GEOMAGNETIC SUDDEN COMMENCEMENTS (from SGD Explanation of Data Reports)

Sudden Commencements and Solar Flare Effects - These reports are provided by 
Observatorio del Ebro, Roquetes, Spain, on behalf of the IAGA Service on 
Rapid Magnetic Variations.  The Sudden Commencements (ssc) and Solar Flare 
effects (sfe) are from magnetograms of the worldwide network of magnetic 
observatories.  The stations, together with their abbreviations, are given in 
the series IAGA Bulletin No. 32 which contains the yearly compilation of these 
data.  Before January 1966 these reports were published periodically in 
Journal of Geophysical Research.  From then until 1970 they were published 
quarterly in Solar-Geophysical Data (SGD).

Beginning with December 1970 these data are published monthly and, thus, are 
based on fewer reports and differ slightly from similar data published 
previously.  The decision to publish this less complete report was made in 
order to make the data available more rapidly.  The table for ssc's gives 
date and UT time of event with stations by three-letter abbreviations grouped 
by quality A, B, C, or -, where A means very remarkable; B means fair, but 
unmistakable; and C means very poor, doubtful, and - means no quality figure 
given.  The * means that the ssc, at least in one component, was preceded by 
a small reversed impulse.  For ssc's, only events reported by at least five 
observatories are reported.  The list of sfe's gives the beginning and ending 
of the event in UT and all reported cases are reported.  If an sfe is 
confirmed by solar or ionospheric events, the name of the reporting 
observatory is underlined or a + sign appears in the digital file.