Study On The Ionospheric Instability Inducing Effect Of Chemical Releases

Ionospheric chemical release is an important part of the theoretical research on ionosphere and one of the effective techniques of artificially modifying and utilizing of ionospheric space environment.In this dissertation,ionospheric instability induced by chemical release is investigated on the basis of ionospheric instability theory,and the key influence factor of instability development is also discussed.Instability triggering effects of chemical release can be theoretically analyzed by the linear growth rate.However,the linear growth rate corresponds to the early stage of instability development,which can only partially determine the occurrence probability of ionospheric irregularities.Hence,the ionospheric simulation method that can describe the overall instability development processes is also used to study the instability triggering effects of chemical release.Further more,the simulated irregularities are usually confirmed by the morphyology of the irregularities,therefore,some preliminary quantitative research on the ionospheric simulation is carried out based on the Constrained Interplation Profile algorithm.The main work is as follows:1.The simulation investigation on key influence factors of the ionospheric instability development indicates that there is an inflection point in the instability development process,which can represent the generation of irregularities in topside F region.When the reflection point appears,the plasma bubble will reach the topside F region rapidly and bifuricate to form irregularities.It is found that there is an exponential correlation between the initial R-T growth rate and the appearance of inflection point,and there is a power law correlation between the initial perturbation and the appearance of inflection point.2.According to the point chemical release model,the ionospheric perturbation effects produced by sulfur hexafluoride(SF₆)and barium(Ba)under different release settings is investigated respectively,the duration of the chemical release perturbation and influence of the geomagnetic is discussed.Duration of the perturbation caused by chemical release is about ten minutes to less than an hour.The dense electron cloud produced by Ba is stretched along the magnetic-curve;the depletion hole produced by SF₆ is‘squashed'along the magnetic curve in the restoration process.3.With application of both lienear growth rate theory and nonlinear simulation method,the instability triggering effect of chemical release is studied,and the chemical recombination perturbation caused by SF₆ release is analyzed for the first time.The growth rate perturbation caused by Ba release is as high as 10^-2 orders of magnitude at the beginning,and decreases to less than 10^-3 in 10 seconds.Considering the chemical recombination effect of SF₆,the growth rate perturbation of SF₆ release is negative at the begining,and a positive growth rate perturbation of 10^-2 orders of magnitude appears after 1 minute and lasts for minutes to tens of minutes.The simulation results show that SF₆ releases can effectively induce ionospheric instability.Even if the ionospheric conditions are affirmed to be stable by instability theory,SF₆ releases may also initiate irregularities'generation.When the ionospheric condition is suitable for the irregularities'generation,SF₆ release will lead to rapid formation of irregularities with complicated structures.4.Combined with scintillation theory,structural properties of simulated irregularities are quantitatively investigated.Based on ionospheric simulation using constrained interplation profile algorithm,the empirical PSD and electron density variance profile of simulated irregularities are analyzed in detail for the first time.The PSD of both natural and chemical irregularities is in good agreement with Shkarofsky's spectrum,which is the theoretical spectral density function of irregularities.Substituting the empirical PSD and the variance profile into scintillation calculation,results are in good agreement with scintillatin theory.The consistency between computation and theory not only provides ideas for the quantitative verification of ionospheric simulation,but also shows that ionospheric simulation can be extended to the study of ionospheric scintillation.Researches on the ionospheric instability triggering effect of the chemical release not only can be used to plan the best release time and location for space active experiment,but also promote the studies on the evolution mechanism of ionospheric instability.