Statistical Studies Of Polar Ionospheric VHF Scintillations

Radio waves through the ionosphere irregularity can generate signal intensity variation and phase fluctuation,which is ionospheric scintillation.Ionospheric scintillation can lead to error and distortion of the receiving signals,thereby influencing the effect of the communication and navigation,in severe case may even result in losing lock and failure of related system of communication.Therefore,to carry out statistical research of the ionospheric scintillation has important scientific significance on scintillation activity modeling and forecasting.Statistical features of the occurrence of scintillation along with the geomagnetic activity,seasons and local time,also including the power spectrum and probability density of polar ionospheric VHF scintillations at yellow river station,Svalbard between Oct.2011 and Oct.2015 are investigated.The results show:(1)The scintillation index S4 concentrates in the range between 0.2 and 1.5,the proportion is up to 89%when S4 is greater than 0.4,on the other hand,scintillation spectrum index mainly concentrating in the range between 1.4 and 2,besides n is obviously proportional to S4.At the meantime,with the increase of spectral index n,the scintillation index S4 tends towards stability.(2)There are three main types of power spectrum of the scintillation.a)The scintillation power spectrum curve is relatively flat in the low frequency band,and decreases rapidly by negative power rate in the high frequency band.b)It's similar to the first curve,the difference is firstly rising at the low frequency.c)Scintillation power spectrum in the high frequency end of the "broken","broken" phenomenon usually appears in the very large scintillation index.(3)We can inverse irregularity using power spectrum of the scintillation,the scale of the irregularity and drift velocity as the scintillation occurs may be obtained,and there is influence between the evolution and movement of irregularity and power spectrum of the scintillation.(4)The geomagnetic disturbance shows an obvious inhibitory effect on the strong ionospheric scintillation whose index S4 is over 1.5,while showing some degree of inhibition on the ionospheric scintillation whose index S4 is over 0.4.On the whole,the incidence of the ionospheric scintillation is the highest in spring and the lowest in autumn,there is no strong dependence of scintillations and seasons.(5)The relationship of the scintillation and the local time shows that the incidence is lower at night and come to the highest after noon.(6)Analyzing all the scintillation events,using variance statistical mathematical methods directly to explore the fitting effect of Nakagami-m distribution and Rayleigh distribution for different signal intensity of the scintillation probability density,the results show that probability density of the signal intensity of the scintillation is closer to Nakagami-m when S4 is less than 0.6,and closer to Rayleigh when S4 is more than 0.6.