| Summary: | In this thesis, knowledge on the production mechanisms of small scale (meter and decameter) irregularities in the auroral E region is advanced, both theoretically and experimentally. In the theoretical part of the thesis, the linear fluid theory of the Farley-Buneman (F-B) and gradient drift (G-D) plasma instabilities is considered. A general 2-D dispersion equation is derived and analyzed. Then, a review of existing nonlinear theories is given. The thrust is on the theory predictions with respect to the phase velocity of plasma waves. As an expansion of the theory, one new effect in the F-B instability evolution is considered, a secondary instability of a turbulent background of the primary F-B waves. It is shown that in a system of F-B modes the energy can flow from the short-wavelength (primary) to long-wavelength (secondary) structures (inverse cascade), contrary to the currently dominating idea that the energy of unstable waves is transferred to the smaller-scale structures. The phase velocity of the secondary waves propagating along the electron flow was found to be close to the electron streaming velocity and not saturated at the ion acoustic speed of the plasma. A possibility of decameter wave generation through this mechanism is envisioned. Experimentally, data of 2 separate experiments carried out in the auroral E region to study phase velocity of meter and decameter irregularities are considered. First, nearly simultaneous measurements of two Super Dual Auroral Radar Network (SuperDARN) HF radars (12 MHz, scatter from decameter waves, λ = 12 m) and one VHF radar (50 MHz, scatter from meter waves, λ = 3 m) at the Antarctic Syowa station are compared. It is demonstrated that HF echoes exhibit quite different characteristics as compared to VHF echoes so that HF echoes with low (< 350 m s⁻¹) and high (> 350 m s⁻¹) Doppler velocities are proposed to consider separately. Observations indicate that the high-velocity HF echoes exhibit properties similar to VHF echoes while the low-velocity HF echoes ...
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