Recent ionospheric observations report anomalous total electron content (TEC) deviations prior strong earthquakes. We discuss common fetures of the pre-earthquake TEC disturbances on the basis of statistics covering 5...Recent ionospheric observations report anomalous total electron content (TEC) deviations prior strong earthquakes. We discuss common fetures of the pre-earthquake TEC disturbances on the basis of statistics covering 50 strong seismic events during 2005-2006. The F2-layer ionospheric plasma drift under action of the electric fields of seismic origin is proposed as the main reason of producing TEC anomalies. The origin of such electric fields is discussed in terms of the lithosphere-atmosphere-ionosphere coupling system. This theory is supported by numerical simulations using global Upper Atmosphere Model (UAM). UAM calculations show that the vertical electric current with the density of about 20 - 40 nA/m2 flowing between the Earth and ionosphere over an area of about 200 by 2000 km is required to produce the TEC disturbances with the amplitude of about 30% - 50% relatively to the non-disturbed conditions. Ionosphere responses on the variations of the latitudinal position, direction and configuration of the vertical electric currents have been investigated. We show that not only the vertical component of the ionospheric plasma drift but also horizontal components play an important role in producing pre-earthquake TEC disturbances.展开更多
The analysis of existing method for calculation of total content of electrons (TEC) in ionosphere using GPS occultation method does show that due to different values of signal/noise ration in GPS signals ?and , the ne...The analysis of existing method for calculation of total content of electrons (TEC) in ionosphere using GPS occultation method does show that due to different values of signal/noise ration in GPS signals ?and , the new method of optimum measurements of relevant frequency components of TEC measured by phase and code methods should be developed. The optimum quantity of measurements of the above-mentioned frequency components is determined taking into account the limitation imposed on general number of necessary measurements.展开更多
Possible ionospheric disturbances relating to the May 12, 2008, MsS.0 Wenchuan earthquake were identified by Global Positioning System （GPS）-derived total electron content （TEC）, ion- osonde observations, the glob...Possible ionospheric disturbances relating to the May 12, 2008, MsS.0 Wenchuan earthquake were identified by Global Positioning System （GPS）-derived total electron content （TEC）, ion- osonde observations, the global ionospheric map （GIM）, and electron density profiles detected by the Constellation Observation System for Meteorology Ionosphere and Climate （COSMIC）. We applied a statistical test to detect anomalous TEC signals and found that a unique enhancement in TEC, recorded at 16 GPS stations, appeared on May 9, 2008. The critical fre- quency at F2 peak （foF2）, observed by the Chinese ionosondes, and maximal plasma frequency, derived from COSMIC data, revealed a characteristic similar to GPS TEC variations. The GIM showed that the anomalous variations of May 9 were located southeast of the epicenter. Using GPS data from 13 stations near the epicenter, we analyzed the TEC variations of satellite orbit traces during 04：00-11：00 UT. We found that TEC decreased to the east and increased to the southeast of the epicenter during this period. Results showed that the abnormal disturbance on May 9 was probably an ionosphenc precursor of the Wenchuan earthquake of May 12, 2008.展开更多
The global ionosphere maps(GIM)provided by the International GNSS Service(IGS)are extensively utilized for ionospheric morphology monitoring,scientific research,and practical application.Assessing the credibility of G...The global ionosphere maps(GIM)provided by the International GNSS Service(IGS)are extensively utilized for ionospheric morphology monitoring,scientific research,and practical application.Assessing the credibility of GIM products in data-sparse regions is of paramount importance.In this study,measurements from the Crustal Movement Observation Network of China(CMONOC)are leveraged to evaluate the suitability of IGS-GIM products over China region in 2013-2014.The indices of mean error(ME),root mean square error(RMSE),and normalized RMSE(NRMSE)are then utilized to quantify the accuracy of IGS-GIM products.Results