Service International des Indices Géomagnétiques
International Service of Geomagnetic Indices

Dst index

Dst time resolution: 1-hour (UT) interval
unit: nT
Available from 1957 onwards
Type of index Equatorial index horizontal component disturbances
Purpose To monitor the axis-symmetric magnetic signature of magnetosphere currents, including mainly the ring current, the tail currents and also the magnetopause Chapman-Ferraro current.
Network made of 4 low latitude stations
(see list of actual and previous Dst magnetic observatories)
Derivation Dst is computed (*) using 1-hour values from four low latitude observatories (sufficiently distant from the auroral and equatorial electrojets to inhibit noise from these two sources).

In each station, for each hour, local Dst values are computed using the following protocol:
   (i) contributions to horizontal field (H) from the background field (non-transient field of core and crustal origin) and the solar regular daily variation are subtracted from the observed value of H ;
   (ii) the so-obtained residual is normalized to the dipole equator.

For each 1-hour UT interval, the Dst index is the average of the local Dst hourly mean values at the four observatories.

It has to be noted that the Dst calculation requires good baseline control of the instruments from geomagnetic observatories.

(*) More specific and detailed information may be found on the WDC for Geomagnetism - Kyoto website devoted to Dst.
ISGI Collaborating Institute WDC for Geomagnetism - Kyoto, Japan
IAGA endorsed IAGA Bulletin 27, 1969, p. 123, resolution 2
Origin of name Name "Dst" came from "Disturbance storm-time"
Citation World Data Center for Geomagnetism, Kyoto, Nose M., Iyemori T., Sugiura M. and Kamei T. (2015) - Geomagnetic Dst index, IAGA Bull., 40, IUGG, Paris, DOI:10.17593/14515-74000.
Historical references • Sugiura, M. (1964) - Hourly values of equatorial Dst for the IGY, Ann. Int. Geophys. Year, 35, 9, Pergamon Press, Oxford. Get PDF (3860K)
• Sugiura, M., and T. Kamei (1991) - Equatorial Dst index 1957-1986, IAGA Bull., 40, IUGG, Paris. Get PDF (1487K)