Global observations of proton and electron auroras in a substorm

S. B. Mende (1), H. U. Frey (1), M. Lampton (1), J.-C. Gerard (2), B. Hubert (2), 
S. Fuselier (3), J. Spann (4), R. Gladstone (5), and J. L. Burch (5)

1 Space Sciences Laboratory, University of California, Berkeley
2 University of Liege, Liege, Belgium
3 Lockheed-Martin Palo Alto Research Laboratories, Palo Alto, CA
4 George C. Marshall Spaceflight Center, Huntsville, AL
5 Southwest Research Institute, San Antonio, Texas 

This is the first report of a substorm observed by the IMAGE FUV instruments 
permitting global observations of electron and proton produced auroras. On the 28th 
of June 2000 at 1956 UT in the pre-substorm phaselo at early evening local time the
proton aurora was equatorward of the electron precipitation and near midnight they
were collocated. There was bright electron and proton aurora in the post midday
afternoon side. The sudden brightening of the aurora at substorm onset near midnight 
is seen in the electrons only although there are protons present at this location. 
During the expansive phase both the electron and protons expand poleward. The 
electron aurora forms a bright surge at the poleward boundary while the protons just 
show diffuse spreading. The peak intensity of the protons did not change substantially 
during the entire event. The proton aurora is brighter on the dusk while the electron 
aurora on the dawn side. As the electron surge expands poleward it leaves the protons 
behind. The electrons form a discrete auroral feature near the aurora-polar cap 
boundary, which is devoid of substantial energetic (>1 keV) proton precipitation. The 
presence of precipitating protons at the point where the initial brightening is seen 
shows that substorms are initiated on closed field lines. 

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Geophysical Research Letters, Vol. 28, No. 6, pp. 1139-1142, March 15, 2001