Detection Of Seismic Ionosphere Anomaly Based On Ground-Based GNSS And COSMIC Data

Usually,there are many abnormal variations of different scales occurring in the ionosphere.In recent years,the research on the small and medium-scale disturbances during the preparation and after the shock has become a hot topic.With the development of GNSS technology,ionospheric products with different scales and spatial-temporal resolutions will be widely used in the detection of ionospheric space-time variation and seismic ionospheric anomaly.In addition,by the COSMIC data with global coverage,the vertical structure changes of the ionosphere can be effectively analyzed.The main work and achievements of this paper are as follows:(1)The CMONOC(Crustal Movement Observation Network of Chin a)GNSS observations were used to inverse the high-precision regional ionosphere data over China.By introducing the baseline variable Brs,the STEC(Slant Total Electron Content)data are quickly calculated as the data basis for coseismic ionosphere disturbance(CID).Furthermore,the low-order spherical harmonic function is adapted to construct regional ionosphere map(RIM)with the geographical span of 15°N-55°N and 70°E-140°E,the spatial resolution of 1°×1°.At different scales,we combine RIM and GIM(Global Ionosphere Map)to detect the variation of ionosphere.(2)Based on the sufficient STEC observation data in seismogenic area,the single shell layer model(shell model)of the NmF2 layer near the epicenter is used to analyse the propagation characteristics of CIDs induced by Lushan earthquake(Mw6.6,2014.4.20).It is found that the CID horizontal propagation velocity was in accordance with the acoustic wave propagation velocity.Affected by the geomagnetic-field,CID mainly propagated along the southeast direction at the azimuth of 190°,which was almost parallel to the local magnetic-line.(3)Combined with different ionospheric data from ground-based GNSS to COSMIC electron density profile,the fine variation and vertical structure of ionospheric anomalies before New Zealand(Mw7.8,2016.11.13),Japan(Mw6.9,2016.11.21),Lushan(Mw6.6,2014.4.20),Mexico(Mw8.2,2018.2.17)earthquakes were analysed respectively.In the analysis of New Zealand and Japan earthquakes,a high-precision ionospheric background field is constructed by using Singular Spectrum Analysis,and then the global ionospheric disturbance signal is studied.It is found that there are obvious local TEC anomalies over the two earthquakes 16th days before the New Zealand earthquake and 11th days before the Japan earthquake respectively,implying a high possibility of seismic ionosphere effect in the geomagnetic storm environment.Based on the RIM data,the TEC variations before Lushan earthquake are studied.The results show that there are obvious ionospheric disturbances in the 27-25th,19th and 14-12th,days before Lushan earthquake.After excluding the effects of external environment and diurnal variation of the thermal layer on the ionosphere,the ionospheric disturbances in 14-12th days prior to the shock may be related to Lushan earthquake.The study on the ionospheric anomalies of Mexico earthquake shows that the CAS(Chinese Academy of Sciences)GIM products with high temporal resolution isare helpful to discovery more detailed changes in the ionospheric structure,especially the sudden variation within a short time(30 minutes)during peak period.(4)According to the occultation data of COSMIC,the ionospheric Vertical structural disturbances within 15 days before the Chilean earthquake(Mw8.8,2010.2.27)are analysed.The results show that there are obvious disturbances in the F layer near the epicenter on January 15,February 21 and 25,with the maximum exceeding 50%,and obvious local effeects.In addition,the variation of electron density at different heights before the Chilean earthquake shows that the seismiic-ionosphere effect is.most significant in the F layer,and the certain stratification differences happened in ionosphere at different heights.