What is the KP Index?
The KP index (from the German Planetarische Kennziffer) is a measure of global geomagnetic activity on a scale of 0 to 9. It was developed by Julius Bartels in 1939 and is now the international standard used by space weather agencies worldwide.
Geomagnetic activity is caused by solar wind — the constant stream of charged particles flowing from the Sun. When the solar wind is fast or carries a southward-pointing magnetic field (negative Bz), it interacts with Earth's magnetosphere and drives electrical currents in the upper atmosphere. Those currents produce the aurora borealis.
KP is derived every 3 hours from magnetometer readings at 13 ground stations around the world. Values below 5 are considered "quiet" to "active"; values of 5 or above represent geomagnetic storms.
KP Scale — Aurora Visibility by Level
The auroral oval expands equatorward as KP rises. Higher KP = aurora visible at lower latitudes.
Only visible at very high latitudes like Svalbard or northern Alaska. Faint arc on the horizon.
Visible in Tromsø, Rovaniemi, Fairbanks on clear nights. Faint to moderate display.
Good display visible in Iceland, northern Scotland. Active curtains and rays.
Northern lights visible in southern Scandinavia, Canada, northern USA. Bright and dynamic.
Overhead aurora in Scandinavia. Visible in central Europe and northern states of the USA.
Rare event. Aurora visible across much of Europe and the continental USA. Dramatic colours.
Exceptionally rare. Aurora can reach the Mediterranean and southern USA. Once-in-a-decade event.
Bz — The Secret Factor
KP alone doesn't tell the whole story. The Bz component of the interplanetary magnetic field (IMF) is equally critical. Bz is the north-south orientation of the magnetic field carried by solar wind.
Solar wind couples strongly with Earth's field. Energy flows into magnetosphere. Aurora intensifies. Bz < -10 nT is excellent.
Solar wind is deflected. Even a high KP can produce weak aurora if Bz is strongly positive. Watch Bz alongside KP.
AuroraVision shows live Bz on the forecast page and factors it into the visibility score.
Frequently Asked Questions
What is the KP index?
KP (Planetarische Kennziffer — German for "planetary index") is a global measure of geomagnetic disturbance caused by solar wind activity. It runs from 0 (completely quiet) to 9 (extreme geomagnetic storm). Higher KP = more widespread and intense aurora.
Who measures the KP index?
NOAA's Space Weather Prediction Center (SWPC) derives KP from magnetometer readings at 13 ground stations worldwide. It is updated every 3 hours with a 15-minute delay. AuroraVision uses NOAA SWPC real-time data updated every 2 minutes.
What KP do I need to see the aurora in Iceland?
Iceland sits at 64–66°N latitude. A KP of 3–4 is usually enough to see aurora from Iceland on a clear night. Higher KP produces more dramatic, overhead displays. KP 2 can show faint aurora far from city lights.
What KP do I need to see aurora in Norway / Tromsø?
Tromsø is at 69.6°N — inside the auroral oval. KP 2 or even KP 1 can produce visible aurora there. This is why Tromsø is one of the world's best aurora destinations.
Is KP the only factor in aurora visibility?
No. Cloud cover, light pollution and the Bz component of the interplanetary magnetic field all matter. AuroraVision combines KP + local cloud cover + solar wind Bz into a single 0–100 visibility score.