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Acoustic travel time measurements are used to investigate the spatial and temporal variability of air temperature and wind fields in the atmospheric surface layer. The observational system consists of several sound sources and receivers, which were distributed over an apparently horizontal homogeneous terrain to calculate a two-dimensional distribution of air temperature using a tomographic algorithm. Parallel to the tomographic measurements, all components of the energy balance of the investigated surface are observed using conventional micrometeorological methods. The sum of these components of the energy balance must theoretically be equal to zero. However, the sum of the observed components often add up to an unexplainable residuum. It can be shown here that the diurnal variability of the residuum of such energy balance measurements and the simultaneously observed diurnal variability of the horizontal gradients in the air temperature field seem to be closely related. This is a hint that the known difficulties in observing a closed energy balance with conventionally micrometeorological methods could be due to the disregarding of the horizontal nonhomogeneous airflow conditions.
Raabe et al. (Thu,) studied this question.