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Ann. Geophys., 21, 2271-2280, 2003
www.ann-geophys.net/21/2271/2003/
© European Geosciences Union 2003
A substorm in midnight auroral precipitation
V. G. Vorobjev1, O. I. Yagodkina1, G. V. Starkov1, and Ya. I. Feldstein2
1Polar Geophysical Institute, Russian Academy of Sciences, Apatity, Murmansk region, 184200, Russia
2IZMIRAN, Russian Academy of Sciences, Troitsk, Moscow region, 142190, Russia
Abstract. DMSP F7 spacecraft observations for
the whole of 1986 were used
to construct the empirical model of the midnight auroral
precipitation during a substorm. The model includes the
dynamics of different auroral precipitation boundaries and
simultaneous changes in average electron precipitation energy
and energy flux in different precipitation regions during
all substorm phases, as well as the IMF and solar
wind plasma signatures during a substorm. The analysis of
the model shows a few important features of precipitation. (1)
During the magnetic quietness and just before the
beginning of the substorm expansive phase the latitudinal width
of the auroral precipitation in the nightside sector is
about 5 – 6° CGL, while that of the
auroral oval is about 2 – 3° CGL during such periods. (2)
For about 5 min before the
substorm onset a decrease in the average precipitating electron
energy in the equatorward part of auroral zone was observed
simultaneously, with an increase in both the average electron
energy and energy flux of electron precipitation in
the poleward part of the auroral zone. (3) The isotropy boundary
position in the beginning of the substorm expansive phase
coincides well with the inner edge of the central plasma
sheet. The analysis of interplanetary medium parameters shows
that, on average, during the substorm development, the
solar wind dynamic pressure was about 1.5 times that
of the magnetic quietness period. Substorms occurred predominantly
during the southward IMF orientation, suggesting that
substorm onset often was not associated with the
northern turn or decrease in the southward interplanetary Bz
. The Northern Hemisphere’s
substorms occurred generally during
the positive interplanetary By
in winter, and they were
observed when the interplanetary By
was negative in summer.
Key words. Ionosphere (auroral ionosphere; particle precipitation)
–
Magnetospheric physics (storm and substorm; magnetosphere-ionosphere
interaction)
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