PARAMETRISATION

Some atmospheric processes are below the grid-scale/wavelength of operational meteorological computer models and cannot be handled explicitly by such schemes - for example individual showers, which are not only important for local weather, but have a feedback effect within the atmosphere that needs to be included in the NWP routines to maintain a realistic model of the real atmosphere. Larger scale model parameters (e.g. wind vector, temperature, humidity) are used to diagnose and represent the effects of such sub-gridscale processes: this is know as parametrisation.