It has been proven that carrier smoothing and differential global positioning system （DGPS） are effective to improve the accuracy of pseudorange by reducing the noise in it and eliminating almost all the common mode...It has been proven that carrier smoothing and differential global positioning system （DGPS） are effective to improve the accuracy of pseudorange by reducing the noise in it and eliminating almost all the common mode errors between the ground station and user. However, another issue coming with local area augmentation system （LAAS） is how to find an adaptive smoothing window width to minimize the error on account of ionosphere delay and multipath. Based on the errors analysis in carrier smoothing process, a novel algorithm is formulated to design adaptive Hatch filter whose smoothing window width flexibly varies with the characteristic of ionosphere delay and multipath in the differential carrier smoothing process. By conducting the simulation in LAAS and after compared with traditional Hatch filers, it reveals that not only the accuracy of differential correction, but also the accuracy and the robustness of positioning results are significantly improved by using the designed adaptive Hatch filter.展开更多
A future Chinese mission is introduced to study the coupling between magnetosphere,ionosphere and thermosphere,i.e.the Magnetosphere-Ionosphere-Thermosphere Coupling Small Satellite Constellation(MIT).The scientific o...A future Chinese mission is introduced to study the coupling between magnetosphere,ionosphere and thermosphere,i.e.the Magnetosphere-Ionosphere-Thermosphere Coupling Small Satellite Constellation(MIT).The scientific objective of the mission is to focus on the outflow ions from the ionosphere to the magnetosphere.The constellation is planning to be composed of four small satellites;each small satellite has its own orbit and crosses the polar region at nearly the same time but at different altitude.The payloads onboard include particle detectors,electromagnetic payloads,auroral imagers and neutral atom imagers.With these payloads,the mission will be able to investigate acceleration mechanism of the upflow ions at different altitudes.Currently the orbits have been determined and prototypes of some have also been completed.Competition for next phase selection is scheduled in late 2015.展开更多
Comparison of regular(diurnal,seasonal and solar cycle)variations of high-latitude,mid-latitude and low-latitude ionospheric characteristics has been provided on basis of local empirical models of the peak electron de...Comparison of regular(diurnal,seasonal and solar cycle)variations of high-latitude,mid-latitude and low-latitude ionospheric characteristics has been provided on basis of local empirical models of the peak electron density and the peak height.The local empirical models were derived from the hand-scaled ionogram data recorded by DPS-4 digisondes located at Norilsk(69°N,88°E),Irkutsk(52°N,104°E)and Hainan(19°N,109°E)for a 6-year period from December,2002 to December,2008.The technique used to build the local empirical model is described.The primary focus is diurnal-seasonal behavior under low solar activity and its change with increasing solar activity.Both common and specific features of the high-latitude(Norilsk),mid-latitude(Irkutsk)and low-latitude(Hainan)regular variations were revealed using their local empirical models.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
In this national biannual report, we will outline some recent progresses in ionospheric studies conducted by Chinese scientists since 2012. The mentioned aspects include: the solar activity control of the ionosphere; ...In this national biannual report, we will outline some recent progresses in ionospheric studies conducted by Chinese scientists since 2012. The mentioned aspects include: the solar activity control of the ionosphere; couplings between the ionosphere, lower atmosphere and plasmasphere;ionospheric climatology and disturbances; ionospheric irregularities and scintillation; models, data assimilation and simulations; unusual phenomena of the ionosphere; possible seismic signatures presented in ionospheric observations, and some methodology progresses. These progresses will enhance our ability to observe the ionosphere, provide more reasonable understanding about the states of the ionosphere and underlying fundamental processes, and stimulate ionospheric modeling, forecasting and related applications.展开更多
The Chinese Meridian Project(CMP)is a major national science and technology infrastructure constructed in two steps.The first phase of the CMP has been operating for more than a solar cycle.From 2022 to 2023,utilizing...The Chinese Meridian Project(CMP)is a major national science and technology infrastructure constructed in two steps.The first phase of the CMP has been operating for more than a solar cycle.From 2022 to 2023,utilizing the monitoring data collected by the CMP,scientists made major breakthroughs in fields of ionosphere,middle and upper atmosphere,and coupling between layers.The construction of the second phase of the CMP is nearly finished,and the project is expected to operate as a whole in 2025 after national acceptance of the second phase.The whole project was built in an architecture of so-called“One Chain,Three Networks and Four Focuses”.It is promising to make a three-dimensional observation of the whole solar-terrestrial space.The science community is looking forward to the great contribution of the CMP to space weather and space physics research.展开更多