revealed distinct local time and latitudinal dependencies in IGS-GIM errors,with substantially high errors at nighttime(NRMSE:39%)and above 40°latitude(NRMSE:49%).Seasonal differences also emerged,with larger equinoctial deviations(NRMSE:33.5%)compared with summer(20%).A preliminary analysis implied that the irregular assimilation of sparse IGS observations,compounded by China’s distinct geomagnetic topology,may manifest as error variations.These results suggest that modeling based solely on IGS-GIM observations engenders inadequate representations across China and that a thorough examination would proffer the necessary foundation for advancing regional total electron content(TEC)constructions.展开更多
Ionosphere delay is one of the main sources of noise affecting global navigation satellite systems, operation of radio detection and ranging systems and very-long-baseline-interferometry. One of the most important and...Ionosphere delay is one of the main sources of noise affecting global navigation satellite systems, operation of radio detection and ranging systems and very-long-baseline-interferometry. One of the most important and common methods to reduce this phase delay is to establish accurate nowcasting and forecasting ionospheric total electron content models. For forecasting models, compared to mid-to-high latitudes, at low latitudes, an active ionosphere leads to extreme differences between long-term prediction models and the actual state of the ionosphere. To solve the problem of low accuracy for long-term prediction models at low latitudes, this article provides a low-latitude, long-term ionospheric prediction model based on a multi-input-multi-output, long-short-term memory neural network. To verify the feasibility of the model, we first made predictions of the vertical total electron content data 24 and 48 hours in advance for each day of July 2020 and then compared both the predictions corresponding to a given day, for all days. Furthermore, in the model modification part, we selected historical data from June 2020 for the validation set, determined a large offset from the results that were predicted to be active, and used the ratio of the mean absolute error of the detected results to that of the predicted results as a correction coefficient to modify our multi-input-multi-output long short-term memory model. The average root mean square error of the 24-hour-advance predictions of our modified model was 4.4 TECU, which was lower and better than5.1 TECU of the multi-input-multi-output, long short-term memory model and 5.9 TECU of the IRI-2016 model.展开更多
电离层总电子含量(Total Electron Content,TEC)的监测与预报是空间环境研究的重要内容,对卫星通讯和导航定位等有重要意义.TEC值影响因素较多,很难确定精确物理模型来对其进行预测.本文设计了基于注意力机制的LSTM模型(Att-LSTM),采用...电离层总电子含量(Total Electron Content,TEC)的监测与预报是空间环境研究的重要内容,对卫星通讯和导航定位等有重要意义.TEC值影响因素较多,很难确定精确物理模型来对其进行预测.本文设计了基于注意力机制的LSTM模型(Att-LSTM),采用过去24小时TEC观测数据对未来TEC进行预测.选择北半球东经100°上,每2.5°纬度选择一个位置,共计36个位置来验证本文提出模型的性能,并与主流的深度学习模型如DNN、RNN、LSTM进行对比实验.取得了如下成果:(1)在选定的36个地区未来2小时单点预测上,基于本文的Att-LSTM模型的TEC预测性能明显优于其他对比模型;(2)讨论了纬度对Att-LSTM预测未来2小时TEC值时性能的影响,发现在北纬0°到60°之间,Att-LSTM预测性能随着纬度的升高而略有降低,在北纬62.5°~87.5°之间,模型预测性能出现扰动,预测效果略差;(3)讨论了磁暴期和磁静期模型的预测性能,发现无论是磁暴期还是磁静期,本文模型预测性能均较好;(4)还讨论了对未来多时点预测效果,实验结果表明,本文所提出的模型对未来2、4个小时的预测拟合度R-Square均超过0.95,预测结果比较可靠,对未来6、8、10个小时预测拟合度最高为0.7934,预测拟合度R-Square下降迅速,预测结果不可靠.展开更多
The total electron content (TEC) data during the total eclipse of March 9, 1997 were collected, which were observed by means of nine GPS receivers located at the eastern Asia. The responses of total TEC to the eclipse...The total electron content (TEC) data during the total eclipse of March 9, 1997 were collected, which were observed by means of nine GPS receivers located at the eastern Asia. The responses of total TEC to the eclipse were analyzed. The results show that: 1) the eclipse led to apparent decrement in TEC that lasted for six to eight hours; 2) the maximum decrement occurred after the middle of the eclipse with time delays varying from twenty minutes to about three hours; 3) the maximum absolute deviations of TEC on the eclipse day do not show a simple and consistent relationship to the maximum solar obscuration.展开更多
