Hunt mode — Lyngenfjord · Beach

A magnetometer measures the Earth’s magnetic field. When a substorm surges the electric current that runs about 100 km up along the auroral oval, the field on the ground beneath it drops by hundreds of nanotesla (nT) within minutes — the sharp dip a magnetogram shows.

This reads the nearest of the Finnish Meteorological Institute’s eight magnetometers, Kilpisjärvi, against its own last 24 hours: 150 nT either way is active, a 300 nT drop a substorm, 600 a strong one. It measures the sky over the station — up to about 300 km away it still speaks for yours — and says nothing about cloud. Kp and Hp30 are planetary; this is local, and minutes old.