According to the Doppler sensitive of the phase coded pulse compression signal, a Doppler estimating and compensating method based on phase is put forward to restrain the Doppler sidelobes, raise the signal-to-noise r...According to the Doppler sensitive of the phase coded pulse compression signal, a Doppler estimating and compensating method based on phase is put forward to restrain the Doppler sidelobes, raise the signal-to-noise ratio and improve measuring resolution. The compensation method is used to decompose the echo to amplitude and phase, and then compose the new compensated echo by the amplitude and the nonlinear component of the phase. Furthermore the linear component of the phase can be used to estimate the Doppler frequency shift. The computer simulation and the real data processing show that the method has accurately estimated the Doppler frequency shift, successfully restrained the energy leakage on spectrum, greatly increased the echo signal-to-noise ratio and improved the detection performance of the radio system in both time domain and frequency domain.展开更多
In this report,we outline works done by scientists from the Mainland of China on various ionospheric topics after the release of the National Report of China in 2020 on ionospheric researchto the Committee on Space Re...In this report,we outline works done by scientists from the Mainland of China on various ionospheric topics after the release of the National Report of China in 2020 on ionospheric researchto the Committee on Space Research(COSPAR).More than 170 papers were published in 2020-2021.The current report covers the following topics:ionospheric space weather,ionospheric structures and climatology,ionospheric dynamics and couplings,ionospheric irregularity and scintillation,modeling and data assimilation,and ionosphere and sounding techniques.Planetary ionospheres are included for the first time.展开更多
The ionosphere varies over multiple time scales,which are classified into two categories: the climatology and weather variations.In this national report,we give a brief summary of recent progresses in ionospheric clim...The ionosphere varies over multiple time scales,which are classified into two categories: the climatology and weather variations.In this national report,we give a brief summary of recent progresses in ionospheric climatology with focus on(1) the seasonal variations,(2) solar cycle effects, and(3) empirical modeling of the ionosphere.The seasonal variations of the ionosphere have been explored in many works to give a more detailed picture with regional and global features at various altitudes by analyzing the observation data from various sources and models.Moreover,a series of studies reported the response of the ionosphere to solar cycle variations,which revealed some novel and detailed features of solar activity dependence of ionospheric parameters at different altitudes. These investigations have improved our understanding on the states of the ionosphere and underlying fundamental processes,provided clues to future studies on ionospheric weather,and guided ionospheric modeling,forecasting and related applications.展开更多
The ionospheric responses to two strong storms on 17-19 August 2003 and 22-23 January 2004 are studied,using the data from Irkutsk(52.5°N,104°E) and Hainan(19.5°N,109°E) ionospheric stations.The an...The ionospheric responses to two strong storms on 17-19 August 2003 and 22-23 January 2004 are studied,using the data from Irkutsk(52.5°N,104°E) and Hainan(19.5°N,109°E) ionospheric stations.The analysis of variations in relative deviations of the critical frequency △f_0F_2 revealed that at middle latitudes(Irkutsk) negative disturbances were observed in the summer ionosphere; positive and negative ones,in the winter ionosphere during the main and recovery phases respectively.At low latitudes(Hainan),the disturbances were positive in all the cases considered. Mechanisms of the disturbances were analyzed with the aid of empirical models of the neutral atmosphere NRLMSISE-00 and thermospheric wind HWM07.The main factors determining △f_0F_2 variations at middle latitudes during the storms were demonstrated to be the disturbed equatorward thermospheric wind transporting the disturbed atmospheric composition,the increase in the atomic oxygen concentration,and the passage of internal gravity waves.At low latitudes,the effects associated with neutral composition variations are less significant than those of the thermospheric wind and electric fields.展开更多
The Chinese Meridian Project is a ground-based space environment monitoring facility in China.The first phase of the project has been put into formal operation since 2012 after 4-year’s construction.It consists of 15...The Chinese Meridian Project is a ground-based space environment monitoring facility in China.The first phase of the project has been put into formal operation since 2012 after 4-year’s construction.It consists of 15 observatories located roughly along 120°E longitude and 30°N latitude,with each observatory equipped with multiple instruments to monitor space environment.Based on the huge observational data accumulated,significant scientific achievements have been made with more than 300 peer-reviewed journal papers published.In this report,scientific results from the past two years have been reviewed with topics covering fields of geomagnetic,atmosphere,ionosphere,and their responses to solar activities.The excellent achievements from the Phase I of Chinese Meridian Project lay a good foundation for Phase II,which has already been approved with the official kick-off of construction in November 2019.It will conceive an unprecedented contribution to global space weather community from China.展开更多
