Information on lightning can be obtained from the electromagnetic waves that it emits. These waves can be detected with the help of antennas. MeteoSwiss obtains its data on lightning strikes from the company Météorage, which operates its own antennas network.

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 lightning strike is recorded via various antennas. 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 antennas. 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 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. Cloud-to-cloud lightning is also detected, and the method used for this captures up to 70% of these strikes.

MeteoSwiss receives the following parameters from the company Météorage for each lightning event:

• Time of strike to a high level of precision
• 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/intracloud)
• Shape and size of the ellipse that can be said to contain the location of the strike with a 50-percent level of confidence

MeteoSwiss creates various products on the basis of this information (e.g. lightning density maps). Lightning strikes are calculated for all automatic monitoring stations (SwissMetNet) within a radius of 3 kilometres (local strikes around the monitoring station) and 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.