Abstract
A new method to determine horizontal wind direction fluctuations σθ is presented based on the hypothesis of a Gaussian distribution of wind direction that gradually moves to a circular, uniform distribution under near-clam conditions. A theoretical formulation for σθ, the persistence of wind and the total horizontal standard deviation σ, is provided and supported by experimental observation both in a complex terrain valley site and in an open grassland spot in Spain. Comparisons of the proposed model with observations yielded a fairly good agreement making the theoretical functions a straightforward procedure for use in atmospheric dispersion calculations. The method also provides insights on either the residual diffusivity in near-calm conditions or the maximal observable standard deviation.
