The term space weather refers to phenomena caused by solar wind and solar flares in the near-Earth space and the upper part of the Earth's atmosphere. Aurora borealis is the most visible form of space weather. Disturbances that can be measured on the Earth's surface also occur in the Earth's magnetic field in connection with auroras.

The bar chart shows the magnitude of these geomagnetic disturbances during 24 hours. The map shows latest observations at the locations of the observation stations. The value shown is the R-index, which measures the rate of change of the magnetic field within a 10-minute interval.

For each measuring station, there are two threshold values that describe how the probability of auroras increases. When the lower but not the upper threshold is crossed, auroras are possible, but they are usually dim. Then the bars in the diagram are coloured yellow and the markings on the map change to yellow squares.

When the upper threshold is exceeded, it is very likely that one can see auroras. Then the bars are coloured red and the markings on the map become red rhombuses.

The service is based on the measurements from the automatic magnetometer stations maintained by the Finnish Meteorological Institute. The measurements for Sodankylä are generated by the Sodankylä Geophysical Observatory of the University of Oulu. Images by all-sky cameras and other space weather products are available at our ISES RWC Finland website.

See also the press release Greater accuracy for aurora borealis service.