Anomalous variation in GPS TEC prior to the 11 April 2012 Sumatra earthquake

On 11 April 2012, a strong earthquake of magnitude Ms8.6 occurred near the west coast of Northern Sumatra, Indonesia. In this paper, we investigated the morphological characteristics of anomalous variations in Global Positioning System Total Electron Content (GPS TEC) prior to the earthquake by the method of the statistical analysis. It was found the TEC anomaly was firstly decreased, then, it became more enhanced, finally, it decreased, the peak of anomaly enhancement arose from 13:00–17:00 LT on April 5 lasted for ～4 hours and the anomalous ionospheric regions extended to ～40^° in longitude and ～20^° in latitude, its location did not coincide with the vertical projection of the epicenter, but lies at the north and south of the geomagnetic equator, meanwhile, corresponding ionospheric anomalies are also observed in the magneto conjugate region. Potential causes of these results are discussed,eliminating the ionospheric anomalies that may be caused by solar activities and magnetic storms, it can be concluded that the observed obvious anomalous variation in GPS TEC on April 5 were possibly related to the earthquake.     

A statistical study on the temporal distribution of ionospheric TEC anomalies prior to M7.0+ earthquakes during 2003–2012

In this paper, we conduct a new statistical study on the temporal distribution of the Global Positioning System Total Electron Content (GPS TEC) anomalies prior to the earthquakes with magnitude M≥7.0 in the global area during 2003–2012 by the method of statistical analysis. The temporal distribution of the ionospheric TEC anomalies prior to the earthquakes with magnitude M≥7.0 is for the first time studied. It has been observed that the ionospheric negative anomalies mainly occur in one week prior to the earthquakes, and only when the magnitude is greater than or equal to 7.6, the ionospheric anomalies will have the greatest probability of occurrence in the afternoon to sunset (i.e. between 12:00 and 18:00 local time). They last for approximate 2 hr, but the chance of detecting the significant enhancement in the ionospheric TEC seems not to be a function of time and there is no clear tendency for positive anomalies. In addition, the relationship of the occurrence rate of pre-earthquake ionospheric anomalies and the magnitude of the earthquake is discussed, and it is found that the observed ionospheric TEC anomalies within several days before the earthquakes are highly likely to be related with the earthquakes because the occurrence rate of pre-earthquake ionospheric anomalies seems to increase slightly with the earthquake magnitude increasing.     

Ionospheric total electron content seismo-perturbation after Japan’s March 11, 2011, M=9.0 Tohoku earthquake under a geomagnetic storm; a nonlinear principal component analysis

Nonlinear principal component analysis (NLPCA) is implemented to analyze the spatial pattern of total electron content (TEC) anomalies 3 hours after Japan’s Tohoku earthquake that occurred at 05:46:23 on 11 March, 2011 (UTC) (M _w =9). A geomagnetic storm was in progress at the time of the earthquake. NLPCA and TEC data processing were conducted on the global ionospheric map (GIM) for the time between 08:30 to 09:30 UTC, about 3 hours after this devastating earthquake and ensuing tsunami. Analysis results show stark earthquake-associated TEC anomalies that are widespread, and appear to have been induced by two acoustic gravity waves due to strong shaking (vertical acoustic wave) and the generation of the tsunami (horizontal Rayleigh mode gravity wave). The TEC anomalies roughly fit the initial mainshock and movement of the tsunami. Observation of the earthquake-associated TEC anomalies does not appear to be affected by a contemporaneous geomagnetic storm.     

