Formulation of TKE based empirical diffusivity relations from turbulence measurements and incorporation in a Lagrangian particle dispersion model

Abstract

In this paper a turbulence kinetic energy (TKE) based empirical formulation for turbulent diffusion is developed from ultra sonic anemometer measurements at a tropical coastal site Kalpakkam situated on the southeast coast of India. The diffusivity relationship is validated against an independent observation from SODAR. This formulation for turbulent diffusion is incorporated in a particle trajectory model FLEXPART-WRF. Under this formulation the turbulent component of the motion of pseudo particles in the model can be related to the TKE. Two case studies of dispersion simulation are carried out by incorporating the new relationship in FLEXPART-WRF. In the first case the simulated plume spread is compared against a real smoke plume from an accidental oil tank fire obtained from satellite image (MODIS-TERRA). In the second case, observed plume in the Hanford tracer experiment is simulated and normalized concentration profiles at different arcs are compared with that of the simulation. Results demonstrate that the simulated TKE using Mellor–Yamada–Nakanishi–Niino scheme in the Weather Research & Forecasting along with the new relationships for TKE apportionment simulate the dispersion pattern better than the Hanna scheme based on surface layer parameterization.