A theoretical model of ionospheric electric fields at mid-and low-latitudes is developed.In the geomagnetic dipolar coordinate system,the ionospheric dynamo equations were solved,and the ionospheric electric potential...A theoretical model of ionospheric electric fields at mid-and low-latitudes is developed.In the geomagnetic dipolar coordinate system,the ionospheric dynamo equations were solved,and the ionospheric electric potential and electric field were derived respectively.Major parameters for the model inputs,such as the neutral winds,the densities and temperatures of electron,ions and neutrals,are obtained from empirical models.The global ionospheric electrical potential and field at mid-and low-latitudes derived from our model are largely in agreement with the results presented by other authors and the empirical model.Using our model,it is found that the diurnal component of the HWM93 wind mainly contributed to the formation of the vertical electric field,while the semidiurnal component mainly contributed to the zonal electric field.Finally,by adjustment of the input F region winds and conductivities,most discrepancies between our model and the empirical one can be eliminated,and it is proved that the F region dynamo is the most significant contribution to the electric fields.展开更多
This brief report reviews the recent developments in ionospheric physics studies made by Chinese scientists. It covers areas from the numerical simulations and theoretical researches on ionospheric properties, ionosph...This brief report reviews the recent developments in ionospheric physics studies made by Chinese scientists. It covers areas from the numerical simulations and theoretical researches on ionospheric properties, ionospheric disturbances, space weather events in the ionosphere to ionospheric obserwtions.展开更多
The Chinese Meridian Project(CMP)is a major national science and technology infrastructure invested and constructed by the Chinese government.The project builds space environment observation stations,focusing on the m...The Chinese Meridian Project(CMP)is a major national science and technology infrastructure invested and constructed by the Chinese government.The project builds space environment observation stations,focusing on the monitoring of the space environment over China,so as to provide a monitoring basis for clarifying the regional characteristics of the space environment over China and its relationship with global change,and making important innovative scientific achievements.The first phase of the CMP passed the national acceptance in 2012.It has been running for nearly ten years and has accumulated more than 8 TB monitoring data.These data are all available to all data users through the data center of the project.From 2020 to 2021,users of CMP data have completed a series of original works,which have solved current scientific problems in the field of space physics research.On the other hand,they also make us look forward to the completion of the second phase of CMP and its application benefits in national major strategic needs and cutting-edge scientific research.展开更多
The perfect sequences are so ideal that all out-of-phase autocorrelation coefficients are zero, and if the sequences are used as the coding modulating signal for the phase-modulated radar, there will be no interferenc...The perfect sequences are so ideal that all out-of-phase autocorrelation coefficients are zero, and if the sequences are used as the coding modulating signal for the phase-modulated radar, there will be no interference of side lobes theoretically. However, it has been proved that there are no binary perfect sequences of period 4 〈 n ≤ 12100. Hence, the almost perfect sequences with all out-of-phase autocorrelation coefficients as zero except one are of great practice in engineering. Currently, the cyclic difference set is one of most effective tools to analyze the binary sequences with perfect periodic autocorrelation function. In this article, two characteristic formulas corresponding to the autocorrelation and symmetric structure of almost perfect sequences are calculated respectively. All almost perfect sequences with period n, which is a multiple of 4, can be figured out by the two formulas. Several almost perfect sequences with different periods have been hunted by the program based on the two formulas and then applied to the simulation program and practical application for ionospheric sounding.展开更多
The Experimental Satellite on Electromagnetism Monitoring(ESEM) was proposed in 2003 and proved in 2013 after 10-years' scientific demonstration. The ESEM mission was proposed to be the first satellite of space-ba...The Experimental Satellite on Electromagnetism Monitoring(ESEM) was proposed in 2003 and proved in 2013 after 10-years' scientific demonstration. The ESEM mission was proposed to be the first satellite of space-based geophysical fields observation system in China with a lot of application prospects in earthquake science, geophysics, space sciences and so on. And coincide with the mission objectives, the satellite decides to use the Circular Sun Synchronous Orbit with an altitude of 507 km and descending node time at 14:00 LT. The payload assemble includes 8 instruments,Search-Coil Magnetometer, Electric Field Detector, High precision Magnetometer, GNSS occupation Receiver, Plasma Analyzer, Langmuir Probe, Energetic Particle Detector, and Three-frequency Transmitter. According to the planned schedule, the satellite is due to be launched in 2016–2017 and will be onboard operated for 5 years.展开更多
