See Attached File.

The Broad Upshifted Maximum is one of the prominent features of the Stimulated Electromagnetic Emission (SEE) excited in the ionosphere pumped by powerful HF radio waves. BUM exists when   () and occupies quite wide frequency range above the pump wave frequency   from 10-12 kHz till  100-150 kHz,  is the electron cyclotron frequency. The BUM peak frequency   approximately follows the empirical relation . The high frequency flank of the BUM (above the BUM peak frequency)  commonly exhibits an exponential power spectrum decreasing towards higher frequencies.  This dependence suggests that the plasma waves, responsible for the  BUM  are excited by a parametric four-wave interaction 2PW UH+EB (2 pump wave quanta transform to Upper Hybrid quant at the BUM frequency and Electron Bernstein quant at . Also, the lower hybrid (LH) oscillations participate in the process.

The fully adequate theory of the BUM is not constructed yet, despite of the BUM id observed during approximately 45 years.

The author suggests that the LH oscillations are localized in a small-scale cylindrical density depletion  in the plane perpendicular to a homogeneous and static geomagnetic field. They form cylindrical modes characterized by the frequency, an azimuthal mode number and radial wave number. The localized LH modes are associated with multi-cell plasma drift patterns. For sufficiently strong driving fields, the time signal of the LH electron and ion density fluctuations at a fixed position in the simulation plane exhibit an approximately exponential power spectrum, thereby being evidence of deterministic chaos. The exponential spectrum is connected to pulse-type features of Lorentzian form in the time signal.

The author suggests that the LH oscillations with the exponential power spectrum can be responsible for the exponential power spectrum of the UH waves, and therefore, for the BUM exponential power spectrum.  

The idea and its demonstration in numerical simulation is look quite interesting. In my opinion, the paper should be published as it is.

But the author writes that the present simulation results are not totally consistent with the experimental results. So, it the efforts are required  for further development of the idea..