Variations of TEC near the Indian Equatorial Ionospheric anomaly (EIA) stations by GPS measurements during descending phase of solar activity (2005 -2009)

NASA Astrophysics Data System (ADS)

Kumar, Sanjay; Singh, Abhay Kumar

The dual frequency Global Positioning System (GPS) data recorded at Varanasi (geographic latitude 250, 16 N longitude 820, 59 E) and Kanpur (geographic latitude 260, 30 N longitude 800, 12 E) stations, near the equatorial ionosphere anomaly (EIA) in India, have been analyzed to retrieve total electron content (TEC). The daily peak value of vertical total electron content (VTEC) has been utilized to study the variability of EIA. Present paper studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on EIA. It has been found that EIA yield their maximum values during the equinox months and minimum during summer and winter. The correlations of EIA with solar as well as geomagnetic indices have been also discussed. Key words: Total electron contents (TECs), EIA, GPS.

Observations of the Weddell Sea Anomaly in the ground-based and space-borne TEC measurements

NASA Astrophysics Data System (ADS)

Zakharenkova, Irina; Cherniak, Iurii; Shagimuratov, Irk

2017-08-01

The Weddell Sea Anomaly (WSA) is a summer ionospheric anomaly, which is characterized by a greater nighttime ionospheric density than that in daytime in the region near the Weddell Sea. We investigate the WSA signatures in the ground-based TEC (vertical total electron content) by using GPS and GLONASS measurements of the dense regional GNSS networks in South America. We constructed the high-resolution regional TEC maps for December 2014-January 2015. The WSA effects of the TEC exceed the noontime values are registered starting from 17 LT, it reaches its maximum at 01-05 LT and starts to disappear after 09 LT. Maximal TEC enhancements were as large as a factor of 2.5-3.5 and were registered at 03-04 LT. This effect was mainly localized in the geographical region of 55°S-75°S latitude and 80°W-30°W longitude, close to the Antarctic Peninsula. Further, we examined the WSA occurrence in the topside ionosphere by using GPS measurements from a zenith-looking GPS antenna on board three Swarm satellites to determine topside TEC (above ∼500 km altitude) at the topside ionosphere-plasmasphere system. Global maps of the topside TEC indicated that the zone with significant WSA effect in the topside TEC (TEC increase ∼2-4 times the noontime level) had a large spatial extent over southern Pacific and Atlantic Ocean. It was observed around 150°W-20°W and between 40°S and 70°S during 23 LT - 06 LT. For the first time, the WSA signatures were shown in the topside TEC data derived from the GPS measurements onboard the Swarm constellation. Independently, two other instruments - FORMOSAT-3/COSMIC radio occultation electron density profiles and in situ measurements by the Langmuir Probe instrument onboard Swarm satellites - were able to confirm: (1) the same location of the WSA zone as revealed in Swarm TEC; (2) the most-pronounced WSA effect, as a maximal electron density exceed over the noontime values, corresponds to altitudes above 400-500 km.

Ionosphere Profile Estimation Using Ionosonde & GPS Data in an Inverse Refraction Calculation

NASA Astrophysics Data System (ADS)

Psiaki, M. L.

2014-12-01

A method has been developed to assimilate ionosonde virtual heights and GPS slant TEC data to estimate the parameters of a local ionosphere model, including estimates of the topside and of latitude and longitude variations. This effort seeks to better assimilate a variety of remote sensing data in order to characterize local (and eventually regional and global) ionosphere electron density profiles. The core calculations involve a forward refractive ray-tracing solution and a nonlinear optimal estimation algorithm that inverts the forward model. The ray-tracing calculations solve a nonlinear two-point boundary value problem for the curved ionosonde or GPS ray path through a parameterized electron density profile. It implements a full 3D solution that can handle the case of a tilted ionosphere. These calculations use Hamiltonian equivalents of the Appleton-Hartree magneto-plasma refraction index model. The current ionosphere parameterization is a modified Booker profile. It has been augmented to include latitude and longitude dependencies. The forward ray-tracing solution yields a given signal's group delay and beat carrier phase observables. An auxiliary set of boundary value problem solutions determine the sensitivities of the ray paths and observables with respect to the parameters of the augmented Booker profile. The nonlinear estimation algorithm compares the measured ionosonde virtual-altitude observables and GPS slant-TEC observables to the corresponding values from the forward refraction model. It uses the parameter sensitivities of the model to iteratively improve its parameter estimates in a way the reduces the residual errors between the measurements and their modeled values. This method has been applied to data from HAARP in Gakona, AK and has produced good TEC and virtual height fits. It has been extended to characterize electron density perturbations caused by HAARP heating experiments through the use of GPS slant TEC data for an LOS through the heated zone. The next planned extension of the method is to estimate the parameters of a regional ionosphere profile. The input observables will be slant TEC from an array of GPS receivers and group delay and carrier phase observables from an array of high-frequency beacons. The beacon array will function as a sort of multi-static ionosonde.

Linear time series modeling of GPS-derived TEC observations over the Indo-Thailand region

NASA Astrophysics Data System (ADS)

Suraj, Puram Sai; Kumar Dabbakuti, J. R. K.; Chowdhary, V. Rajesh; Tripathi, Nitin K.; Ratnam, D. Venkata

2017-12-01

This paper proposes a linear time series model to represent the climatology of the ionosphere and to investigate the characteristics of hourly averaged total electron content (TEC). The GPS-TEC observation data at the Bengaluru international global navigation satellite system (GNSS) service (IGS) station (geographic 13.02°N , 77.57°E ; geomagnetic latitude 4.4°N ) have been utilized for processing the TEC data during an extended period (2009-2016) in the 24{th} solar cycle. Solar flux F10.7p index, geomagnetic Ap index, and periodic oscillation factors have been considered to construct a linear TEC model. It is evident from the results that solar activity effect on TEC is high. It reaches the maximum value (˜ 40 TECU) during the high solar activity (HSA) year (2014) and minimum value (˜ 15 TECU) during the low solar activity (LSA) year (2009). The larger magnitudes of semiannual variations are observed during the HSA periods. The geomagnetic effect on TEC is relatively low, with the highest being ˜ 4 TECU (March 2015). The magnitude of periodic variations can be seen more significantly during HSA periods (2013-2015) and less during LSA periods (2009-2011). The correlation coefficient of 0.89 between the observations and model-based estimations has been found. The RMSE between the observed TEC and model TEC values is 4.0 TECU (linear model) and 4.21 TECU (IRI2016 Model). Further, the linear TEC model has been validated at different latitudes over the northern low-latitude region. The solar component (F10.7p index) value decreases with an increase in latitude. The magnitudes of the periodic component become less significant with the increase in latitude. The influence of geomagnetic component becomes less significant at Lucknow GNSS station (26.76°N, 80.88°E) when compared to other GNSS stations. The hourly averaged TEC values have been considered and ionospheric features are well recovered with linear TEC model.

Comparison of GPS-TEC variation during quiet and disturbed period using the Holt-Winter method and IRI-2012 model over Malaysia

NASA Astrophysics Data System (ADS)

Ahmed Ismail, Nouf Abd Emunim; Abdullah, Mardina; Hasbi, Alina Marie

2016-07-01

Total Electron Content (TEC) is the main parameter in the ionosphere that has significant effects on radio wave; it changes the speed and direction of the signal propagation, causing the delay of the Global Positioning System (GPS) signals. Therefore, it is crucial to validate the performance of the ionospheric model to reveal the variety of ionospheric behaviour during quiet and disturbed period. This research presents the performance evaluation of the statistical Holt-Winter method and IRI-2012 model using three topside electron density options: IRI-2001, IRI01-corr and NeQuick with the observed GPS-TEC during quiet and disturbed period. The GPS-TEC data were derived from the dual frequency GPS receiver at JUPEM (Department of Survey and Mapping Malaysia), from the UUMK station (north Peninsular Malaysia) at geographic coordinates of 6.46°N-100.50°E and geomagnetic coordinates of 3.32°S-172.99°E and TGPG station (south Peninsular Malaysia) at geographic coordinates of 1.36°N-104.10°E and geomagnetic coordinates of 8.43°S -176.53°E, during March of 2013. The maximum value of the GPS-TEC was at the post noon time at 17:00 LT and the minimum was in the early morning from 6:00-7:00 LT. During the quiet period, the maximum GPS-TEC at the UUMK station was 52 TECU while at the TGPG station, it was 60 TECU. During the disturbed period, when intense geomagnetic storm occurred on 17 March 2013, the maximum GPS-TEC recorded was 58 TECU and 65 TECU in UUMK and TGPG station, respectively. The diurnal hourly variation during the quiet period indicated that IRI-2001, IRI01-corr, and NeQuick had overestimation agreement during the day hours except for the time between 11:00-19:00 LT when IRI01-corr and NeQuick showed underestimation, while during 13:00-20:00 LT, IRI-2001 showed slight underestimation whereas the Holt-Winter method showed good agreement with GPS-TEC. During the disturbed period, IRI-2001 showed overestimation agreement for all hours, while the IRI01-corr and NeQuick model did not show any changes during the geomagnetic storm event. The Holt-Winter method showed better agreement with the GPS-TEC for both the UUMK and TGPG stations. The correlation between the observed and modeled GPS-TEC during the quiet and disturbed period for the UUMK station showed a slightly better correlation compared to the TGPG station. The Holt-Winter method showed good correlation of around 0.98 during the quiet period and 0.95 during the disturbed period, while IRI-2001, IRI01-corr, and NeQuick had comparatively lower correlation of around ≈ 0.8 during the quiet period and ≈ 0.7 during the disturbed period. Overall, this research concludes that the Holt-Winter method effectively the GPS-TEC with good correlation during the quiet and disturbed period in the equatorial region over Malaysia.

Ionospheric earthquake effects detection based on Total Electron Content (TEC) GPS Correlation

NASA Astrophysics Data System (ADS)

Sunardi, Bambang; Muslim, Buldan; Eka Sakya, Andi; Rohadi, Supriyanto; Sulastri; Murjaya, Jaya

2018-03-01

Advances in science and technology showed that ground-based GPS receiver was able to detect ionospheric Total Electron Content (TEC) disturbances caused by various natural phenomena such as earthquakes. One study of Tohoku (Japan) earthquake, March 11, 2011, magnitude M 9.0 showed TEC fluctuations observed from GPS observation network spread around the disaster area. This paper discussed the ionospheric earthquake effects detection using TEC GPS data. The case studies taken were Kebumen earthquake, January 25, 2014, magnitude M 6.2, Sumba earthquake, February 12, 2016, M 6.2 and Halmahera earthquake, February 17, 2016, M 6.1. TEC-GIM (Global Ionosphere Map) correlation methods for 31 days were used to monitor TEC anomaly in ionosphere. To ensure the geomagnetic disturbances due to solar activity, we also compare with Dst index in the same time window. The results showed anomalous ratio of correlation coefficient deviation to its standard deviation upon occurrences of Kebumen and Sumba earthquake, but not detected a similar anomaly for the Halmahera earthquake. It was needed a continous monitoring of TEC GPS data to detect the earthquake effects in ionosphere. This study giving hope in strengthening the earthquake effect early warning system using TEC GPS data. The method development of continuous TEC GPS observation derived from GPS observation network that already exists in Indonesia is needed to support earthquake effects early warning systems.

High-resolution station-based diurnal ionospheric total electron content (TEC) from dual-frequency GPS observations

NASA Astrophysics Data System (ADS)

ćepni, Murat S.; Potts, Laramie V.; Miima, John B.

2013-09-01

electron content (TEC) estimates derived from Global Navigation Satellite System (GNSS) signal delays provide a rich source of information about the Earth's ionosphere. Networks of Global Positioning System (GPS) receivers data can be used to represent the ionosphere by a Global Ionospheric Map (GIM). Data input for GIMs is dual-frequency GNSS-only or a mixture of GNSS and altimetry observations. Parameterization of GNSS-only GIMs approaches the ionosphere as a single-layer model (SLM) to determine GPS TEC models over a region. Limitations in GNSS-only GIM TEC are due largely to the nonhomogenous global distribution of GPS tracking stations with large data gaps over the oceans. The utility of slant GPS ionospheric-induced path delays for high temporal resolution from a single-station data rate offers better representation of TEC over a small region. A station-based vertical TEC (TECV) approach modifies the traditional single-layer model (SLM) GPS TEC method by introducing a zenith angle weighting (ZAW) filter to capture signal delays from mostly near-zenith satellite passes. Comparison with GIMs shows the station-dependent TEC (SD-TEC) model exhibits robust performance under variable space weather conditions. The SD-TEC model was applied to investigate ionospheric TEC variability during the geomagnetic storm event of 9 March 2012 at midlatitude station NJJJ located in New Jersey, USA. The high temporal resolution TEC results suggest TEC production and loss rate differences before, during, and after the storm.

