global ionospheric maps
Recently Published Documents


TOTAL DOCUMENTS

60
(FIVE YEARS 34)

H-INDEX

8
(FIVE YEARS 2)

2021 ◽  
Vol 14 (1) ◽  
pp. 20
Author(s):  
Yanfeng Dong ◽  
Chengfa Gao ◽  
Fengyang Long ◽  
Yuxiang Yan

Many studies have reported that there is a coupling mechanism between ionosphere and earthquake (EQ). Ionospheric anomalies in the form of abnormal increases and decreases of ionospheric Total Electron Content (TEC) are even regarded as precursors to EQs. In this paper, TEC anomalies associated with three major EQs were investigated by Global Ionospheric Maps (GIMs) and GPS-TEC, including Kumamoto-shi, Japan—EQ occurred on 15 April 2016 with Mw = 7.0; Jinghe, China—EQ occurred on 8 August 2017 with Mw = 6.3; and Lagunas, Peru—EQ occurred on 26 May 2019 with Mw = 8.0. It was found that the negative ionospheric anomalies linger above or near the epicenter for 4–10 h on the day of the EQ. For each EQ, the 10-min sampling interval of TEC was extracted from three permanent GPS stations around the epicenter within 10 days before and after the EQ. Variations of TEC manifest that the negative ionospheric anomalies first appear 10 days before the EQ. From 5 days before to 2 days after the main shock, the negative ionospheric anomalies were more prominent than the other days, with the amplitude of negative ionospheric anomaly reaching −3 TECu and the relative ionospheric anomaly exceeding 20%. In case of Kumamoto-shi EQ, the solar-geomagnetic conditions were not quiet (Dst < −30 nT, Kp > 4, and F10.7 > 100 SFU) on the suspected EQ days. We discussed the differences between ionospheric anomalies caused by active solar-geomagnetic conditions and EQ. Combining the analysis results of Jinghe EQ and Lagunas EQ, under quiet solar-geomagnetic conditions (Dst > −30 nT, Kp < 4, and F10.7 < 100 SFU), it can be found that TEC responds to various solar-geomagnetic conditions and EQ differently. The negative ionospheric anomalies could be considered as significant signals of upcoming EQs. These anomalies under different solar-geomagnetic conditions may be effective to link the lithosphere and ionosphere in severe seismic zones to detect EQ precursors before future EQs.


Space Weather ◽  
2021 ◽  
Author(s):  
Qi Liu ◽  
Manuel Hernández‐Pajares ◽  
Haixia Lyu ◽  
Michi Nishioka ◽  
Heng Yang ◽  
...  

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Zishen Li ◽  
Ningbo Wang ◽  
Ang Liu ◽  
Yunbin Yuan ◽  
Liang Wang ◽  
...  

AbstractAs a new Ionosphere Associate Analysis Center (IAAC) of the International GNSS Service (IGS), Chinese Academy of Sciences (CAS) started the routine computation of the real-time, rapid, and final Global Ionospheric Maps (GIMs) in 2015. The method for the generation of CAS rapid and final GIMs and recent updates are presented in the paper. The quality of CAS post-processed GIMs is assessed during 2015–2018 after the maximum of solar cycle 24. To perform an independent and fair assessment, Jason-2/3 Vertical Total Electron Contents (VTEC) are first used as the references over the ocean. GPS differential Slant TECs (dSTEC) generated from 55 Multi-GNSS Experimental (MGEX) stations of the IGS are also employed, which provides a complementing way to evaluate the ability of electron content models to reproduce the spatial and temporal gradients in the ionosphere. During the test period, Jet Propulsion Laboratory (JPL) GIMs present significantly positive deviations compared to the Jason VTEC and GPS dSTEC. Technical University of Catalonia (UPC) rapid GIM UQRG exhibits the best performance in both Jason VTEC and GPS dSTEC analysis. The CAS GIMs show comparable performance with the results of the first four IAACs of the IGS. As expected, the poor performance of all GIMs is in equatorial regions and the high latitudes of the southern hemisphere. The consideration of generating multi-layer or three-dimensional ionospheric maps is emphasized to mitigate the inadequacy of ionospheric single-layer assumption in the presence of pronounced latitudinal gradients. The use of ionospheric observations from the new GNSS constellations and other space- or ground-based observation techniques is also suggested in the generation of future GIMs, given the sparse GPS/GLONASS stations in the southern hemisphere.


