Study On The Distribution Characteristics And Seismic Response Of Ionosphere Using COSMIC Occultation Data

Space-based GPS radio occultation detection technology by global coverage and high vertical resolution can provide invaluable information for the global ionospheric activity. This paper mainly elaborates on the basic theory of ionosphere and GPS radio occultation detection technology. We first discuss on data processing and research methods using COSMIC occultation data. The study on distribution variations of different regions of ionospheric parameters and vertical distribution of Ne in different solar activity conditions have not been reported widely. We focus on this and study two aspects on the distribution characteristics and seismic response of ionosphere. The main works and results can be summarized as follows:1Data analysis and research methods of COSMIC occultationThe study provides temporal distribution variation of NmF2、foF2and hmF2by fourier approximation fitting method. Then we establish B spline model and spherical harmonic model for obtaining higher spatial resolution of global ionospheric data. We take the calculation result by IRI model as the reference for testing validity of methods.The results calculated by B function model expand faster and calculation time is shorter, which can effectively reflect small area distribution characteristics of ionosphere. But the results calculated by spherical harmonic model show smaller average residual than the results calculated by B spline model and can effectively reflect global distribution characteristics of ionosphere, which distribution is smoother. Spherical harmonics calculation results provide support for subsequent research.2Study on the distribution characteristics of ionosphere1) Ionospheric NmF2and foF2show significant annual periodicity. The semiannual variation of NmF2and foF2are strong in magnetic middle and magnetic low latitude in the daytime. The maximum values of wave are in March and April or September and October; Annual variation of NmF2and foF2are evident in parts of the southern hemisphere and the northern mid-latitude60°-120°E region in the nighttime. The peaks of wave are in northern hemisphere summer or southern hemisphere summer. In addition, NmF2and foF2have obvious annual anomaly and semiannual anomaly in middle and low latitude. The enhanced solar activity expands the spatial extent of equatorial anomaly.2) Ionospheric hmF2has no obvious regular change in the nighttime, and its distribution is in the range200-400km. There is no evident annual variation in magnetic latitude10°S-10°N region, and its distribution is in the range300-400km; There exists annual variation in some areas of magnetic latitude10°-20°S and magnetic latitude10°-20°N region. The annual variation of hmF2is evident in most of magnetic middle latitude regions> magnetic latitude20°-30°S and magnetic latitude20°-30°N, and its distribution is in the range200km-400km. The enhanced solar activity causes the increased variation amplitude of hmF2, especially in equator and low latitude region.3) Ionospheric Ne shows Weddell Sea anomaly variation in the nighttime at250km-500km altitude. The maximum values of Ne are at300-400km altitude. The enhanced solar activity expands the spatial extent of Weddell Sea anomaly at300km-500km altitude. The enhanced solar activity also expands the spatial extent of equatorial ionization anomaly at250km-350km altitude. Ne is dominated by seasonal variation in the daytime. There is no obvious seasonal variation in the nighttime.3Study on typical cases of earthquake1) We provide data analysis methods to study ionospheric anomaly variation. We focus on three great earthquakes, and consider the impact of geomagnetic activity and solar activity using COSMIC occultation, GPS TEC and geomagnetic observation data. Relative change of NmF2increase significantly after Wenchuan earthquake, which change is between1-1.5. The correlation coefficients decrease to0.6after Wenchuan earthquake. The TEC power spectrum amplitudes of24h diurnal wave and12h semi-diurnal wave change significantly in the period of earthquake occurrence. Relative change of NmF2increase significantly after Yutian earthquake, which change is between0.8-1.2. Geomagnetic vertical component enhance before Yutian earthquake. But electromagnetic effects induced by Yutian earthquake needs further study. Relative change of NmF2increase significantly after Yushu earthquake, which change is between0.6-0.8. Geomagnetic vertical components decrease to OnT after Yushu earthquake. There exists phenomenon of ionospheric disturbances during three earthquakes activities. There exists phenomenon of geomagnetic disturbances after Wenchan and Yushu earthquake. Earthquake cases result show that the larger the magnitude, the greater the relative change of NmF2. 2) SAMI2model simulation and observation results testify that additional electric field can cause distribution of ionosphere by the example of Wenchuan earthquake. Abnormal electric mechanism to explain the seismic response of the ionosphere may be more reasonable.