Modeling of local ionospheric time varying characteristics based on singular value decomposition over low-latitude GPS stations

Singular Value Decomposition (SVD) model is implemented to recognize the Total Electron Content (TEC) time series of daily, temporal as well as seasonal characteristics throughout the 24th solar cycle period of the year 2015 in the study. The Vertical (vTEC) analysis has been carried out with Global Positioning System (GPS) data sets collected from five stations from India namely GNT, Guntur (16.44^° N, 80.62^° E), and IISC, Bangalore (12.97^° N, 77.59^° E), LCK2, Lucknow (26.76^° N, 80.88^° E), one station from Thailand namely AITB, Bangkok (14.07^° N, 100.61^° E), and one station from South Andaman Island namely PBR, Port Blair (11.43^° N, 92.43^° E), located in low latitude region. The first five singular value modes constitute about 98% of the total variance, which are linearly transformed from the observed TEC data sets. So it is viable to decrease the number of modeling parameters. The Fourier Series Analysis (FSA) is carried out to characterize the solar-cycle, annual and semi-annual dependences through modulating the first three singular values by the solar (F10.7) and geomagnetic (Ap) indices. The positive correlation coefficient (0.75) of daily averaged GPS–TEC with daily averaged F10.7 strongly supports the temporal variations of the ionospheric features depends on the solar activity. Further, the significance and reliability of the SVD model is evaluated by comparing it with GPS–TEC data and the standard global model (Standard Plasma-Spherical Ionospheric Model, SPIM and International Reference Ionosphere, IRI 2016).     

汶川地震前后的气象异常

有研究认为局地气象异常与地震之间存在着一定的相关性,那么震惊中外的汶川大地震前后有没有气象异常呢？应用NCEP再分析资料,以1988—2007年20年间局地气象要素的平均值和标准偏差为基准,通过构建气象异常指数对2008年5月12日汶川发生的大地震前后的日平均气温、日最高气温、日最低气温、日平均降水强度和日平均气压等5项气象要素指标的异常状况进行了分析,结果表明在地震前2个月的时间内有异常状况出现,并且其变化幅度和持续时间都比较长,在地震过后这些异常并未立即消失;从5项气象要素异常空间分异来看,汶川是气象异常的中心地带,表征了汶川地震与局地气象之间存在着一定的相关性。尽管气象异常是否是地震发生的必然前兆尚待进一步考证,但出现在汶川特大地震前后的气象异常再次给我们一个提示,即气象异常与地震的关系值得深入研究。     

Possible Ionospheric Electromagnetic Perturbations Induced by the Ms7.1 Yushu Earthquake

The power spectrum density (PSD) of magnetic field in the ELF/VLF band recorded by the experiment IMSC onboard the DEMETER satellite were used to study the Ms7.1 Yushu earthquake taking place on April 13, 2010 in China. The results indicate that possible ionospheric electromagnetic perturbations occurring 4?days before the earthquake in the frequency range [370–897?Hz]. Along the orbit 30880_up, which passed over the epicenter area on 9 April, enhanced PSD value of magnetic field at 410?Hz was detected both over the epicentral area and its conjugate point in the southern hemisphere. While on revisited orbits during other days (before and after the earthquake) the magnetic field spectra remained at a relatively low level. In order to be sure that the electromagnetic disturbances were induced by this Yushu earthquake, relative variations of the magnetic field in the ELF/VLF range [370–897?Hz] were calculated and compared with the normal background during 3?years (2007, 2008 and 2009) in the time interval from Jan. 1st to Apr. 30 and in the area [23°N–43°N, 86°E–106°E]. The results show that the normal level of magnetic field in this area is relatively low (~10^?7?nT²/Hz), but a large increase occurred from Apr. 1st to Apr. 14 which exceeds 5σ_b. After the earthquake, the magnetic field in the ELF/VLF range gradually decreased. In order to exclude the influence of geomagnetic field activity, we selected only the data recorded during magnetically quiet local night-times. In addition, artificial noises were also removed from the dataset used in the present paper. Therefore the observed perturbations were independent of geomagnetic field disturbances, and might be attributed to seismic activity.     