Temporal and spatial variation of ionosphere can influence our daily communication activities. By solving the one-year global positioning system （GPS） data of Shandong Continuous Operational Reference System （SDCOR...Temporal and spatial variation of ionosphere can influence our daily communication activities. By solving the one-year global positioning system （GPS） data of Shandong Continuous Operational Reference System （SDCORS） in 2012, we modeled the single-layer spherical harmonic model of vertical total electron content （TEC） over Shandong Province, China, and analyzed the time series of TEC in 2012. The ionosphere over Shandong in 2012 was in the peak year of solar activity. The ionospheric model over Shandong was calibrated and verified using data of the Center for Orbit Determination in Europe （CODE） and the Crustal Movement Observation Network of China （CMONOC）, respectively. The ionosphere is greatly influenced by latitude and solar activity and has the phenomenon of Winter anomaly and semiannual anomaly as well as the session change, diurnal variation, monthly change and seasonal variations. So we can grasp the regularity of temporal and spatial distribution of ionosphere over Shandong, China.展开更多
For spaceborne synthetic aperture radar （SAR） imaging,the dispersive ionosphere has significant effects on the propagationof the low frequency （especially P-band） radar signal. Theionospheric effects can be a sign...For spaceborne synthetic aperture radar （SAR） imaging,the dispersive ionosphere has significant effects on the propagationof the low frequency （especially P-band） radar signal. Theionospheric effects can be a significant source of the phase error inthe radar signal, which causes a degeneration of the image qualityin spaceborne SAR imaging system. The background ionosphericeffects on spaceborne SAR through modeling and simulation areanalyzed, and the qualitative and quantitative analysis based onthe spatio-temporal variability of the ionosphere is given. A novelionosphere correction algorithm （ICA） is proposed to deal with theionospheric effects on the low frequency spaceborne SAR radarsignal. With the proposed algorithm, the degradation of the imagequality caused by the ionosphere is corrected. The simulation resultsshow the effectiveness of the proposed algorithm.展开更多
Space weather determines the state of the ionosphere,which is especially important to know during disturbances.To study this state,the period of March 7-17,2012,which was recommended by SCOSTEP for detailed studies an...Space weather determines the state of the ionosphere,which is especially important to know during disturbances.To study this state,the period of March 7-17,2012,which was recommended by SCOSTEP for detailed studies and called CAWSES-II,was selected.In this period,the behavior of parameters of the solar wind(SW)and the interplanetary magnetic field(IMF)show a number of features.In this paper,we study their relationship with the total electron content(TEC)and the critical frequency(foF2)of the ionosphere at the 110°meridian,near which several ionosondes are located,in the range of 20°N-62.5°N.The correlation coefficients of TEC and foF2 with the SW and IMF parameters for the month and the selected period are calculated.The ionosphere showed the considered disturbances in different ways in different latitudinal zones:negative anomalies are observed at high latitudes,and positive ones at low latitudes.A distinctive feature is the presence of signs of a super-fountain effect.Deviations of TEC and foF2 from their medians can be significant.The IRI model reacted in the latitude range 40°N-62.5°N in the form of negative anomalies,although positive anomalies were observed in the TEC.At lower latitudes,no reaction was observed.For all factors(F10.7,Dst,Kp,IMF,Np),three zones(high-latitude,midlatitude,and low-latitude)are distinguished for different coefficients.The strongest influence of disturbances on the correlation coefficients is observed in the zone of 37.5°N 62.5°N.展开更多
For years great interest has been taken in the effects of physical phenomena on ionosphere structure. A total solar eclipse was visible in North America on August 21 st, 2017. This event offered a great opportunity fo...For years great interest has been taken in the effects of physical phenomena on ionosphere structure. A total solar eclipse was visible in North America on August 21 st, 2017. This event offered a great opportunity for remote sensing the ionospheric behavior under the eclipse condition. In this study we investigated the effects of total solar eclipse on variations of Total Electron Content(TEC), and consequently deviations on regional models of Vertical TEC(VTEC), as well as variations in ionospheric scintillation