Multiscale Eulerian member of NCEP's National Environmental Modeling System

The unified Non-hydrostatic Multi-scale Model on the B grid (NMMB) is being developed at NCEP within the National Environmental Modeling System (NEMS). The finite-volume horizontal differencing employed in the model preserves important properties of differential operators and conserves a variety of basic and derived dynamical and quadratic quantities. Among these, conservation of energy and enstrophy improves the accuracy of nonlinear dynamics of the model. The nonhydrostatic dynamics were formulated in such a way as to avoid overspecification. In the global limit, “across the pole” polar boundary conditions are used, and the polar filter selectively slows down the wave components of the basic dynamical variables that would otherwise propagate faster in the zonal direction than the fastest wave propagating in the meridional direction.

A global forecasting system based on the NMMB was set up and run for more than a year in order to test and tune it, and in particular, to examine its potential for medium range weather forecasting. The system was initialized and verified using the analyses of NCEP's Global Forecasting System (GFS). The overall global skill of the large scale medium range forecasts produced by the system has been comparable to that of other major medium range forecasting systems. The computational efficiency of the model on parallel computers has been quite satisfactory and competitive with that of other major systems. Interestingly, even though the NMMB and GFS were starting from the same analyses, the skill of individual medium range forecasts was often disparate. When one model produced a bad forecast, the forecast from the other model could be quite good. Such behavior appears potentially advantageous for application of the two models for ensemble forecasting.

Within efforts to upgrade the physical package of the model on the mesoscales, a new approach is being investigated concerning the problem of shallow cloud topped marine boundary layers. The problem of application of moist convection parameterization with single digit resolutions also has been addressed within the context of the BMJ adjustment scheme by reducing deficit saturation pressures.