2021 ◽  
Author(s):  
Monika Karki ◽  
Ashok Silwal ◽  
Narayan Prasad Chapagain ◽  
Prakash Poudel ◽  
Sujan Prasad Gautam ◽  
...  

Abstract The present study analyses the variations in the ionospheric total electron content (TEC) prior to and during the 2015 Gorkha Earthquake in Nepal (Mw = 7.8) on 25 April 2015, utilising data from the widely distributed Global Positioning System (GPS) network. This study aimed to determine the association between ionospheric TEC anomalies and the occurrence of earthquakes. The finding shows that anomalous TEC changes occurred several days to a few hours prior to the major impending events. The results reveal that deviations in vertical total electron content (VTEC) at distant locations from the epicentre are less than those observed at the epicentre, implying that variation in ionospheric VTEC is nearly inversely proportional to the distance of GPS stations from the epicentre. In view of the solar-terrestrial environment, the pre-earthquake ionospheric anomalies could be associated with the 2015 Gorkha Earthquake. The VTEC anomaly was identified when it crosses the upper bound (UB) or lower bound (LB). The outcomes additionally show that TEC variation was dominant in the vicinity of the earthquake epicentre. We also observed contrast in TEC throughout the globe using global ionospheric maps at regular 2-hour UT intervals, the day before, during and after the earthquake. As a result, we observed that areas heavily influenced by TEC were found to be transposed from eastern sectors to western sectors through the equatorial plane. TEC Maps indicate that most of the Indian regions, Northern China, Nepal, Bhutan, were heavily affected, indicating the earthquake's onset influence on the day of the event. Furthermore, we examined the cross-correlation of the SGOC station's TEC with the rest of the stations and discovered that the correlation increased gradually with epicentral distance from the surrounding stations, which was an intriguing result.


2021 ◽  
Vol 13 (16) ◽  
pp. 3096
Author(s):  
Min Li ◽  
Yunbin Yuan

Observable-specific bias (OSB) parameterization allows observation biases belonging to various signal types to be flexibly addressed in the estimation of ionosphere and global navigation satellite system (GNSS) clock products. In this contribution, multi-GNSS OSBs are generated by two different methods. With regard to the first method, geometry-free (GF) linear combinations of the pseudorange and carrier-phase observations of a global multi-GNSS receiver network are formed for the extraction of OSB observables, and global ionospheric maps (GIMs) are employed to correct ionospheric path delays. Concerning the second method, satellite and receiver OSBs are converted directly from external differential code bias (DCB) products. Two assumptions are employed in the two methods to distinguish satellite- and receiver-specific OSB parameters. The first assumption is a zero-mean condition for each satellite OSB type and GNSS signal. The second assumption involves ionosphere-free (IF) linear combination signal constraints for satellites and receivers between two signals, which are compatible with the International GNSS Service (IGS) clock product. Agreement between the multi-GNSS satellite OSBs estimated by the two methods and those from the Chinese Academy of Sciences (CAS) is shown at levels of 0.15 ns and 0.1 ns, respectively. The results from observations spanning 6 months show that the multi-GNSS OSB estimates for signals in the same frequency bands may have very similar code bias characteristics, and the receiver OSB estimates present larger standard deviations (STDs) than the satellite OSB estimates. Additionally, the variations in the receiver OSB estimates are shown to be related to the types of receivers and antennas and the firmware version. The results also indicate that the root mean square (RMS) of the differences between the OSBs estimated based on the CAS- and German Aerospace Center (DLR)-provided DCB products are 0.32 ns for the global positioning system (GPS), 0.45 ns for the BeiDou navigation satellite system (BDS), 0.39 ns for GLONASS and 0.22 ns for Galileo.


