共查询到17条相似文献,搜索用时 0 毫秒
1.
Mei Li Michel Parrot 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(3):974-984
Results of a statistical variation of total ion density observed in the vicinity of epicenters as well as around magnetically conjugated points of earthquakes are presented in this paper. Two data sets are used: the ion density measured by DEMETER during about 6.5?years and the list of strong earthquakes (MW?≥?4.8) occurring globally during this period (14,764 earthquakes in total). First of all, ionospheric perturbations with 23–120?s observation time corresponding to spatial scales of 160–840?km are automatically detected by a software (64,287 anomalies in total). Second, it is checked if a perturbation could be associated either with the epicenter of an earthquake or with its magnetically conjugated point (distance?<?1500?km and time?<?15?days before the earthquake). The index Kp?<?3 is also considered in order to reduce the effect of the geomagnetic activity on the ionosphere during this period. The results show that it is possible to detect variations of the ionospheric parameters above the epicenter areas as well as above their conjugated points. About one third of the earthquakes are detected with ionospheric influence on both sides of the Earth. There is a trend showing that the perturbation length increases as the magnitude of the detected EQs but it is more obvious for large magnitude. The probability that a perturbation appears is higher on the day of the earthquake and then gradually decreases when the time before the earthquake increases. The spatial distribution of perturbations shows that the probability of perturbations appearing southeast of the epicenter before an earthquake is a little bit higher and that there is an obvious trend because perturbations appear west of the conjugated point of an earthquake. 相似文献
2.
X. Zhang Z. Zeren M. Parrot R. Battiston J. Qian X. Shen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
ULF/ELF electric field perturbations in the ionosphere have been widely observed by the satellites. In this paper, we develop a method of Logarithm Electric Field Intensity (LEFI) to automatically distinguish this kind of disturbances based on the spectrum intensity and its damping exponent with frequency in electromagnetic signals. This method is applied to DEMETER data processing around Chile earthquakes with magnitude larger than 6.0. It is found that 2/3 earthquakes have shown obvious ULF/ELF electric field perturbations in this region. The temporal and spatial distributions of electron density and temperature were compared with that of electric field, which proved the existence of irregularities above epicentral area. Finally, the coupling mechanism of earthquake-ionosphere is discussed based on multi-parameter analysis. 相似文献
3.
S.R. Tojiev B.J. Ahmedov H.E. Eshkuvatov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Tashkent International Heliophysical Year (IHY) station is a member of Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) network being operated globally to study the ionosphere and the magnetosphere with the help of electromagnetic waves in Very Low Frequency (VLF) band. Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008. We have studied VLF amplitude anomalies related to the EQs occurred in 2008–2009 years with magnitude more than 5 on the path way from the VLF transmitters to the Tashkent station assuming that propagation of VLF ground-based transmitters signals can be perturbed by EQ preparation detectable from the ground-based measurements in the VLF bands. For analyzing narrowband data we have used the nighttime fluctuation (NF) method paying attention to the data obtained during the local nighttime (20:00 LT–04:00 LT) in Tashkent where the VLF receiver is operating. The mean nighttime amplitude (or trend) and nighttime fluctuation are found to increase significantly before the EQ occurred on the path way from the transmitters to the receiver. The obtained results have revealed an agreement with VLF amplitude anomalies observed in Tashkent VLF station during the strong EQs occurred on the path way from the transmitters to the receiver. Some results are presented to show the probing potentiality of VLF waves to predict short term EQs with high magnitude. 相似文献
4.
Tobias G.W. Verhulst Stanimir M. Stankov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(9):2245-2251
A total solar eclipse occurred on 21 August 2017, with the path of totality starting over the North Pacific Ocean, crossing North-America and ending over the Mid-Atlantic Ocean slightly North of the equator. As a result, a partial solar eclipse was observed as far away as the Western Europe. The ionospheric observatory in Dourbes, Belgium, was right on the edge of the partial eclipse and was exposed for a very short period of only few minutes just before the local sunset. High-resolution ionospheric measurements were carried out at the observatory with collocated digital ionosonde and GNSS receivers. The data analysis revealed a clear wave-like pattern in the ionosphere that can be seen arriving before the local onset of the eclipse. The paper details the analysis and provides a possible explanation of the observed phenomenon. 相似文献
5.
