基于GPS TEC的尼泊尔MW7.8地震同震电离层扰动研究

基于GPS数据对2015年尼泊尔M W7.8地震引起的同震电离层扰动进行统计与FFT频谱分析,探究地震电离层TEC扰动传播的时空特性。结果表明,震后5 min起出现明显的TEC扰动异常现象,持续时间超过6 min,呈现增大-减小-增大的变化趋势;扰动由震中向东、东北等方向传播,速率分别为2336.36 m/s和455.52~937.64 m/s;扰动的中心频率为3~7 mHz,符合瑞利波与声波引发的扰动频段。

Manifestation of earthquake preparation zone in the ionosphere before 2021 Sonitpur,Assam earthquake revealed by GPS-TEC data

Global Positioning System(GPS)Continuously Operating Reference Station(CORS)data analysis shows that the ionosphere’s electron density variability is linked to the deformation and stress accumulation in the Earth’s crust.Anomalies in ionosphere total electron content(TEC)variability before 2021 M6.4 Sonitpur,Assam earthquake were detected using L1 and L2 GPS frequencies that showed three distinct abnormalities on April 3,9,10,2021.Pearson’s correlation coefficient(r)of TEC decreases in the CORS that lies away from the earthquake epicenter,indicating the possibilities of a positive relationship between TEC variability and earthquake epicenter.TEC concentration also decreases towards the epicenter within the earthquake preparation zone(EPZ).It is also observed that the Pearson’s correlation coefficient(r)of TEC decreases linearly near the EPZ.The study demonstrates the possibilities of determining the TEC anomalous zone in the ionosphere that coincides with the EPZ in the crustal rocks.The research indicated the possibilities of magnitude estimation of an impending earthquake based on the TEC anomalous zone in the ionosphere using closely spaced dense CORS network data.

The influence of ionospheric thin shell height on TEC retrieval from GPS observation

We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content（TEC） derived from a small scale Global Positioning System（GPS） network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagnetically quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as～8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of～3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350-500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.

利用中国GPS站网对地震波引发的大尺度电离层扰动的观测

地震瑞利波在沿地表传输时衰减很慢,其能量在远离震中的区域仍然能够激发大气和电离层扰动.本文利用中国境内的GPS接收机网络观测电离层总电子含量(total electron content,TEC),分析了2011年日本地震后在中国区域上空产生的电离层扰动.研究发现,瑞利波的能量从地面经大气耦合传输到电离层高度,导致在中国区域上空电离层出现与瑞利波传播同步的TEC扰动.利用中东部的稠密接收机网络,还揭示了扰动的大尺度二维空间结构:瑞利波经过后产生的TEC扰动呈条带状,在中纬度地区沿西北—东南方向排列,而在低纬度大致为东西方向.条带的转向可能与地磁场作用下的中性-离子耦合过程有关,大气波动导致的等离子扰动倾向于沿磁力线方向(向南)传播,从而形成垂直磁力线方向(东西)的波前结构.这是首次在远离震中的区域使用GPS站网研究地震波耦合电离层扰动的大尺度二维空间结构.

两次强震前华南地区电离层TEC异常特征研究

基于广州GPS-TEC监测网的VTEC数据,用连续15天的平均值和标准差作为参考,分析了华南地区电离层VTEC异常在2006年12月26日台湾南部恒春海域7.2级地震和2008年5月12日汶川8级地震前的活动特征。结果发现:强震前8天内,华南地区电离层连续出现异常扰动。在此基础上,分析了两次强震前华南地区电离层VTEC的异常响应特征,并和相关文献提到的强震前VTEC异常特征进行了对比,进而对地震引起电离层扰动的机理作了初步的讨论。

2009年6至7月华南地区电离层TEC扰动研究

电离层TEC(Total Electron Content)扰动与多种扰动源相关联.2009年6至7月期间存在地震和日全食的扰动源.利用广州地区GPS监测网在2009年6至7月连续监测到的TEC数据,通过采用前15天数据的滑动窗口对数据进行处理,从时间序列和空间分布两方面分析了华南地区电离层TEC扰动特征.结果显示,2009年6至7月华南地区电离层TEC扰动和该时期发生的地震以及日全食事件可能有关联;2009年7月多个地震发生引起的电离层扰动特征为,震前出现的是正异常,发震当天或震后有可能是正异常,也有可能是负异常;7月22日日全食当天TEC扰动为正异常,推测该正异常是地磁活动、地震活动及日全食综合效应的结果.

