Farley-Buneman instability in the weakly ionised medium

The Farley-Buneman instability (FBI) which is electrostatic streaming instability is known to create plasma irregularities in the ionospheric E-regions at height where electrons are strongly magnetised and ions are unmagnetised. The interplay between Earth´s electric and magnetic field give rise to cross field motion of the ionised medium leading to this instability. The relative motion between plasma and neutral particles due to collisional drag of the ions by the neutral flows can also cause the development of similar instability. However, in a weakly ionised medium, inertia of the neutral matter can no longer be overlooked. Therefore, investigation of FBI in weakly ionised medium should be considered incomplete. The neglect of neutral dynamics is justified for the high frequency fluctuations. However, when fluctuation frequencies are low or ultra low, neutral dynamics can not be overlooked. The role of neutral in exciting FBI in magnetised electron and weakly magnetised ion plasma is investigated. The results are applied to the structure formation in the lower mesosphere.