Ionospheric total electron content disturbance associated with May 12, 2008,Wenchuan earthquake

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.

Analysis of ionospheric VTEC disturbances before and after the Yutian Ms7.3 earthquake in the Xinjiang Uygur Autonomous Region

An earthquake with a magnitude of Ms7.3 hit Yutian in the Xinjiang Uygur Autonomous Region on February 14, 2014. This research investigates the interference phenomena in solar activities and geomagnetics, and adopts the quartile method to analyze the Global Ionosphere Map （GIM） Vertical Total Electron Content （VTEC） data provided by the Center for Orbit Determination in Europe （CODE）, as well as the difference between GIM VTEC and International Reference Ionosphere （IRI） VTEC data. The ionospheric VTEC disturbances at the earthquake epicenter are examined before and after the event. At UTC 8：00 on February 2, a strong VTEC disturbance emerged in the sky near the epicenter. A strong VTEC disturbance also emerged in the sky of the southern Hemisphere area, which is symmetric with the areas north of the equator. The methods used in analysis of the difference between GIM VTEC and IRI VTEC information can effectively fill the gaps in analysis that uses only the GIM VTEC data.

Carrier frequency disturbance distributions on GPS during equatorial ionospheric scintillation

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.

Spectral investigation of traveling ionospheric disturbances:IONOLAB-FFT

Ionosphere is an important layer of atmosphere which is under constant forcing from both below due to gravitational, geomagnetic and seismic activities, and above due to solar wind and galactic radiation. Spatio-temporal variability of ionosphere is made up of two major components that can be listed as spatio-temporal trends and secondary variabilities that are due to disturbances in the geomagnetic field, gravitational waves and coupling of seismic activities into the upper atmosphere and ionosphere. Some of these second order variabilities generate wave-like oscillations in the ionosphere which propagate at a certain frequency, duration and velocity. These oscillations cause major problems for navigation and guidance systems that utilize GNSS （Global Navigation Satellite Systems）. In this study, the frequency and duration of wave-like oscillations are determined using a DFT （Discrete Fourier Transform） based algo- rithm over the STEC （slant total electron content） values estimated from single GPS （Global Positioning System） station. The performance of the developed method, namely IONOLAB-FFT, is first determined using synthetic oscillations with known frequencies and durations. Then, IONOLAB-FFr is applied to STEC data from various midlatitude GPS stations for detection of frequency and duration of both medium and large scale TIDs （traveling ionospheric disturbances）. It is observed that IONOLAB-FFr can estimate TIDs with more than 80% accuracy for the following cases： frequencies from 0.6 mHz to 2.4 mHz and durations longer than 10 min; frequencies from 0.15 mHz to 0.6 mHz and durations longer than 50 min; fre- quencies higher than 0.29 mHz and durations longer than 50 rain.

Interaction between Equatorial Plasma Bubbles and a Medium-Scale Traveling Ionospheric Disturbance,observed by OI 630 nm airglow imaging at Bom Jesus de Lapa,Brazil

OI 630.0 nm airglow observations,from a new observatory at Bom Jesus de Lapa,were used to study the interaction between EPBs(Equatorial Plasma Bubbles)and the MSTID(Medium-Scale Traveling Ionospheric Disturbance)over the Northeast region in Brazil.On the night of September 16 to 17,2020,an EPB was observed propagating eastward,in an apparent fossil stage,until it interacted with a dark band electrified MSTID(e MSTID).After the interaction,four EPBs merged,followed by an abrupt southward development and bifurcations.Analysis of the data suggests that an eastward polarization electric field,induced by the dark band e MSTID,forced the EPB into an upward drift,growing latitudinally along the magnetic field lines and then bifurcating.

