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Ann. Geophys., 18, 799-806, 2000
www.ann-geophys.net/18/799/2000/
© European Geosciences Union 2000
The generation of non aspect sensitive plasma density irregularities by field aligned drifts in the lower ionosphere
T. R. Robinson1 and K. Schlegel2
1University of Leicester, Leicester, UK
e-mail: txr@ion.le.ac.uk
2Max-Planck-Institut für Aeronomie, Katlenburg-Lindau, Germany
Correspondence to: T. R. Robinson
Abstract. A theory of the generation of plasma density
irregularities with virtually no aspect sensitivity, in the lower ionosphere at
high latitudes, by electron drifts aligned with the geomagnetic field, is
presented. The theory is developed through fluid equations in which the
destabilising mechanism involves positive feedback from electron collisional
heating. When field aligned electron drift speeds exceed a few km s-1,
this effect destabilises waves with wavelengths in excess of a few tens of
metres in the lower E-region, where collisional effects are sufficiently large.
Furthermore, the threshold conditions are almost independent of the wave
propagation direction and the unstable waves propagate at speeds well below the
ion acoustic speed. The role that this new instability may play in recent radar
backscatter observations of short scale irregularities propagating in directions
close to that of the geomagnetic field, in the lower E-region is also
considered.
Key words: Ionosphere (auroral ionosphere; ionospheric
irregularities; plasma waves and instabilities)
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