Carlo Scotto 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
A long temporal series of simulated ionograms was generated with a superimposed secular variation of −14 km/century on the hmF2 parameter. These ionograms were interpreted by the automatic scaling program Autoscala. By applying four different empirical formulas, four artificial series of hmF2 were generated and then processed with the same methods used by other authors for real data sets. Data analysis of the simulated ionograms revealed the artificially imposed long-term trend. These results lead to the conclusion, that regardless of the empirical formula used, the accuracy of hmF2 from ionosonde measurements would be adequate to observe a long-term trend of −14 km/century. 相似文献
6.
J. Olwendo P.J. Cilliers O. Ming 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3187-3201
Ionospheric irregularities are well-known phenomena associated with ionospheric scintillation. These irregularities comprise steep electron density gradients in the equatorial F region some 1 to 2 h after sunset in regions close to the geomagnetic equator. Using the IGS network of GNSS receivers spread across the low-latitude region over the African sector, we present the monthly trends in ionospheric irregularity activity levels based on Rate of TEC Index (ROTI) during the declining phase of solar 24. The monthly trends are statistically represented by counts of the night time ROTI values exceeding a threshold of 0.4 TECU/min. A clear trend emerges on the irregularity occurrence across the African sector: during the first four months of the year, the irregularity occurrence is highly pronounced on the western side of the region. The irregularity occurrence then shifts to the eastern side during the months of May, June, July, and August. During the last four months of the year, the irregularity occurrence is again more intense on the western side of Africa than on the eastern side. The occurrence of irregularity structures on only one side of the region during a given night is an unusual feature reported here for the first time. 相似文献
7.
Yi-Ying Ho Hau-Kun Jhuang Yung-Chih Su Jann-Yenq Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
In this paper we examine the pre-earthquake ionospheric anomalies by the total electron content (TEC) extracted from GIM (global ionospheric map) and the electron density (Ne) observed by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite during the 2010 M8.8 Chile earthquake. Temporal variations show the nighttime TEC and Ne simultaneously increase 9–19 days before the earthquake. A cross-comparison of data recorded during the period of 1 February to 3 March in 2006–2010 confirms the above temporal anomalies specifically appear in 2010. The spatial analyses show that the anomalies tend to appear over the epicenter. 相似文献
8.
Shivalika Sarkar A.K. Gwal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
First comparison of in situ density fluctuations measured by the DEMETER satellite with ground based GPS receiver measurements at the equatorial anomaly station Bhopal (geographic coordinates (23.2°N, 77.6°E); geomagnetic coordinates (14.29°N, 151.12°E)) for the low solar activity year 2005, are presented in this paper. Calculation of the diurnal maximum of the strength of the equatorial electrojet, which can serve as precursor to ionospheric scintillations in the anomaly region is also done. The Langmuir Probe experiment and Plasma Analyzer onboard DEMETER measure the electron and ion densities respectively. Irregularities in electron density distribution cause scintillations on transionospheric links and there exists a close relationship between an irregularity and scintillation. In 40% of the cases, DEMETER detects the irregularity structures (dNe/Ne ? 5% and dNi/Ni (O+) ? 5%) and GPS L band scintillations (S4 ? 0.2) are also observed around the same time, for the low solar activity period. It is found that maximum irregularity intensity is obtained in the geomagnetic latitude range of 10–20° for both electron density and ion density. As the GPS signals pass through this irregularity structure, scintillations are recorded by the GPS receiver installed at the equatorial anomaly station, Bhopal it is interesting to note that in situ density fluctuations observed on magnetic flux tubes that pass over Bhopal can be used as indicator of ionospheric scintillations at that site. Many cases of density fluctuations and associated scintillations have been observed during the descending low solar activity period. The percentage occurrence of density irregularities and scintillations shows good correspondence with diurnal maximum of the strength of electrojet, however this varies with different seasons with maximum correspondence in summer (up to 66%) followed by equinox (up to 50%) and winter (up to 46%). Also, there is a threshold value of EEJ strength to produce density irregularities ((dNe/Ne)max ? 5%) and for moderate to strong scintillations (S4 ? 0.3) to occur. For winter this value is found to be ∼40 nT whereas for equinox and summer it is around 50 nT. 相似文献
9.
