Dispersion processes and parameterizations

Understanding and predicting the processes by which airborne pollutants and aerosols are transported in the atmosphere is important for a range of problems from local to global scales.  The Met Office's Numerical Atmospheric-dispersion Modelling Environment (Met Office Dispersion Model) is a sophisticated tool capable of simulating many atmospheric dispersion phenomena and associated physical and chemical processes.
 
The Met Office has a long history of research into, and providing advice on, the atmospheric transport and dispersion of contaminants, which extends back to the First World War. During the 1960's with the advent of computers the Met Office was at the forefront in developing the first simple dispersion computer models. However, it was the Chernobyl incident in 1986 that triggered the start of the development around the world of sophisticated atmospheric dispersion models. From this the Met Office Numerical Atmospheric-dispersion Modelling Environment (NAME) was born and became fully operational in 1993.

Over the following years the model has been developed with appropriate functionality for it to be utilised for emergency response activities, air quality applications, impact assessment, source attribution and research. The latest version of the model includes a three dimensional representation of the atmosphere and parameterizes a wide range of physical processes such as radioactive decay, dry and wet deposition and deep convective mixing.  The model has a capability to give statistical predictions, using both meteorological ensembles for large scale uncertainties, and parameterizations of turbulent fluctuations for small-scale variability.  Coded in a modular approach it is capable of using embedded sub-models for representing modifications to the flow caused by, for example, small scale terrain or building effects as well as having others added.  The model is generally driven by data from numerical weather prediction models such as the Met Office's Unified Model, but can also utilise single site met observations for short range dispersion.  Recent advances include substantial improvements to the treatment of deposition and sedimentation, the addition of an Eulerian sub-model, and substantial improvements in efficiency through redesign of the way meteorology is loaded into the model and through parallel processing and code optimisation.

Maintaining this leading capability for dispersion modelling and ensuring that the model benefits from the latest scientific and technical advances is the responsibility of the Dispersion Processes and Parameterizations group.

Key aims

• To carry out research in the field of atmospheric dispersion.
• To develop and improve NAME.

Current projects

• MPI parallelisation of NAME.
• Improvements to the representation of effects of urban environments on dispersing plumes within NAME.
• Modelling of volcanic umbrella clouds within NAME.
• Ongoing validation of NAME against tracer experiments.
• Scientific collaboration and developments with a number of UK universities (e.g. Reading, Imperial College, Cambridge).
• Research on concentration fluctuations and buoyancy-driven flows.