the numerics of physical parametrization in the ecmwf model

The numerical aspects of physical parametrization are discussed mainly in the context of the ECMWF Integrated Forecasting System. Two time integration techniques are discussed. With parallel splitting the tendencies of all the parametrized processes are computed independently of each other. With sequential splitting, tendencies of the explicit processes are computed first and are used as input to the subsequent implicit fast process. It is argued that sequential splitting is better than parallel splitting for problems with multiple time scales, because a balance between processes is obtained during the time integration. It is shown that sequential splitting applied to boundary layer diffusion in the ECMWF model leads to much smaller time truncation errors than does parallel splitting. The so called Semi-Lagrangian Averaging of Physical Parametrizations (SLAVEPP), as implemented in the ECMWF model, is explained. The scheme reduces time truncation errors compared to standard first order methods, although a few implementation questions remain. In the scheme fast and slow processes are handled differently and it remains a research topic to find the optimal way of handling convection and clouds. Process specific numerical issues are discussed in the context of the ECMWF parametrization package. Examples are the non-linear stability problems in the vertical diffusion scheme, the stability related mass flux limit in the convection scheme and the fast processes in the cloud microphysics. Vertical resolution in the land surface scheme is inspired by the requirement to represent diurnal to annual time scales. Finally, a new coupling strategy between atmospheric models and land surface schemes is discussed. It allows for fully implicit coupling also for tiled land surface schemes

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Face à ces questions sensibles pour l’avenir du Grand Paris, les 15 équipes pluridisciplinaires, d’architectes, d’urbanistes et de chercheurs qui composent le Conseil scientifique de l’Atelier International du Grand Paris, présentent les résultats de leur recherches, leurs analyses et leurs propositions. Ces réflexions, qui donneront lieu à la parution d’un livre, constituent autant d’éclairages pour répondre aux enjeux métropolitains et aux défis quantitatifs et qualitatifs de l’évolution du logement et des modes d’habiter dans le Grand Paris. > du 1er au 7 juillet : Une exposition organisée autour de films courts réalisés par les quinze équipes de l’AIGPainsi qu’autour de parcours de trois photographes de l’agence Magnum dans le Grand Paris : Patrick Zachmann, Marc Power et Olivia Arthur. • La restitution d’ateliers participatifs organisés par des équipes de l’AIGP sur des territoires du Grand Paris