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Ann. Geophys., 23, 2989-2995, 2005
www.ann-geophys.net/23/2989/2005/
© European Geosciences Union 2005
Predicting the occurrence of super-storms
N. Srivastava
Udaipur Solar Observatory, Physical Research Laboratory, P.O. Box 198, Udaipur, India
Abstract. A comparative study of five super-storms (Dst<-300 nT) of
the current solar cycle after the launch of SoHO, to identify
solar and interplanetary variables that influence the magnitude of
resulting geomagnetic storms, is described. Amongst solar
variables, the initial speed of a CME is considered the most
reliable predictor of the strength of the associated geomagnetic
storm because fast mass ejections are responsible for building up
the ram pressure at the Earth's magnetosphere. However, although
most of the super-storms studied were associated with high speed
CMEs, the Dst index of the resulting geomagnetic
storms varied between -300 to -472 nT. The most intense storm
of 20 November 2003, (Dst ~ -472 nT) had its source in
a comparatively smaller active region and was associated with a
relatively weaker, M-class flare while all other super-storms had
their origins in large active regions and were associated with
strong X-class flares. However, this superstorm did not show any
associated extraordinary solar and interplanetary characteristics.
The study also reveals the challenge in the reliable prediction of the
magnitude of a geomagnetic storm from solar and interplanetary
variables.
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