The ionosphere, as the largest and least predictable error source, its behavior cannot be observed at all places simultaneously. The confidence bound, called the grid ionospheric vertical error(GIVE), can only be dete...The ionosphere, as the largest and least predictable error source, its behavior cannot be observed at all places simultaneously. The confidence bound, called the grid ionospheric vertical error(GIVE), can only be determined with the aid of a threat model which is used to restrict the expected ionospheric behavior. However, the spatial threat model at present widespread used, which is based on fit radius and relative centroid metric(RCM), is too conservative or the resulting GIVEs will be too large and will reduce the availability of satellite-based augmentation system(SBAS). In this paper, layered two-dimensional parameters, the vertical direction double RCMs, are introduced based on the spatial variability of the ionosphere. Comparing with the traditional threat model, the experimental results show that the user ionospheric vertical error(UIVE) average reduction rate reaches 16%. And the 95% protection level of conterminous United States(CONUS) is 28%, even under disturbed days, which reaches about 5% reduction rates.The results show that the system service performance has been improved better.展开更多
In the equatorial region,deep amplitude fading in global positioning system(GPS)signals frequently occurs during the strong ionospheric scintillation,it can lead to the loss of lock in GPS carrier tracking loops,and r...In the equatorial region,deep amplitude fading in global positioning system(GPS)signals frequently occurs during the strong ionospheric scintillation,it can lead to the loss of lock in GPS carrier tracking loops,and result in increased positioning error and even navigation interruption.The relationships between amplitude scintillation indices and detrended carrier frequency are investigated,based on GPS L1 C/A signals during the last peak of the solar cycle at the low latitude site of São Josédos Campos,Brazil(23.2S,45.9W)from 2013 to 2015.Corresponding mathematic model of the probability distribution function is built for the first time to provide statistical analysis on the above relationships.The results show that the standard carrier frequencies reveal an almost linear relation with the amplitude scintillation indices.Moreover,the frequency widths of detrended frequency are proportional to levels of amplitude scintillation when the value of the peak probability is lower than the corresponding boundary.A conclusion can be drawn that different levels of amplitude scintillation will influence the fluctuation of the carrier frequency.The analysis will provide useful guidance to set the receiver’s bandwidth with respect to the different scintillation levels and design the advanced tracking algorithms to improve the robustness and precision of the GPS receiver.展开更多
The ionospheric effect from solar activity can be seen as the background in the process of detecting the ionospheric precursor prior to strong earthquakes.The ionospheric variation induced by the forthcoming earthquak...The ionospheric effect from solar activity can be seen as the background in the process of detecting the ionospheric precursor prior to strong earthquakes.The ionospheric variation induced by the forthcoming earthquake can be covered by the strong solar background during the period of high solar activity.The issue of how to remove the ionospheric effect from solar radiation is of outstanding significance.In this paper,a method of Empirical Mode Decomposition(EMD) is used to eliminate the solar background.As a case study,the global ionospheric map TEC before the M9.0 Tohoku earthquake on 11 March 2011 is analyzed.After the effect of solar radiation is removed using the EMD method,the precursor of the imminent earthquake is more obvious.The ionospheric anomaly had a local character and only appeared close to the earthquake epicenter while the useful signals were covered by the solar radiation background with traditional method,which implies that the EMD method is effective in eliminating solar radiation background.展开更多
基金supported by the National Natural Science Foundationof China (60974104)the National Defense Technical Foundation of Shipbuilding Industry (08J3.8.8)
文摘It has been proven that carrier smoothing and differential global positioning system （DGPS） are effective to improve the accuracy of pseudorange by reducing the noise in it and eliminating almost all the common mode errors between the ground station and user. However, another issue coming with local area augmentation system （LAAS） is how to find an adaptive smoothing window width to minimize the error on account of ionosphere delay and multipath. Based on the errors analysis in carrier smoothing process, a novel algorithm is formulated to design adaptive Hatch filter whose smoothing window width flexibly varies with the characteristic of ionosphere delay and multipath in the differential carrier smoothing process. By conducting the simulation in LAAS and after compared with traditional Hatch filers, it reveals that not only the accuracy of differential correction, but also the accuracy and the robustness of positioning results are significantly improved by using the designed adaptive Hatch filter.
