How strongly Earth's magnetic field is currently being disturbed.
The Disturbance Storm Time index measures geomagnetic storm severity in nanoTeslas, from the average horizontal magnetic field at four near-equatorial observatories, hourly. It tracks the growth and recovery of the ring current in Earth's magnetosphere — the lower the value, the more energy is stored there. Below −50 nT indicates a moderate storm, below −100 nT a severe one. The chart compares observations against the model's predictions.
The Kp index is a geomagnetic activity index derived from magnetometers around the world, measured every three hours. It is quasi-logarithmic from 0 to 9, where 5 indicates a moderate storm, 7 a severe storm, and 9 an extreme storm.