Research On The Statistical Characteristics And Prediction Model Of Ionospheric Spread-F At The Low-and Mid-Latitudes In China

The ionosphere is an important part of the near-Earth space environment,which has an important impact on the radio propagation of information systems.Driven by a variety of factors from the solar and geomagnetic activities,the upper atmosphere and even the lower atmosphere near the ground,various irregular structures will appear in the ionosphere.Spread-F is one of the most common irregular structures in the ionosphere,and its temporal and spatial variations can lead to complex radio propagation effects,thus affecting the performance of radio systems.It has always been an interesting topic in the study of radio environment and ionospheric space weather.In order to deepen the understanding of the variation of ionospheric spread-F at low-and mid-latitudes,and improve the ability of precise modeling,forecasting and radio propagation application in China,based on the ionospheric observation data from several stations in China and Japan,the regional statistical characteristics of the spread-F at lowand mid-latitudes are systematically analyzed.The correlation between the spread-F and the F2-layer critical frequency(fo F2),virtual height(h'F),sporadic E layer(Es layer)and ionospheric scintillation effect is studied in detail.On this basis,the prediction method of Spread-F occurrence probability at low-and mid-latitudes is studied.The main results are as follows:1.Based on the ionosonde data of 12 stations in China and Japan for many years,the temporal and spatial variations of ionospheric frequency spread-F and range spread-F at low-and mid-latitudes are studied.The results show that the spread-F occurrence percentages varies more significantly in the longitudinal chain than in the latitudinal chain,and the spread-F occurrence percentages in coastal and marine areas is higher than that in inland areas between 35°N~45°N.It is found that the frequency spread-F occurrences vary linearly with fo F2,while the range spread-F occurrences vary quadratically with h'F,and the expression of the fitting curve is obtained.These results deepen the understanding of the occurrence regularity of ionospheric spread-F and its regional variation characteristics at low-and mid-latitudes in China.2.Using the ionosonde data from Haikou,Guangzhou,Beijing and Changchun stations,the correlation between spread-F and ionospheric F-layer parameters of fo F2 and h'F is studied.The threshold of fo F2 which controlled the frequency spread-F events and the correlation between range spread-F occurrences with h'F are obtained.The results show that the threshold of fo F2 decreases while the latitude increases.The range spread-F occurrence percentages increase with the increase of h'F,and are the highest at 240-290 km.The occurrence percentages decrease with the further increase of h'F.It is found that the frequency spread-F satisfies the linear relationship with fo F2,while the range spread-F satisfies the quadratic relationship with h'F,and the expression of the fitting curve is given.This result deepens the understanding of the intrinsic relationship between the spread-F and the background parameters of the ionospheric F-layer.3.The correlation between spread-F and ionospheric scintillation,as well as the sporadic E layer,is analyzed by using the ionosonde and scintillation data from several stations.It is found that the correlation coefficient between range spread-F and scintillation is as high as 0.7~0.9,and the correlation coefficient decreases with the increase of latitude.Meanwhile,spread-F occurrence percentages increase with the decrease of the difference between fo Es and fb Es.It is found that the spread-F occurrence percentages satisfy the relationship of cubic curve with the difference between fo Es and fb Es,and the expression of fitting curve is obtained.These results improve our understanding of the correlation between spread-F and other irregularities.4.Based on the parameters of solar and geomagnetic activity index,fo F2,h'F and neural network algorithm,a new prediction method of spread-F occurrence percentages is proposed.This method adopts fo F2 and h'F as input parameters of the prediction model compared with the existing prediction methods.Compared with the existing prediction methods,the average mean square deviation of the improved model is about 7% higher than that of the existing prediction models,and the improved model can be better used to predict the spread-F occurrence percentages in China.