MeteoSwiss receives lightning localisation data to enable it to accurately record lightning. This data provides information on the time, location and intensity of the lightning, among other details. MeteoSwiss creates thunderstorm maps on this basis and, where necessary, issues warnings.
Lightning detection network
Information on lighting can be obtained from the electromagnetic waves that it emits. These waves can be detected with the help of antennae. MeteoSwiss obtains its data on lightning strikes from the company Météorage, which operates its own antennae network. Météorage is part of the European Cooperation for Lightning Detection (EUCLID), which coordinates the distribution of lightning data across Europe.
How the locations of lightning strikes are determined
The exact location of a lightning strike is determined as part of a combined process. Each individual lighting strike is recorded via various antennae. The location of the strike can be determined by means of triangulation; this is based on the different impact angles which are measured by the antennae. Each antenna also ascertains the precise time at which the electromagnetic wave reaches it. By comparing these times, the coordinates of the lightning flash can be calculated. It is usually possible to specify the location of the strike to within a distance of around 1,000 metres. The level of precision is largely independent of the local topography. Lightning strikes in mountain regions can be pinpointed just as well as in lowland areas.
Available lightning data
On average, 95% of cloud-to-ground lightning is observed using this method. While cloud-to-cloud lightning is also detected, the method used here only captures around 45% of these strikes. MeteoSwiss receives the following parameters from the company Météorage for each lightning event:
- Time of the strike with accuracy to one tenth of a second
- Longitude and latitude of the location of the strike
- Polarity and intensity of the lightning
- Number of main flashes (strokes)
- Type of lightning (cloud-to-ground or cloud-to-cloud lightning)
- Shape and size of the ellipse that can be said to contain the location of the strike with a 90% level of confidence
MeteoSwiss creates various products on the basis of this information (e.g. thunderstorm maps). For all automatic monitoring stations (SwissMetNet), lightning strikes are detected within a radius of 3 kilometres (local strikes) and of between 3 and 30 kilometres (distant strikes). These readings are used to calculate various totals (number of lightning strikes every ten minutes, hour, month and year) as well as peak values.