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Ann. Geophys., 20, 1349-1359, 2002
www.ann-geophys.net/20/1349/2002/
© European Geosciences Union 2002
Estimation of the characteristic energy of electron precipitation
C. F. del Pozo, M. J. Kosch, and F. Honary
Department Communication Systems, Lancaster University, Lancaster LA1 4YR, UK
Correspondence to: C. F. del Pozo
(c.del.pozo@lancaster.ac.uk)
Abstract. Data from simultaneous
observations (on 13 February 1996, 9 November 1998, and 12 February 1999) with
the IRIS, DASI and EISCAT systems are employed in the study of the energy
distribution of the electron precipitation during substorm activity. The
estimation of the characteristic energy of the electron precipitation over the
common field of view of IRIS and DASI is discussed. In particular, we look
closely at the physical basis of the correspondence between the characteristic
energy, the flux-averaged energy, as defined below, and the logarithm of the
ratio of the green-light intensity to the square of absorption. This study
expands and corrects results presented in the paper by Kosch et al. (2001). It
is noticed, moreover, that acceleration associated with diffusion processes in
the magnetosphere long before precipitation may be controlling the shape of the
energy spectrum. We propose and test a "mixed" distribution for the
energy-flux spectrum, exponential at the lower energies and Maxwellian or
modified power-law at the higher energies, with a threshold energy separating
these two regimes. The energy-flux spectrum at Tromsø, in the 1–320 keV
range, is derived from EISCAT electron density profiles in the 70–140 km
altitude range and is applied in the "calibration" of the optical
intensity and absorption distributions, in order to extrapolate the flux and
characteristic energy maps.
Key words. Ionosphere (auroral
ionosphere; particle precipitation; particle acceleration)
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