Parametric Instability Analysis Of Ionosphere Heated By High Power Radio Waves

A series of physical phenomena occur when powerful radio waves(usually termed as a pump)are injected into the ionosphere,such as Artificial Airglow,Anomalous Absorption,Stimulated Electromagnetic Emission and small-scale field aligned irregularity,these phenomena are closely related to parametric instability.Since the 1950s,theoretical and experimental studies on parametric instability have been a hot research field in ionospheric heating.So far,there are still many experimental phenomena that can not be explained by the existing theory.In addition,in the process of data processing,the result caculated by GUISDAP software is often missing a portion of data,so we use the ion spectra caulated by RTG to make it complete.In this paper,the experimental phenomena are analyzed by using the twice heating data of EISCAT combined with the principle of incoherent scattering radar parameter inversion.The results are as follows.1)When the pump is operated near the fourth electron gyrofrequency,the UHF radar observation shows some strong enhancements in electron temperature,electron density,ion line,and the up-shifting and spread of plasma lines.Based on some existing theories,we find the following:Firstly,Langmuir waves scattering off lower hybrid density fluctuations and strong Langmuir Turbulence(SLT)in the Zakharov model cannot completely explain the up-shifting and spread of plasma lines,but the data suggest that this phenomenon is related to the super-thermal electron and should be researched further;Secondly,the spatiotemporal consistency between the enhancement in electron density/electron temperature reaches up to 3?4 times that of the undisturbed state and HF-induced ion lines(HFILs)suggest that SLT excited by parametric instability plays a significant role in superthermal electron formation and electron acceleration;Thirdly,some enhancements in HFILs and HF-induced plasma lines(HFPLs)are generated by parametric decay instability(PDI)during underdense heating in the third cycle,we suggest that this is due to the existence of a second cutoff in the upper hybrid dispersion relation as derived from a kinetic description.2)In the alternating heating experiment of O wave and X wave,when the pump is switched on,the UHF radar observation shows some strong enhancements in electron temperature,electron density,ion lines and plasma lines near the reflection altitude.Based on some existing theories,we find the following:Firstly,during the experiment,the frequency among plasma line(f_L),ion line(f_ia)and pump(f_h)matchesf_L=f_h-3f_ia andf_L=f_h-5f_ia occasionally demonstrate that the cascade process occurred.Secondly,comparing the electron density calculated by ion spectrum integral with that obtained by GUISDAP,we found that the increase in electron density near the reflection altitude do not correspond to true increase in electron density and should be the result of an enhancement of ion line excited by parametric decay instability(PDI)around the reflection altitude.Thirdly,the UHF radar observation shows some apparent enhancements over a wide altitude range in electron density during X-mode pulse which also do not,in fact,correspond to a true increase in electron density,but due to the enhancement in ion line or the enhancement in radar backscatter induced by some unknown mechanism.