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Nirupama Raghavan and Swati Basu

Abstract

A one dimensional model of the neutral planetary boundary layer is used to predict the wind velocity and coefficient of eddy diffusivity throughout the 2-km planetary boundary layer. Comparison with routine radiosonde observations show that at 500 m, the model predictions of wind speed are within 1.2σ of the observed values where σ is the probable error of the observed values. An interesting correlation between the height of maximum diffusion and length scale (u */f) of the neutral boundary layer has emerged out of this study.

The velocity and diffusivity profiles from the PBL model are then used in the solution of a three-dimensional advection diffusion equation for the dispersal of nonreactive pollutants in the atmosphere. The results indicate that it is possible to select stack heights to ensure maximum dilution of a pollutant immediately on release and thereby minimize its long-range transport.

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Swati Basu, G. R. Iyengar, and A. K. Mitra

Abstract

The impact of two parameterization schemes for the atmospheric boundary layer in predicting monsoon circulation over the Indian region has been studied using a Global Spectral Model. The performance of the nonlocal closure scheme for the boundary layer has been tested in the operational global model of the National Centre for Medium Range Weather Forecasting (NCMRWF) for its possible implementation and operational use. Keeping the parameterization schemes for all other physical processes the same, the performance of the nonlocal closure scheme is studied and compared with the performance of the operational local closure scheme of the boundary layer processes. Incorporation of the nonlocal closure scheme shows marginal impact in the prediction of the flow pattern. However, systematic improvement in the precipitation distribution over the Indian region is seen with the incorporation of a nonlocal closure scheme during the month of August 1999. Location of the precipitation maximum along the west coast of the southern peninsula is better predicted. The skill score for predicting areas of higher precipitation is increased with the nonlocal closure scheme. The systematic errors of the model are also reduced with the inclusion of the nonlocal closure scheme. An efficient transport mechanism in the vertical associated with the nonlocal closure scheme could be one of the main reasons for the better performance.

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