Gertie Geertsema
In cases of environmental disasters caused by e.g. emission of toxic gases or radioactive material, KNMI activates a special calamity service. For this purpose, a group of seven calamity meteorologists is on call every moment of the day. KNMI's role to supply weather information during emergencies is included in municipal and provincial disaster management plans. Civil services, fire departments and the police can be provided with weather information directly by the calamity meteorologist on duty, through a dedicated telephone connection.
Whenever a disaster occurs within Europe which causes the release of toxic material into the atmosphere, it is of utmost importance to determine as soon as possible where this material is headed to. Computer models have been developed to calculate the dispersion of toxic gases.
PUFF is run on an operational workstation. The model has been tested initially using measurements of the dispersion of radioactivity caused by the accident in the nuclear power plant of Chernobyl in 1986. A few years later, in 1994, a dedicated dispersion experiment called ETEX (European Tracer EXperiment) was carried out, which has provided many useful data for the testing of PUFF and other European dispersion models.
Maintaining a disaster management organisation is always a difficult task: such an organisation is rarely needed, but when a disaster does occur, it is of the greatest importance to act accurately and promptly. The ETEX experiments provided a unique opportunity to test disaster managemnt organisations in a most realistic manner. They also showed that European dispersion models were far from perfect, and that further research was necessary. Therefore it was decided to continue the ETEX collaboration within an international follow-up experiment, RTMOD (real time modelling), in which long distance dispersion models have been intercompared. RTMOD, finished in the beginning of 2000, in its turn was succeeded by the European concerted action ENSEMBLE ("Methods to Reconcile Disparate National Forecasts of Medium and Long Range Forecasts"). Within ENSEMBLE, the predictions of various dispersion models are compared to one another. An internet-based system has been set up to present the analyses of and differences between the available models in a concise manner.A list of the participating institues can be found on the ENSEMBLE home page .
The physics contained in the CALM model is practically identical to that of the PUFF model. The meteorological input, however, is supplied only manually in CALM. The forecaster provides both observed and predicted vales for wind at 10m level, the atmospheric stability and the mixing height.
The model requests input data from the meteorologist, then draws a map of the Netherlands indicating the position of the source, and requests a weather forecast for that position at the time of issue. Using these data, the new position of the toxic cloud at 10m height is calculated. In the background, the trajectory of the cloud center of mass is kept up to date. After the model calculations have been performed, a map is shown with the derived trajectories and an indication of how and where to the cloud will disperse.
More information on the ETEX experiment
More information on the European "concerted action" ENSEMBLE via the ENSEMBLE homepage.