Application of Astronomic Time-latitude Residuals in Earthquake Prediction

After the earthquake (Ms = 6.1) occurred in Luquan county of Yunnan province on April 18, 1985, the relationship between major earthquakes and astronomical time-latitude residuals (ATLR) of a photoelectric astrolabe in Yunnan Observatory was analyzed. ATLR are the rest after deducting the effects of Earth’s whole motion from the observations of time and latitude. It was found that there appeared the anomalies of the ATLR before earthquakes which happened in and around Yunnan, a seismic active region. The reason of the anomalies is possibly from change of the plumb line due to the motion of the groundmass before earthquakes. Afterwards, using studies of the anomalous characters and laws of ATLR, we tried to provide the warning information prior to the occurrence of a few major earthquakes in the region. The significant synchronous anomalies of ATLR of the observatory appeared before the earthquake of magnitude 6.2 in Dayao county of Yunnan province, on July 21, 2003. It has been again verified that the anomalies possibly provide the prediction information for strong earthquakes around the observatory.     

Observations of outflowing ion beams on auroral field lines at altitudes of many earth radii

The composition, energy and angular characteristics of upward flowing ionospheric ions at altitudes greater than ～ 20,000 km have been studied by means of the PROGNOZ-7 ion composition experiment. Very narrow beams, having widths corresponding to a mirroring altitude of the order a few thousand kilometers or less, may be found up to altitudes exceeding 30,000 km on the nightside. At much higher altitudes and in regions connected to the dayside/flank boundary layer and plasma mantle, the beams are much broader than expected from adiabatic particle motions from an ionospheric source/acceleration region, suggesting that pitch angle scattering or transverse acceleration processes are present there. Considerable mass dispersion effects have also been observed in some upward flowing ionospheric ion beams. The peak energy for the O⁺ ions may differ by several keV compared to that for the H⁺ ions in one and the same ion beam at altitudes above ～ 20,000 km. The O⁺ ions in these beams have gained considerably more energy than H⁺ in the acceleration process. Many examples with a much higher O⁺ than H⁺ content in the beam have been observed. Possible mechanisms giving rise to the observed effects are discussed, one being several kV of potential drop below the neutral H, O-crossover altitude (500–1500 km). At altitudes where the upflowing ionospheric ions are intermixed with magnetosheath ions, mass dispersion effects are also observed. This dispersion often appears to be the result of a velocity filtering effect caused by the dawn-dusk electric field (earthward convection).     

Response of the Total Electron Content of Terrestrial Ionosphere to GRB041227

At 21:30 UT on 2004 December 27 an extremely strong gamma-ray burst swept across the earth and caused the part of the terrestrial upper atmosphere exposed to it to produce extra ionization. Sudden ionospheric disturbance (SID) events were simultaneously observed at many of the very low frequency (VLF) electric wave observing stations. Analyses of the X-ray data of the GOES satellite as well as the solar wind and interplanetary data of the ACE satellite with the relevant theories show that the observed SID event observed was indeed caused by GRB041227. We calculated the response of the total electron content (TEC) of the terrestrial ionosphere to this γ-ray burst using the observed data provided by the international GPS service network (IGS) and the data processing method of coherent summation. The result indicates that the GRB041227 produced by the SGR1806-20 had an evident effect on the terrestrial ionosphere: in the course of the burst the average ionospheric TEC increased, to a maximum size of about 0.04 TECU (1 TECU = 10¹⁶ el/m²), equivalent to a solar flare with importance of C or lower. The calculated result demonstrates once again that a remote celestial body can also affect the terrestrial space environment to some extent.     

Statistical Test of the Correlation Between Earthquakes and Solid Tidal Waves: Implication to Hazard Prediction

The statistical correlation between earthquakes and the characteristics of solid Earth tide was investigated. Worldwide data on earthquakes (4018?M?≥?6.0) from January 1, 1973 to December 31, 2003 were analyzed. The distributions (D) of three relationships among earthquakes and solid tidal forces derived by composite force FI_i [D (FI_i)], azimuth A_i [D (A_i)], and elevation E_i [D (E_i)] from 1,200 waves were examined. These relationships indicate the probability of earthquakes. Twelve large-amplitude waves were investigated in detail to determine if earthquakes can be predicted. A test model P(t, λ, φ, d) consisting of three different wave groups was designed using these distributions. The values of tidal force, including the size and direction of tidal waves at any given time and place, were converted to test the probability of an earthquake. The converted values were then applied to trace and ascertain the great M?=?9.0 Northern Sumatra earthquake on December 26, 2004. Although the results selected from both the 12 maximum-amplitude waves or the 50 best correlation waves did not match well, the model can be significantly improved to produce only a day’s difference when all the 1,200 waves are employed. Therefore, further studies should be conducted to test if this method can be adopted in accurately predicting the occurrence of earthquakes, including time, relevant size, and location.     