CEDAR-GEM Challenge for Systematic Assessment of Ionosphere/Thermosphere Models in Predicting TEC During the 2006 December Storm Event

NASA Astrophysics Data System (ADS)

Shim, J. S.; Rastätter, L.; Kuznetsova, M.; Bilitza, D.; Codrescu, M.; Coster, A. J.; Emery, B. A.; Fedrizzi, M.; Förster, M.; Fuller-Rowell, T. J.; Gardner, L. C.; Goncharenko, L.; Huba, J.; McDonald, S. E.; Mannucci, A. J.; Namgaladze, A. A.; Pi, X.; Prokhorov, B. E.; Ridley, A. J.; Scherliess, L.; Schunk, R. W.; Sojka, J. J.; Zhu, L.

2017-10-01

In order to assess current modeling capability of reproducing storm impacts on total electron content (TEC), we considered quantities such as TEC, TEC changes compared to quiet time values, and the maximum value of the TEC and TEC changes during a storm. We compared the quantities obtained from ionospheric models against ground-based GPS TEC measurements during the 2006 AGU storm event (14-15 December 2006) in the selected eight longitude sectors. We used 15 simulations obtained from eight ionospheric models, including empirical, physics-based, coupled ionosphere-thermosphere, and data assimilation models. To quantitatively evaluate performance of the models in TEC prediction during the storm, we calculated skill scores such as RMS error, Normalized RMS error (NRMSE), ratio of the modeled to observed maximum increase (Yield), and the difference between the modeled peak time and observed peak time. Furthermore, to investigate latitudinal dependence of the performance of the models, the skill scores were calculated for five latitude regions. Our study shows that RMSE of TEC and TEC changes of the model simulations range from about 3 TECU (total electron content unit, 1 TECU = 1016 el m-2) (in high latitudes) to about 13 TECU (in low latitudes), which is larger than latitudinal average GPS TEC error of about 2 TECU. Most model simulations predict TEC better than TEC changes in terms of NRMSE and the difference in peak time, while the opposite holds true in terms of Yield. Model performance strongly depends on the quantities considered, the type of metrics used, and the latitude considered.

Observing Traveling Ionospheric Disturbances Caused by Tsunamis Using GPS TEC Measurements

NASA Technical Reports Server (NTRS)

Galvan, David A.; Komjathy, Attila; Hickey, Michael; Foster, James; Mannucci, Anthony J.

2010-01-01

Ground-based Global Positioning System (GPS) measurements of ionospheric Total Electron Content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events: the American Samoa earthquake of September 29, 2009, and the Chile earthquake of February 27, 2010. Fluctuations in TEC correlated in time, space, and wave properties with these tsunamis were observed in TEC estimates processed using JPL's Global Ionospheric Mapping Software. These TEC estimates were band-pass filtered to remove ionospheric TEC variations with wavelengths and periods outside the typical range of internal gravity waves caused by tsunamis. Observable variations in TEC appear correlated with the tsunamis in certain locations, but not in others. Where variations are observed, the typical amplitude tends to be on the order of 1% of the background TEC value. Variations with amplitudes 0.1 - 0.2 TECU are observable with periods and timing affiliated with the tsunami. These observations are compared to estimates of expected tsunami-driven TEC variations produced by Embry Riddle Aeronautical University's Spectral Full Wave Model, an atmosphere-ionosphere coupling model, and found to be in good agreement in some locations, though there are cases when the model predicts an observable tsunami-driven signature and none is observed. These TEC variations are not always seen when a tsunami is present, but in these two events the regions where a strong ocean tsunami was observed did coincide with clear TEC observations, while a lack of clear TEC observations coincided with smaller tsunami amplitudes. There exists the potential to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for early warning systems.

Validation of the technique for absolute total electron content and differential code biases estimation

NASA Astrophysics Data System (ADS)

Mylnikova, Anna; Yasyukevich, Yury; Yasyukevich, Anna

2017-04-01

We have developed a technique for vertical total electron content (TEC) and differential code biases (DCBs) estimation using data from a single GPS/GLONASS station. The algorithm is based on TEC expansion into Taylor series in space and time (TayAbsTEC). We perform the validation of the technique using Global Ionospheric Maps (GIM) computed by Center for Orbit Determination in Europe (CODE) and Jet Propulsion Laboratory (JPL). We compared differences between absolute vertical TEC (VTEC) from GIM and VTEC evaluated by TayAbsTEC for 2009 year (solar activity minimum - sunspot number about 0), and for 2014 year (solar activity maximum - sunspot number 110). Since there is difference between VTEC from CODE and VTEC from JPL, we compare TayAbsTEC VTEC with both of them. We found that TayAbsTEC VTEC is closer to CODE VTEC than to JPL VTEC. The difference between TayAbsTEC VTEC and GIM VTEC is more noticeable for solar activity maximum (2014) than for solar activity minimum (2009) for both CODE and JPL. The distribution of VTEC differences is close to Gaussian distribution, so we conclude that results of TayAbsTEC are in the agreement with GIM VTEC. We also compared DCBs evaluated by TayAbsTEC and DCBs from GIM, computed by CODE. The TayAbsTEC DCBs are in good agreement with CODE DCBs for GPS satellites, but differ noticeable for GLONASS. We used DCBs to correct slant TEC to find out which DCBs give better results. Slant TEC correction with CODE DCBs produces negative and nonphysical TEC values. Slant TEC correction with TayAbsTEC DCBs doesn't produce such artifacts. The technique we developed is used for VTEC and DCBs calculation given only local GPS/GLONASS networks data. The evaluated VTEC data are in GIM framework which is handy when various data analyses are made.

Application of IRI-Plas in Ionospheric Tomography and HF Communication Studies with Assimilation of GPS-TEC

NASA Astrophysics Data System (ADS)

Arikan, Feza; Gulyaeva, Tamara; Sezen, Umut; Arikan, Orhan; Toker, Cenk; Hakan Tuna, MR.; Erdem, Esra

2016-07-01

International Reference Ionosphere is the most acknowledged climatic model of ionosphere that provides electron density profile and hourly, monthly median values of critical layer parameters of the ionosphere for a desired location, date and time between 60 to 2,000 km altitude. IRI is also accepted as the International Standard Ionosphere model. Recently, the IRI model is extended to the Global Positioning System (GPS) satellite orbital range of 20,000 km. The new version is called IRI-Plas and it can be obtained from http://ftp.izmiran.ru/pub/izmiran /SPIM/. A user-friendly online version is also provided at www.ionolab.org as a space weather service. Total Electron Content (TEC), which is defined as the line integral of electron density on a given ray path, is an observable parameter that can be estimated from earth based GPS receivers in a cost-effective manner as GPS-TEC. One of the most important advantages of IRI-Plas is the possible input of GPS-TEC to update the background deterministic ionospheric model to the current ionospheric state. This option is highly useful in regional and global tomography studies and HF link assessments. IONOLAB group currently implements IRI-Plas as a background model and updates the ionospheric state using GPS-TEC in IONOLAB-CIT and IONOLAB-RAY algorithms. The improved state of ionosphere allows the most reliable 4-D imaging of electron density profiles and HF and satellite communication link simulations.This study is supported by TUBITAK 115E915 and joint TUBITAK 114E092 and AS CR 14/001.

Research on global plasmaspheric electron content by using LEO occultation and GPS data

NASA Astrophysics Data System (ADS)

Chen, Peng; Yao, Yibin

2015-05-01

This paper investigates the characteristics of global plasmaspheric electron content (pTEC) using COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) occultation and GPS (Global Positioning System) data. The ionospheric electron content (iTEC) within 100-1000 km was obtained by fitting the COSMIC occultation electron density profiles, and the pTEC was obtained by subtracting the iTEC from CODE (Center for Orbit Determination in Europe) GIM (global ionosphere maps) TEC provided by University of Bern. This paper also investigates the characteristics of pTEC variations with local time, latitude and season. The results show that in 2011, the worldwide average of pTEC was 4.02 TECu, which is consistent with the findings of other studies. The pTEC shows significant diurnal variation characteristics, that is, pTEC is higher during daytime than during nighttime, but the percentage contribution of pTEC to GPS TEC is higher during nighttime than during daytime. The pTEC varies with the seasons, pTEC hemispheres symmetrically during spring and autumn, while pTEC in the summer hemisphere is higher than that in the winter hemisphere. Moreover, the percentage contribution of pTEC to GPS TEC (total electron content) is higher in winter hemisphere than in summer hemisphere.

Performance of Solar Proxy Options of IRI-Plas Model for Equinox Seasons

NASA Astrophysics Data System (ADS)

Sezen, Umut; Gulyaeva, Tamara L.; Arikan, Feza

2018-02-01

International Reference Ionosphere (IRI) is the most acclaimed climatic model of the ionosphere. Since 2009, the range of the IRI model has been extended to the Global Positioning System (GPS) orbital height of 20,000 km in the plasmasphere. The new model, which is called IRI extended to Plasmasphere (IRI-Plas), can input not only the ionosonde foF2 and hmF2 but also the GPS-total electron content (TEC). IRI-Plas has been provided at www.ionolab.org, where online computation of ionospheric parameters is accomplished through a user-friendly interface. The solar proxies that are available in IRI-Plas can be listed as sunspot number (SSN1), SSN2, F10.7, global electron content (GEC), TEC, IG, Mg II, Lyman-α, and GEC_RZ. In this study, ionosonde foF2 data are compared with IRI-Plas foF2 values with the Consultative Committee International Radio (CCIR) and International Union of Radio Science (URSI) model choices for each solar proxy, with or without the GPS-TEC input for the equinox months of October 2011 and March 2015. It has been observed that the best fitting model choices in Root Mean Square (RMS) and Normalized RMS (NRMS) sense are the Jet Propulsion Laboratory global ionospheric maps-TEC input with Lyman-α solar proxy option for both months. The input of TEC definitely lowers the difference between the model and ionosonde foF2 values. The IG and Mg II solar proxies produce similar model foF2 values, and they usually are the second and third best fits to the ionosonde foF2 for the midlatitude ionosphere. In high-latitude regions, Jet Propulsion Laboratory global ionospheric map-TEC inputs to IRI-Plas with Lyman-α, GEC_RZ, and TEC solar proxies are the best choices. In equatorial region, the best fitting solar proxies are IG, Lyman-α, and Mg II.

Case study of ISWI in Vietnam: A comparison of ionospheric parameters observed over Ho Chi Minh with IRI predictions

NASA Astrophysics Data System (ADS)

Lan, Hoang Thai; Tam, Dao Ngoc Hanh

2014-01-01

For the contribution of Vietnam to ISWI activities, there are 3 GPS receivers, 3 Ionosondes, 1 AWESOME and 1 MAGDAS operating in Vietnam. With a special geographical position stretching from the north tropic to the magnetic equator, Vietnam is an interesting area to supplement the data for the Global Space Weather Model. The Ionosphere is an important indicator of Space Weather and the International Reference Ionosphere (IRI) model has become widely accepted. The first task of ionospheric science in a new location is often comparing the observed data with IRI. This paper presents the results of comparisons of the foF2 and TEC observed over Ho Chi Minh City (10.51 N, 106.33 E) with the values calculated according to the IRI-2007 in order to evaluate the applicability of the model in forecasting for the equatorial region of Vietnam. We compare the critical frequency of layer F (foF2) and Total Electron Content (TEC) values for two phases of solar activity. The results show very good diurnal correlations between the observed foF2 and TEC with IRI values in the decreasing solar activity period 2003 ± 2006 (the deviation < 15%). In the increasing period 2009 ± 2012, good correlation was in the morning time before the foF2 peak at about 10 LT, with a deviation about 10% (except 2012). However, after 10 LT, the IRI-foF2 values rose up and the deviations were about 25% to 30%, especially during evening. In the years with low solar activity (SSN < 40), the IRI-foF2 are almost always higher than the observed foF2 data and vice versa for the years with SSN > 40. This is a note for correction IRI model applying for Vietnam. The comparison of the TEC shows that the correlation between GPS-TEC and IRI-TEC generally was good with coefficients k > 0.8 and R > 0.9 for the period 2006 - 2010. The worst relationship were March, April, September, October, November and December 2011, corresponding to periods when the TEC gradients are highest. The phenomenon of decline in the TEC at noon over Ho Chi Minh City observed pretty weak. This phenomenon appeared only in a few months from April to September, when the ionization is high. In the period from 0 to 5 am local time, the average minimum GPS-TEC observed over Ho Chi Minh City is about 3 tecu, while the IRI-TEC value is ~ 0.3. Thus, the IRI-TEC values should be recalibrated.

Comparison of GPS-derived TEC with IRI-2012 and IRI-2007 TEC predictions at Surat, a location around the EIA crest in the Indian sector, during the ascending phase of solar cycle 24

NASA Astrophysics Data System (ADS)

Patel, N. C.; Karia, S. P.; Pathak, K. N.

