Dst Index
Definition
An hourly index measuring geomagnetic storm strength via the ring current circling Earth.
In plain language
During storms, a huge electric current loops around the planet and weakens the surface magnetic field near the equator. Dst measures that dip — the deeper the negative number, the bigger the storm.
The science
Dst averages low-latitude magnetometer deviations, dominated by ring current intensity. Moderate storms reach −50 to −100 nT; superstorms exceed −250 nT. The 1859 Carrington Event is estimated near −900 nT or beyond.
Why it matters for aurora viewing
Dst is the scientist's storm ruler — useful for ranking events and reading storm phase, less so for tonight's go/no-go call.
See this in action on tonight's data.