基金Supported by the Strategic Priority Research Program on Space Science(XDA04060201)of Chinese Academy of Sciencesthe Chinese Academy of Sciences"Hundred Talented Program"(Y32135A47S)+2 种基金the Chinese National Science Foundation(411774149)the Specialized Research Fund for State Key laboratory of Chinathe Chinese Academy of Sciences Visiting Fellowship for Researchers from Developing Countries
文摘A future Chinese mission is introduced to study the coupling between magnetosphere,ionosphere and thermosphere,i.e.the Magnetosphere-Ionosphere-Thermosphere Coupling Small Satellite Constellation(MIT).The scientific objective of the mission is to focus on the outflow ions from the ionosphere to the magnetosphere.The constellation is planning to be composed of four small satellites;each small satellite has its own orbit and crosses the polar region at nearly the same time but at different altitude.The payloads onboard include particle detectors,electromagnetic payloads,auroral imagers and neutral atom imagers.With these payloads,the mission will be able to investigate acceleration mechanism of the upflow ions at different altitudes.Currently the orbits have been determined and prototypes of some have also been completed.Competition for next phase selection is scheduled in late 2015.
基金Supported by Russian Foundation for Basic Research(13-05-91159-GFEN_a)Project 14.518.11.7065 and agreement N8388 of the Ministry of Education and Science of the Russian Federation+1 种基金the National Natural Science Foundation(41274146)the Specialized Research Fund for State Key Laboratory in China
文摘Comparison of regular(diurnal,seasonal and solar cycle)variations of high-latitude,mid-latitude and low-latitude ionospheric characteristics has been provided on basis of local empirical models of the peak electron density and the peak height.The local empirical models were derived from the hand-scaled ionogram data recorded by DPS-4 digisondes located at Norilsk(69°N,88°E),Irkutsk(52°N,104°E)and Hainan(19°N,109°E)for a 6-year period from December,2002 to December,2008.The technique used to build the local empirical model is described.The primary focus is diurnal-seasonal behavior under low solar activity and its change with increasing solar activity.Both common and specific features of the high-latitude(Norilsk),mid-latitude(Irkutsk)and low-latitude(Hainan)regular variations were revealed using their local empirical models.
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Supported by National Natural Science Foundation of China(41231065)the Project of Chinese Academy of Sciences(KZZD-EW-01-3)National Key Basic Research Program of China(2012CB825604)
文摘In this national biannual report, we will outline some recent progresses in ionospheric studies conducted by Chinese scientists since 2012. The mentioned aspects include: the solar activity control of the ionosphere; couplings between the ionosphere, lower atmosphere and plasmasphere;ionospheric climatology and disturbances; ionospheric irregularities and scintillation; models, data assimilation and simulations; unusual phenomena of the ionosphere; possible seismic signatures presented in ionospheric observations, and some methodology progresses. These progresses will enhance our ability to observe the ionosphere, provide more reasonable understanding about the states of the ionosphere and underlying fundamental processes, and stimulate ionospheric modeling, forecasting and related applications.