2017-07-01

This paper presents a comparison of GPS-derived TEC with IRI-2012 and IRI-2007 TEC Predictions at Surat (21.16°N Geographic latitude, 72.78°E Geographic longitude, 12.90°N Geomagnetic latitude) a location around the Equatorial Ionisation Anomaly (EIA) crest in the Indian sector, during the Ascending Phase of Solar Cycle 24, for a period of three years (January 2010-December 2012). In this comparison, plasmaspheric electron content (PEC) contribution to the GPS-TEC has been removed. It is observed that percentage PEC contribution to the GPS-TEC varies from about ∼15% (at the noon local time) to about ∼30% (at the morning local time). From the monthly comparison of GPS-TEC with IRI-TEC, it is observed that, TEC predicted by both the models overestimates in June-2012 and underestimates TEC in November-2011, December-2011 and March-2011. For all other months IRI estimates the TEC well. From the seasonal comparison, it is observed that the peak time appears ∼1-h later than the actual peak time in Winter 2010, Summer 2011, and Equinox 2010 and 2012 (the result suggest that it may be due to discrepancies/disagreement of both the versions of the IRI model in estimating the peak density as well as the thickness and shape parameters of the electron density profiles). For the Summer season, the IRI-TEC estimates the TEC well for all the years. Further, the seasonal variation of the GPS-TEC for all the three years matches well with IRI-2012 model compared to IRI-2007 model. Also, the mean annual TEC is predicted well by both the versions of the IRI model.

Simultaneous total electron content and all-sky camera measurements of an auroral arc

NASA Astrophysics Data System (ADS)

Kintner, P. M.; Kil, H.; Deehr, C.; Schuck, P.

2002-07-01

We present an example of Global Positioning System (GPS) derived total electron content (TEC) and all-sky camera (ASC) images that show increases of TEC by ~10 × 1016 electrons m-2 (10 TEC units) occurring simultaneously with auroral light in ASC images. The TEC example appears to be an E region density enhancement produced by two discrete auroral arcs occurring in the late morning auroral oval at 1000 LT. This suggests that GPS signal TEC measurements can be used to detect individual auroral arcs and that individual discrete auroral arcs are responsible for some high-latitude phase scintillations. The specific auroral feature detected was a poleward moving auroral form believed to occur in the polar cap where the ionosphere is convecting antisunward. The magnitude of the rate of change of TEC (dTEC/dt) is comparable to that previously reported. However, the timescales associated with the event, the order of 1 min, suggest that the data sampling technique commonly used by chain GPS TEC receivers (averaging and time decimation) will undersample E region TEC perturbations produced by active auroral displays. The localized nature of this example implies that L1 ranging errors of at least 1.6 m will be introduced by auroral arcs into systems relying on differential GPS for navigation or augmentation. Although the TEC and auroral arcs presented herein occurred in the late morning auroral oval, we expect that the effects of discrete auroral arcs on GPS TEC and subsequent ranging errors should occur at all local times. Furthermore, GPS receivers can be used to detect individual discrete arcs.

Comparison of Two IRI plasmasphere Extensions with GPS-TEC Observations

NASA Technical Reports Server (NTRS)

Gulyaeva, T. L.; Gallagher, Dennis L.

2006-01-01

Comparisons of two model results with Global Positioning System GPS-TEC measurements have been carried out for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The models evaluated are the Global Core Plasma Model (GCPM-2000) and the IRI extension with Russian plasmasphere model (IRI*).Data of 23 observatories providing GPS-TEC and ionosonde data have been used. It is shown that IRI* plasmasphere electron density is greater than GCPM results by an order of magnitude at 6370 km altitude (one Earth's radius) with this excess growing to 2-3 orders of magnitude towards the GPS satellite altitude of 20000 km. Another source of model and GPS-TEC differences is a way of selection of the F2 layer peak parameters driving the models either with ITU-R (former CCIR) maps or ionosonde observations. Plasmasphere amendment to IRI improves accuracy of TEC model predictions because the plasmasphere contribution to the total TEC varies from 10% by daytime under quiet magnetic conditions to more than 50% by night under stormy conditions.

Global Dayside Ionospheric Uplift and Enhancement Associated with Interplanetary Electric Fields

NASA Technical Reports Server (NTRS)

Tsurutani, Bruce; Mannucci, Anthony; Iijima, Byron; Abdu, Mangalathayil Ali; Sobral, Jose Humberto A.; Gonzalez, Walter; Guarnieri, Fernando; Tsuda, Toshitaka; Saito, Akinori; Yumoto, Kiyohumi;

4D computerized ionospheric tomography by using GPS measurements and IRI-Plas model

NASA Astrophysics Data System (ADS)

Tuna, Hakan; Arikan, Feza; Arikan, Orhan

2016-07-01

Ionospheric imaging is an important subject in ionospheric studies. GPS based TEC measurements provide very accurate information about the electron density values in the ionosphere. However, since the measurements are generally very sparse and non-uniformly distributed, computation of 3D electron density estimation from measurements alone is an ill-defined problem. Model based 3D electron density estimations provide physically feasible distributions. However, they are not generally compliant with the TEC measurements obtained from GPS receivers. In this study, GPS based TEC measurements and an ionosphere model known as International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) are employed together in order to obtain a physically accurate 3D electron density distribution which is compliant with the real measurements obtained from a GPS satellite - receiver network. Ionospheric parameters input to the IRI-Plas model are perturbed in the region of interest by using parametric perturbation models such that the synthetic TEC measurements calculated from the resultant 3D electron density distribution fit to the real TEC measurements. The problem is considered as an optimization problem where the optimization parameters are the parameters of the parametric perturbation models. Proposed technique is applied over Turkey, on both calm and storm days of the ionosphere. Results show that the proposed technique produces 3D electron density distributions which are compliant with IRI-Plas model, GPS TEC measurements and ionosonde measurements. The effect of the GPS receiver station number on the performance of the proposed technique is investigated. Results showed that 7 GPS receiver stations in a region as large as Turkey is sufficient for both calm and storm days of the ionosphere. Since the ionization levels in the ionosphere are highly correlated in time, the proposed technique is extended to the time domain by applying Kalman based tracking and smoothing approaches onto the obtained results. Combining Kalman methods with the proposed 3D CIT technique creates a robust 4D ionospheric electron density estimation model, and has the advantage of decreasing the computational cost of the proposed method. Results applied on both calm and storm days of the ionosphere show that, new technique produces more robust solutions especially when the number of GPS receiver stations in the region is small. This study is supported by TUBITAK 114E541, 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

Space Weather Activities of IONOLAB Group: IONOLAB-TEC

NASA Astrophysics Data System (ADS)

Arikan, F.; Sezen, U.; Arikan, O.; Ugurlu, O.; Nayir, H.

2009-04-01

Space Weather (SW) is the concept of changing environmental conditions in outer space and affect Earth and its technological systems. SW is a consequence of the solar activities and the coupling of solar energy on Earth's atmosphere due to the Earth's magnetic field. The monitoring and prediction of SW has utmost importance for HF communication, Satellite communication, navigation and guidance systems, Low Earth Orbit (LEO) satellite systems, Space Craft exit and entry into the atmosphere. Ionosphere is the plasma layer of the atmosphere that is ionized by solar radiation and it is a key player of SW. Ionosphere is a temporally and spatially varying, dispersive, anisotropic and inhomogeneous medium that is characterized primarily by its electron density distribution. IONOLAB is a group of researchers of various disciplines, getting together to handle challenges of the Earth's ionosphere. The team has researchers from Hacettepe University and Bilkent University, Department of Electrical and Electronics Engineering and General Command of Mapping of Turkish Army. One of the most important contributions of IONOLAB group is the automated web-based computation service for Total Electron Content (TEC). TEC corresponds to the line integral of electron density distribution on a given path. TEC can also be expressed as the amount of free electrons within 1 m2 cross-sectional area of the cylinder on the ray path. Global Position System (GPS) provides a cost-effective medium for monitoring of ionosphere using the signals recorded by stationary GPS receivers in estimating TEC. IONOLAB group has developed IONOLAB-TEC for reliable and robust estimates for all latitudes and both calm and disturbed days by using RINEX, IONEX and satellite ephemeris data provided from the IGS centers. IONOLAB-TEC consists of a regularized signal estimation algorithm which combines signals from all GPS satellites for a given instant and a given receiver, for a desired time period or for 24 hours, with 30 s time resolution. IONOLAB-TEC values also include the receiver differential code bias (DCB) for each GPS station estimated uniquely by the IONOLAB-BIAS algorithm. The web based computation program is written in JAVA and it is provided both in Turkish and English at www.ionolab.org. The IONOLAB-TEC computation requires no installation or licensing on the client side. The application has a layered design. Developed components are modular that allows possible changes regarding the estimation method can be easily adapted. Same flexibility is also provided for the data access. Also, presentation of estimation data is architected to support different client types. Currently, the user can login to the IONOLAB-TEC web site and choose the desired location and dates on-line for TEC estimation. The carrier phase leveled TEC estimates of IONOLAB-TEC are provided for the chosen station/s and for the chosen day/s along with two-hourly GIM-TEC estimates of IGS centers. The output is provided in the user designated form either in graphs or an excel data sheet. The IONOLAB-TEC provides robust, reliable, and high resolution TEC estimates and provides a medium for comparison of the GIM-TEC values from the IGS centers.

The Response of Mid-Latitude Ionospheric TEC to Geomagnetic Storms and Solar Flares

NASA Astrophysics Data System (ADS)

Huang, Z.; Roussel-Dupre, R.

2004-12-01

The effects of geomagnetic storms and solar flares on the ionosphere are manifested as large magnitude sudden fluctuations in the Total Electron Content (TEC). In this study, the broadband VHF signal (30-100MHz) data from the Los Alamos Portable Pulser (LAPP) received by the FORTE (Fast Onboard Recording of Transient Events) satellite during the period of 1997-2002 are used to investigate the mean TEC variation response to geomagnetic storm. A total of 14 geomagnetic storms are selected where FORTE-LAPP data are available to derive average TECs during extended storm-time and non-storm time for a given storm. The variations in the ionospheric TECs at Los Alamos, New Mexico are investigated for the 14 selected geomagnetic storms. In most cases (12 out of 14), we see overall enhancements in TEC as a result of geomagnetic storm impact at Los Alamos. The relative enhancements in TEC at Los Alamos due to a geomagnetic storm can reach as high as 3-fold of the normal TEC values. The overall absolute enhancements in TEC at Los Alamos are up to about 30 TECU. The magnitude of TEC enhancements is diversified over all storm categories without a clean-cut relationship between the storm intensity and the TEC enhancement. The mean TEC variation response to geomagnetic storm can be complicated when several consecutive storms occurred in a row and a net TEC reduction may be seen. Data of continuous GPS TEC measurements are collected at a 1-minute time resolution during July 2004 when 5 X-class solar flares occurred from two Allen Osborne Associates ICS-4000Z GPS receivers mounted at the Physics Building at Los Alamos National Laboratory. In detecting effects of solar flares on the ionospheric TEC, we apply appropriate filtering to remove the linear trend of TEC and a coherent processing of TEC variations simultaneously for all the visible GPS satellites in a given time interval. The responses of ionospheric TEC at minute time scale to these powerful impulsive solar flares are investigated. The onset time of the ionospheric response and the magnitude of the TEC fluctuations and its time derivative are examined along with their relationships with the solar flux characteristics, duration of the flare and location of the flare on the Sun, X-ray emission variations during the flares, and local time of the flare occurrence.

Investigation of the Effects of Solar and Geomagnetic Changes on the Total Electron Content: Mid-Latitude Region

NASA Astrophysics Data System (ADS)

Ulukavak, Mustafa; Yalcinkaya, Mualla

2016-04-01

The Global Positioning System (GPS) is used as an important tool for ionosphere monitoring and obtaining the Total Electron Content (TEC). GPS satellites, positioned in the Earth's orbit, are used as sensors to investigate the space weather conditions. In this study, solar and geomagnetic activity variations were investigated between the dates 1 March-30 June 2015 for the mid-latitude region. GPS-TEC variations were calculated for each selected International GNSS Service (IGS) station in Europe. GNSS data was obtained from Crustal Dynamics Data and Information System (CDDIS) archive. Solar and geomagnetic activity indices (Kp, F10.7 ve Dst) were obtained from the Oceanic and Atmospheric Administration (NOAA), the Canadian Space Weather Forecast Centre (CSWFC) and Data Analysis Center for geomagnetism and Space Magnetism Graduate School of Science, Kyoto University (WDC) archives. GPS-TEC variations were determined for the quiet periods of the solar and geomagnetic activities. GPS-TEC changes were then compared with respect to the quiet periods of the solar and geomagnetic activities. Global Ionosphere Maps (GIM) IONEX files, obtained from the IGS analysis center, was used to check the robustness of the GPS-TEC variations. The investigations revealed that it is possible to use the GPS-TEC data for monitoring the ionospheric disturbances.

Investigation of the seismo-ionospheric effects on the base of GPS/GLONASS measurements

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Cherniak, Iu.; Shagimuratov, I.; Suslova, O.

