Abstract :
In a synoptic-scale atmospheric model, winds and subgrid-scale momentum fluxes are influenced by the properties of
the underlying surface. Parametrization schemes have been developed to describe the interactions of the air flow with the
rough surface and small- and mesoscale orography. The schemes interact with each other and with the model’s dynamical
processes. Newparametrizations were introduced to the High Resolution Limited Area Model (HIRLAM), to account for
the subgrid-scale orography effects. Needed orography parameters were derived from a high-resolution digital elevation
data set. A detailed analysis of the momentum fluxes and kinetic energy budget helped to understand the interactions
between parametrizations. Mean and root mean square error, averaged over all observations and forecasts, did not
reveal significant differences between the updated and reference model results. However, more detailed diagnosis of the
forecast-observation differences allowed to show that the new parametrizations of mesoscale and small-scale orography
lead to more realistic low-level wind distribution.
