The Disturbance Storm Time Index

The Dst index is an index of magnetic activity derived from a network of near-equatorial geomagnetic observatories that measures the intensity of the globally symmetrical equatorial electrojet (the "ring current"). Dst is maintained at NGDC and is available via FTP from 1957 to the present.

Dst (Disturbance Storm Time) equivalent equatorial magnetic disturbance indices are derived from hourly scalings of low-latitude horizontal magnetic variation. They show the effect of the globally symmetrical westward flowing high altitude equatorial ring current, which causes the "main phase" depression worldwide in the H-component field during large magnetic storms. This diskette contains the hourly indices for the period 1 Jan 1957 through 30 Sep 1992, as derived by M. Sugiura and T. Kamei, WDC-C2 for Geomagnetism, Faculty of Science, Kyoto University, Kyoto 606, Japan.

Hourly H-component magnetic variations are analyzed to remove annual secular change trends from records of a worldwide array of low-latitude observatories. A cosine factor of the site latitude transforms residual variations to their equatorial equivalents and harmonic analysis isolates the term used as the Dst index. Sugiura described Dst derivation in ANNALS OF THE IGY.

To view data from the Dst Index, please visit the WDC Kyoto Observatory.