NOCTURNAL WIND STRUCTURE OVER LAND AND DISPERSION OF POLLUTANTS - AN ANALYTICAL STUDY

An analytical cum empirical formulation (AE formulation) is proposed t o provide estimates of wind structure and plume width (and sigma(y)) o ver land for dispersion overnight. The formulation is an extension of our earlier studies (McNider et nl., 1993, Atmospheric Environment 27A , 2199-2214; Singh er nl., 1993, Boundary-Layer Met. 63, 397-423) with the basic difference that the latter formulation required the use of the mesoscale numerical model (MSNM) (McNider et al., 1988, Atmospheri c Environment 11, 2445-2462), whereas the present study is a self-cont ained formulation. The study shows that the model results are signific antly dependent on the initial wind profile at t = t(i) (around the ti me of sunset) when the inertial oscillations are expected to be trigge red in the residual layer due to the surface heat flux reversal. The a nalysis shows that the results in respect of sigma(y) obtained from th e AE formulation (based on the logarithmic/hyperbolic profile as an in itial input) are in good agreement with those obtained from the MSNM. During the initial stages of the nocturnal dispersion (similar to firs t hour after sunset), when the traditional Briggs empirical formulatio ns for sigma(y) are valid, it is shown that the AE formulation based o n the logarithmic profile gives results very close to those obtained f rom the Briggs formulation. Since the AE formulation is a simple schem e and requires data routinely available at the meteorological stations , it can be conveniently used by the operational scientists and the re gulatory agencies to provide estimates of the nocturnal wind structure and width of plumes dispersed over land. Copyright (C) 1996 Published by Elsevier Science Ltd