长三角地区电离层变化的GPS监测(英文)

利用GPS双频观测量可获取电离层总电子含量(Total Electron Content,TEC),以监测区域上空电离层的分布和变化特征,从而可以发现不同尺度的电离层异常。该文采用2004年上海地区GPS综合应用网(SCGAN)以及中国地壳运动监测网络(CMONC)的部分台站的观测,计算得到1年时间序列的TEC数据,来研究长三角地区上空的电离层TEC的变化与活动。应用这些数据,综合利用高斯权函数和滑动平均等几种数据处理方法,重点分析和讨论了长三角地区上空电离层的周日变化、周年变化和季节性变化特性,揭示了电离层冬季异常等现象。同时,通过对1年时间序列TEC进行谱分析,得到了其相应的变化周期。

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.

2012年北大北京本校站电离层TEC和闪烁指数集

电离层总电子含量(TEC)和闪烁指数是电离层形态学研究的重要参数。基于二者描述电离层状态,对电离层研究有十分重要的意义。2012年北大北京本校站(116.30°E,39.99°N)电离层TEC和闪烁指数是根据GPS伪距及载波相位观测数据、信号功率、信噪比获得的。该数据集包含电离层垂直TEC、幅度闪烁指数和相位闪烁指数。通过这一数据可以得到电离层TEC同太阳活动、磁暴、电离层暴之间的关系,以及电离层不规则体的逐日变化和暴时特征。本数据集能够为我国众多空间环境相关的研究与工程项目提供数据保障。

北半球电离层中纬槽发生率及其槽极小位置变化的统计研究

本文利用2014年9月到2017年8月全球高时空分辨率TEC数据对北半球四个经度带电离层中纬槽的发生率和槽极小位置的变化进行了统计研究.基于Kp指数,我们引入了一个包含地磁活动变化历史效应的地磁指数(Kp 9)来分析中纬槽位置变化与地磁活动水平的关系.通过与其他地磁活动指数的对比,发现槽极小纬度与Kp 9指数的相关性最好.此外,本文重点分析了中纬槽发生率及槽极小纬度的经度差异、季节变化、地方时变化以及与地磁活动强度等的关系.结果表明,中纬槽的发生率与经度关系不大,主要受到季节、地方时与地磁活动的影响.午夜中纬槽发生率在夏季较低,其随地方时的变化则呈现出负偏态分布的特点,在后半夜发生率更高,而地磁活动增强对中纬槽的发生具有明显的促进作用.对于槽极小纬度,其在四个经度带的分布差异不大,但月变化各不相同,其中-120°经度带呈单峰分布,在夏季槽极小纬度更高,而0°经度带夏季槽极小纬度更低.槽极小的位置显著依赖于地磁活动、地方时以及季节变化.一般说来,地磁活动越强,中纬槽纬度越低.中纬槽位置随地方时的变化有明显的季节差异,冬季昏侧槽极小纬度随地方时变化较快,弱地磁活动条件下22∶00 LT前即达到最低纬度,其后位置几乎保持不变,而两分季槽极小纬度从昏侧至午夜都在降低,夏季槽极小纬度从昏侧连续下降至03∶00 LT左右.

2009年7月22日日全食电离层效应观测

首次利用廊坊中频雷达和武汉、嘉兴、廊坊等三站GPS对2009年7月22日日全食电离层效应进行了观测.日食期间,中频雷达D层78 km高度上电子密度减小了约67%,电子密度为200 cm^(-3)的高度上升了近10 km,GPS/TEC减小了1TECU左右,其变化的最大相位与日食最大相位几乎同步;日食后,观测到周期为2个多小时的电离层扰动现象.

Ionospheric disturbances associated with the 2015 M7.8 Nepal earthquake

Based on the total electron content （TEC） derived from Global Positioning System （GPS） observations of the Crustal Movement Observation Network of China （CMONOC） and the Global Ionosphere Map （GIM） from the Center for Orbit Determination in Europe （CODE）, we detected and analyzed the ionospheric variations during the 2015 M7.8 Nepal earthquake （including the pre-earthquake ionospheric anomalies and coseismic ionospheric disturbances （CIDs） following the main shock）. The analysis of vertical total electron content （VTEC） time series shows that the large-scale ionospheric anomalies appeared near the epicenter two days prior to the earthquake. Moreover, the pre-earthcluake ionospheric anomalies were also observed in the geomagnetically conjugated region. In view of solar-terrestrial environment, the pre-earthquake ionospheric anomalies could be associated with the Nepal earthquake. In addition, we also detected the CIDs through the high-frequency GPS observation stations. The CIDs had obvious oscillated waveforms with the peak-to-peak disturbance amplitudes of about I TECu and 0.4 TECu, which propagated approximately with the horizontal velocities of 877 ±75 m/s and 319 ± 30 m/s, respectively. The former is triggered directly by the acoustic waves which originated from the energy release of the earthquake near the epicenter, while the latter could be stimulated by the acoustic-gravity waves from the partial transformation of the acoustic waves.

