Indices & Scales

A global index of geomagnetic activity, derived from magnetometer readings and reported every three hours on a scale of 0 (quiet) to 9 (extreme storm). Kp is the standard measure used to forecast auroras and satellite disturbances.

The Disturbance storm-time index, which tracks the strength of the equatorial ring current and so measures the intensity of a geomagnetic storm — the more negative the Dst, the stronger the storm.

NOAA's five-level scale for the severity of geomagnetic storms, from G1 (minor) to G5 (extreme), describing the expected effects on power grids, satellites, and navigation.

NOAA's five-level scale for solar radiation (energetic-particle) storms, from S1 to S5, describing the radiation hazard to astronauts, high-altitude flights, and spacecraft.

NOAA's five-level scale for radio blackouts caused by solar-flare X-rays ionising the dayside upper atmosphere, from R1 (minor) to R5 (extreme).