The earthquake-related disturbances in ionosphere and project of the first China seismo-electromagnetic satellite

Based on the case studies and statistical analysis of earthquake-related ionospheric disturbances mainly from DEMETER satellite, ground-based GPS and ionosounding data, this paper summarizes the statisw tical characteristics of earthquake-related ionospheric disturbances, including electromagnetic emissions, plasma perturbations and variation of energetic particle flux. According to the main results done by Chinese scientists, fusing with the existed study from global researches, seismo-ionospheric disturbances usually occurred a few days or hours before earthquake occurrence. Paralleling to these case studies, lithosphere-atmosphere-ionosphere （LAI） coupling mechanisms are checked and optimized. A thermo-electric model was proposed to explain the seismo-electromagnetic effects before earthquakes. A propagation model was put forward to explain the electromagnetic waves into the ionosphere. According to the requirement of earthquake prediction research, China seismo-electromagnetic satellite, the first space-based platform of Chinese earthquake stereoscopic observation system, is proposed and planned to launch at about the end of 2014. It focuses on checking the LAI model and distinguishing earthquake-related ionospheric disturbance. The preliminary design for the satellite will adopt CAST-2000 platform with eight payloads onboard. It is believed that the satellite will work together with the ground monitoring network to improve the capability to capture seismo-electromagnetic information, which is beneficial for earthquake monitoring and prediction researches.

Ionospheric electromagnetic perturbations observed on DEMETER satellite before Chile M7.9 earthquake

Based on the ionospheric electromagnetic data observed on DEMETER satellite of France, the ionospheric electromagnetic signals were analyzed within 10 days before Chile M7.9 earthquake on November 14, 2007. It is found that, low frequency electromagnetic disturbances began to increase in a large scale of latitude, and reached to a maximum one week prior to the earthquake, and at about three days before the quake, the peak values shifted to lower latitude. Taking three days as a group, spatial images of a few parameters were analyzed, from which it can be seen during the five days prior to this earthquake, the amplitude and scale of anomalies are enlarged, while the epicenter is located at the boundary of anomalous region. The anomalous tempo-spatial variation in electron density prior to the earthquake were also obtained in terms of tracing the data from revisited orbits in half a year prior to the quake.

Characteristics of the coseismic geomagnetic disturbances recorded during the 2008 M_w 7.9 Wenchuan Earthquake and two unexplained problems

Twenty-seven FHDZ-M15 combined geomagnetic observation systems(each of which is equipped with a fluxgate magnetometer and a proton magnetometer)had been installed in the China geomagnetic network before the 2008 Wenchuan earthquake,during which coseismic disturbances were recorded by 26 fluxgate magnetometer observatories.The geomagnetic disturbances have similar spatial and temporal patterns to seismic waves,except for various delays.Six proton magnetometer observatories recorded coseismic disturbances with very small amplitudes.In addition,fluxgate magnetometers registered largeamplitude disturbances that are likely to have included responses to seismic waves.However,two problems remain unresolved.First,why do these geomagnetic disturbances always arrive later than P waves?Second,why do the geomagnetic disturbances have spatial and temporal directivity similar to the main rupture direction of the earthquake?Solving these two problems may be crucial to find the mechanism responsible for generating these geomagnetic anomalies.

Removing Solar Radiation Based on the Empirical Mode Decomposition Method for Seismo-Ionospheric Anomaly Before the M9.0 Tohoku Earthquake

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.

Pre-seismic ionospheric anomalies of the 2013 Mw=7.7 Pakistan earthquake from GPS and COSMIC observations

The seismo-ionospheric anomalies may provide some insights about the earthquake.However,preseismic ionospheric anomalies are still challenging.In this paper,seismo-ionospheric anomalies are investigated before the September 24,2013(Mw=7.7)Awaran(Pakistan)earthquake from GPS TEC(Total Electron Content)and COSMIC(Constellation Observing System for Meteorology,Ionosphere and Climate)data.The TEC data are showing anomalies on September 21,2013.The abnormality detected in the temporal data is about 10 TECU beyond the 30-day running median.The percentage deviation of the TEC anomaly on September 21,is 30% above the upper confidence interval.The anomalies prevail 5 in Latitude and 10 in Longitude over the epicenter.The spatial and temporal data of TEC showed anomalies in TEC from UT=08 to UT=12.In addition,the enhancement on September 21,2013 is also very significant in COSMIC data.The results of COSMIC completely agreed with GPS TEC anomalies on September 21,2013.The percentage deviation of the peak plasma frequency on September 21 is 5% of the normal distribution.The storm indices are quiet before and after the earthquake.The pre-sesimic ionospheric anomalies are most probably associated with the 2013 Mw=7.7 Awaran(Pakistan)earthquake.