2012-04-01

During last years the monitoring of the ionospheric effects of different origin is carried out mainly with use of Global Navigating Satellite Systems (GPS / GLONASS). By means of measurements of the signals temporal delays it is possible to do the mapping of total electron content (TEC) in a column of unit cross section through the Earth's ionosphere and investigate its temporal evolution depended on the variations of electron concentration (NmF2) in the F2 ionospheric region. In the given report we present results of analysis of spatial-temporal variability of the ionosphere during the earthquake preparation phase for several major earthquakes which took place in Japan. It was revealed that for considered events mainly positive TEC anomalies appeared 1-5 days prior to the earthquake. The enhancement of electron concentration reached the value of 30-70% relative to the quiet geomagnetic conditions. In order to analyze the revealed effects in more details it was additionally involved data of GPS TEC values over GPS stations located at different distances from earthquake epicenters and data of vertical sounding of the ionosphere (NICT database). The hourly values of critical frequency of ionospheric F2 and Es layers were obtained from manually scaled ionograms recorded at Japanese ionospheric sounding stations Wakkanai, Kokubunji and Yamagawa. Acknowledgments. We acknowledge the IGS community for providing GPS permanent data and WDC for Ionosphere, Tokyo, National Institute of Information and Communications Technology (NICT) for providing ionosonde data. This work was supported by Russian Federation President grant MK-2058.2011.5.

Geographical analysis of equatorial plasma bubbles by GPS and nightglow measurements

NASA Astrophysics Data System (ADS)

Nade, D. P.; Shetti, D. J.; Sharma, A. K.; Taori, A.; Chavan, G. A.; Patil, P. T.; Ghodpage, R. N.; Gurav, O. B.; Nikte, S. S.

2015-11-01

This work about the zonal drift velocity and signature of equatorial plasma bubbles (EPBs) by measurements of global positioning system (GPS) receiver and all sky imager (ASI) operating in India, at the low latitude region. The optical and radio observations have been made from Kolhapur (16.8° N, 74.2° E) and Hyderabad (17.37°N, 78.48°E), respectively. The zonal drift velocity of EPBs has estimated using images of nightglow OI 630.0 nm emission recorded by ASI at Kolhapur. The measurements of total electron content (TEC) using the GPS have carried from the nearby station, Hyderabad. When depletions occurred about 00:37 h (IST) in TEC, the EPBs were found to occur about 5:30 h in optical data of OI 630.0 nm emission. This work focuses on simultaneous measurements of TEC and intensity of OI 630.0 nm emissions for EPBs during nighttime. The occurrence period of EPBs in TEC and OI 630.0 nm has found to be different. To study this difference, the zonal drift velocity of EPBs has established. The averaged eastward velocity of EPBs was found to be 138 m/s. The calculated values of zonal drift velocities are well correlated with that of the empirical model values. This work may be helpful in finding the growth of EPBs over low latitude.

GPS receiver CODE bias estimation: A comparison of two methods

NASA Astrophysics Data System (ADS)

McCaffrey, Anthony M.; Jayachandran, P. T.; Themens, D. R.; Langley, R. B.

2017-04-01

The Global Positioning System (GPS) is a valuable tool in the measurement and monitoring of ionospheric total electron content (TEC). To obtain accurate GPS-derived TEC, satellite and receiver hardware biases, known as differential code biases (DCBs), must be estimated and removed. The Center for Orbit Determination in Europe (CODE) provides monthly averages of receiver DCBs for a significant number of stations in the International Global Navigation Satellite Systems Service (IGS) network. A comparison of the monthly receiver DCBs provided by CODE with DCBs estimated using the minimization of standard deviations (MSD) method on both daily and monthly time intervals, is presented. Calibrated TEC obtained using CODE-derived DCBs, is accurate to within 0.74 TEC units (TECU) in differenced slant TEC (sTEC), while calibrated sTEC using MSD-derived DCBs results in an accuracy of 1.48 TECU.

Comparison of GPS-TEC measurements with NeQuick2 and IRI model predictions in the low latitude East African region during varying solar activity period (1998 and 2008-2015)

NASA Astrophysics Data System (ADS)

Mengistu, E.; Damtie, B.; Moldwin, M. B.; Nigussie, M.

2018-03-01

This paper examines the performances of NeQuick2, the latest available IRI-2016, IRI-2012 and IRI-2007 models in describing the monthly and seasonal mean total electron content (TEC) over the East African region. This is to gain insight into the success of the various model types and versions at characterizing the ionosphere within the equatorial ionization anomaly. TEC derived from five Global Positioning System (GPS) receivers installed at Addis Ababa (ADD, 5.33°N, 111.99°E Geog.), Asab (ASAB, 8.67°N, 116.44°E Geog.), Ambo (ABOO, 5.43°N, 111.05°E Geog.), Nairobi (RCMN, -4.48°N, 108.46°E Geog.) and Nazret (NAZR, 4.78°N, 112.43°E Geog.), are compared with the corresponding values computed using those models during varying solar activity period (1998 and 2008-2015). We found that different models describe the equatorial and anomaly region ionosphere best depending on solar cycle, season and geomagnetic activity levels. Our results show that IRI-2016 is the best model (compared to others in terms of discrepancy range) in estimating the monthly mean GPS-TEC at NAZR, ADD and RCMN stations except at ADD during 2008 and 2012. It is also found that IRI-2012 is the best model in estimating the monthly mean TEC at ABOO station in 2014. IRI show better agreement with observations during June solstice for all the years studied at ADD except in 2012 where NeQuick2 better performs. At NAZR, NeQuick2 better performs in estimating seasonal mean GPS-TEC during 2011, while IRI models are best during 2008-2009. Both NeQuick2 and IRI models underestimate measured TEC for all the seasons at ADD in 2010 but overestimate at NAZR in 2009 and RCMN in 2008. The periodic variations of experimental and modeled TEC have been compared with solar and geomagnetic indices at ABOO and ASAB in 2014 and results indicate that the F10.7 and sunspot number as indices of solar activity seriously affects the TEC variations with periods of 16-32 days followed by the geomagnetic activity on shorter timescales (roughly periods of less than 16 days). In this case, NeQuick2 derived TEC shows better agreement with a long term period variations of GPS-TEC, while IRI-2016 and IRI-2007 show better agreement with observations during short term periodic variations. This indicates that the dependence of NeQuick2 derived TEC on F10.7 is seasonal. Hence, we suggest that representation of geomagnetic activity indices is required for better performance over the low latitude region.

Development of TEC fluctuations in northern and southern hemispheres on the base of GPS observations

NASA Astrophysics Data System (ADS)

Shagimuratov, Irk; Krankowski, Andrzej; Sieradzki, Rafal; Ephishov, I. I.

GPS technique is widely used to study the global structure and dynamics of the ionosphere. In this paper GPS observations carried out at Arctic and Antarctic stations belonging to the IGS network were used to study TEC fluctuations in the high-latitude ionosphere during the ionospheric storms. Dual-frequency GPS phase measurements along individual satellite passes served as raw data. It was shown that ionospheric irregularities of a different scale were devel-oped in the auroral and polar ionosphere. It is a common phenomenon caused phase fluctuations of GPS signals. In November 2009, West Department of IZMIRAN in Kaliningrad (Russia) and University of Warmia and Mazury in Olsztyn (Poland) established computer server for automatic monitoring of these irregularities. The rate of TEC index (ROTI) expressed in TECU/min was used as a measure of TEC fluctuations. During its operation TEC variations related to ionospheric structures of a spatial scale more than 200-300 km were detected. Large-scale ionospheric structures cause an increase in horizontal gradients and difficulties with the carrier phase ambiguity resolution in GPS positioning. In turn, the phase fluctuations can cause cycle-slip effects. At the polar stations, ionospheric structures with TEC enhanced by a factor of 3-5 relative to the background were detected, whereas TEC increased to 5-8 TECU in about 10-15 min. These structures were observed during a storm, as well as during a moderate geomagnetic activity. It can be probably attributed to the polar cap patches. In this study are presented the extended and more detailed analyses of TEC fluctuations in both the northern and southern hemispheres and compare the winter and summer events (November and July 2004 storms). A special attention is given to the features related to TEC fluctuations occur-rence in both hemispheres for conjugated GPS stations. The temporal development of both storms was rather similar. During storms the intensity of irregularities essentially increases and its location expands to equator. Maximal activity of TEC fluctuations took place when IMF Bz component was negative. Storm-time development of TEC fluctuations caused by ionospheric irregularities was controlled by UT. At polar stations TEC fluctuations were more expressed at southern (winter) hemisphere. Over auroral stations the difference of TEC fluctuations oc-currence was less expressed. During storm the strong TEC fluctuations can be registered at subauroral ionosphere (on latitudes lower than 55 CGL). The seasonal effect in this area also took place. Differences and similarities of these storms occurrence of TEC fluctuations with dependence on season are discussed.

Secular variation and fluctuation of GPS Total Electron Content over Antarctica

NASA Astrophysics Data System (ADS)

Jin, Rui; Jin, Shuanggen

2013-01-01

The total electron content (TEC) is an important parameters in the Earth's ionosphere, related to various space weather and solar activities. However, understanding of the complex ionospheric environments is still a challenge due to the lack of direct observations, particularly in the polar areas, e.g., Antarctica. Now the Global Positioning System (GPS) can be used to retrieve total electron content (TEC) from dual-frequency observations. The continuous GPS observations in Antarctica provide a good opportunity to investigate ionospheric climatology. In this paper, the long-term variations and fluctuations of TEC over Antarctica are investigated from CODE global ionospheric maps (GIM) with a resolution of 2.5°×5° every two hours since 1998. The analysis shows significant seasonal and secular variations in the GPS TEC. Furthermore, the effects of TEC fluctuations are discussed.

Simultaneous Global Positioning System observations of equatorial scintillations and total electron content fluctuations

NASA Astrophysics Data System (ADS)

Beach, Theodore L.; Kintner, Paul M.

1999-10-01

One aspect of the Global Positioning System (GPS) is the potential to conduct geophysical research, and worldwide networks of GPS receivers have been established to exploit this potential. Several research groups have begun using this global GPS data to study ionospheric total electron content (TEC) variations, also referred to as GPS phase fluctuations, as surrogates for ionospheric scintillations. This paper investigates the relationship between GPS amplitude scintillations and TEC variations for the same line of sight using observations from Ancón, Peru. These observations were taken under equatorial spread F conditions for three nights in April 1997. As expected, only when the spectrum of TEC fluctuations includes significant power at the Fresnel scale do scintillations appear. We also find that when the TEC fluctuation spectrum includes the Fresnel scale, the S4 scintillation index is roughly proportional to measures of TEC fluctuation for the weak scintillations observed. The proportionality constant varies from night to night, however, casting doubt on the ability to predict GPS S4 successfully from TEC fluctuation data alone. We also present a simple theoretical phase screen model and show that if a relationship between TEC fluctuation measures and S4 exists, that relationship depends on the power spectrum of phase variations at the screen. Unfortunately, the available TEC data, at 30 s per sample (with some aliasing apparently permitted), offer limited spectral information. A preliminary comparison of 1 s/sample data with the same data decimated to a 30 s/sample interval suggests, however, that the level of successful S4 prediction, based on TEC fluctuation measures alone, is comparable at either sample rate.

Dust Storm Signatures in Global Ionosphere Map of GPS Total Electron Content

NASA Astrophysics Data System (ADS)

Lin, Fang-Tse; Shih, Ai-Ling; Liu, Jann-Yenq; Kuo, Cheng-Ling; Lin, Tang-Huang; Lien, Wei-Hung

2016-04-01

In this paper both MODIS data and GIM (global ionosphere map) TEC (total electron content) as well as numerical simulations are used to study ionospheric dust storm effects in May 2008. The aerosol optical depth (AOD) and the LTT (latitude-time-TEC) along the Sahara longitude simultaneously reach their maximum values on 28 May 2008. The LLT (latitude-longitude-TEC) map specifically and significantly increases over the Sahara region on 28 May 2008. The simulation suggests that the dust storm may change the atmospheric conductivity, which in turn modifies the GIM TEC over the Sahara area.

Evaluation of the impact of ionospheric disturbances on air navigation augmentation system using multi-point GPS receivers

NASA Astrophysics Data System (ADS)

Omatsu, N.; Otsuka, Y.; Shiokawa, K.; Saito, S.

