The Kp index is a number from 0 to 9 that measures how disturbed Earth's magnetic field is at a given time, published by space weather agencies including NOAA's Space Weather Prediction Center.
Where it comes from
Kp is derived from measurements at a global network of ground-based magnetometers. Every 3 hours, those readings are combined into a single planetary value — hence "planetary Kp index" — that reflects geomagnetic activity worldwide rather than at one specific location.
What the scale means
- Kp 0-3: Quiet to unsettled. Normal background geomagnetic activity.
- Kp 4: Active. Minor disturbance, generally no operational impact for most users.
- Kp 5-6: Minor to moderate geomagnetic storm (G1-G2 on NOAA's storm scale).
- Kp 7-9: Strong to extreme geomagnetic storm (G3-G5), associated with major solar events.
Why it's published in real time
Kp is driven by solar activity — coronal mass ejections and high-speed solar wind streams interacting with Earth's magnetosphere — which can spike within hours. NOAA updates the planetary Kp index roughly every few minutes to an hour depending on the product, giving anyone affected by geomagnetic conditions a near-current picture rather than yesterday's forecast.
Who tracks it and why
Beyond aurora chasers, Kp is monitored by satellite operators, power grid operators, HF radio users, and — relevant here — drone pilots, because elevated geomagnetic activity can degrade GPS positioning accuracy exactly when precise navigation matters most.