Estimation of HF artificial ionospheric turbulence characteristics using comparison of calculated plasma wave decay rates with the measured decay rates of the stimulated electromagnetic emission

It is shown experimentally that the relaxation time of the stimulated electromagnetic emission (SEE) after the pump wave turn off decreases when frequency of the electromagnetic wave, responsible for the SEE generation (pump wave f0 or diagnostic wave fdw) approaches 4th harmonic of the electron cyclotron frequency fce. Since the SEE relaxation is determined by the damping rate of plasma waves with the same frequency, responsible for the SEE generation, we calculated damping rates of plasma waves with ω∼ωuh (ω is the plasma wave frequency, ωuh is the upper hybrid frequency) for frequencies close to and distant from the double resonance where ωuh∼4ωce (ωce=2πfce). The calculations were performed numerically on the base of linear plasma wave dispersion relation at arbitrary ratio between |Δ|=ω-4ωce and |k‖|VTe (VTe is the electron thermal speed and k‖ is the projection of the wave vector onto the magnetic field direction. A comparison of calculation and experimental results has shown that obtained frequency dependence of the SEE decay rate is similar to the damping rate frequency dependence for plasma waves with wave vectors directed at the angles 60-70° to the magnetic field, and gives a strong hint that oblique upper hybrid plasma waves should be responsible for the SEE generation.