Real-time Internal (Ist) and External (Est) Storm Time Indices
The Dst (Disturbance Storm Time) index is an index of geomagnetic activity derived from a global network of near-equatorial geomagnetic observatories that measures the intensity of magnetospheric “ring current”. The time varying magnetospheric fields induce electric currents in the Earth which in turn give rise to a secondary internal field whose strength is roughly one third of the external field. Hence, the observed Dst index is the sum of the external source field and its induced counterpart. If the Earth were an ideal conductor then the two fields would be exactly in phase. For the real Earth, however, the phase lag and amplitude relation between the induced internal and inducing external field depends on the frequency content of the external source field. Dst is separated into internal storm time index (Ist) and external storm time index (Est) following Maus & Weidelt (GRL, Vol. 31, 2004). The one-minute real-time disturbance storm time index (Dst) is driven by the real-time Dst index provided by the USGS magnetic observatory network. The conductivity model used is the semi-global reference model, Model B, by Utada, Koyama, Shimzu and Chave (GRL, Vol. 30, 2003). Dst, Ist and Est data are available from 2013-11-01.
***Warning. The real-time USGS Dst indices are corrupted due to San Juan observatory disturbance. The Est-Ist calculator should only be used for data prior to 2016-12-31. We apologize for your inconvenience***