inves tigated. Modules for MH determination implemented in five currently used me teorological preprocessors for dispersion models have been tested, too. Par cel methods using a revised coefficient for the excess temperature and Rich ardson number methods using a surface excess temperature worked well under convective conditions. Under stable conditions, the inherent difficulties c all for a combination of several methods (e.g.., mast and sodar). All the t ested parameterisation schemes showed deficiencies under certain conditions , thus requiring more flexible algorithms able to take into account changin g and non-classical conditions. Recommendations are formulated regarding bo th the analysis of profile measurements and the use of parameterisations an d simple models, and suggestions for the preprocessor development and for F uture research activities are presented. (C) 2000 Elsevier Science Ltd. All rights reserved.