Yoshihiro Kakinami Masashi Kamogawa Jann-Yenq Liu Shigeto Watanabe Toru Mogi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Transient ionospheric disturbances in the total electron content (TEC) are examined before and after the M9.0 2011 off the Pacific coast of Tohoku Earthquake to find ionospheric responses to the radiation caused by Fukushima I nuclear power plant accident, which was damaged by the earthquake and tsunamis. The TEC is derived from records of a ground-based receiving network of GPS Earth Observation Network (GEONET) in Japan. Both small enhancement and disturbance of TEC were detected over the nuclear power plant after the radiation was suddenly enhanced on March 14 of 2011, while similar signatures were not detected in the other sudden radiation enhancements. Further, no continuous enhancement and disturbance lasting for more than an hour were observed over the nuclear power plant. Therefore, the results indicate that radioactive materials may not cause the ionospheric disturbance or disturb the ionosphere in highly specific circumstance even if such effects exist. 相似文献
10.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(7):1803-1817
The Quasi-Zenith Satellite System (QZSS) established by the Japan Aerospace Exploration Agency mainly serves the Asia-Pacific region and its surrounding areas. Currently, four in-orbit satellites provide services. Most users of GNSS in the mass market use single-frequency (SF) receivers owing to the low cost. Therefore, it is meaningful to analyze and evaluate the contribution of the QZSS to SF precise point positioning (PPP) of GPS/BDS/GLONASS/Galileo systems with the emergence of GNSS and QZSS. This study compares the performances of three SF PPP models, namely the GRoup and PHase Ionospheric Correction (GRAPHIC) model, GRAPHIC with code observation model, and an ionosphere-constrained model, and evaluated the contribution of the QZSS to the SF PPP of GPS/BDS/GLONASS/Galileo systems. Moreover, the influence of code bias on the SF PPP of the BDS system is also analyzed. A two-week dataset (DOY 013–026, 2019) from 10 stations of the MGEX network is selected for validation, and the results show that: (1) For cut-off elevation angles of 15, 20, and 25°, the convergence times for the static SF PPP of GLONASS + QZSS are reduced by 4.3, 30.8, and 12.7%, respectively, and the positioning accuracy is similar compared with that of the GLONASS system. Compared with the BDS single system, the convergence times for the static SF PPP of BDS + QZSS under 15 and 25° are reduced by 37.6 and 39.2%, the horizontal positioning accuracies are improved by 18.6 and 14.1%, and the vertical components are improved by 13.9 and 21.4%, respectively. At cut-off elevation angles of 15, 20, and 25°, the positioning accuracy and precision of GPS/BDS/GLONASS/Galileo + QZSS is similar to that of GPS/BDS/GLONASS/Galileo. And the convergence times are reduced by 7.4 and 4.3% at cut-off elevation angles of 20 and 25°, respectively. In imitating dynamic PPP, the QZSS significantly improves the positioning accuracy of BDS and GLONASS. However, QZSS has little effect on the GPS-only, Galileo-only and GPS/BDS/GLONASS/Galileo. (2) The code bias of BDS IGSO and MEO cannot be ignored in SF PPP. In static SF PPP, taking the frequency band of B1I whose multipath combination is the largest among the frequency bands as an example, the vertical component has a systematic bias of approximately 0.4–1.0 m. After correcting the code bias, the positioning error in the vertical component is lower than 0.2 m, and the positioning accuracy in the horizontal component are improved accordingly. (3) The SF PPP model with ionosphere constraints has a better convergence speed, while the positioning accuracy of the three models is nearly equal. Therefore the GRAPHIC model can be used to get good positioning accuracy in the absence of external ionosphere products, but its convergence speed is slower. 相似文献
11.
M.A. Chernigovskaya B.G. Shpynev A.S. Yasyukevich D.S. Khabituev K.G. Ratovsky A.Yu. Belinskaya A.E. Stepanov V.V. Bychkov S.A. Grigorieva V.A. Panchenko D. Kouba J. Mielich 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(2):762-776
We present a joint analysis of longitude-temporal variations of ionospheric and geomagnetic parameters at middle and high latitudes in the Northern Hemisphere during the two severe magnetic storms in March and June 2015 by using data from the chains of magnetometers, ionosondes and GPS/GLONASS receivers. We identify the fixed longitudinal zones where the variability of the magnetic field is consistently high or low under quiet and disturbed geomagnetic conditions. The revealed longitudinal structure of the geomagnetic field variability in quiet geomagnetic conditions is caused by the discrepancy of the geographic and magnetic poles and by the spatial anomalies of different scales in the main magnetic field of the Earth. Variations of ionospheric parameters are shown to exhibit a pronounced longitudinal inhomogeneity with changing geomagnetic conditions. This inhomogeneity is associated with the longitudinal features of background and disturbed structure of the geomagnetic field. During the recovery phase of a storm, important role in dynamics of the mid-latitude ionosphere may belong to wave-like thermospheric disturbances of molecular gas, propagating westward for several days. Therefore, it is necessary to extend the time interval for studying the ionospheric effects of strong magnetic storms by a few days after the end of the magnetospheric source influence, while the disturbed regions in the thermosphere continues moving westward and causes the electron density decrease along the trajectories of propagation. 相似文献
12.
