WG 1 : Meteorological parametrization / applications
 
    Leader: Dr  Maria Athanassiadou, Met Office, UK

WG 2: Integrated systems of MetM and CTM: strategy, interfaces and module unification

    Leader: Dr Alexander Baklanov, DMI

WG 3: Mesoscale models for air pollution and dispersion applications

    Leader: Dr Mikhail Sofiev, FMI

WG 4: Development of evaluation tools and methodologies

    Leader: Prof. Dr. Heinke Schluenzen, University of Hamburg
 

All mesoscale models have to simplify the effects of a variety of atmospheric processes through parametrization.  Typically, parametrization schemes have to simulate the effects of:

• Surface fluxes (and, as a result, some sub-surface processes such as heat, moisture and momentum transport)
• Aggregation of these fluxes
• Atmospheric radiation
• Cloud processes including cloud and precipitation microphysics
• Sub-grid flows such as turbulence within and outside the boundary layer, shallow and deep convection and gravity waves.

Many individual schemes have been developed to treat these processes, usually with reference to detailed experimental results from the field and/or using highly detailed reference models (such as Large Eddy Simulation), but compromises must always be made between cost and accuracy. In many real mesoscale flows, furthermore, the interaction between these processes may be of considerable importance, so it is often not sufficient to test individual components.

Different modelling philosophies exist. Some models use a single set of parametrizations, perhaps with small variations of parameters allowed, which may have been carefully tuned to work well together in the applications envisaged. In contrast, other models provide a wide variety of alternatives, with the advantage that different selections may work well in different circumstances, and the disadvantage that a great deal of work is required to establish which options work well together, and none have been
especially designed to work in combination.

Similarly, some approaches are simpler than others, in the sense that they require fewer prognostic equations to describe the atmosphere, though added complexity, and with it, added degrees of freedom and additional parameters, does not guarantee added accuracy. Furthermore, physical parametrizations have to be coupled to numerical solutions of atmospheric dynamics; both the nature of the coupling and the dynamics can have a significant impact on performance.

The overall aim of WG1 will be to provide a framework within which the state of the art of physical parametrization in mesoscale models can be advanced, with particular application to air pollution and dispersion applications. The integration of modules will be considered within WG2 and the performance of models as a whole will be covered in WG4; WG1 will cover purely the individual physical parametrizations and their interactions.

 Details are given in the memorandum of understanding