2021 ◽  
Vol 95 (8) ◽  
Author(s):  
Heng Yang ◽  
Enric Monte-Moreno ◽  
Manuel Hernández-Pajares ◽  
David Roma-Dollase

2021 ◽  
Vol 95 (6) ◽  
Author(s):  
Heng Yang ◽  
Enric Monte-Moreno ◽  
Manuel Hernández-Pajares ◽  
David Roma-Dollase

2021 ◽  
Author(s):  
Gabriel Jerez ◽  
Manuel Hernández-Pajares ◽  
Fabricio Prol ◽  
Daniele Alves ◽  
João Monico

&lt;p&gt;In this work, we present a new method for assessing global ionospheric maps (GIM) by means of ionosonde data. The method proposed is based on the critical frequency at the F&lt;sub&gt;2&lt;/sub&gt; layer directly measured by pairs of ionosondes to assess VTEC (vertical total electron content) values from GIMs. Four strategies were investigated and, the best one was the linear interpolation of squared f&lt;sub&gt;o&lt;/sub&gt;F&lt;sub&gt;2&lt;/sub&gt; based on the VTEC ratio. The analysis was based on the root mean square (RMS) of the differences between the measured and estimated f&lt;sub&gt;o&lt;/sub&gt;F&lt;sub&gt;2&lt;/sub&gt; values at the first ionosonde from each pair. The f&lt;sub&gt;o&lt;/sub&gt;F&lt;sub&gt;2&lt;/sub&gt; were estimated using the values measured at the second ionosonde and interpolated to the position of the first ionosonde with the VTEC values from the GIMs. Besides the RMS values, additional ionospheric indicators (slab thickness and shape function peak) were used to complement the daily analysis. This method was tested over one of the most challenging scenarios, the Brazilian region and near the last solar cycle peak. The assessment considered four ionosondes (combined in six pairs) and thirteen GIM products available at CDDIS (Crustal Dynamics Data Information System), CORG, CODG, EHRG, ESRG, ESAG, IGRG, IGSG, JPLG, UPRG, UPCG, UQRG, WHRG and WHUG. Analysis was conducted using daily, weekly, one year, and four years of data. The analysis with daily data showed that slab thickness and shape function peak could be helpful to identify periods and regions where this method could be applied. The weekly analysis was performed to select the best strategy to interpolate the f&lt;sub&gt;o&lt;/sub&gt;F&lt;sub&gt;2&lt;/sub&gt; values. The analysis of one-year data (2015) was performed considering all GIMs previously mentioned. CODG, IGSG, JPLG, UQRG, WHRG, and WHUG provided the best results, with mean rates of improvement up to 42% in comparison to not using any GIM. The four-year time series (2014-2017) were analyzed considering the two products with better performance for the one-year analysis (CODG and UQRG). With data from 2014-2017, CODG and UQRG provided improvement rates of up to 49%. In general, regional and temporal ionospheric influences could be noticed in the results, with expected larger errors closer to the solar cycle peak in 2014 and at locations with pairs of ionosondes with the larger distance apart. Therefore, we have confirmed the viability of the developed approach as an assessment method to analyze GIMs quality based on ionosonde data.&lt;/p&gt;


2021 ◽  
Vol 95 (3) ◽  
Author(s):  
Jiaojiao Zhao ◽  
Manuel Hernández-Pajares ◽  
Zishen Li ◽  
Ningbo Wang ◽  
Hong Yuan

AbstractAside from the ionospheric total electron content (TEC) information, root-mean-square (RMS) maps are also provided as the standard deviations of the corresponding TEC errors in global ionospheric maps (GIMs). As the RMS maps are commonly used as the accuracy indicator of GIMs to optimize the stochastic model of precise point positioning algorithms, it is of crucial importance to investigate the reliability of RMS maps involved in GIMs of different Ionospheric Associated Analysis Centers (IAACs) of the International GNSS Service (IGS), i.e., the integrity of GIMs. We indirectly analyzed the reliability of RMS maps by comparing the actual error of the differential STEC (dSTEC) with the RMS of the dSTEC derived from the RMS maps. With this method, the integrity of seven rapid IGS GIMs (UQRG, CORG, JPRG, WHRG, EHRG, EMRG, and IGRG) and six final GIMs (UPCG, CODG, JPLG, WHUG, ESAG and IGSG) was examined under the maximum and minimum solar activity conditions as well as the geomagnetic storm period. The results reveal that the reliability of the RMS maps is significantly different for the GIMs from different IAACs. Among these GIMs, the values in the RMS maps of UQRG are large, which can be used as ionospheric protection level, while the RMS values in EHRG and ESAG are significantly lower than the realistic RMS. The rapid and final GIMs from CODE, JPL and WHU provide quite reasonable RMS maps. The bounding performance of RMS maps can be influenced by the location of the stations, while the influence of solar activity and the geomagnetic storm is not obvious.


Sign in / Sign up

Export Citation Format

Share Document