基金Supported by National Major Science and Technology Infrastructure Construction Project:the Chinese Meridian Project(2017-000052-73-01-002390)。
文摘The Chinese Meridian Project(CMP)is a major national science and technology infrastructure constructed in two steps.The first phase of the CMP has been operating for more than a solar cycle.From 2022 to 2023,utilizing the monitoring data collected by the CMP,scientists made major breakthroughs in fields of ionosphere,middle and upper atmosphere,and coupling between layers.The construction of the second phase of the CMP is nearly finished,and the project is expected to operate as a whole in 2025 after national acceptance of the second phase.The whole project was built in an architecture of so-called“One Chain,Three Networks and Four Focuses”.It is promising to make a three-dimensional observation of the whole solar-terrestrial space.The science community is looking forward to the great contribution of the CMP to space weather and space physics research.
基金supported partly by the National Natural Science Foundation of China(40804042)the Post DoctorFoundation of China(20070420919).
文摘According to the Doppler sensitive of the phase coded pulse compression signal, a Doppler estimating and compensating method based on phase is put forward to restrain the Doppler sidelobes, raise the signal-to-noise ratio and improve measuring resolution. The compensation method is used to decompose the echo to amplitude and phase, and then compose the new compensated echo by the amplitude and the nonlinear component of the phase. Furthermore the linear component of the phase can be used to estimate the Doppler frequency shift. The computer simulation and the real data processing show that the method has accurately estimated the Doppler frequency shift, successfully restrained the energy leakage on spectrum, greatly increased the echo signal-to-noise ratio and improved the detection performance of the radio system in both time domain and frequency domain.
基金Supported by National Natural Science Foundation of China(42030202,42188101,42122031)。
文摘In this report,we outline works done by scientists from the Mainland of China on various ionospheric topics after the release of the National Report of China in 2020 on ionospheric researchto the Committee on Space Research(COSPAR).More than 170 papers were published in 2020-2021.The current report covers the following topics:ionospheric space weather,ionospheric structures and climatology,ionospheric dynamics and couplings,ionospheric irregularity and scintillation,modeling and data assimilation,and ionosphere and sounding techniques.Planetary ionospheres are included for the first time.
基金supported by the Chinese Academy of Sciences(KZZD-EW-01-3)National Key Basic Research Program of China(2012- CB825604)National Natural Science Foundation of China(41074112,41174137)
文摘The ionosphere varies over multiple time scales,which are classified into two categories: the climatology and weather variations.In this national report,we give a brief summary of recent progresses in ionospheric climatology with focus on(1) the seasonal variations,(2) solar cycle effects, and(3) empirical modeling of the ionosphere.The seasonal variations of the ionosphere have been explored in many works to give a more detailed picture with regional and global features at various altitudes by analyzing the observation data from various sources and models.Moreover,a series of studies reported the response of the ionosphere to solar cycle variations,which revealed some novel and detailed features of solar activity dependence of ionospheric parameters at different altitudes. These investigations have improved our understanding on the states of the ionosphere and underlying fundamental processes,provided clues to future studies on ionospheric weather,and guided ionospheric modeling,forecasting and related applications.
基金Supported by the Russian Foundation for Basic Research(11-05-91153,11-05-00908)Program of the Division of EarthSciences,Russian Academy of Sciences(No.8)+1 种基金National Natural Science Foundation of China(41274146,41074114)the Specialized Research Fund for State Key Laboratory of China
文摘The ionospheric responses to two strong storms on 17-19 August 2003 and 22-23 January 2004 are studied,using the data from Irkutsk(52.5°N,104°E) and Hainan(19.5°N,109°E) ionospheric stations.The analysis of variations in relative deviations of the critical frequency △f_0F_2 revealed that at middle latitudes(Irkutsk) negative disturbances were observed in the summer ionosphere; positive and negative ones,in the winter ionosphere during the main and recovery phases respectively.At low latitudes(Hainan),the disturbances were positive in all the cases considered. Mechanisms of the disturbances were analyzed with the aid of empirical models of the neutral atmosphere NRLMSISE-00 and thermospheric wind HWM07.The main factors determining △f_0F_2 variations at middle latitudes during the storms were demonstrated to be the disturbed equatorward thermospheric wind transporting the disturbed atmospheric composition,the increase in the atomic oxygen concentration,and the passage of internal gravity waves.At low latitudes,the effects associated with neutral composition variations are less significant than those of the thermospheric wind and electric fields.
