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Ann. Geophys., 18, 1172-1181, 2000
www.ann-geophys.net/18/1172/2000/
© European Geosciences Union 2000
Auroral E-region electron density gradients measured
C. Haldoupis1, K. Schlegel2, and G. Hussey3
1Physics Department, University of Crete, Iraklion, Greece
2Max-Planck Institut für Aeronomie, Katlenburg-Lindau, Germany
3Department of Physics and Engineering Physics, University Saskatchewan, Canada
Abstract. In the theory of E-region plasma
instabilities, the ambient electric field and electron density gradient are both
included in the same dispersion relation as the key parameters that provide the
energy for the generation and growth of electrostatic plasma waves. While there
exist numerous measurements of ionospheric electric fields, there are very few
measurements and limited knowledge about the ambient electron density gradients,
∇Ne, in the E-region plasma. In this work, we
took advantage of the EISCAT CP1 data base and studied statistically the
vertical electron density gradient length, Lz=Ne/(dNe/dz),
at auroral E-region heights during both eastward and westward electrojet
conditions and different ambient electric field levels. Overall, the prevailing
electron density gradients, with Lz ranging from 4 to 7 km,
are found to be located below 100 km, but to move steadily up in altitude as the
electric field level increases. The steepest density gradients, with Lz
possibly less than 3 km, occur near 110 km mostly in the eastward electrojet
during times of strong electric fields. The results and their implications are
examined and discussed in the frame of the linear gradient drift instability
theory. Finally, it would be interesting to test the implications of the present
results with a vertical radar interferometer.
Key words: Ionosphere (auroral ionosphere; ionospheric
irregularities; plasma waves and instabilities)
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