A nonlocal theory of the high‐latitude Farley‐Buneman instability

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Abstract
The linear theory of E region irregularities predicts that the unstable plasma waves should be strongly field aligned. At high latitudes, however, the medium is strongly inhomogeneous in the magnetic field direction owing mainly to neutral density changes, while the thickness of the layer itself rarely exceeds 20 km. The net result is that the waves acquire large positive parallel group velocities and can quickly escape from the unstable layer. Using a linear nonlocal fluid formulation of the Farley‐Buneman theory of the irregularities, we have found that, even in the presence of a 50 mV/m field, waves between 10 m and 50 m or greater in size will reach a finite amplitude due to convective effects produced by the inhomogeneity of the medium. We have also found that at shorter wavelengths, while the instability retains an absolute character, nonlocal properties can produce new effects, for example, the appearance of a multiple layering of the unstable region with a concentration of large‐amplitude waves in layers 2 to 5 km wide.