基金Supported by the Open Research Project of Large Research Infrastructures of Chinese Academy of Sciences,the Study on the Interaction between Low/Mid-latitude Atmosphere and Ionosphere Based on the Chinese Meridian Project,and the Chinese Meridian Project。
文摘The Chinese Meridian Project is a ground-based space environment monitoring facility in China.The first phase of the project has been put into formal operation since 2012 after 4-year’s construction.It consists of 15 observatories located roughly along 120°E longitude and 30°N latitude,with each observatory equipped with multiple instruments to monitor space environment.Based on the huge observational data accumulated,significant scientific achievements have been made with more than 300 peer-reviewed journal papers published.In this report,scientific results from the past two years have been reviewed with topics covering fields of geomagnetic,atmosphere,ionosphere,and their responses to solar activities.The excellent achievements from the Phase I of Chinese Meridian Project lay a good foundation for Phase II,which has already been approved with the official kick-off of construction in November 2019.It will conceive an unprecedented contribution to global space weather community from China.
基金Supported by National Natural Science Foundation of China(40974094,41274159)
文摘A theoretical model of ionospheric electric fields at mid-and low-latitudes is developed.In the geomagnetic dipolar coordinate system,the ionospheric dynamo equations were solved,and the ionospheric electric potential and electric field were derived respectively.Major parameters for the model inputs,such as the neutral winds,the densities and temperatures of electron,ions and neutrals,are obtained from empirical models.The global ionospheric electrical potential and field at mid-and low-latitudes derived from our model are largely in agreement with the results presented by other authors and the empirical model.Using our model,it is found that the diurnal component of the HWM93 wind mainly contributed to the formation of the vertical electric field,while the semidiurnal component mainly contributed to the zonal electric field.Finally,by adjustment of the input F region winds and conductivities,most discrepancies between our model and the empirical one can be eliminated,and it is proved that the F region dynamo is the most significant contribution to the electric fields.
基金Supported by the National Natural Science Foundation of China (No.49790020) and Important Basis Research Project of China (No. G2000078407)
文摘This brief report reviews the recent developments in ionospheric physics studies made by Chinese scientists. It covers areas from the numerical simulations and theoretical researches on ionospheric properties, ionospheric disturbances, space weather events in the ionosphere to ionospheric obserwtions.
文摘The Chinese Meridian Project(CMP)is a major national science and technology infrastructure invested and constructed by the Chinese government.The project builds space environment observation stations,focusing on the monitoring of the space environment over China,so as to provide a monitoring basis for clarifying the regional characteristics of the space environment over China and its relationship with global change,and making important innovative scientific achievements.The first phase of the CMP passed the national acceptance in 2012.It has been running for nearly ten years and has accumulated more than 8 TB monitoring data.These data are all available to all data users through the data center of the project.From 2020 to 2021,users of CMP data have completed a series of original works,which have solved current scientific problems in the field of space physics research.On the other hand,they also make us look forward to the completion of the second phase of CMP and its application benefits in national major strategic needs and cutting-edge scientific research.
基金This poject was supported by the National Natural Science Foundation of China (40474066).
文摘The perfect sequences are so ideal that all out-of-phase autocorrelation coefficients are zero, and if the sequences are used as the coding modulating signal for the phase-modulated radar, there will be no interference of side lobes theoretically. However, it has been proved that there are no binary perfect sequences of period 4 〈 n ≤ 12100. Hence, the almost perfect sequences with all out-of-phase autocorrelation coefficients as zero except one are of great practice in engineering. Currently, the cyclic difference set is one of most effective tools to analyze the binary sequences with perfect periodic autocorrelation function. In this article, two characteristic formulas corresponding to the autocorrelation and symmetric structure of almost perfect sequences are calculated respectively. All almost perfect sequences with period n, which is a multiple of 4, can be figured out by the two formulas. Several almost perfect sequences with different periods have been hunted by the program based on the two formulas and then applied to the simulation program and practical application for ionospheric sounding.