Ionospheric Effects of Geomagnetic Storms in Different Longitude Sectors

This paper analyzes the state of the ionosphere during two geomagnetic storms of a different intensity evolving in different sectors of local time in different seasons. There were used the data from a network of ionospheric stations located in the opposite longitudinal sectors of 80°-150° E and 250°-310° E.This analysis has permitted us to conclude that the detected differences in the variations of the disturbances are likely to be determined by the local time difference of the geomagnetic storm development, its intensity and by the different illumination conditions of the ionosphere.

Ionospheric disturbance analysis of the January 15,2022 Tonga eruption based on GPS data

Hunga Tonga-Hunga Ha’apai climactic eruption on January 15,2022,released enormous energy that affected the ionosphere over the Pacific Rim.We analyzed ionospheric disturbance following volcanic eruptions using near-field(<1000 km),regional(1000–5000 km),and far-field(5000–12000 km) global positioning system(GPS) observations.The results indicate that the near-field ionospheric perturbation that occurred 8–15 min after the cataclysmic eruption was mainly derived from the shock wave(~1000 m/s) generated by the blast,while the low-frequency branch with long-distance propagation characteristics over the regional and the far-field was mainly associated with atmospheric Lamb waves(~330 m/s).Moreover,the amplitude of disturbance and background total electron content(TEC) are related proportionally.The intensity of the volcanic eruption and the background ionospheric conditions determine the magnitude of ionospheric responses.TEC perturbations were invisible on the reference days.Furthermore,the source location and onset time were calculated using the ray tracing technique,which confirms that the Tonga event triggered the ionospheric anomaly beyond the crater.Finally,the change in the frequency of the perturbations coincided with the arrival of the initial tsunami,implying the generation of a meteotsunami.

2020年7月22日阿拉斯加7.8级地震同震电离层扰动分析

利用全球导航卫星系统(GNSS)、电离层测高仪和地震仪数据,从振幅及波形、时空分布、传播速度与方向、时频域等角度对2020年阿拉斯加7.8级地震同震电离层扰动(Co-seismic ionospheric disturbances,CIDs)特性进行探究.卫星G03、G04和G09在地震西部探测到3类CIDs,最大扰动幅度约0.1 TECU (1 TECU=10^(16) el/m~2),并且均沿着地震断层破裂延伸方向(西南方向)传播;而在地震北部与东部未发现CIDs.根据CIDs的速度及中心频率将其分为三类,第一类为高速传播的CIDs(速度约为2.93 km·s^(-1)),中心频率约11 mHz,符合瑞利波激发的电离层扰动特征;第二类CIDs的传播速度约为1.69 km·s^(-1)和1.55 km·s^(-1),中心频率约4.5 mHz和4.7 mHz,符合声波引起的电离层扰动频率;第三类CIDs速度约为0.98 km·s^(-1)和1.11 km·s^(-1),中心频率约2.9 mHz,可能为声波引起的另一类电离层扰动.同时,利用CIDs时空数据估计的CIDs扰动源位置与震中较为接近,进一步说明电离层扰动由地震激发.通过对GNSS站及地震仪位移的分析,估计了地震瑞利波沿西南方向传播速度与第一类CIDs较为吻合,验证了第一类CIDs由瑞利波激发,且断层的垂直位移是引起电离层扰动的重要因素.测高仪观测到电离层临界频率(f_(0)F_(2))发生显著波动,探测到CIDs的传播速度约1.02 km·s^(-1),传播速度和方向与卫星G03、G04探测的CIDs较为吻合,推断其属于第三类CIDs.

