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Ann. Geophys., 23, 1623-1635, 2005
www.ann-geophys.net/23/1623/2005/
© European Geosciences Union 2005
Variations of auroral hydrogen emission near substorm onset
L. P. Borovkov, B. V. Kozelov, L. S. Yevlashin, and S. A. Chernouss
Polar Geophysical Institute, Apatity, Murmansk region, 184209 Russia
Abstract. The results of coordinated optical ground-based observations of the auroral
substorm on 26 March 2004 in the Kola Peninsula are described. Imaging
spectrograph data with high spectral and temporal resolution recorded the
Doppler profile of the Hα hydrogen emission; this allows us to
estimate the average energy of precipitating protons and the emission
intensity of the hydrogen Balmer line. Two different populations of
precipitating protons were observed during an auroral substorm. The first of
these is associated with a diffuse hydrogen emission that is usually
observed in the evening sector of the auroral oval and located equatorward
of the discrete electron arcs associated with substorm onset. The average
energy of the protons during this precipitation was ~20–35 keV, and
the energy flux was ~3x10–4Joule/m2s. The second
proton population was observed 1–2min after the breakup during 4–5min of the expansion phase of substorm into the zone of bright, discrete
auroral structures (N-S arcs). The average energy of the protons in this
population was ~60 keV, and the energy flux was ~2.2x10–3Joule/m2s. The observed spatial structure of hydrogen
emission is additional evidence of the higher energy of precipitated protons
in the second population, relative to the protons in the diffuse aurora. We
believe that the most probable mechanism of precipitation of the second
population protons was pitch-angle scattering of particles due to
non-adiabatic motion in the region of local dipolarization near the
equatorial plane.Keywords. Auroral ionosphere; Particle precipitation;
Storms and substorms
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