Every weekday we provide a forecast of geomagnetic activity for the next three days starting at midday. We forecast the average activity level for the whole 24 hours and the maximum level, which is the peak expected level of activity at any point during the 24 hours. These forecasts are provided in terms of categories of geomagnetic activity, as explained below.
At BGS we group geomagnetic activity into categories to be able to quickly and clearly communicate the range of geomagnetic activity expected.
From January 2014 we have changed the way we classify geomagnetic activity. See the table below for a comparison between the old and new categories along with the NOAA space Weather Scale for Geomagnetic Storms.
The Kp index provides a measure of the planetary geomagnetic activity ranging from 0 to 9. It is derived for each 3-hour interval from the K-indices at 13 geomagnetic observatories around the globe located at northern and southern latitudes between around 35° and 60°. The K-index is a quasi-logarithmic scale from 0 to 9, specific to each observatory, which indicates the range of geomagnetic activity within each 3 hour interval.
|Kp||BGS categories pre 2014||BGS categories since 2014||NOAA G-scales|
|<3+||QUIET-UNSETTLED||Kp < 3+||QUIET||Kp < 3+|
|3+||ACTIVE||3+ < Kp < 5-||ACTIVE||3+ < Kp < 5-|
|5-||MINOR STORM||5- < Kp < 6-||STORM G1||5- < Kp < 5+||G1||Kp = 5|
|6-||MAJOR STORM||6- < Kp < 8-||STORM G2||6- < Kp < 6+||G2||Kp = 6|
|7-||STORM G3||7- < Kp < 7+||G3||Kp = 7|
|8-||SEVERE STORM||Kp > 8-||STORM G4||8- < Kp < 9-||G4||Kp = 8|
|9o||STORM G5||Kp = 9o||G5||Kp = 9|