On the substantial anomalous absorption regime at the extraordinary wave decay into trapped and propagating upper hybrid waves

We analyze the strong nonlinear regime of low power-threshold parametric decay instability (PDI) of a pump extraordinary wave. The PDI leads to the excitation of two upper hybrid (UH) waves only one of which is trapped in the vicinity of the local maximum of a non-monotonic density profile. The pump depletion and the multi-step secondary decays of the localized daughter UH wave are treated as the mechanisms leading to the instability saturation. It is shown that in the case of the even-step secondary cascade decay of trapped primary UH wave the pump wave depletion is responsible for the transition of a nonlinear phenomenon into a stationary regime, and the strong anomalous absorption is possible.