N. Zolotukhina N. Polekh E. Romanova A. Polyakova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We report work utilizing 15-min resolution ionospheric data obtained with DPS-4 digisonde in 2003–2011 to study the seasonal variations in amplitudes and phases of the most powerful spectral components of the F2 layer critical frequency (foF2) and peak height (hmF2) fluctuations over Irkutsk (52.5°N, 104.0°E). We show that fluctuations of both parameters contain quasi-harmonic components with periods of Tn = 24/n h (n = 1–7). The number of distinct spectral peaks varies from 3 in summer to 7 in winter. Amplitude and phase characteristics of the diurnal (n = 1) and semidiurnal (n = 2) components is studied using the data sets extracted from the original data sets with band-pass filter. It has been found that the amplitudes of diurnal/semidiurnal foF2 and diurnal hmF2 components are maximum in winter and minimum in summer. Amplitudes of the diurnal components vary gradually; those of the foF2 semidiurnal one, abruptly, thus forming a narrow winter maximum in November–January. The phase (local time of maximum) of the diurnal foF2 component increases gradually by 4–6 h from winter to summer. The phase of the semidiurnal foF2 component is nearly stable in winter/summer and sharply decreases (increases) by 2–3 h near the spring (autumn) equinox. The phase of the diurnal component of hmF2 (local time of minimum) varies slightly between 1130 and 1300 LT; that of the semidiurnal one decreases (increases) by 4–6 h from January to March (from September to November). The results obtained show that the main features of seasonal variations in the diurnal and semidiurnal components of the mid-latitude F2 layer parameters recur consistently during the solar activity growth and decline phases. 相似文献
13.
V.K.D. Srinivasu N. Dashora D.S.V.V.D. Prasad K. Niranjan S. Gopi Krishna 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(7):1761-1775
This study presents unique perspectives of occurrence and strength of low latitude ionospheric scintillations on multiple signals of Global Navigation Satellite System (GNSS) and its frequency dependence using continuous observation records of 780 nights. A robust comparative analysis is performed using scintillation index, S4 and its variation during pre-midnight and post-midnight duration from a GNSS receiver located at Waltair (17.7°N, 83.3°E), India, covering period from July 2014 to August 2016. The results, generally exhibit the impact of declining phase of solar cycle 24 on occurrence and strength of scintillations, which, however, is evidently different over different frequencies transmitted from different GNSS systems. A deeper quantitative analysis uniquely reveals that apart from the solar cycle and seasonal effects, the number of visible satellites of a selected GNSS markedly affect the occurrence and also the strength. Processing scheme of adopting 6 hourly time windows of pre-midnight and post-midnight brought a novel result that the strength and occurrence of strong scintillations decrease with declining solar activity during pre-midnight hours but remarkably increase for moderate and weak scintillations during post-midnight. The physical processes that dominate the post-midnight equatorial ionosphere are invoked to explain such variations that are special during declining solar activity. Finally, inter-GNSS signal analysis in terms of the effect of strong, moderate and weak scintillations is presented with due consideration of number of satellite passes affected and frequency dependence of mean S4. The quantitative results of this study emphasize for the first time effect of low latitude scintillation on GNSS signals in Indian zone under changing background solar and seasonal conditions. 相似文献
14.