阿拉斯加2021年8.2级地震同震电离层扰动特征及对比分析

为分析2021年7月29日阿拉斯加8.2级地震引起的电离层响应,利用地震附近的全球导航卫星系统(Global Navigation Satellite System,GNSS)观测数据估算电离层总电子含量(Ionospheric Total Electron Content,TEC)及同震电离层扰动(Coseismic Ionospheric Disturbances,CIDs).从多角度对CIDs的时空分布特征进行分析,并与阿拉斯加2018年7.9级走滑型地震以及2020年7.8级逆断层地震引起的CIDs对比.在地震西南方向探测到两类CIDs,最大扰动振幅约0.8 TECU(1 TECU=1016 el/m^(2)),并且在西南方向距离震中约1094 km的测高站EA653探测到CIDs.在震中西北、东北和北方向探测到传播速度相近的CIDs.根据CIDs的速度和频率大小将CIDs分为两类,第一类CIDs的传播速度为1.87 km·s^(-1),频率约为3.8 mHz,可能由地震声波引起,扰动量级最大;第二类CIDs的传播速度为0.85~1.09 km·s^(-1),中心频率约在3.0 mHz或者5.7 mHz附近,为地震声波引起的另一类电离层扰动.逆断层地震引起的CIDs比走滑型地震更加显著,表明地震引起的垂直地表运动在CIDs的形成中起主要作用.三次地震在西南方向均引起显著的CIDs,与地震破裂方向较为一致,该地区大地震引起的CIDs可能具有较为明显的方向性,具体形成机制有待于进一步研究.

基于GPS TEC的2022年1月15日汤加火山喷发激起的电离层行扰分析

2022年1月15日南太平洋汤加海底火山发生剧烈喷发,是近30年来最大规模的火山爆发,产生的强烈大气波动为开展火山喷发电离层扰动研究提供了难得的机会。本文利用GPS数据探测火山附近、新西兰、澳大利亚和中国地区的电离层扰动,从波形、频率、传播速度和时空分布等角度分析汤加火山喷发电离层行扰(TIDs)的特征,并利用电离层测高站、海平面监测站和大气压监测站的观测数据进一步验证TIDs的传播特征。研究结果发现,汤加火山喷发在其附近区域、新西兰、澳大利亚和中国地区引起了3类TIDs。在火山附近东、西、南、北方向上均探测到第一类TIDs, TIDs的传播速度为617~972 m/s,该类TIDs极有可能由火山喷发产生的声波引起。汤加火山喷发仅在火山附近东、西方向引起第二类TIDs,其传播速度分别为472 m/s和418 m/s,可能由声波传播过程中衍生的声重力波或者混合波引起,形成机理有待进一步研究。汤加火山喷发在新西兰、澳大利亚和中国地区引发了第三类TIDs,其传播速度为328~352 m/s,该类TIDs与Lamb波密切相关。

基于短波段电离层探测数据分析地下核爆引起的电离层扰动

同全球导航卫星系统(global navigation satellite system, GNSS)获取电离层总电子含量(total electron content, TEC)数据相比,传统的电离层垂测、斜测等短波段数据具有特征参数丰富、高度分辨率高、历史数据多等优点。为利用电离层垂测和斜测数据,研究地下核爆引起的电离层扰动。利用2016年1月6日朝鲜地下核试验当天的斜测、垂测数据分析电离层扰动现象。结果表明,本次地下核爆造成的行波电离层扰动为小尺度电离层扰动,传播速度为150.3~158.7 m/s。同时核爆发生后0.5 h在距离爆点421.4 km处,观测到F2层临界频率(critical frequency of the F2layer, foF2)较月中值增加了0.7 MHz,较1月5日、1月7日在协调世界时(coordinated universal time, UTC)2:00 UTC的增加了0.5 MHz,极有可能是地下核爆通过岩石圈-大气圈-电离层圈耦合机制造成电离层电子浓度增加。本文分析结果与其他文献资料非常吻合。由此可见,基于短波段电离层探测方式感知电离层扰动从而实现地下核爆炸事件的监测,是一种有效的核爆电离层效应监测手段,可与其他直接监测手段相印证,提高核爆事件监测能力。

子午工程二期电离层高频多普勒监测仪初步观测结果

子午工程二期计划在漠河、北京、武汉、深圳四地分别建设由一个发射站和三个接收站构成的电离层高频多普勒监测台阵.本文介绍了为此研制的电离层高频多普勒监测仪的进展和试观测期间取得的一些观测结果.通过与电离层测高仪进行交叉对比,设备的性能和探测能力得到了验证.目前该设备已部署7个站点进行试观测,本文报告了该设备探测到的太阳耀斑导致的电离层扰动、电离层行进式扰动、大尺度电场导致的多站同时扰动等多种现象.未来子午工程二期建成后,该设备将具备我国上空北至漠河、南至广东的电离层扰动监测能力,并与其它探测手段融合发挥空间天气综合监测网络的最大效能.

