Analysis Of Ionospheric Periodic Characteristics And TEC Diurnal Cycle Modelling

The ionosphere is an important part of Sun-Earth space environment.With the development of science and technology,human activities(navigation,electronic communication)are more closely related to the variation of ionosphere.The dramatic changes in the ionosphere will have devastating effects on communication systems,power grid systems,positioning systems and so on.Therefore,the study of the variation characteristics of the incoming air separation layer has become a hot spot in space weather research.Based on GNSS TEC data,the correlation between TEC oscillation period characteristics and solar radiation(EUV)and geomagnetic condition(Ap)is deeply analyzed,and the temporal and spatial distribution of the oscillation is analyzed.The multiple regression model is established,which provides a theoretical basis for the prediction of short and imminent scales in the ionosphere.The main contents of this paper are as follows:(1)Based on the correlation analysis between GIM TEC and solar 0.1-50 nm band EUV radiation and Ap index of geomagnetic field,it is found that TEC quasi 27 day oscillation characteristics are strongly correlated with geomagnetic latitude.Its amplitude is basically symmetrical with the geomagnetic equator,and reaches its maximum in the high latitude region.In the low latitude region,noon and midnight 27 days period showed different distribution patterns.Through multiple regression analysis,it is found that in most of the world,the influence of EUV radiation is in 65%-100%,and the influence of geomagnetic field is 0%-35%.Using the power spectrum analysis and band pass filter,the quasi 27 day oscillation characteristics of the global total electron content(GEC)are analyzed.The results show that the relative size of GEC27 varies from 1%to 17%in GEC.This indicates that the 27 day variation is an important factor in the overall variation observed by the ionosphere.By using multiple linear regression model,the relationship between SEM,F10.7 and GEC27 cycle variation was compared,and the correlation between SEM and GEC27 data was the best.(2)Using Fourier transform,the GEC,RSSN(Relative Sunspot Number),solar EUV radiation of 0.1-50nm and 26-34nm band,Kp and Dst index are analyzed.The results showed that there is a deviation from the 27 day of the 21.5 day quasi periodic oscillation of ionosphere and solar activity index.The analysis of nearly 5 solar activity cycles shows that the quasi periodic signals of 21?23 days will appear repeatedly during the solar activity rising period.This paper analyzes the physical mechanism of the shock signal,using the sun around the central meridian[-100,° 10°]within the scope of the solar activity are,get the time series every day after 21.5 days cumulative confirmed that the quasi periodic vibration may be excited by combined effects of rotation and the evolution of the sun.(3)On the basis of the above research,the diurnal variation characteristics of global ionospheric TEC are analyzed,and the spatial and seasonal variation rules are summarized.The solar radiation is the main reason for the formation of the ionosphere,and the change of the solar altitude caused by the rotation of the earth makes the ionosphere show significant diurnal variation The movement of the direct point of the sun caused by the revolution of the earth makes the neutral atmospheric density component and the ionospheric ionization density show significant spatial characteristics and seasonal characteristics,thus making the diurnal variation of the ionosphere show different characteristics in different positions and seasons.In this chapter,the diurnal variation characteristics of the global ionospheric TEC are analyzed,and the spatial and seasonal variations of the ionosphere are summarized.(4)An ionospheric diurnal TEC model is proposed,which includes DOY(day of year)and LT(local time)parameters.The correlation coefficient between the model and the original data is more than 0.9,and the diurnal variation of the ionosphere is well reflected.It lays a foundation for further study of ionospheric variation.