Ionospheric plasma acceleration at Mars: ASPERA-3 results

The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on-board the Mars Express spacecraft (MEX) measured penetrating solar wind plasma and escaping/accelerated ionospheric plasma at very low altitudes (250 km) in the dayside subsolar region. This implies a direct exposure of the martian topside atmosphere to solar wind plasma forcing leading to energization of ionospheric plasma. The ion and electron energization and the ion outflow from Mars is surprisingly similar to that over the magnetized Earth. Narrow “monoenergetic” cold ion beams, ion beams with broad energy distributions, sharply peaked electron energy spectra, and bidirectional streaming electrons are particle features also observed near Mars. Energized martian ionospheric ions (O⁺, O⁺₂, CO⁺₂, etc.) flow in essentially the same direction as the external sheath flow. This suggests that the planetary ion energization couples directly to processes in the magnetosheath/solar wind. On the other hand, the beam-like distribution of the energized plasma implies more indirect energization processes like those near the Earth, i.e., energization in a magnetized environment by waves and/or parallel (to B) electric fields. The general conditions for martian plasma energization are, however, different from those in the Earth's magnetosphere. Mars has a weak intrinsic magnetic field and solar wind plasma may therefore penetrate deep into the dense ionospheric plasma. Local crustal magnetization, discovered by Acuña et al. [Acuña, M.J., Connerey, J., Ness, N., Lin, R., Mitchell, D., Carlsson, C., McFadden, J., Anderson, K., Rème, H., Mazelle, C., Vignes, D., Wasilewski, P., Cloutier, P., 1999. Science 284, 790-793], provide some dayside shielding against the solar wind. On the other hand, multiple magnetic anomalies may also lead to “hot spots” facilitating ionospheric plasma energization. We discuss the ASPERA-3 findings of martian ionospheric ion energization and present evidences for two types of plasma energization processes responsible for the low- and mid-altitude plasma energization near Mars: magnetic field-aligned acceleration by parallel electric fields and plasma energization by low frequency waves.     

电离层TEC对小耀斑的响应

利用国际GPS观测网(IGS)提供的多个台站的观测数据,分析了M级别以下的小、暗太阳耀斑对向阳面电离层TEC的影响．利用传统分析方法的结果表明,从单条视线(LOS)观测数据得到的电离层TEC及其时间变化率曲线来看,由于它们的波动水平和正常情况下的背景电离层变化相当,使此类小耀斑的信息完全淹没在背景噪声中,不能够显示和分辨出耀斑的发生．利用相干求和的数据处理方法,选用向阳面18个GPS台站的观测数据研究了一次C级SF耀斑引起的电离层TEC增加,结果发现,这种方法能有效地消除背景电离层变化噪声,电离层对耀斑的响应非常清楚和明显,这通常只能在X级别的大耀斑中看到．和GOES卫星X射线数据相比,电离层TEC变化的时间特征和耀斑爆发的开始、最大和结束时间均有很好的符合,其最大平均TEC增量在0．1TECU以下,和X级别的大耀斑相比有一个或多个量级上的差别．     

Ionospheric disturbances: Evidence for the contraction of the plasmasphere during severe geomagnetic storms

Continuous measurements of the ionospheric total electron content (TEC) provide a parameter well suited for the study of F-region disturbance effects. In this investigation, five cases of large and rapid drops in TEC observed near the sunset period are interpreted as being due to the contraction of the plasmasphere to L values less than 3. A model calculation is performed for the specific case of 1 November 1968 using simultaneous Alouette I data to define the position and magnitude of the ionospheric trough. The results indicate that the motion of a deep trough across the ray path from a geostationary satellite to an observing station can cause drastic changes in the measured amounts of Faraday rotation and therefore in the derived values of TEC. All of the TEC data sources available for the five events are then examined in an attempt to describe more completely the latitude dependence of the effects. It is suggested that during severe geomagnetic storms, the large and rapid decays in TEC during the 18–21 LT period to values significantly below normal can be used as a criterion to determine the approximate latitudinal extent of the contracted plasmasphere.     