occurrence. Although variations of TEC due to total solar eclipse are studied thoroughly by many authors, but the effect of solar eclipse on ionospheric scintillation has never been considered before. Our study is based on measurements from a high-rate GPS network over North America on the day of eclipse, a day before and after its occurrence, on the other hand, GPS measurements from groundbased stations on similar days were used to model TEC on the day of event, and also one day before and after it. The results of this study demonstrate that solar eclipse reduced scintillation occurrence at the totality region up to 28 percent and TEC values showed a decrease of maximum 7 TECU. Considering TEC models, our study showed apparent variations in the regional models, which confirms previous studies on ionospheric responses to eclipse as well as theoretical assumptions.展开更多
Ionosphere layer is the atmosphere region which reflects radio waves for telecommunication. The density in particles in this layer influences the quality of communication. This study deals with the effects of Total El...Ionosphere layer is the atmosphere region which reflects radio waves for telecommunication. The density in particles in this layer influences the quality of communication. This study deals with the effects of Total Electron Contents (TEC) on the critical frequency of radio waves in the F2-layer. Total Electron Contents parameter symbolizes electron bulk surface density in ionosphere layer. Above critical frequency value in F2 layer (foF2), radio waves pass through ionosphere. The knowledge of this value enables to calibrate transmission frequencies. In this study, we consider TEC effects on foF2 under quiet time conditions during the maximum and the minimum of solar cycle 22, at Ouagadougou station, in West Africa. The study also considers the effects of seasons and the hourly variability of TEC and foF2. This work shows winter anomaly on foF2 and TEC on minimum and maximum of solar cycle phase respectively. Running International Reference Ionosphere (IRI) model enables to carry out the effects of TEC on foF2 by use of their monthly average values. This leads to a new approach to calibrate radio transmitters.展开更多
电离层闪烁导致卫星导航信号在传播过程中幅度与相位发生随机波动,严重影响接收机的性能。为模拟真实的受电离层闪烁影响的卫星导航信号,以供接收机进行性能测试,提出了基于电离层总电子含量(Total Electron Content,TEC)数据的电离层...电离层闪烁导致卫星导航信号在传播过程中幅度与相位发生随机波动,严重影响接收机的性能。为模拟真实的受电离层闪烁影响的卫星导航信号,以供接收机进行性能测试,提出了基于电离层总电子含量(Total Electron Content,TEC)数据的电离层闪烁仿真方法。该方法通过输入卫星观测文件与导航电文获得电离层的TEC和仰角,利用TEC数据和各卫星仰角,估计出受电离层闪烁影响的各卫星导航信号幅度闪烁指数和相位闪烁指数,结合Cornell模型实现卫星导航信号模拟。该方法充分考虑了卫星导航信号闪烁指数获取困难,以及电离层闪烁对不同卫星导航信号的影响,能够高保真反演卫星导航信号。试验结果表明,该方法反演的电离层闪烁与实际发生的闪烁具有良好的一致性。展开更多
文摘Recent ionospheric observations report anomalous total electron content (TEC) deviations prior strong earthquakes. We discuss common fetures of the pre-earthquake TEC disturbances on the basis of statistics covering 50 strong seismic events during 2005-2006. The F2-layer ionospheric plasma drift under action of the electric fields of seismic origin is proposed as the main reason of producing TEC anomalies. The origin of such electric fields is discussed in terms of the lithosphere-atmosphere-ionosphere coupling system. This theory is supported by numerical simulations using global Upper Atmosphere Model (UAM). UAM calculations show that the vertical electric current with the density of about 20 - 40 nA/m2 flowing between the Earth and ionosphere over an area of about 200 by 2000 km is required to produce the TEC disturbances with the amplitude of about 30% - 50% relatively to the non-disturbed conditions. Ionosphere responses on the variations of the latitudinal position, direction and configuration of the vertical electric currents have been investigated. We show that not only the vertical component of the ionospheric plasma drift but also horizontal components play an important role in producing pre-earthquake TEC disturbances.
文摘The analysis of existing method for calculation of total content of electrons (TEC) in ionosphere using GPS occultation method does show that due to different values of signal/noise ration in GPS signals ?and , the new method of optimum measurements of relevant frequency components of TEC measured by phase and code methods should be developed. The optimum quantity of measurements of the above-mentioned frequency components is determined taking into account the limitation imposed on general number of necessary measurements.
