What Is the Kp Index?
A simple guide to the number that drives every aurora forecast.
Current Kp Index
0.67
Quiet
The Kp index is a global measure of geomagnetic activity on a scale from 0 to 9. The higher the number, the further from the poles the aurora can be seen.
Recent Kp Activity
The Kp Scale, Level by Level
0
Very quiet. Aurora confined to the highest latitudes.
1
Quiet. Faint aurora possible directly under the oval.
2
Quiet. Aurora visible from far-northern locations.
3
Unsettled. Aurora reaches places like Tromsø and Fairbanks.
4
Active. Aurora brightens and moves equatorward.
5
G1 Minor storm. Visible from the northern tier of the US.
6
G2 Moderate storm. Visible from mid-northern latitudes.
7
G3 Strong storm. Aurora seen well into mid-latitudes.
8
G4 Severe storm. Visible from much of the continental US.
9
G5 Extreme storm. Aurora possible at unusually low latitudes.
Why the Kp Index Matters for Aurora
The aurora forms in an oval around each magnetic pole. When the Kp index rises, that oval expands toward the equator, bringing the aurora into view for people at lower latitudes. A location far north may see aurora at Kp 2, while somewhere further south might need Kp 6 or higher.
The Kp index is calculated every three hours from a network of magnetometers around the world. Aurora Calculator combines this with NOAA's OVATION model to estimate viewing chances for specific cities.
Source: NOAA SWPC · Updated every few minutes