Sensitivity Analysis of Atmospheric Dispersion Simulations by FLEXPART to the WRF-Simulated Meteorological Predictions in a Coastal Environment

In this study the sensitivity of the atmospheric dispersion model FLEXPART-WRF to the meteorological data inputs simulated by the mesoscale model ARW in the Kalpakkam coastal environment is examined. High-resolution simulations are conducted with ARW using four alternative planetary boundary layer parameterizations (YSU, MYNN, ACM2 and BL) for a typical period 14–22 Sep 2010 characterized with wide variability in atmospheric flow conditions at the coastal site. Observations generated through a field meteorological experiment are used to study the model sensitivity. Wind field, mixed layer depth, temperature and friction velocity are considered as parameters to evaluate dispersion uncertainty from FLEXPART. Results indicate that the simulated dispersion patterns are influenced by meteorological model forecasts using various boundary layer physics options. It has been found that the ensemble mean of all the meteorological members is closer to the observations than the individual cases. Of the various members the YSU and MYNN are found to give best meteorological simulations in the ensemble. The computed dispersion with various meteorological members indicate that ACM2 and BL simulate highest and least diffusivities leading to widely spread plume in the case of ACM2 and relatively narrow plume with BL, respectively. The ensemble mean of all the simulations is found to yield a better representation of the plume under various possible atmospheric conditions. The meteorological members YSU and MYNN are found to give minimum variance and fractional bias with respect to the ensemble. The minimum uncertainty in tracer concentration estimates due to meteorological uncertainty is −30 to 30 % obtained with MYNN. The results demonstrate that the dispersion model results are sensitive to the mesoscale model meteorological simulations.