Quick Substorm Development During Initial 10 Minutes of 2003-10-29 Magnetic
Storm

M. Yamauchi, T. Iyemori, H. Frey, and M. Henderson


Global geomagnetic field data, IMAGE FUV data, and many other in-situ
observations are  presented for the initial 10 minutes of the magnetic storm
starting 29 October 2003 at around 06:10  UT.  The data set shows a quick
development of large geomagnetic activities associated with  westward
electrojets in the ionosphere immediately (within one minute) after the sudden 
commencement (SC).  Two independent strong westward electrojets (> 2000 nT)
started  simultaneously, one in the evening-midnight sector and the other in the
morning sector, and both  activities expanded accompanying aurora.  While the
midnight activity is clearly a substorm onset,  the nature of the morning
activity is not clear because the latter corresponds to a strong sunward 
convection inside the inner magnetosphere and is more similar to a substorm than
to a cusp-related  activity.  An even stronger geomagnetic activity (nearly 4000
nT) started only 6 minutes after the  SC at post-midnight where and when the
above two expanding activities met each other, although  the relation between
the onset of 4000 nT activity and the preceding expansions is not clear.  
Considering the activity level and its timing, these strong westward electrojets
were most likely  triggered by the interplanetary shock and maintained by the
direct energy pumping from the solar  wind with anonymous mechanisms. 

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Submitted to Journal of Geophysical Research, 2005