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Tetsuro Tamura
Department of Environmental Science and Technology, Tokyo Institute of Technology 4259 Nagatsuta, Yokohama 226-8502, Japan

Kenichi Ohta
Department of Environmental Science and Technology, Tokyo Institute of Technology, G5-7, 4259 Nagatuda, Midori-ku, Yokohama 226-8502, Japan


This study discusses the characteristics of a plume dispersion in various types of thermally stratified stable turbulent boundary layers. Large eddy simulations (LES) of incompressible turbulent flows with the buoyancy effects based on the Boussinesq approximation are carried out for simulating atmospheric turbulent boundary layers. Concentration field inside a turbulent boundary layer, where gas is released from an elevated source point, is also obtained by using LES concept for a passive scalar. Dynamic procedure is used for estimation of Smagorinsky type of eddy viscosity model representing the sub-grid scale turbulent motions. LES results are validated by comparing with the previous experimental data or plotting plume spreading width in the Pasquill-Gifford diagrams. For modelling of stable boundary layers, we consider two kinds of temperature profiles whose inversion layers locate at the different heights according to the atmospheric stability or nocturnal time. Concentration fluctuations, especially peak values of concentration is focussed on, so we estimate a fitting of the computed time-sequential data with various probability distribution functions of concentration and statistically clarify the occurrence of peak concentration.