On the interpretation of the sudden commencement of geomagnetic storms

This article describes a method for recognizing sudden commencement events using digital differentiating filters. This method is applied to INTERMAGNET observatory data. Maximum amplitude derivatives for the magnetic components (X, Y, Z) and the total intensity (F) of the geomagnetic field are introduced, and the decision-making rule is formulated. The authors developed a procedure for selecting optimal digital differentiating filters. Estimates of probabilities of correct and false recognition of sudden commencements were obtained. The calculations of the probabilistic characteristics have confirmed the effectiveness of the method.

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The solar causes of major geomagnetic storms

Annales Geophysicae ◽

10.1007/s00585-994-0113-5 ◽

1994 ◽

Vol 12 (2/3) ◽

pp. 113-120 ◽

Cited By ~ 5

Author(s):

S. Bravo ◽

A. L. Rivera

Keyword(s):

Solar Wind ◽

Geomagnetic Storms ◽

Sudden Commencement ◽

Interplanetary Scintillation ◽

Solar Wind Disturbances

Abstract. In this paper we reanalyse the set of ten major geomagnetic storms which occurred between August 1978 and December 1979. We relate them to the characteristics of the solar wind disturbances which caused them and the solar sources of such disturbances as tracked by means of interplanetary scintillation. It seems to us that the shock causing the sudden commencement and the plasma behind it with an important long-lasting Bz south component (Bz.

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Seasonal variations in the occurrence of geomagnetic storms

Annales Geophysicae ◽

10.1007/s00585-996-0286-1 ◽

1996 ◽

Vol 14 (3) ◽

pp. 286-289 ◽

Cited By ~ 4

Author(s):

John R. Taylor ◽

Mark Lester ◽

Timothy K. Yeoman

Keyword(s):

Solar Wind ◽

Seasonal Variations ◽

Annual Variation ◽

Geomagnetic Storms ◽

Magnetic Activity ◽

Magnetic Storms ◽

Sudden Commencement ◽

Sudden Commencements ◽

Solar Wind Origin

Abstract. Seasonal variations in the onset of magnetic storms are investigated. For the purposes of this study storms have been defined as events in which Dst falls below –50 nT for at least four consecutive hours. The storms have been classified as either storm sudden commencements (SSCs; storms initiated by a sudden commencement) or as storm gradual commencements (SGCs; all other storms). It is found that the semi-annual variation of magnetic activity is reflected in the occurrence statistics of SGC events only, indicative that the solar wind origin is different for SSCs and SGCs. It is suggested that the heliospheric latitude model of seasonal magnetic activity is relatively ineffective in modulating the previously observed seasonal variations in the occurrence of magnetic storms.

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Extended main phase of some sudden commencement great geomagnetic storms with double SSCs

Journal of Atmospheric and Solar-Terrestrial Physics ◽

10.1016/s1364-6826(99)00049-8 ◽

1999 ◽

Vol 61 (13) ◽

pp. 993-1000 ◽

Cited By ~ 2

Author(s):

B.J Srivastava ◽

Habiba Abbas ◽

D.R.K Rao ◽

B.M Pathan

Keyword(s):

Geomagnetic Storms ◽

Sudden Commencement ◽

Main Phase

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Disappearing Solar Filaments and Interplanetary Shock Waves

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000016866 ◽

1983 ◽

Vol 5 (2) ◽

pp. 202-204 ◽

Cited By ~ 1

Author(s):

C. S. Wright

Keyword(s):

Geomagnetic Storms ◽

Close Association ◽

Interplanetary Shock ◽

Sudden Commencement ◽

The Sun ◽

Type Ii ◽

Type Iv ◽

Magnetohydrodynamic Shock ◽

Solar Filaments ◽

Sudden Commencements

The close association between flare events having metric radio type II and type IV bursts and the subsequent occurrence of sudden commencement geomagnetic storms is well known. In such cases it has been amply demonstrated (e.g. Malitson et al. 1973; Cane et al. 1982) that the sudden commencement (SC) is caused by the same magnetohydrodynamic shock which originates near the Sun and which produces the type II burst. Recently, a study of geomagnetic storms thought to be associated with the disappearance of filaments from quiet regions of the Sun (Joselyn and McIntosh 1981) showed that several of these storms began with marked sudden commencements.

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