Characteristics Of Mid- And Low-latitude Ionospheric Irregularity And Scintillation

Ionosphere contains a variety of irregularities. The formation mechanism, observation and the radio signal propagation effects of the ionospheric irregularities have always been an area of much concern in the ionosphere research. The ionoshperic scintillations of the satallite signal in amplitude, phase, angle of arrival, caused by the ionospheric electron density irregularities, result in a communication system error, space-based radar imaging performance degradation and navigation and positioning accuracy decline.The relevant work focuses on the morphology, variation of the mid- and low-latitude ionospheric irregularities and the statistical characteristics of the trans-ionospheric radio signal, which is supported by the defense pre-research fund and National Natural Science Foundation and the Fundamental Research Funds for the Central Universities. As basis, a brief review is given on the layered structure and morphology of ionosphere and the ionospheric vertical sounding systems firstly. The main topics and results are as follows:First, based on the characteristics of ionospheric plasma, Rayleigh-Taylor instability of the equatorial ionospheric irregularities formation theory is investigated, and the linear instability growth rate is derived. The evolution of the ionospheric electron density perturbations and the temporal and spatial distribution of linear instability growth rate are numerically analyzed. The instability growth rate is negative above the peak height and positive below the peak height. The instability growth rate at a certain height varies significantly with local time, with a maximum value at about 22:00LT.Second, by using the ionospheric scintillation monitoring data, a statistical analysis of ionospheric scintillation in GPS satellite signals at low-latitude regions(Kunming and Haikou) and in UHF satellite signal at mid-latitude regions(Xi’an) are made, including local time, daily, seasonal distribution and other statistical characteristics. The results showed that GPS ionospheric scintillation events in low-latitude regions(Haikou and Kunming) occurred mainly in spring and autumn night, with the highest incidence at 21:00LT-1:00LT. And UHF ionospheric scintillation events in mid-latitude region (Xi’an) concentrated in summer night, with the highest incidence at midnight 23:00LT. The scintillation events at Xi’an station occurred about one hour delay than that at Kunming station, and about two hours delay than that at Haikou station.Third, with the use of the ionospheric vertical sounding data, temporal distribution characteristics of spread F layer and sporadic E layer occurred in mid-latitude region(Xi’an) are statistically analyzed, and the relevance of the mid-latitude ionospheric irregularities observation and magnetic, solar activity is discussed. The results showed that mid-latitude ionosphere spread F occured mainly in the summer nighttime, and Es occured mainly in summer daytime. The relevance of Spread F and Es incidence is not significant with solar activity, and is positive with geomagnetic activity. The obvious bimodal distribution of Es occurrence with local time is shown. The correlation coefficient of spread F and scintillation events at summer nighttime is 0.869.Fourth, based on the multiple phase screen theory, the ionospheric scintillation characteristics in the mid- and low-latitude regions(Haikou, Wuhan and Xi’an) are studied with a analysis of the influence of the ionosphere and irregularities on the satellite signal scintillation. A method is presented for analyzing the ionospheric equivalent thickness based on phase screen model. The results showed that the ionospheric variation with height has a certain effect on the signal scintillation characteristics, and that the impact varies significantly with local time. In mid- and low-latitude of China, the equivalent ionospheric thickness based on phase screen model is located in the range of 270-370 km, and the conclusion can be used as theoretical reference for engineering applications of phase screen propagation model.Fifth, by using the dual-band, dual-point Mutual Coherence Function of plane pulse wave, the second order statistics of the satellite signal through the ionosphere is studied. The numerical results showed that the ionospheric inhomogeneity effects on the coherence properties of satellite signal are considerable, and varies significantly with latitude and local time.