Electron‐ion collision effects on the formation of prompt striations in the ionosphere

Electron‐ion collisions have been included in the analysis of electrostatic, purely growing, finite ion‐gyroradius, flute instabilities generated by a loss cone distribution of energetic ions in the ionosphere. It is shown that the collisions not only reduce the growth rate below the value predicted by collisionless theory but also result in a second lower growth rate mode not found in collisionless theory. Although the electron‐ion collision frequency is larger than the ion‐gyrofrequency for the parameters of the Buaro barium release experiment, the growth rate of the linearly most unstable mode is not appreciably modified by the collisions from the value predicted from collisionless theory. Electron‐ion collisions have a greater impact on the instability as the electron density is increased. Complete stabilization through electron‐ion collisions requires densities in excess of 8.7 × 10 7 cm −3 .