基金supported financially by Science for Earthquake Resilience(XH14064Y)the open foundation of the State Key Laboratory of Geodesy and Earth's Dynamics(SKLGED2014-5-2-E)
文摘Possible ionospheric disturbances relating to the May 12, 2008, MsS.0 Wenchuan earthquake were identified by Global Positioning System （GPS）-derived total electron content （TEC）, ion- osonde observations, the global ionospheric map （GIM）, and electron density profiles detected by the Constellation Observation System for Meteorology Ionosphere and Climate （COSMIC）. We applied a statistical test to detect anomalous TEC signals and found that a unique enhancement in TEC, recorded at 16 GPS stations, appeared on May 9, 2008. The critical fre- quency at F2 peak （foF2）, observed by the Chinese ionosondes, and maximal plasma frequency, derived from COSMIC data, revealed a characteristic similar to GPS TEC variations. The GIM showed that the anomalous variations of May 9 were located southeast of the epicenter. Using GPS data from 13 stations near the epicenter, we analyzed the TEC variations of satellite orbit traces during 04：00-11：00 UT. We found that TEC decreased to the east and increased to the southeast of the epicenter during this period. Results showed that the abnormal disturbance on May 9 was probably an ionosphenc precursor of the Wenchuan earthquake of May 12, 2008.
基金the National Key R&D Program of China(Grant No.2022YFF0503702)the National Natural Science Foundation of China(Grant Nos.42074186,41831071,42004136,and 42274195)+1 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK20211036)the Specialized Research Fund for State Key Laboratories,and the University of Science and Technology of China Research Funds of the Double First-Class Initiative(Grant No.YD2080002013).
文摘The global ionosphere maps(GIM)provided by the International GNSS Service(IGS)are extensively utilized for ionospheric morphology monitoring,scientific research,and practical application.Assessing the credibility of GIM products in data-sparse regions is of paramount importance.In this study,measurements from the Crustal Movement Observation Network of China(CMONOC)are leveraged to evaluate the suitability of IGS-GIM products over China region in 2013-2014.The indices of mean error(ME),root mean square error(RMSE),and normalized RMSE(NRMSE)are then utilized to quantify the accuracy of IGS-GIM products.Results revealed distinct local time and latitudinal dependencies in IGS-GIM errors,with substantially high errors at nighttime(NRMSE:39%)and above 40°latitude(NRMSE:49%).Seasonal differences also emerged,with larger equinoctial deviations(NRMSE:33.5%)compared with summer(20%).A preliminary analysis implied that the irregular assimilation of sparse IGS observations,compounded by China’s distinct geomagnetic topology,may manifest as error variations.These results suggest that modeling based solely on IGS-GIM observations engenders inadequate representations across China and that a thorough examination would proffer the necessary foundation for advancing regional total electron content(TEC)constructions.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0302101)the Initiative Program of State Key Laboratory of Precision Measurement Technology and Instrument。
文摘Ionosphere delay is one of the main sources of noise affecting global navigation satellite systems, operation of radio detection and ranging systems and very-long-baseline-interferometry. One of the most important and common methods to reduce this phase delay is to establish accurate nowcasting and forecasting ionospheric total electron content models. For forecasting models, compared to mid-to-high latitudes, at low latitudes, an active ionosphere leads to extreme differences between long-term prediction models and the actual state of the ionosphere. To solve the problem of low accuracy for long-term prediction models at low latitudes, this article provides a low-latitude, long-term ionospheric prediction model based on a multi-input-multi-output, long-short-term memory neural network. To verify the feasibility of the model, we first made predictions of the vertical total electron content data 24 and 48 hours in advance for each day of July 2020 and then compared both the predictions corresponding to a given day, for all days. Furthermore, in the model modification part, we selected historical data from June 2020 for the validation set, determined a large offset from the results that were predicted to be active, and used the ratio of the mean absolute error of the detected results to that of the predicted results as a correction coefficient to modify our multi-input-multi-output long short-term memory model. The average root mean square error of the 24-hour-advance predictions of our modified model was 4.4 TECU, which was lower and better than5.1 TECU of the multi-input-multi-output, long short-term memory model and 5.9 TECU of the IRI-2016 model.