Nabeel Ahmad Samia Faiz Gurmani Abdul Basit Muhammad Ali Shah Talat Iqbal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(8):2491-2503
In this research work, we have performed comparative diurnal variations of atmospheric Potential Gradient (PG) of fair-weather days by using the data of three stations installed in Northern, Pakistan for the year 2018. We investigated the impact of both local and global factors and meteorological parameters in the diurnal variation of atmospheric Potential Gradient on the annual and seasonal time scale. We observed two peaks, primary and secondary. This is because of the land-based measurements of annual and seasonal variations. The annual average curve of Potential Gradient of all three stations: Islamabad (CES), Muzaffarabad (MZF), and Balakot (BKT) demonstrated a notable deviation from the standard oceanic Carnegie curve. The atmospheric Potential Gradient variations are due to numerous meteorological factors e.g., air pollution, humidity, aerosol particles, fog, and temperature. Among three stations, the MZF station is located in highland (mountainous) and it demonstrated a higher atmospheric Potential Gradient. We further differentiate the results of our three stations with global results for authenticity and observed coherence between them. In addition, a positive correlation of fair-weather Potential Gradient is observed with temperature and a notable correlation between relative humidity and atmospheric Potential Gradient for all the three observatories. 相似文献
15.
Richa Trivedi Amit Jain Sudhir Jain A.K. Gwal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
GPS satellites data obtained at Bhopal (23.16° N, 77.36° E, geomagnetic latitude 14.23° N) India were analyzed to study the TEC changes during several geomagnetic storms (−300 nT < Dst < −50 nT) occurred in 2005–2007. We had segregated the storms according to the Dst value, i.e. moderate storms (−100 nT < Dst ? −50 nT), strong storms (−150 nT < Dst < −100 nT), and severe storms (Dst less than −150 nT). Total of 21 geomagnetic storms (10 moderate, 9 strong, 2 severe) are considered for the present study. Deviation in vertical total electron content (VTEC) during the main phase of the storm was found to be associated with the prompt penetration of electric field originated due to the under-shielding and over-shielding conditions for almost all geomagnetic storms discussed in this paper. For most of the storms VTEC shows the positive percentage deviation during the main phase while it shows positive as well as the negative deviation during the recovery phase of the storms. The −80% deviation in VTEC was found for geomagnetic storm occurred on July 17, 2005 and the negative trend continued for recovery phase of the storm. This was mainly due to the thermospheric composition changes by Joule heating effect at auroral latitudes that generate electric field disturbance at low latitudes. Traveling ionospheric disturbances (TIDs) were responsible for the formation of wave like nature in VTEC for the storms occurred on May 15, 2005, whereas it was not observed for storm occurred on August 24, 2005. 相似文献
16.
H.J. Völk E.G. Berezhko L.T. Ksenofontov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):473-476
For the case of Tycho’s supernova remnant (SNR), we present the relation between the blast wave and contact discontinuity radii calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is very close to the shock radius. Therefore a consistent explanation of these observations can be given in terms of efficient CR acceleration which makes the medium more compressible. 相似文献
17.
Muhammad Sadiq Zulfiqar Ahmad 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
A statistical comparison has been made between gravity field parameters derived from different global geopotential models (GGMs) and observed gravity anomalies, gravimetric geoid and GPS-Leveling data. The motivation behind this study is the selection of best possible global geopotential model that best matches statistically with the local observed data in Pakistan. This will facilitate in decreasing the load on observed data for the development of regional gravimetric geoid in remove-compute-restore technique when used in the Stokes’s integral for computation of the residual part. It is observed that combined geopotential models such as EGM96 and PGM200A, EIGEN-GL04C and EIGEN-CG03C reflect the better match in the total spectral range of gravity and GPS-Leveling data. Results of the precise local geoid model also indicate similar characteristics. A very-high-degree model “EGM2008” (degree/order 2160) exhibits relatively superior statistical fit with observed ground data in Pakistan region. For satellite-only models an increasing trend in the standard deviation can be seen with maximum of about ∼4 m in difference between GPS-Leveling and corresponding GGM’s geoid with increase in the order from 50 to 120 and then it decreases afterwards. However, for the EIGEN-CHAMP03SP, standard deviation saturates to a value of 3.4 m. This is an indication of contamination in the long to medium wavelength part, i.e. 50–100° for the satellite-only models. Moreover, the models DEOS-CHAMP-01C, GGM02C and then ITG-GRACE03 appear to have better fit for medium to long wavelength and can possibly be recommended for use as long wavelength part with the local observed data. While a hybrid geopotential model selection can be achieved through the selection from either of DEOS-CHAMP-01C, GGM02C, GGM02S, EIGEN-GRACE02S or ITG-GRACE03 in the long wavelength (to degree and order 40) and EGM96, PGM200A, EIGEN-GL04C, EIGEN-CG03C or even EGM2008 in medium to short wavelength, i.e. from degree 41 to maximum degree and order. 相似文献