The ionospheric response to wave-accelerated electrons at the poleward auroral
boundary

Semeter, J., G. Sivjee, H. Frey, J.W. Bonnell, C.W. Carlson


The local ionospheric response to an auroral intensification at the poleward
auroral boundary has been investigated using the incoherent scatter radar (ISR)
and optical instrumentation at Sondrestrom, Greenland, in conjunction with
space-borne measurements by the IMAGE and FAST satellites. ISR elevation scans
through the illuminated region revealed filamentary columns of enhanced plasma
density, ~5 km in latitude by ~200 km in altitude. Column densities were
typically 5e11/m3 above background and often constant over a broad range of
altitudes. The brightness of the O+ 732-733 nm multiplet, monitored
simultaneously by a near infrared spectrometer, exceeded 1.2 kR during one
4-minute period (a factor of 4 brighter than previously reported auroral
measurements). A time- dependent model was developed to relate O+ emission
intensities to O+ column densities for a given illumination time. The results
suggested that the electron source was composed of kilometer-scale flux tubes
locked in the ExB flow for several minutes whose average energy that varied
temporally between <100 eV and >1 keV over their illumination lifetime.
Conjugate electrons measured by the FAST satellite at 1700 km showed evidence
for energization by inertial Alfven waves. Ionization rates computed from these
spectra were sufficient to account for the observed filamentary ionospheric
structure. The implications of these ionization patterns for electrodynamic
coupling with the magnetosphere are discussed.

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Submitted Journal of Geophysical Research, 2005JA011226, 2005