文摘电离层总电子含量(Total Electron Content,TEC)的监测与预报是空间环境研究的重要内容,对卫星通讯和导航定位等有重要意义.TEC值影响因素较多,很难确定精确物理模型来对其进行预测.本文设计了基于注意力机制的LSTM模型(Att-LSTM),采用过去24小时TEC观测数据对未来TEC进行预测.选择北半球东经100°上,每2.5°纬度选择一个位置,共计36个位置来验证本文提出模型的性能,并与主流的深度学习模型如DNN、RNN、LSTM进行对比实验.取得了如下成果:(1)在选定的36个地区未来2小时单点预测上,基于本文的Att-LSTM模型的TEC预测性能明显优于其他对比模型;(2)讨论了纬度对Att-LSTM预测未来2小时TEC值时性能的影响,发现在北纬0°到60°之间,Att-LSTM预测性能随着纬度的升高而略有降低,在北纬62.5°~87.5°之间,模型预测性能出现扰动,预测效果略差;(3)讨论了磁暴期和磁静期模型的预测性能,发现无论是磁暴期还是磁静期,本文模型预测性能均较好;(4)还讨论了对未来多时点预测效果,实验结果表明,本文所提出的模型对未来2、4个小时的预测拟合度R-Square均超过0.95,预测结果比较可靠,对未来6、8、10个小时预测拟合度最高为0.7934,预测拟合度R-Square下降迅速,预测结果不可靠.
文摘The total electron content (TEC) data during the total eclipse of March 9, 1997 were collected, which were observed by means of nine GPS receivers located at the eastern Asia. The responses of total TEC to the eclipse were analyzed. The results show that: 1) the eclipse led to apparent decrement in TEC that lasted for six to eight hours; 2) the maximum decrement occurred after the middle of the eclipse with time delays varying from twenty minutes to about three hours; 3) the maximum absolute deviations of TEC on the eclipse day do not show a simple and consistent relationship to the maximum solar obscuration.
基金supported by the National Natural Science Foundation of China(No.41374009)the National Basic Science and Technology Special Project of China(No. 2015FY310200)+1 种基金the Shandong Natural Science Foundation of China (No.ZR2013DM009)the SDUST Research Fund(No. 2014TDJH101)
文摘Temporal and spatial variation of ionosphere can influence our daily communication activities. By solving the one-year global positioning system （GPS） data of Shandong Continuous Operational Reference System （SDCORS） in 2012, we modeled the single-layer spherical harmonic model of vertical total electron content （TEC） over Shandong Province, China, and analyzed the time series of TEC in 2012. The ionosphere over Shandong in 2012 was in the peak year of solar activity. The ionospheric model over Shandong was calibrated and verified using data of the Center for Orbit Determination in Europe （CODE） and the Crustal Movement Observation Network of China （CMONOC）, respectively. The ionosphere is greatly influenced by latitude and solar activity and has the phenomenon of Winter anomaly and semiannual anomaly as well as the session change, diurnal variation, monthly change and seasonal variations. So we can grasp the regularity of temporal and spatial distribution of ionosphere over Shandong, China.
基金supported by the National Natural Science Foundation of China(61222108)the Research Fund for the Doctoral Program of Higher Education of China(20120203130001)+1 种基金the Fundamental Research Funds for the Central Universities(2015HGBZ01062015HGQC0005)
文摘For spaceborne synthetic aperture radar （SAR） imaging,the dispersive ionosphere has significant effects on the propagationof the low frequency （especially P-band） radar signal. Theionospheric effects can be a significant source of the phase error inthe radar signal, which causes a degeneration of the image qualityin spaceborne SAR imaging system. The background ionosphericeffects on spaceborne SAR through modeling and simulation areanalyzed, and the qualitative and quantitative analysis based onthe spatio-temporal variability of the ionosphere is given. A novelionosphere correction algorithm （ICA） is proposed to deal with theionospheric effects on the low frequency spaceborne SAR radarsignal. With the proposed algorithm, the degradation of the imagequality caused by the ionosphere is corrected. The simulation resultsshow the effectiveness of the proposed algorithm.
