Dst Index

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.

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.

Dst is the scientist's storm ruler — useful for ranking events and reading storm phase, less so for tonight's go/no-go call.