K-index and Kp-index of Geomagnetic Activity

Recent G5 Extreme Geomagnetic Storm and sudden radio blackout in our region prompted me to learn more about geomagnetic activity. I have been seeing posts on Kp index on Twitter (X) profile of many of my amateur radio contacts. K-index measures the disturbance in the horizontal component of Earth’s magnetic field. K-index values range from 0-9 with 1 indicating calm while 5 or more indicates a geomagnetic storm. Geomagnetic storm is a disturbance in the Earth’s magnetosphere caused by solar wind particles, typically after a coronal mass ejection or CME from the sun. Geomagnetic storms have been graded according to the NOAA G-scale from G1 to G5, of which G1 is minor and G5 extreme. During the last G5 event, aurora was recorded from Ladakh, India at 34 degrees North latitude as well as from higher latitudes in North America.

K-index is derived from maximum fluctuation of horizontal component of Earth’s magnetic field as measured by a magnetomemeter during a three-hour interval. It may be noted that observatories at higher geomagnetic latitude require higher levels of fluctuation for a given K-index. Kp index or planetary Kp-index is derived by calculating a weighted average of K-indices from a network of global geomagnetic observatories at mid-latitude locations. NOAA Space Weather Prediction Center uses near real time data from ground based magnetometers that relay data. The relevant observatories are located in United States, Canada, United Kingdom, Germany and Australia.