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A theory of the generation of plasma densityirregularities with virtually no aspect sensitivity, in the lower ionosphere athigh latitudes, by electron drifts aligned with the geomagnetic field, ispresented. The theory is developed through fluid equations in which thedestabilising mechanism involves positive feedback from electron collisionalheating. When field aligned electron drift speeds exceed a few km s<sup>-1</sup>,this effect destabilises waves with wavelengths in excess of a few tens ofmetres in the lower E-region, where collisional effects are sufficiently large.Furthermore, the threshold conditions are almost independent of the wavepropagation direction and the unstable waves propagate at speeds well below theion acoustic speed. The role that this new instability may play in recent radarbackscatter observations of short scale irregularities propagating in directionsclose to that of the geomagnetic field, in the lower E-region is alsoconsidered.  <b>Key words:</b> Ionosphere (auroral ionosphere; ionosphericirregularities; plasma waves and instabilities

The generation of non aspect sensitive plasma density irregularities by field aligned drifts in the lower ionosphere