2013-12-01

In recent years, GPS has been utilized for navigation system for airplanes. Propagation delays in the ionosphere due to total electron content (TEC) between GPS satellite and receiver cause large positioning errors. In precision measurement using GPS, the ionospheric delay correction is generally conducted using both GPS L1 and L2 frequencies. However, L2 frequency is not internationally accepted as air navigation band, so it is not available for positioning directly in air navigation. In air navigation, not only positioning accuracy but safety is important, so augmentation systems are required to ensure the safety. Augmentation systems such as the satellite-based augmentation system (SBAS) or the ground-based augmentation system (GBAS) are being developed and some of them are already in operation. GBAS is available in a relatively narrow area around airports. In general, it corrects for the combined effects of multiple sources of positioning errors simultaneously, including satellite clock and orbital information errors, ionospheric delay errors, and tropospheric delay errors, using the differential corrections broadcast by GBAS ground station. However, if the spatial ionospheric delay gradient exists in the area, correction errors remain even after correction by GBAS. It must be a threat to GBAS. In this study, we use the GPS data provided by the Geographical Survey Institute in Japan. From the GPS data, TEC is obtained every 30 seconds. We select 4 observation points from 24.4 to 35.6 degrees north latitude in Japan, and analyze TEC data of these points from 2001 to 2011. Then we reveal dependences of Rate of TEC change Index (ROTI) on latitude, season, and solar activity statistically. ROTI is the root-mean-square deviation of time subtraction of TEC within 5 minutes. In the result, it is the midnight of the spring and the summer of the solar maximum in the point of 26.4 degrees north latitude that the value of ROTI becomes the largest. We think it is caused by plasma bubbles, and the maximum value of ROTI is about 6 TECU/min. Since it is thought that ROTI is an index representing the spatial ionospheric delay gradient, we can evaluate the effect of spatial ionospheric delay gradient to GBAS. In addition, we will discuss azimuth angle dependence of ROTI. We have found that ROTI tends to be high when the GPS satellites are seen westward. Initial analysis results in Indonesia show a similar feature. This feature could arise from the westward tilt of the plasma bubbles with altitude. More detailed results will be reported in this presentation.

Comparison of COSMIC RO Data with European Digisondes and GPS TEC measurements

NASA Astrophysics Data System (ADS)

Zakharenkova, Irina; Krypiak-Gregorczyk, Anna; Shagimuratov, Irk; Krankowski, Andrzej; Lagovsky, Anatoly

FormoSat-3/COSMIC now provides unprecedented global coverage of GPS occultations mea-surements, each of which yields the ionosphere electron density information with high vertical resolution. However systematic validation work is still needed before using the powerful RO technique for sounding the ionosphere on a routine basis. In the given study electron density profiles retrieved from the Formosat-3/COSMIC RO measurements were compared with differ-ent kinds of ground-based observations. We used the ionospheric data recorded by European digisondes of DIAS network (Rome, Ebro, Arenosillo, Athens, Chilton, Pruhonice and Julius-ruh) for temporal interval of 2007-2009 and compare these ground measured data with the GPS COSMIC RO ionospheric profiles. It was revealed that in general the form of COSMIC profile in the bottom side is in a good agreement with ionosonde profiles, the heights of the peak density value are also good comparable. Special attention was focused to the question of the topside part of electron density profile. Practically for all analyzed cases there are observed the understated values of electron density in the topside part of the ionosonde profiles in compare with RO profiles. As the topside ionosonde profile is obtained by fitting a model to the peak electron density value, the COSMIC radio occultation measurements can make an important contribution to the investigation of the topside part of the ionosphere. In order to assess the ac-curacy of the COSMIC ionospheric electron density retrievals, coincidences of ionosonde data with COSMIC NmF2 values have been examined. NmF2 was calculated from the observed critical plasma frequency foF2 of the F2 layer. Values of foF2 have been scaled manually from ionograms for all considered time-location cases to avoid the evident risks related with using of the autoscaled data. The created scatter plots show a high degree of correlation between two independent estimates of NmF2. Also it was analyzed the variation of NmF2 for the considered seasons depending on day-time and night-time conditions. Also it was analyzed the total elec-tron content values calculated for the nearest ground-based GPS stations located in European region. To compare GPS TEC with RO and ionosondes' data these profiles were integrated. In general bottom parts of COSMIC and ionosondes' data are in a rather good agreement while the topside can be varied greatly that is the evidence of difference in the topside parts of these profiles. GPS TEC values are greater than COSMIC and ionosondes' data as TEC contains IEC and PEC. This procedure can be useful to estimate the impact of PEC into TEC. Results of the given comparisons can be important to validate the reliability of the COSMIC iono-spheric observations using the RO technique. We acknowledge the Taiwan's National Space Organization (NSPO) and the University Corporation for Atmospheric Research (UCAR) for providing the COSMIC Data. We are grateful to European Digital Upper Atmosphere Server (DIAS) for providing the ionosondes' products and to International GNSS Service (IGS) for GPS Data.

Variation of TEC and related parameters over the Indian EIA region from ground and space based GPS observations during the low solar activity period of May 2007-April 2008

NASA Astrophysics Data System (ADS)

Chakravarty, S. C.; Nagaraja, Kamsali; Jakowski, N.

2017-03-01

The annual variations of ionospheric Total Electron Content (TEC), F-region peak ionisation (NmF2) and the ionospheric slab thickness (τ) over the Indian region during the low solar activity period of May 2007-April 2008 have been studied. For this purpose the ground based TEC data obtained from GAGAN measurements and the space based data from GPS radio occultation technique using CHAMP have been utilised. The results of these independent measurements are combined to derive additional parameters such as the equivalent slab thickness of the total and the bottom-side ionospheric regions (τT and τB). The one year hourly average values of all these parameters over the ionospheric anomaly latitude region (10-26°N) are presented here along with the statistical error estimates. It is expected that these results are potentially suited to be used as base level values during geomagnetically quiet and undisturbed solar conditions.

High Temporal and Spatial Resolution Global GPS TEC Observations of the 2015 St. Patrick Day Storm

NASA Astrophysics Data System (ADS)

Vierinen, J.

2015-12-01

High spatiotemperal resolution global GPS TEC measurements of the 2015 St. Patrick's day storm are presented. The high resolution data is useful, as it clearly shows the high latitude convection patterns, the equatorward progression of the auroral region, the tongue of ionization, as well as the increased electron density in the equatorial anomaly region. The measurements are compared with high power large aperture radar and passive radar measurements of coherent and incoherent scatter at Millstone Hill. Regions of fast convection identified in the GPS TEC data are found to coincide with coherent scatter in both radar data. Convection velocities determined from GPS TEC are compared with those obtained from incoherent scatter radar measurements.

Investigating the performance of neural network backpropagation algorithms for TEC estimations using South African GPS data

NASA Astrophysics Data System (ADS)

Habarulema, J. B.; McKinnell, L.-A.

2012-05-01

In this work, results obtained by investigating the application of different neural network backpropagation training algorithms are presented. This was done to assess the performance accuracy of each training algorithm in total electron content (TEC) estimations using identical datasets in models development and verification processes. Investigated training algorithms are standard backpropagation (SBP), backpropagation with weight delay (BPWD), backpropagation with momentum (BPM) term, backpropagation with chunkwise weight update (BPC) and backpropagation for batch (BPB) training. These five algorithms are inbuilt functions within the Stuttgart Neural Network Simulator (SNNS) and the main objective was to find out the training algorithm that generates the minimum error between the TEC derived from Global Positioning System (GPS) observations and the modelled TEC data. Another investigated algorithm is the MatLab based Levenberg-Marquardt backpropagation (L-MBP), which achieves convergence after the least number of iterations during training. In this paper, neural network (NN) models were developed using hourly TEC data (for 8 years: 2000-2007) derived from GPS observations over a receiver station located at Sutherland (SUTH) (32.38° S, 20.81° E), South Africa. Verification of the NN models for all algorithms considered was performed on both "seen" and "unseen" data. Hourly TEC values over SUTH for 2003 formed the "seen" dataset. The "unseen" dataset consisted of hourly TEC data for 2002 and 2008 over Cape Town (CPTN) (33.95° S, 18.47° E) and SUTH, respectively. The models' verification showed that all algorithms investigated provide comparable results statistically, but differ significantly in terms of time required to achieve convergence during input-output data training/learning. This paper therefore provides a guide to neural network users for choosing appropriate algorithms based on the availability of computation capabilities used for research.

Investigation of seismo-ionospheric effects associated with Elazig and Van earthquakes in Turkey

NASA Astrophysics Data System (ADS)

Shagimuratov, I.; Cherniak, Iu.; Zakharenkova, I.; Tepenitsyna, N.; Yakimova, G.

2012-04-01

This report presents the specific features of TEC (total electron content of the ionosphere) behavior associated with earthquakes 08 March 2010 (Elazıg, Mw 6.1) and devastating earthquake with M 7.3, occurred on 23 October 2011 in Van. For this purpose we used both the GPS TEC data from the nearest to the epicenter GPS-IGS stations and constructed TEC maps over Europe. The favorable circumstance for this analysis was the quiet geomagnetic situation during the period previous to the earthquakes (the sum of Kp didn't exceed 5 for first and less than 15 for second case). The typical anomaly was found out one week prior to Elazıg earthquake and three days prior to Van earthquake as the day-time significant increase of TEC at the nearest stations up to the value of 50% relative to the background condition. To estimate the spatial dimensions of seismo-ionospheric anomaly the differential mapping method was used. Anomalous TEC enhancement was registered since 10 UT and reached the maximal value of 45-55% at 18-20 UT. So, the seismo-ionospheric anomaly was found out as the cloud-shaped increase of total electron content of the ionosphere, it had a well-defined local character and it was situated in the immediate vicinity of the earthquake epicenter area. Acknowledgments. The authors are grateful to the IGS community for providing GPS permanent data and to the USGS Earthquake Hazards Program for the detailed earthquake information. The research leading to these results has received funding from the European Union Sevenths Framework Program (FP7/20017-2013) under grant agreement No. 263502 - PRE-EARTHQUAKES project.

Detection of Geomagnetic Pulsations of the Earth Using GPS-TEC Data

NASA Astrophysics Data System (ADS)

Koroglu, Ozan; Arikan, Feza; Köroǧlu, Meltem; Sabri Ozkazanc, Yakup

2016-07-01

The magnetosphere of the Earth is made up of both magnetic fields and plasma. In this layer, plasma waves propagate as Ultra Low Frequency (ULF) waves having mHz scale frequencies. ULF waves are produced due to complicated solar-geomagnetic interactions. In the literature, these ULF waves are defined as pulsations. The geomagnetic pulsations are classified into main two groups as continuous pulsations (Pc) and irregular pulsations (Pi). These pulsations can be determined by ionospheric parameters due to the complex lithosphere-ionosphere-magnetosphere coupling processes. Total Electron Content (TEC) is one of the most important parameters for investigating the variability of ionosphere. Global Positioning System (GPS) provides a cost-effective means for estimating TEC from GPS satellite orbital height of 20,000 km to the ground based receivers. Therefore, the time series of GPS-TEC inherently contains the above mentioned ULF waves. In this study, time series analysis of GPS-TEC is carried out by applying periodogram method to the mid-latitude annual TEC data. After the analysis of GPS-TEC data obtained for GPS stations located in Central Europe and Turkey for 2011, it is observed that some of the fundamental frequencies that are indicators of Pc waves, diurnal and semi-diurnal periodicity and earth-free oscillations can be identified. These results will be used in determination of low frequency trend structure of magnetosphere and ionosphere. Further investigation of remaining relatively low magnitude frequencies, all Pi and Pc can be identified by using time and frequency domain techniques such as wavelet analysis. This study is supported by the joint TUBITAK 115E915 and joint TUBITAK114E092 and AS CR 14/001 projects.

Investigation of Ionospheric Precursors of 23 October 2011, Mw=7.2 Earthquake in Van, Turkey

NASA Astrophysics Data System (ADS)

Deviren, M. N.; Arikan, F.; Sezen, U.; Arikan, O.

2012-04-01

In recent years, a strong coupling between ionospheric disturbances and seismic activity has been observed through the increase of ion temperatures, critical frequencies of ionospheric layers and Total Electron Content (TEC) before high magnitude earthquakes. TEC is defined as total number of electrons over a ray path through the ionosphere. TEC can be estimated in a cost-effective way with dual-frequency Global Positioning Satellite (GPS) System receivers. The unit of TEC is given by TECU where 1 TECU = 1016 el/m2. In this study, the disturbances in daily TEC values before 23 October 2011, Mw=7.2 Earthquake in Van, Turkey are investigated using Turkish National Permanent GPS Network (TNPGN-Active). Earthquake Day Period (EDP) is chosen between October 1 and 31, 2011. Daily TEC values, for each station and each day, are estimated as IONOLAB-TEC (www.ionolab.org ) with 30 s time resolution. EDP-TEC values are compared with an Average Quiet Day TEC (AQDT) which is obtained by averaging the TEC values between 25 and 28 March, 2011. Statistical comparison is accomplished using Symmetric Kullback-Leibler Divergence (SKLD), which is also a method for measuring entropy of a system. It has been previously observed that SKLD is a better method for measuring the amount of disturbances compared to L2 norm and cross-correlation coefficient. AQDT is also compared with magnetically Quiet Day Period (QDP) from 25 to 28 April, 2011, during which Kp and Dst indices indicate a very quiet ionospheric and magnetospheric period. Also, in order to measure the variability between the consecutive days, TEC values for each day during EDP and QDP are compared with the TEC values of the following day. A third measure of W-index is also applied to identify the local disturbances in the ionosphere, where TEC of a given day is compared to the median of seven days prior to the day of investigation logarithmically. Since W-index is obtained for each epoch, the within-the-day variability can also be monitored. It has been observed that peak TEC values for all stations in TNPGN increase 10 to 15 TECU two days prior to the earthquake. The SKLD values for comparison of EDP and AQDT also peak on 21st of October, 2011, two days prior to the earthquake. Since ionospheric disturbance can be observed on all days prior to the earthquake, comparison of TEC for consecutive days for each station using SKLD does not provide extra information. The W-index values indicate that there may be small scale variability for stations closer to the earthquake epicenter. When compared with previous earthquakes that occurred in Turkey with magnitudes 4.5 and 5.2 on Richter scale, this 7.2 magnitude earthquake has been felt as an ionospheric disturbance for stations especially on Northern Anatolian Fault. The results also indicate the need for constant monitoring and statistical decision theory for detection of earthquake precursors. This study is supported by TUBITAK EEEAG Grant 109E055.

