Improved Turbulence Parameterization
Turbulence parameterization in mesoscale wind field models such as MM5 and WRF are usually based on a scheme developed by Mellor and Yamada in 1982. This system of equations is under-determined. Therefore, a set of empirical numbers (which are considered as constants today) is needed to close this system. The present values of these empirical numbers, which are still quite close to those suggested by Mellor and Yamada, lead, e.g., to an underestimation of the turbulence intensity in wind field simulations.
Recent accurate measurements with enhanced instruments allow for revisiting the determination of these empirical numbers. This leads partly to considerably changed values for these numbers. Test simulations with WRF show that turbulence intensity is estimated much better when the new values are used. This issue is presently investigated in a PhD study which is to be finalized by the end of 2011.