长三角地区电离层变化的GPS监测

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。     

Existence and stability of the non-collinear libration points in the restricted three body problem when both the primaries are ellipsoid

This paper deals with the existence and stability of the non-collinear libration points in the restricted three-body problem when both the primaries are ellipsoid with equal mass and identical in shape. We have determined the equations of motion of the infinitesimal mass which involves elliptic integrals and then we have investigated the existence and stability of the non-collinear libration points. This is observed that the non-collinear libration points exist only in the interval 52^°<φ<90^° and form an isosceles triangle with the primaries. Further we observed that the non collinear libration points are unstable in 52^°<φ<90^°.     

Assessing the Constrained Harmonic Mean Method for Deriving the Kinematics of ICMEs with a Numerical Simulation

In this study we use a numerical simulation of an artificial coronal mass ejection (CME) to validate a method for calculating propagation directions and kinematical profiles of interplanetary CMEs (ICMEs). In this method observations from heliospheric images are constrained with in-situ plasma and field data at 1 AU. These data are used to convert measured ICME elongations into distance by applying the harmonic mean approach, which assumes a spherical shape of the ICME front. We used synthetic white-light images, similar to those observed by STEREO-A/HI, for three different separation angles between remote and in-situ spacecraft of 30^°, 60^°, and 90^°. To validate the results of the method, the images were compared to the apex speed profile of the modeled ICME, as obtained from a top view. This profile reflects the “true” apex kinematics because it is not affected by scattering or projection effects. In this way it is possible to determine the accuracy of the method for revealing ICME propagation directions and kinematics. We found that the direction obtained by the constrained harmonic mean method is not very sensitive to the separation angle (30^° sep: ?=W7; 60^° sep: ?=W12; 90^° sep: ?=W15; true dir.: E0/W0). For all three cases the derived kinematics agree relatively well with the real kinematics. The best consistency is obtained for the 30^° case, while with growing separation angle the ICME speed at 1 AU is increasingly overestimated (30^° sep: ΔV _arr≈??50 km?s^?1, 60^° sep: ΔV _arr≈+?75 km?s^?1, 90^° sep: ΔV _arr≈+?125 km?s^?1). Especially for future L₄/L₅ missions, the 60^° separation case is highly interesting in order to improve space-weather forecasts.     

GPS监测电离层活动的方法和最新进展

全球定位系统(GPS)可以快速、准确地提供电离层总电子含量(TEC)信息。简要介绍了GPS技术精确测量TEC、监测电离层的原理和方法，指出进行TEC绝对量估计时求解差分群延迟(DCB)的重要性，以及建立多层和实时电离层监测模型的必要性。分析了影响TEC估计的主要误差源，着重介绍了目前GPS监测电离层的最新成果和进展。     

Ionospheric corrections via PIM and real-time data

We describe a method for removing ionospheric effects from single-frequency radio data a posteriori. This method is based on a theoretical climatological model developed by the USAF, which returns along the line of sight to the source. Together with a model of , ionospheric delay and Faraday rotation values ensue. If contemporaneous ionospheric data – GPS TEC observations or ionosonde profiles – exist, they can be incorporated to update the modeled n_e.     

利用时间序列模型预报电离层TEC

以IGS(international GPS service)发布的电离层TEC(total electron content)资料为样本,用时间序列模型对全球的电离层总电子含量进行了预报.在时间序列预报模型中,不同的定阶方法导致不同的预报结果;实践证明本文使用的BIC定阶准则较好地实现了电离层总电子含量的预报.结果表明:对10 d左右的预报时间段,时间序列模型的TEC计算结果相对精度高,预报相对精度优于60%的网格点数在总网格点数中所占百分比可达90%以上.