Imaging the topside ionosphere and plasmasphere with ionospheric tomography using COSMIC GPS TEC

NASA Astrophysics Data System (ADS)

Pinto Jayawardena, Talini S.; Chartier, Alex T.; Spencer, Paul; Mitchell, Cathryn N.

2016-01-01

GPS-based ionospheric tomography is a well-known technique for imaging the total electron content (TEC) between GPS satellites and receivers. However, as an integral measurement of electron concentration, TEC typically encompasses both the ionosphere and plasmasphere, masking signatures from the topside ionosphere-plasmasphere due to the dominant ionosphere. Imaging these regions requires a technique that isolates TEC in the topside ionosphere-plasmasphere. Multi-Instrument Data Analysis System (MIDAS) employs tomography to image the electron distribution in the ionosphere. Its implementation for regions beyond is yet to be seen due to the different dynamics present above the ionosphere. This paper discusses the extension of MIDAS to image these altitudes using GPS phase-based TEC measurements and follows the work by Spencer and Mitchell (2011). Plasma is constrained to dipole field lines described by Euler potentials, resulting in a distribution symmetrical about the geomagnetic equator. A simulation of an empirical plasmaspheric model by Gallagher et al. (1988) is used to verify the technique by comparing reconstructions of the simulation with the empirical model. The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) is used as GPS receiver locations. The verification is followed by a validation of the modified MIDAS algorithm, where the regions' TEC is reconstructed from COSMIC GPS phase measurements and qualitatively compared with previous studies using Jason-1 and COSMIC data. Results show that MIDAS can successfully image features/trends of the topside ionosphere-plasmasphere observed in other studies, with deviations in absolute TEC attributed to differences in data set properties and the resolution of the images.

Nighttime Medium-Scale Traveling Ionospheric Disturbances From Airglow Imager and Global Navigation Satellite Systems Observations

NASA Astrophysics Data System (ADS)

Huang, Fuqing; Lei, Jiuhou; Dou, Xiankang; Luan, Xiaoli; Zhong, Jiahao

2018-01-01

In this study, coordinated airglow imager, GPS total electron content (TEC), and Beidou geostationary orbit (GEO) TEC observations for the first time are used to investigate the characteristics of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) over central China. The results indicated that the features of nighttime MSTIDs from three types of observations are generally consistent, whereas the nighttime MSTID features from the Beidou GEO TEC are in better agreement with those from airglow images as compared with the GPS TEC, given that the nighttime MSTID characteristics from GPS TEC are significantly affected by Doppler effect due to satellite movement. It is also found that there are three peaks in the seasonal variations of the occurrence rate of nighttime MSTIDs in 2016. Our study revealed that the Beidou GEO satellites provided fidelity TEC observations to study the ionospheric variability.

A Fast Algorithm for Automatic Detection of Ionospheric Disturbances Using GPS Slant Total Electron Content Data

NASA Astrophysics Data System (ADS)

Efendi, Emre; Arikan, Feza; Yarici, Aysenur

2016-07-01

Solar, geomagnetic, gravitational and seismic activities cause disturbances in the ionospheric region of upper atmosphere for space based communication, navigation and positioning systems. These disturbances can be categorized with respect to their amplitude, duration and frequency. Typically in the literature, ionospheric disturbances are investigated with gradient based methods on Total Electron Content (TEC) data estimated from ground based dual frequency Global Positioning System (GPS) receivers. In this study, a detection algorithm is developed to determine the variability in Slant TEC (STEC) data. The developed method, namely Differential Rate of TEC (DRoT), is based on Rate of Tec (RoT) method that is widely used in the literature. RoT is usually applied to Vertical TEC (VTEC) and it can be defined as normalized derivative of VTEC. Unfortunately, the resultant data obtained from the application of RoT on VTEC suffer from inaccuracies due to mapping function and the resultant values are very noisy which make it difficult to automatically detect the disturbance due to variability in the ionosphere. The developed DRoT method can be defined as the normalized metric norm (L2) between the RoT and its baseband trend structure. In this study, the error performance of DRoT is determined using synthetic data with variable bounds on the parameter set of amplitude, frequency and period of disturbance. It is observed that DRoT method can detect disturbances in three categories. For DRoT values less than 50%, there is no significant disturbance in STEC data. For DRoT values between 50 to 70 %, a medium scale disturbance can be observed. For DROT values over 70 %, severe disturbances such Large Scale Travelling Ionospheric Disturbances (TID) or plasma bubbles can be observed. When DRoT is applied to the GPS-STECdata for stations in high latitude, equatorial and mid-latitude regions, it is observed that disturbances with amplitudes larger than 10% of the difference between the minimum and maximum values of STEC; frequencies higher than 0.15 mHz; and durations longer than 10 minutes can be automatically detected with more than 80% accuracy. This study is supported by TUBITAK EEAG 115E915 project.

Receiver DCB estimation and GPS vTEC study at a low latitude station in the South Pacific

NASA Astrophysics Data System (ADS)

Prasad, Ramendra; Kumar, Sushil; Jayachandran, P. T.

2016-11-01

The statistical estimation of receiver differential code bias (DCB) of the GSV4004B receiver at a low latitude station, Suva (lat. 18.15°S, long. 178.45°E, Geomag. Lat. 21.07°S), Fiji, and the subsequent behaviour of vTEC, are presented. By means of least squares linear regression fitting technique, the receiver DCB was determined using the GPS vTEC data recorded during the year 2010, CODE TEC and IRI-2012 model for 2010. To substantiate the results, minimization of the standard deviation (SD) method was also used for GPS vTEC data. The overall monthly DCB was estimated to be in the range of 62.6 TECU. The vTEC after removing the resultant monthly DCB was consistent with other low latitude observations. The GPS vTEC 2010 data after eliminating the resultant DCB were lower in comparison to Faraday rotation vTEC measurements at Suva during 1984 primarily due to higher solar activity during 1984 as compared to 2010. Seasonally, vTEC was maximum during summer and minimum during winter. The winter showed least vTEC variability whereas equinox showed the largest daytime variability. The geomagnetic disturbances effect showed that both vTEC and its variability were higher on magnetically disturbed days as compared to quiet days with maximum variability in the daytime. Two geomagnetic storms of moderate strengths with main phases in the local daytime showed long duration (∼52 h) increase in vTEC by 33-67% which can be accounted by changes in E×B drifts due to prompt penetration of storm-time auroral electric field in the daytime and disturbance dynamo electric field in the nighttime to low latitudes.

Performance evaluation of ionospheric time delay forecasting models using GPS observations at a low-latitude station

NASA Astrophysics Data System (ADS)

Sivavaraprasad, G.; Venkata Ratnam, D.

2017-07-01

Ionospheric delay is one of the major atmospheric effects on the performance of satellite-based radio navigation systems. It limits the accuracy and availability of Global Positioning System (GPS) measurements, related to critical societal and safety applications. The temporal and spatial gradients of ionospheric total electron content (TEC) are driven by several unknown priori geophysical conditions and solar-terrestrial phenomena. Thereby, the prediction of ionospheric delay is challenging especially over Indian sub-continent. Therefore, an appropriate short/long-term ionospheric delay forecasting model is necessary. Hence, the intent of this paper is to forecast ionospheric delays by considering day to day, monthly and seasonal ionospheric TEC variations. GPS-TEC data (January 2013-December 2013) is extracted from a multi frequency GPS receiver established at K L University, Vaddeswaram, Guntur station (geographic: 16.37°N, 80.37°E; geomagnetic: 7.44°N, 153.75°E), India. An evaluation, in terms of forecasting capabilities, of three ionospheric time delay models - an Auto Regressive Moving Average (ARMA) model, Auto Regressive Integrated Moving Average (ARIMA) model, and a Holt-Winter's model is presented. The performances of these models are evaluated through error measurement analysis during both geomagnetic quiet and disturbed days. It is found that, ARMA model is effectively forecasting the ionospheric delay with an accuracy of 82-94%, which is 10% more superior to ARIMA and Holt-Winter's models. Moreover, the modeled VTEC derived from International Reference Ionosphere, IRI (IRI-2012) model and new global TEC model, Neustrelitz TEC Model (NTCM-GL) have compared with forecasted VTEC values of ARMA, ARIMA and Holt-Winter's models during geomagnetic quiet days. The forecast results are indicating that ARMA model would be useful to set up an early warning system for ionospheric disturbances at low latitude regions.

The First Use of Coordinated Ionospheric Radio and Optical Observations Over Italy: Convergence of High-and Low-Latitude Storm-Induced Effects

NASA Astrophysics Data System (ADS)

Cesaroni, C.; Alfonsi, L.; Pezzopane, M.; Martinis, C.; Baumgardner, J.; Wroten, J.; Mendillo, M.; Musicò, E.; Lazzarin, M.; Umbriaco, G.

2017-11-01

Ionospheric storm effects at midlatitudes were analyzed using different ground-based instruments distributed in Italy during the 13-15 November 2012 geomagnetic storm. These included an all-sky imager (ASI) in Asiago (45.8°N, 11.5°E), a network of dual-frequeny Global Navigation Satellite Systems receivers (Rete Integrata Nazionale GPS network), and ionosondes in Rome (41.8°N, 12.5°E) and San Vito (40.6°N, 17.8°E). GPS measurements showed an unusual enhancement of total electron content (TEC) in southern Italy, during the nights of 14 and 15 November. The ASI observed colocated enhancements of 630 nm airglow at the same time, as did variations in NmF2 measured by the ionosondes. Moreover, wave-like perturbations were identified propagating from the north. The Ensemble Empirical Mode Decomposition, applied to TEC values revealed the presence of traveling ionospheric disturbances (TIDs) propagating southward between 01:30 UT and 03:00 UT on 15 November. These TIDs were characterized by weak TEC oscillations ( ±0.5 TEC unit), period of 45 min, and velocity of 500 m/s typical of large-scale TIDs. Optical images showed enhanced airglow entering the field of view of the ASI from the N-NE at 02:00 UT and propagating to the S-SW, reaching the region covered by the GPS stations after 03:00 UT, when TEC fluctuations are very small ( ±0.2 TEC unit). The enhancement of TEC and airglow observed in southern Italy could be a consequence of a poleward expansion of the northern crest of the equatorial ionization anomaly. The enhanced airglow propagating from the north and the TEC waves resulted from energy injected at auroral latitudes as confirmed by magnetometer observations in Scandinavia.

Short term variations of total electron content (TEC) fitting to a regional GPS network over the Kingdom of Saudi Arabia (KSA)

NASA Astrophysics Data System (ADS)

Alothman, A. O.; Alsubaie, M. A.; Ayhan, M. E.

2011-09-01

The ionosphere is a dispersive medium for radio waves with the refractive index which is a function of frequency and total electron content (TEC). TEC has a strong diurnal variation in addition to monthly, seasonal and solar cycle variations and small and large scale irregularities. Dual frequency GPS observations can be utilized to obtain TEC and investigate its spatial and temporal variations. We here studied short term TEC variations over the Kingdom of Saudi Arabia (KSA). A regional GPS network is formed consisting of 16 sites in and around KSA. GPS observations, acquired between 1st and 11th February 2009, were processed on a daily basis by using the Bernese v5.0 software and IGS final products. The geometry-free zero difference smoothed code observables were used to obtain two hour interval snapshots of TEC and their RMS errors at 0.5 × 0.5 degree grid nodes and regional ionosphere models in a spherical harmonics expansion to degree and order six. The equatorial ionized anomaly (EIA) is recovered in the south of 20°N from 08:00 to 12:00 UT. We found that day-by-day TEC variation is more stable than the night time variation.

A Year-Long Comparison of GPS TEC and Global Ionosphere-Thermosphere Models

NASA Astrophysics Data System (ADS)

Perlongo, N. J.; Ridley, A. J.; Cnossen, I.; Wu, C.