GPS detection of the coseismic ionospheric disturbances following the 12 May 2008 M7.9 Wenchuan earthquake in China

Here we report two cases of coseismic ionospheric disturbances observed through a GPS network in China after the great Wenchuan earthquake at 06:28 UT on 12 May,2008.One is detected 7.9 min after the earthquake and had an intensive"N"shape oscillated waveform with a pronounced amplitude of about 1 TECU,which propagates approximately southward to the distance about 1000 km with the horizontal phase velocity of 600±84 m/s and the period of 9.5±1.3 min.The other is detected8.5 min after the earthquake and has an oscillated waveform more like a positive pulse with an amplitude of about 0.5 TECU,which propagates eastward to the distance about 800 km with the horizontal phase velocity of 720±59 m/s and the period of7.4±0.8 min.These two coseismic ionospheric disturbances are caused by the acoustic gravity waves excited by partial transformation of the acoustic waves originated from the energy release of the earthquake,somewhere near the epicenter.The directional preferences of these two coseismic ionospheric disturbances may be associated with the oblique geomagnetic field lines and the background winds filtering effect.

Monitoring traveling ionospheric disturbances using the GPS network around China during the geomagnetic storm on 28 May 2011

Larger-scale traveling ionospheric disturbances (LSTIDs) are studied using the total electron content (TEC) data observed from 246 GPS receivers in and around China during the medium storm on 28 May 2011. It is the first attempt to get the two-dimensional TEC perturbation maps in China. Two LSTID events are detected: one is in southwestern China before midnight propagating from low to middle latitude to the distance of about 1200 km with the phase front extending to about 500 km, and the other is in northeastern China after midnight propagating from middle to low latitudes to the distance of about 1200 km with the phase front extending to nearly 1400 km. By using the multichannel maximum-entropy method, we get the propagation parameters of these two LSTIDs. The LSTID that occurs before midnight has a higher horizontal phase velocity and a larger damping rate corresponding to the after midnight LSTID, and this may be caused by the relatively large vertical background TEC 0 and high atmospheric temperature in the southwest of China before midnight. According to the variations of magnetic H component observed in high latitudes, the source region for the after midnight LSTID is likely to be located 1400-2600 km east of 140°E and north of 42°N; the before midnight LSTID is propably excited by the atmospheric gravity waves (AGWs) generated by the Joule heating of the equatorial electrojet.

Large-Scale Traveling Ionospheric Disturbances Observed by GPS Receivers in Antarctica

The paper examines the propagation direction and velocity of large-scale traveling ionospheric disturbances （LST1Ds） during extreme geomagnetic storms in the 23rd solar cycle （e.g., October 2003 and November 2003 storms） using GPS observations. In the analysis, the time delay between the vertical total electron content （VTEC） structures at Scott Base, McMurdo, Davis and Casey GPS stations and the distance between these stations were the main parameters in the determination of LSTIDs propagation speed and direction. The observations during October and November 2003 storms show obvious time delay between the total electron content （TEC） enhancement signatures at these stations. The time delay suggests a movement of the ionospheric disturbances from higher to lower latitudes during the October storm with a velocity of 800-1 200 m/s and poleward propagation of LSTIDs during the November storm with a ve- locity of 300-400 m/s. The equatorward or poleward expansion of LSTIDs during the October and November 2003 storms is probably caused by the disturbances of the neutral temperature occurring close to the dayside convection throat or by the neutral wind oscillation induced by atmospheric gravity waves （AGW） launched from the aurora region.