基金financially supported by the Ministry of Science and Higher Education of the Russian Federation(State assignment in the field of scientific activity,Southern Federal University,N 0852-2020-0015)。
文摘Space weather determines the state of the ionosphere,which is especially important to know during disturbances.To study this state,the period of March 7-17,2012,which was recommended by SCOSTEP for detailed studies and called CAWSES-II,was selected.In this period,the behavior of parameters of the solar wind(SW)and the interplanetary magnetic field(IMF)show a number of features.In this paper,we study their relationship with the total electron content(TEC)and the critical frequency(foF2)of the ionosphere at the 110°meridian,near which several ionosondes are located,in the range of 20°N-62.5°N.The correlation coefficients of TEC and foF2 with the SW and IMF parameters for the month and the selected period are calculated.The ionosphere showed the considered disturbances in different ways in different latitudinal zones:negative anomalies are observed at high latitudes,and positive ones at low latitudes.A distinctive feature is the presence of signs of a super-fountain effect.Deviations of TEC and foF2 from their medians can be significant.The IRI model reacted in the latitude range 40°N-62.5°N in the form of negative anomalies,although positive anomalies were observed in the TEC.At lower latitudes,no reaction was observed.For all factors(F10.7,Dst,Kp,IMF,Np),three zones(high-latitude,midlatitude,and low-latitude)are distinguished for different coefficients.The strongest influence of disturbances on the correlation coefficients is observed in the zone of 37.5°N 62.5°N.
基金under bi-lateral project DEAREST(project number:SCHU 1103/15-1)funded by German Research Foundation(DFG)Ministry of Science and Technology of Taiwan(MOST)
文摘For years great interest has been taken in the effects of physical phenomena on ionosphere structure. A total solar eclipse was visible in North America on August 21 st, 2017. This event offered a great opportunity for remote sensing the ionospheric behavior under the eclipse condition. In this study we investigated the effects of total solar eclipse on variations of Total Electron Content(TEC), and consequently deviations on regional models of Vertical TEC(VTEC), as well as variations in ionospheric scintillation occurrence. Although variations of TEC due to total solar eclipse are studied thoroughly by many authors, but the effect of solar eclipse on ionospheric scintillation has never been considered before. Our study is based on measurements from a high-rate GPS network over North America on the day of eclipse, a day before and after its occurrence, on the other hand, GPS measurements from groundbased stations on similar days were used to model TEC on the day of event, and also one day before and after it. The results of this study demonstrate that solar eclipse reduced scintillation occurrence at the totality region up to 28 percent and TEC values showed a decrease of maximum 7 TECU. Considering TEC models, our study showed apparent variations in the regional models, which confirms previous studies on ionospheric responses to eclipse as well as theoretical assumptions.
文摘Ionosphere layer is the atmosphere region which reflects radio waves for telecommunication. The density in particles in this layer influences the quality of communication. This study deals with the effects of Total Electron Contents (TEC) on the critical frequency of radio waves in the F2-layer. Total Electron Contents parameter symbolizes electron bulk surface density in ionosphere layer. Above critical frequency value in F2 layer (foF2), radio waves pass through ionosphere. The knowledge of this value enables to calibrate transmission frequencies. In this study, we consider TEC effects on foF2 under quiet time conditions during the maximum and the minimum of solar cycle 22, at Ouagadougou station, in West Africa. The study also considers the effects of seasons and the hourly variability of TEC and foF2. This work shows winter anomaly on foF2 and TEC on minimum and maximum of solar cycle phase respectively. Running International Reference Ionosphere (IRI) model enables to carry out the effects of TEC on foF2 by use of their monthly average values. This leads to a new approach to calibrate radio transmitters.
文摘电离层闪烁导致卫星导航信号在传播过程中幅度与相位发生随机波动,严重影响接收机的性能。为模拟真实的受电离层闪烁影响的卫星导航信号,以供接收机进行性能测试,提出了基于电离层总电子含量(Total Electron Content,TEC)数据的电离层闪烁仿真方法。该方法通过输入卫星观测文件与导航电文获得电离层的TEC和仰角,利用TEC数据和各卫星仰角,估计出受电离层闪烁影响的各卫星导航信号幅度闪烁指数和相位闪烁指数,结合Cornell模型实现卫星导航信号模拟。该方法充分考虑了卫星导航信号闪烁指数获取困难,以及电离层闪烁对不同卫星导航信号的影响,能够高保真反演卫星导航信号。试验结果表明,该方法反演的电离层闪烁与实际发生的闪烁具有良好的一致性。