Atmosphere-ionosphere response to the M9 Tohoku earthquake revealed by multiinstrument space-borne and ground observations:Preliminary results

We retrospectively analyzed the temporal and spatial variations of four different physical parameters characterizing the state of the atmosphere and ionosphere several days before the M9 Tohoku, Japan earthquake of March 11, 2011. The data include outgoing long wave radiation （OLR）, GPS/TEC, lower Earth orbit ionospheric tomography and critical frequency foF2. Our first results show that on March 7th a rapid increase of emitted infrared radiation was observed from the satellite data and an anomaly developed near the epicenter. The GPS/TEC data indicate an increase and variation in electron density reaching a maximum value on March 8. Starting from this day in the lower ionosphere also there was confirmed an abnormal TEC variation over the epicenter. From March 3 to 11 a large increase in electron concentration was recorded at all four Japanese ground-based ionosondes, which returned to normal after the main earthquake. The joint preliminary analysis of atmospheric and ionospheric parameters during the M9 Tohoku, Japan earthquake has revealed the presence of related variations of these parameters implying their connection with the earthquake process. This study may lead to a better understanding of the response of the atmosphere/ionosphere to the great Tohoku earthquake.

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.

2000年7月14日特大耀斑引起的电离层TEC突然增强现象

利用GPS网观测研究太阳耀斑爆发引起的电离层电子浓度总含量的突然增强(SITEC)现象.首先,根据电离层的Chapman电离理论,分析得出耀斑爆发引起的TEC时间变化率与太阳耀斑的有效辐射通量成正比、与太阳天顶角的Chapman函数成反比的结论.为了验证Chapman电离理论的这一简单推论,利用2000年7月14日特大太阳耀斑爆发期间中国、东南亚及澳大利亚的GPS网观测的TEC资料,统计分析了TEC的时间变化率与天顶角的Chapman函数的倒数间的相关性,发现两者确有很好的正比关系,从而证明了Chapman电离理论的正确性与可用性.结果表明,将GPS的观测用于太阳耀斑爆发等引起的电离层突然骚扰的研究,可以发挥GPS观测精度高、空间范围大、时间连续性好等优点,从而定量地揭示出与太阳爆发相关的电离层扰动过程.对电离层中的空间天气的监测与研究具有重要意义.

Using the GPS observations to reconstruct the ionosphere three-dimensionally with an ionospheric data assimilation and analysis system(IDAAS)

Using an international reference ionosphere(IRI)model as a background ionosphere and applying the Kalman filter to update the state with observations,we develop an ionosphere data assimilation analysis system(IDAAS)to reconstruct a three-dimensional(3D)ionosphere with the GPS slant TEC and ionosonde data over east-south Asia.The preliminary results with the GPS data collected over east-south Asia on 30 June 2005 showed that inversed slant TEC has very good correlation with the observations both for the GPS sites being and not being involved in reconstruction.The inversed NmF2 and vertical TEC both demonstrate great improvement of agreement with those observed from ionosondes and TOPEX satellite independently.

Cold plasma redistribution throughout geospace

The redistribution of the electrically charged cold plasma of ionospheric origin involves the equatorial,low,mid,auroral,and polar-latitude regions in a multi-step,system-wide process linking the regions of geospace.Observations with ground and space-based instruments characterize the geospace plume-regularly occurring channels of enhanced plasma density flowing at both ionospheric and magnetospheric altitudes.Convection in the SAPS channel transports the eroded material to the noontime cusp in the ionosphere and to the dayside magnetopause at high altitudes.As the fluxes of cold plume plasma traverse the cusp and enter the polar cap,they form the polar tongue of ionization.At the cusp the plume plasma provides a rich source of heavy ions for the magnetospheric injection and acceleration via the mechanisms operative on those field lines.