Verification of the meteorological pre–processor MEPDIM

The Norwegian Institute for Air Research (NILU) has carried out a year of direct measurements of standard deviations of wind fluctuations (σv and σw) on an island off the west coast of Norway. These measurements have been used for the evaluation of estimated values based on the meteorological pre–processor MEPDIM. The physical basis for this metprocessor is provided by parameterisation of the structure of the atmospheric boundary layer, including interaction with the surface. The statistical evaluation of estimated versus observed turbulence parameters gave best results of stable atmospheric conditions, with correlation values of 0.91 and 0.92 for σv and σw, respectively. σw was overestimated, because stable atmospheric conditions restrict the development of vertical turbulent motions in the atmospheric boundary layer over the island. For unstable atmospheric conditions, both σv and σw were overestimated. This can be explained by the location of the measurements on an island, where the development of a convective boundary layer is limited compared with inland conditions. For the specific measurement site, modified equations have been proposed in order to reduce the effect of the convective turbulence for unstable atmospheric conditions and reduce the overprediction of σw for stable atmospheric conditions. After this modification, a linear regression close to σest=σobs was obtained for stable conditions. For unstable conditions, improvements were achieved for the linear regression. However, the constants are still high, which implies that improved empirical equations should be applied to this area for unstable atmospheric conditions.