Meteorology for nuclear accidents

MeteoSwiss operates the CN-MET wind analysis and forecasting system for nuclear incidents in Switzerland and neighbouring countries. It comprises a monitoring network that has been optimised for this specific purpose, along with the COSMO-1 weather forecasting model. This combination of measurements and the COSMO-2 model provides an important basis for the provision of emergency management in Switzerland.

In close cooperation with the Federal Nuclear Safety Inspectorate (ENSI), MeteoSwiss has developed the CN-MET (Centrale Nucléaire et METéorologie) wind analysis and forecasting system, which began operating at the end of 2009. This system includes a large number of special measuring devices as well as the COSMO-1 weather forecasting model. The combination of precise measurements and high-resolution model forecasts makes it possible to determine wind fields and weather developments around Switzerland's nuclear power stations and those in neighbouring countries and thus to calculate the dispersion of contaminated air masses. Both the ENSI and the National Emergency Operations Centre (NAZ) use the information to assess the current situation. On this basis, the NAZ is able to take measures to protect the population.

Special measuring devices

Bilder eines Windprofilers und eines Temperatur- und Feuchte-Radiometers.
Wind profilers (left) and temperature radiometers (right), which continually measure vertical profiles for wind, temperature and humidity

MeteoSwiss has developed a specific monitoring network for the CN-MET system. It measures the atmospheric properties above the Swiss Plateau in detail, in particular in the direct vicinity of the Swiss nuclear power plants. The monitoring network comprises three different monitoring systems.

  • At the sites in Schaffhausen, Payerne, and Grenchen, remote sensing instruments – wind profilers and temperature radiometers – continually measure the wind, temperature, and humidity from the ground up to an altitude of several kilometres. The wind profiler is a radar which measures the radial velocities along beams pointing in the vertical and four near-vertical directions. On this basis, the horizontal wind speed for all altitudes up to 8 kilometres above the ground can be calculated. The temperature radiometers derive the temperature from the intensity of the atmosphere's natural microwave radiation.
  • High telecommunications towers stretching 100 to 250 metres above the ground and equipped with meteorological measuring devices are situated on the peaks of the Üetliberg, St. Chrischona, Bantiger, and Stockeren.
  • At the nuclear power plant sites, MeteoSwiss also measures turbulence in addition to the usual SwissMetNet parameters.

This special monitoring network is supplemented by the ground-level monitoring network of MeteoSwiss SwissMetNet, which comprehensively records the meteorological parameters close to the ground.

Dispersion calculations with the COSMO-1 forecasting model

The measurements taken by the three wind profilers and by SwissMetNet are fed into the MeteoSwiss local weather forecasting model, COSMO-1. On a grid network with a horizontal grid box size of 1.1 kilometres, the model calculates the weather developments for the coming 33 hours in the Alpine region every three hours. 

The high-resolution wind and precipitation fields of COSMO-1 enable the forecasting of the dispersion of contaminated air masses as well as the washing out and deposition of radioactive substances. MeteoSwiss provides delay-free forecasts for wind and precipitation as well as other meteorological parameters to the Federal Nuclear Safety Inspectorate (ENSI) and dispersion calculations to the National Emergency Operations Centre (NAZ). In parallel to this and working on the basis of the relevant measurements and dispersion calculations, the MeteoSwiss meteorologists is responsible for providing both institutions with advice regarding the current weather situation and further meteorological developments in the event of a nuclear accident.

NADAM: Automatic Dose Alarm and Monitoring Network

In addition to the CN-MET system, MeteoSwiss also operates the NADAM monitoring network on behalf of the National Emergency Operations Centre (NAZ). More than 60 automated meteorological stations are equipped with special sensors which measure the level of radioactive radiation (local dose rate). Together with the precipitation data, the local snow depths and other meteorological parameters, MeteoSwiss transmits the NADAM data to the NAZ every ten minutes. If a specific threshold is exceeded (1 micro-Sv/h), an automatic alarm is triggered at the NAZ.

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