Spatial Variations in Stimulated Electromagnetic Emissions from the Ionosphere Above High Frequency Radio Wave Heating Facilities

Stimulated electromagnetic emission (SEE) is an important tool for understanding the interactions of high power radio waves that reflect in the ionosphere during experiments with ground high frequency (HF) heating facilities.The HF facilities launch an upward beam of pump waves that couple with the ionosphere near the reflection altitude to generate a secondary, downward electromagnetic wave that is detectable by receivers on the ground.The downward SEE waves have frequency shifts from the pump, corresponding to the excitation of low frequency (2) emissions such as ion acoustic, lower hybrid, ion Bernstein, and ion cyclotron waves.When the pump wave is above a threshold, processes such as mode conversion and parametric decay instabilities excite high frequency (2) electric field oscillations near the reflection altitude.The relationship between the frequencies of the pump oscillations (0) and the resultant daughter oscillations (1 and 2) are 0 = 1 + 2 with 1 >> 2 [1].The shifts in the high frequency oscillations are always downward but upshifted oscillations at frequency (3) can be produced by nonlinear mixing of the pump wave with a low frequency wave giving 3 = 0 + 2.All of this occurs when both frequency () matching and wave vector (k) matching conditions are satisfied.A vector dispersion function, k = D(), gives the relationship between the wave frequency and the wave propagation direction; and the wavenumber matching conditions are given by k0 = k1 + k2.