Live Kp Index & Geomagnetic Storm Scale

The number in the box is the planetary K index: one figure, 0 to 9, for how disturbed Earth's magnetic field has been over the last three hours. It is built from a network of magnetometer observatories spread around the world. Each one records how far the horizontal field wandered from its quiet-day baseline during the window, that deviation becomes a local K value, and the weighted average across the network is Kp. The scale is quasi-logarithmic, so the step from 7 to 8 covers far more disturbance than the step from 1 to 2.

Kp is a measurement, not a forecast. The three-hour window has to close before the value exists, so what you are reading describes what the magnetosphere already did rather than what it is about to do. For warning you have to look upstream, at the solar wind arriving at L1, which leads the ground response by roughly fifteen to sixty minutes depending on how fast the plasma is moving. This page re-reads the feed every five minutes, but a new planetary value only appears every three hours.

The word planetary is the part that misleads people. Kp is an average, and a single observatory can be far more disturbed than the planetary figure suggests. A substorm can light up one band of longitudes for twenty minutes while Kp sits at 4, which is why the aurora sometimes appears on a night the index called unremarkable — and why a high Kp is no promise that your own patch of sky is active. The scale also runs out at the top: once a storm is deep into 9, Kp has nothing left to say about how much worse it is getting.

From Kp 5 upward NOAA labels the disturbance on the G-scale, and that is the label with operational meaning: grid operators watch it for geomagnetically induced currents, HF radio operators for absorption at high latitudes, satellite operators for drag and surface charging. Below 5 there is no G number at all. For what a given reading means for a night outdoors, the aurora forecast turns it into a viewline, and the flare monitor covers what the Sun is doing to cause it.

The geomagnetic storm scale

G5 Extreme — Kp 9

Power grids can experience voltage collapse, satellites lose orientation control, and HF radio is out for days in places.

G4 Severe — Kp 8

Grid operators see widespread voltage control problems, spacecraft charging rises, and HF radio is intermittent for hours.

G3 Strong — Kp 7

Surface charging on satellites, drag increases on low orbits, and HF radio is unreliable at high latitudes.

G2 Moderate — Kp 6

High-latitude power systems can see alarms, and HF radio fades at higher latitudes.

G1 Minor — Kp 5

Minor grid fluctuations, small effects on satellite operations, and aurora visible from the far north of the US.

Active — Kp 4

Active but below storm level. Aurora stays near the polar regions, though a substorm can briefly push it further south.

Unsettled — Kp 3

The field is stirring without reaching storm level. Worth watching if you are already far north.

Quiet — Kp 0–2

No geomagnetic storm. Aurora is confined to the auroral oval over the high Arctic.