National Institute of Geophysics Geodesy and Geography

Planetary Kp Index is a measure of the Earth's magnetic field perturbation. It is given in relative units, which are ranged between 0 and 9, depending on the level of the field perturbation. The scale is shown above.

The Kp index value is determined by the geomagnetic data at 12 stations situated in the Northern and Southern hemisphere. The results are published after the end of the calendar month. There are methods for determining the approximate value of the Kp index, i.e. the Earth’s magnetic field perturbation at each current moment, which are designated for a release to the interested bodies and the society. The anomalies of the Earth's magnetic field are caused by the solar wind, i.e. streams of charged particles ejected from the Sun, which upon entering the Earth's atmosphere generate currents that cause variations of the Earth's magnetic field. Due to this fact it is possible to determine the degree of the Earth's magnetic field perturbation by the solar wind parameters. This problem can be solved through the availability of the current data provided by the geo-stationary satellite Advanced Composition Explorer (ACE) located outside the Earth’s atmosphere. A methodology developed by a scientific group from the Geophysical Institute - BAS is able to calculate an approximate estimate of the Kp index, called Kpm, by using the satellite data available every 15 minutes. This Kpm estimate is published automatically at the web site. The confidence interval for this value at 50% probability is 0.63. Additionally, the predicted Kpm values for the next six hours from the current time are published as well. The predicted value is calculated on the base of the geomagnetic activity behavior over the past two days by using the Wiener - Hopf method.