文摘The Experimental Satellite on Electromagnetism Monitoring(ESEM) was proposed in 2003 and proved in 2013 after 10-years' scientific demonstration. The ESEM mission was proposed to be the first satellite of space-based geophysical fields observation system in China with a lot of application prospects in earthquake science, geophysics, space sciences and so on. And coincide with the mission objectives, the satellite decides to use the Circular Sun Synchronous Orbit with an altitude of 507 km and descending node time at 14:00 LT. The payload assemble includes 8 instruments,Search-Coil Magnetometer, Electric Field Detector, High precision Magnetometer, GNSS occupation Receiver, Plasma Analyzer, Langmuir Probe, Energetic Particle Detector, and Three-frequency Transmitter. According to the planned schedule, the satellite is due to be launched in 2016–2017 and will be onboard operated for 5 years.
基金supported by the National Natural Science Foundation of China(41304024)
文摘The ionosphere, as the largest and least predictable error source, its behavior cannot be observed at all places simultaneously. The confidence bound, called the grid ionospheric vertical error(GIVE), can only be determined with the aid of a threat model which is used to restrict the expected ionospheric behavior. However, the spatial threat model at present widespread used, which is based on fit radius and relative centroid metric(RCM), is too conservative or the resulting GIVEs will be too large and will reduce the availability of satellite-based augmentation system(SBAS). In this paper, layered two-dimensional parameters, the vertical direction double RCMs, are introduced based on the spatial variability of the ionosphere. Comparing with the traditional threat model, the experimental results show that the user ionospheric vertical error(UIVE) average reduction rate reaches 16%. And the 95% protection level of conterminous United States(CONUS) is 28%, even under disturbed days, which reaches about 5% reduction rates.The results show that the system service performance has been improved better.
基金This work was supported by the National Key Research and Development Plan of China(2018YFB0505103)the National Natural Science Foundation of China(61873064)the Science and Technology Project of State Grid Corporation of China(SGSHJX00KXJS1901531).
文摘In the equatorial region,deep amplitude fading in global positioning system(GPS)signals frequently occurs during the strong ionospheric scintillation,it can lead to the loss of lock in GPS carrier tracking loops,and result in increased positioning error and even navigation interruption.The relationships between amplitude scintillation indices and detrended carrier frequency are investigated,based on GPS L1 C/A signals during the last peak of the solar cycle at the low latitude site of São Josédos Campos,Brazil(23.2S,45.9W)from 2013 to 2015.Corresponding mathematic model of the probability distribution function is built for the first time to provide statistical analysis on the above relationships.The results show that the standard carrier frequencies reveal an almost linear relation with the amplitude scintillation indices.Moreover,the frequency widths of detrended frequency are proportional to levels of amplitude scintillation when the value of the peak probability is lower than the corresponding boundary.A conclusion can be drawn that different levels of amplitude scintillation will influence the fluctuation of the carrier frequency.The analysis will provide useful guidance to set the receiver’s bandwidth with respect to the different scintillation levels and design the advanced tracking algorithms to improve the robustness and precision of the GPS receiver.
基金Supported by the Seismic Public Welfare Scientific Research Special Appropriation Project of China(201008007)the National Natural Science Foundation of China(41004066)
文摘The ionospheric effect from solar activity can be seen as the background in the process of detecting the ionospheric precursor prior to strong earthquakes.The ionospheric variation induced by the forthcoming earthquake can be covered by the strong solar background during the period of high solar activity.The issue of how to remove the ionospheric effect from solar radiation is of outstanding significance.In this paper,a method of Empirical Mode Decomposition(EMD) is used to eliminate the solar background.As a case study,the global ionospheric map TEC before the M9.0 Tohoku earthquake on 11 March 2011 is analyzed.After the effect of solar radiation is removed using the EMD method,the precursor of the imminent earthquake is more obvious.The ionospheric anomaly had a local character and only appeared close to the earthquake epicenter while the useful signals were covered by the solar radiation background with traditional method,which implies that the EMD method is effective in eliminating solar radiation background.