2018-02-01

The prevalence of GPS total electron content (TEC) observations has provided an opportunity for extensive global ionosphere-thermosphere model validation efforts. This study presents a year-long data-model comparison using the Global Ionosphere-Thermosphere Model (GITM) and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). For the entire year of 2010, each model was run and compared to GPS TEC observations. The results were binned according to season, latitude, local time, and magnetic local time. GITM was found to overestimate the TEC everywhere, except on the midlatitude nightside, due to high O/N2 ratios. TIE-GCM produced much less TEC and had lower O/N2 ratios and neutral wind speeds. Seasonal and regional biases in the models are discussed along with ideas for model improvements and further validation efforts.

Atmospheric processes in reaction of Northern Sumatra Earthquake sequence Dec 2004-Apr 2005

NASA Astrophysics Data System (ADS)

Ouzounov, D.; Pulinets, S.; Cervone, G.; Singh, R.; Taylor, P.

2005-05-01

This work describes our first results in analyzing data from different and independent sources ûemitted long-wavelength radiation (OLR), surface latent heat flux (SHLF) and GPS Total Electron Content (TEC) collected from ground based (GPS) and satellite TIR (thermal infra-red) data sources (NOAA/AVHRR, MODIS). We found atmosphere and ionosphere anomalies one week prior to both the Sumatra-Andaman Islands earthquake (Dec 26, 2004) and M 8.7 - Northern Sumatra, March 28, 2005. We analyzed 118 days of data from December 1, 2004 through April 1, 2005 for the area (0°-10°,north latitude and 90°-100° east longitude) which included 125 earthquakes with M>5.5. Recent analysis of the continuous OLR from the Earth surface indicates anomalous variations (on top of the atmosphere) prior to a number of medium to large earthquakes. In the case of M 9.0 - Sumatra-Andaman Islands event, compared to the reference fields for the months of December between 2001 and 2004, we found strongly OLR anomalous +80 W/m2 signals (two sigma) along the epicentral area on Dec 21, 2004 five days before the event. In the case of M8.7 March 28, 2005 anomalues signatures over the epicenter appears on March 26 is much weaker (only +20W/m2) and have a different topology. Anomalous values of SHLF associated with M9.0 - Sumatra-Andaman Islands were found on Dec 22, 2005 (SLHF +280Wm2) and less intensity on Mar 23, 2005 (SLHF +180Wm2). Ionospheric variations (GPS/TEC) associated with the Northern Sumatra events were determine by five Regional GPS network stations (COCO, BAKO, NTUS, HYDE and BAST2). For every station time series of the vertical TEC (VTEC) were computed together with correlation with the Dst index. On December 22, four days prior to the M9.0 quake GPS/TEC data reach the monthly maximum for COCO with minor DST activity. For the M 8.7-March 28 event, the increased values of GPS/TEC were observed during four days (March 22-25) in quiet geomagnetic background. Our results need additional validation and the could be explained within the framework of a model of Lithosphere-Atmosphere-Ionosphere coupling, supporting the hypothesis of a relationship between a thermodynamic processes produced by increasing tectonic stresses in the Earth's crust and attendant electro-chemical interactions between the crust and the atmosphere/ionosphere.

Simultaneous response of NmF2 and GPS-TEC to storm events at Ilorin

NASA Astrophysics Data System (ADS)

Joshua, B. W.; Adeniyi, J. O.; Oladipo, O. A.; Doherty, P. H.; Adimula, I. A.; Olawepo, A. O.; Adebiyi, S. J.

2018-06-01

A comparative study of both TEC and NmF2 variations during quiet and disturbed conditions has been investigated using simultaneous measurements from dual frequency Global Positioning System (GPS) receiver and a DPS-4 Digisonde co-located at Ilorin (Geog. Lat. 8.50°N, Long. 4.50°E, dip. - 7.9°). The results of the quiet time variations of the two parameters show some similarities as well as differences in their structures. The values of both parameters generally increase during the sunrise period attaining a peak around the noon and then decaying towards the night time. The onset time of the sunrise growth is observed to be earlier in TEC than in NmF2. The rate of decay of TEC was observed to be faster than that of the NmF2 in most cases. Also, the noon 'bite-outs', leading to the formation of pre-noon and post-noon peaks, are prominent in the NmF2 structure and was hardly noticed in TEC. Results of the variations of both TEC and NmF2 during the 5 April, 10 May and 3 August 2010 geomagnetic storm events showed a simultaneous deviations of both parameters from the quiet time behavior. The magnitude of the deviations is however most pronounced in NmF2 structure than in TEC. We also found that the enhancement observed in the two parameters during the storm events generally corresponds to decrease in hmF2.

GPS TEC Fluctuations in the Low and High Latitudes During the 2015 St. Patrick`s Day Storm

NASA Astrophysics Data System (ADS)

Chung, Jong-Kyun; Hong, Junseok; Yoo, Sung-Moon; Kim, Jeong-Han; Jee, Geonhwa; Hegai, Valery V.

2017-12-01

As a part of collaborative efforts to understand ionospheric irregularities, the Korea ionospheric scintillation sites (KISS) network has been built based on global positioning system (GPS) receivers with sampling rates higher than 1 Hz. We produce the rate of TEC index (ROTI) to represent GPS TEC fluctuations related to ionospheric irregularities. In the KISS network, two ground-based GPS sites at Kiruna (marker: KIRN; geographic: 67.9° N, 21.4° E; geomagnetic: 65.2° N) and Chuuk (marker: CHUK; geographic: 7.5° N, 151.9° E; geomagnetic: 0.4° N) were selected to evaluate the ROTI value for ionospheric irregularities during the occurrence of the 2015 St. Patrick’s Day storm. The KIRN ROTI values in the aurora region appear to be generally much higher than the CHUK ROTI values in the EIA region. The CHUK ROTI values increased to 0.5 TECU/min around UT=13:00 (LT=23:00) on March 16 in the quiet geomagnetic condition. On March 17, 2015, CHUK ROTI values more than 1.0 TECU/min were measured between UT=9:00 and 12:00 (LT=19:00 and 22:00) during the first main phase of the St. Patrick’s Day storm. This may be due to ionospheric irregularities by increased pre-reversal enhancement (PRE) after sunset during the geomagnetic storm. Post-midnight, the CHUK ROTI showed two peaks of 0.5 TECU/min and 0.3 TECU/min near UT=15:00 (LT=01:00) and UT=18:00 (LT=04:00) at the second main phase. The KIRN site showed significant peaks of ROTI around geomagnetic latitude=63.3° N and MLT=15:40 on the same day. These can be explained by enhanced ionospheric irregularities in the auroral oval at the maximum of AE index

Equatorial ionization anomaly development as studied by GPS TEC and foF2 over Brazil: A comparison of observations with model results from SUPIM and IRI-2012

NASA Astrophysics Data System (ADS)

Nogueira, P. A. B.; Abdu, M. A.; Souza, J. R.; Batista, I. S.; Bailey, G. J.; Santos, A. M.; Takahashi, H.

2013-11-01

The equatorial ionization anomaly (EIA) development is studied using the total electron content (TEC) observed by the Global Positioning System (GPS) satellites, the F2-layer critical frequency (foF2) as measured by digisondes operated in the Brazilian sector, and by model simulation using the SUPIM (Sheffield University Plasmasphere Ionosphere Model). We have used two indices based on foF2 and TEC to represent the strength of the EIA Southern Anomaly Crest (SAC), which are denoted, respectively, by SAC(foF2) and SAC(TEC). Significant differences in the local time variations of the EIA intensity, as represented by these two indices, are investigated. The observed SAC indices are compared with their values modeled by the SUPIM and also by the International Reference Ionosphere (IRI)-2012. The SUPIM simulations that use the standard E×B plasma drift and neutral air wind models are found to provide acceptable representations of the observed foF2 and TEC, and hence the indices SAC(foF2) and SAC(TEC) during daytime, whereas the IRI-2012 model is not, except during the post-midnight/sunrise hours. It is found that the differences in the local time variations between the SAC(foF2) and SAC(TEC) can be reduced by limiting the TEC integrations in height up to an altitude of 630 km in the SUPIM calculations. It is also found that when the EIA intensity is calculated for an intermediate dip latitude (12°S) the difference between the local time variation patterns of the two corresponding indices in the experimental data and in the SUPIM results is reduced. For the IRI-2012 values, the subequatorial station modification does not appear to have any effect.

Study of Ionospheric TEC from GPS observations and comparisons with IRI and SPIM model predictions in the low latitude anomaly Indian subcontinental region

NASA Astrophysics Data System (ADS)

Panda, S. K.; Gedam, S. S.; Rajaram, G.

2015-04-01

The present study investigates variation of the ionospheric total electron content (TEC) in the low latitude Indian sub-continental region from the GPS observations and its comparison with the global ionosphere maps (GIMs), standard international reference ionosphere (IRI 2012), and the standard plasmasphere-ionosphere model (SPIM) for the period from November 2011 to October 2012 that corresponds to the progressive phase towards the midst of the solar cycle-24. Observations during quiet period show diurnal maximum of TEC occurring around 14:00-16:00 IST, with relatively broader and longer duration of local maximum at Bangalore and behave reversely towards Delhi. The secondary maximum of TEC was markedly noticeable at Bangalore during the months of March and September, and only in the month of September at Hyderabad and Mumbai. However, the relatively higher TEC during December month than the June is ascribed to the winter anomaly which is more prevalent during the high solar activity periods. The prevailing instability in latitudes of anomaly crest during January 2012 is possibly due to the seasonal variation of lunar tidal effects, modulating the EEJ strength at the equator. The studies covered the period of a strong geomagnetic storm during 6-11 March 2012 (SYM-H: -149 nT) which resulted in positive deviation of GPS-TEC at Bangalore (↑ 20%), Hyderabad (↑ 22%), and Lucknow (↑ 94%) compared to the mean quiet days level. The relatively large deviation of TEC at Lucknow could be attributed to the poleward shifting of the anomaly crest, manifested by enhanced fountain effect at the equator. Studies confirm excellent agreement (80-85%) of GPS-TEC with IGS-GIM at Bangalore and Hyderabad with the exception of the night-time hours (Deviations >50%). However relatively larger deviation of GPS-TEC from GIM-TEC at Delhi could be due to the unavailability of IGS stations in the proximity of the position. Predictions of the SPIM model (extension of IRI up to GPS altitude) exhibit much higher deviation from the in situ GPS observations as well as GIM and IRI outputs during quiet periods. Correspondingly, either of the models (IRI and SPIM) did not respond well to the arrival of the sudden storm commencements (SSCs) during the storm period (6-11 March 2012). When SPIM is used instead of IRI, the overestimation from GPS-TECs are further exaggerated by 13-18% (December solstice), 27-37% (March equinox), 15-31% (June solstice), and 20-32% (September equinox) during peak hours of the period. We attribute the relatively more deviation of the SPIM than the IRI model possibly due to its plasmaspheric extension to the IRI model by adding the Russian SMI model of high latitude characteristics. Hence, we emphasize the further improvement in the model with due consideration of the driving forces at play in the region, for reliable predictions of the low latitude ionosphere.

Performance evaluation of linear time-series ionospheric Total Electron Content model over low latitude Indian GPS stations

NASA Astrophysics Data System (ADS)

Dabbakuti, J. R. K. Kumar; Venkata Ratnam, D.

2017-10-01

Precise modeling of the ionospheric Total Electron Content (TEC) is a critical aspect of Positioning, Navigation, and Timing (PNT) services intended for the Global Navigation Satellite Systems (GNSS) applications as well as Earth Observation System (EOS), satellite communication, and space weather forecasting applications. In this paper, linear time series modeling has been carried out on ionospheric TEC at two different locations at Koneru Lakshmaiah University (KLU), Guntur (geographic 16.44° N, 80.62° E; geomagnetic 7.55° N) and Bangalore (geographic 12.97° N, 77.59° E; geomagnetic 4.53° N) at the northern low-latitude region, for the year 2013 in the 24th solar cycle. The impact of the solar and geomagnetic activity on periodic oscillations of TEC has been investigated. Results confirm that the correlation coefficient of the estimated TEC from the linear model TEC and the observed GPS-TEC is around 93%. Solar activity is the key component that influences ionospheric daily averaged TEC while periodic component reveals the seasonal dependency of TEC. Furthermore, it is observed that the influence of geomagnetic activity component on TEC is different at both the latitudes. The accuracy of the model has been assessed by comparing the International Reference Ionosphere (IRI) 2012 model TEC and TEC measurements. Moreover, the absence of winter anomaly is remarkable, as determined by the Root Mean Square Error (RMSE) between the linear model TEC and GPS-TEC. On the contrary, the IRI2012 model TEC evidently failed to predict the absence of winter anomaly in the Equatorial Ionization Anomaly (EIA) crest region. The outcome of this work will be useful for improving the ionospheric now-casting models under various geophysical conditions.

Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: An Integration of GPS and Galileo Systems

NASA Astrophysics Data System (ADS)

Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Wei, Yong; Mazzoni, Augusto; Crespi, Mattia

2017-04-01

Tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances are studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and for the first time, we estimate slant TEC (sTEC) variations in a real-time scenario from GPS and Galileo constellations. Specifically, we study the 2016 New Zealand tsunami event using GNSS receivers with multi-constellation tracking capabilities located in the Pacific region. We compare sTEC estimates obtained using GPS and Galileo constellations. The efficiency of the real-time sTEC estimation using the VARION algorithm has been demonstrated for the 2012 Haida Gwaii tsunami event. TEC variations induced by the tsunami event are computed using 56 GPS receivers in Hawai'i. We observe TEC perturbations with amplitudes up to 0.25 TEC units and traveling ionospheric disturbances moving away from the epicenter at a speed of about 316 m/s. We present comparisons with the real-time tsunami model MOST (Method of Splitting Tsunami) provided by the NOAA Center for Tsunami Research. We observe variations in TEC that correlate well in time and space with the propagating tsunami waves. We conclude that the integration of different satellite constellations is a crucial step forward to increasing the reliability of real-time tsunami detection systems using ground-based GNSS receivers as an augmentation to existing tsunami early warning systems.

A fast algorithm for automatic detection of ionospheric disturbances: DROT

NASA Astrophysics Data System (ADS)

Efendi, Emre; Arikan, Feza

2017-06-01

Solar, geomagnetic, gravitational and seismic activities cause disturbances in the ionospheric region of upper atmosphere that may disrupt or lower the quality of space based communication, navigation and positioning system signals. These disturbances can be categorized with respect to their amplitude, duration and frequency. Typically in the literature, ionospheric disturbances are investigated with gradient based methods on Total Electron Content (TEC) data estimated from ground based dual frequency Global Positioning System (GPS) receivers. In this study, a fast algorithm is developed for the automatic detection of the variability in Slant TEC (STEC) data. STEC is defined as the total number of electrons on the ray path between the ground based receiver and GPS satellite in the orbital height of 20,000 km. The developed method, namely, Differential Rate of TEC (DROT), is based on Rate of Tec (ROT) method. ROT is widely used in the literature and it is usually applied to Vertical TEC (VTEC) that corresponds to the projection of STEC to the vertical direction along the ray path at the Ionospheric Pierce Point (IPP) using a mapping function. The developed DROT method can be defined as the normalized metric norm between the ROT and its baseband trend structure. In this study, the performance of DROT is determined using synthetic data with variable bounds on the parameter set of amplitude, frequency and duration of disturbance. It is observed that DROT method can detect disturbances in three categories. For DROT values less than 50%, there is no significant disturbance in STEC data. For DROT values between 50% and 70%, a medium scale disturbance can be observed. For DROT values over 70%, severe disturbances such as Large Scale Traveling Ionospheric Disturbances (LSTIDs) can be observed. DROT method is highly sensitive to the amplitude of the wave-like oscillations. For a disturbance amplitude as low as 1.01 TECU, the disturbances that have durations longer than or equal to 20 min and frequencies higher than 1.095 mHz; or frequencies higher than 0.511 mHz and durations longer than 55 min can be detected automatically with DROT values of 50%. When DROT method is applied to midlatitude STEC values for disturbed days, it is observed that DROT method can detect the disturbances in near-real time, even if the GPS data from the station is uploaded with 15 min intervals.

A Comparative Study of the Ionospheric TEC Measurements Using Global Ionospheric Maps of GPS, TOPEX Radar and the Bent Model

NASA Technical Reports Server (NTRS)

Ho, C.; Wilson, B.; Mannucci, A.; Lindqwister, U.; Yuan, D.

1997-01-01

Global ionospheric mapping (GIM) is a new, emerging technique for determining global ionospheric TEC (total electron content) based on measurements from a worldwide network of Global Positioning System (GPS) receivers.

TEC variability near northern EIA crest and comparison with IRI model

NASA Astrophysics Data System (ADS)

Aggarwal, Malini

2011-10-01

Monthly median values of hourly total electron content (TEC) is obtained with GPS at a station near northern anomaly crest, Rajkot (geog. 22.29°N, 70.74°E; geomag. 14.21°N, 144.9°E) to study the variability of low latitude ionospheric behavior during low solar activity period (April 2005 to March 2006). The TEC exhibit characteristic features like day-to-day variability, semiannual anomaly and noon bite out. The observed TEC is compared with latest International Reference Ionosphere (IRI) - 2007 model using options of topside electron density, NeQuick, IRI01-corr and IRI-2001 by using both URSI and CCIR coefficients. A good agreement of observed and predicted TEC is found during the daytime with underestimation at other times. The predicted TEC by NeQuick and IRI01-corr is closer to the observed TEC during the daytime whereas during nighttime and morning hours, IRI-2001 shows lesser discrepancy in all seasons by both URSI and CCIR coefficients.

Estimation of total electron content (TEC) using spaceborne GPS measurements

NASA Astrophysics Data System (ADS)

Choi, Key-Rok; Lightsey, E. Glenn

2008-09-01

TerraSAR-X (TSX), a high-resolution interferometric Synthetic Aperture Radar (SAR) mission from DLR (German Aerospace Center, Deutsches Zentrum für Luft-und Raumfahrt), was successfully launched into orbit on June 15, 2007. It includes a dual-frequency GPS receiver called IGOR (Integrated GPS Occultation Receiver), which is a heritage NASA/JPL BlackJack receiver. The software for the TSX IGOR receiver was specially-modified software developed at UT/CSR. This software was upgraded to provide enhanced occultation capabilities. This paper describes total electron content (TEC) estimation using simulation data and onboard GPS data of TerraSAR-X. The simulated GPS data were collected using the IGOR Engineering Model (EM) in the laboratory and the onboard GPS data were collected from the IGOR Flight Model (FM) on TSX. To estimate vertical total electron content (vTEC) for the simulation data, inter-frequency biases (IFB) were estimated using the "carrier to code leveling process." For the onboard GPS data, IFBs of GPS satellites were retrieved from the navigation message and applied to the measurements.

Anomalous variation in GPS based TEC measurements prior to the 30 September 2009 Sumatra Earthquake

NASA Astrophysics Data System (ADS)

Karia, Sheetal; Pathak, Kamlesh

This paper investigates the features of pre-earthquake ionospheric anomalies in the total elec-tron content (TEC) data obtained on the basis of regular GPS observations from the GPS receiver at SVNIT Surat (21.16 N, 72.78 E Geog) located at the northern crest of equatorial anomaly region. The data has been analysed for 5 different earthquakes that occurred during 2009 in India and its neighbouring regions. Our observation shows that for the cases of the earthquake, in which the preparation area lies between the crests of the equatorial anomaly close to the geomagnetic equator the enhancement in TEC was followed by a depletion in TEC on the day of earthquake, which may be connected to the equatorial anomaly shape distortions. For the analysis of the ionospheric effects of one of such case-the 30 September 2009 Sumatra earthquake, Global Ionospheric Maps of TEC were used. The possible influence of the earth-quake preparation processes on the main low-latitude ionosphere peculiarity—the equatorial anomaly—is discussed.

Validation of measured poleward TEC gradient using multi-station GPS with Artificial Neural Network based TEC model in low latitude region for developing predictive capability of ionospheric scintillation

NASA Astrophysics Data System (ADS)

Sur, D.; Paul, A.

2017-12-01

The equatorial ionosphere shows sharp diurnal and latitudinal Total Electron Content (TEC) variations over a major part of the day. Equatorial ionosphere also exhibits intense post-sunset ionospheric irregularities. Accurate prediction of TEC in these low latitudes is not possible from standard ionospheric models. An Artificial Neural Network (ANN) based Vertical TEC (VTEC) model has been designed using TEC data in low latitude Indian longitude sector for accurate prediction of VTEC. GPS TEC data from the stations Calcutta (22.58°N, 88.38°E geographic, magnetic dip 32°), Baharampore (24.09°N, 88.25°E geographic, magnetic dip 35°) and Siliguri (26.72°N, 88.39°E geographic; magnetic dip 40°) are used as training dataset for the duration of January 2007-September 2011. Poleward VTEC gradients from northern EIA crest to region beyond EIA crest have been calculated from measured VTEC and compared with that obtained from ANN based VTEC model. TEC data from Calcutta and Siliguri are used to compute VTEC gradients during April 2013 and August-September 2013. It has been observed that poleward VTEC gradient computed from ANN based TEC model has shown good correlation with measured values during vernal and autumnal equinoxes of high solar activity periods of 2013. Possible correlation between measured poleward TEC gradients and post-sunset scintillations (S4 ≥ 0.4) from northern crest of EIA has been observed in this paper. From the observation, a suitable threshold poleward VTEC gradient has been proposed for possible occurrence of post-sunset scintillations at northern crest of EIA along 88°E longitude. Poleward VTEC gradients obtained from ANN based VTEC model are used to forecast possible ionospheric scintillation after post-sunset period using the threshold value. It has been observed that these predicted VTEC gradients obtained from ANN based VTEC model can forecast post-sunset L-band scintillation with an accuracy of 67% to 82% in this dynamic low latitude region. The use of VTEC gradients from ANN based VTEC model removes the necessity of continuous operation of multi-station ground based TEC receivers in this low latitude region.

Classification of the Regional Ionospheric Disturbance Based on Machine Learning Techniques

NASA Astrophysics Data System (ADS)

Terzi, Merve Begum; Arikan, Orhan; Karatay, Secil; Arikan, Feza; Gulyaeva, Tamara

2016-08-01

In this study, Total Electron Content (TEC) estimated from GPS receivers is used to model the regional and local variability that differs from global activity along with solar and geomagnetic indices. For the automated classification of regional disturbances, a classification technique based on a robust machine learning technique that have found wide spread use, Support Vector Machine (SVM) is proposed. Performance of developed classification technique is demonstrated for midlatitude ionosphere over Anatolia using TEC estimates generated from GPS data provided by Turkish National Permanent GPS Network (TNPGN-Active) for solar maximum year of 2011. As a result of implementing developed classification technique to Global Ionospheric Map (GIM) TEC data, which is provided by the NASA Jet Propulsion Laboratory (JPL), it is shown that SVM can be a suitable learning method to detect anomalies in TEC variations.

Equatorial late-afternoon periodic TEC fluctuations observed by multiple GPS receivers

NASA Astrophysics Data System (ADS)

Tsugawa, T.; Maruyama, T.; Saito, S.; Ishii, M.

2009-12-01

We report, for the first time, equatorial periodic total electron content (TEC) fluctuations observed in the late afternoon by multiple GPS receivers. As a part of Southeast Asia low-latitude ionospheric network (SEALION), GPS receivers at Chiang Mai and Chumphon, Thailand, have been operated since 2005. We found that periodic TEC fluctuations (PTF) with the periods of 15-30 minutes are often observed at these two sites in the spring (Apr-May) late afternoon. Further investigations using multiple GPS receivers in Southeast Asia revealed that the PTFs propagate at 150-200 m/s away from the equator and their amplitudes depend on the satellite azimuth angle. Statistical study of the PTF activity at different latitudes and longitudes clarified that the PTFs are not observed at mid-latitudes, and their seasonal variations are different at different longitudes and at geomagnetically conjugate regions. These observational results indicate that the PTFs are caused by the atmospheric gravity waves (AGW) which are generated in the equatorial lower atmosphere and propagate away from the equator. Simultaneous GPS-TEC and ionosonde observations at Chumphon revealed that the day-to-day variations of PTF activities are well correlated with those of the rate of TEC change index (ROTI) and the occurrence of equatorial spread F (ESF) after the sunset, indicating the PTFs may be related with the onset of the ESF and plasma bubbles.

Study of TEC and foF2 with the Help of GPS and Ionosonde Data over Maitri, Antarctica

NASA Astrophysics Data System (ADS)

Khatarkar, Prakash; Gwal, Ashok Kumar

Prakash Khatarkar, Purusottam Bhaware, Azad Ahmad Mansoori, Varsha Kachneria, Shweta Thakur, and A. K. Gwal Abstract The behavior of ionosphere can be diagnosed by a number of techniques. The common techniques used are the space based Global Positioning System and the ground based Ionosonde. We have compared the variability of ionospheric parameters by using two different techniques GPS and Ionosonde, during December 2009 to November 2010 at the Indian base station Maitri (11.45E, 70.45S). The comparison between the measurements of two techniques was realized through the Total Electron Content (TEC) parameters derived by using different methods. The comparison was made diurnally, seasonally, polar day and polar night variations and the annually. From our analysis we found that a strong correlation exists between the GPS derived TEC and Ionosonde derived foF2 during the day period while during the night time the correlation is insignificant. At the same time we found that a strong correlation exists between the Ionosonde and GPS derived TEC. The pattern of variation of ionospheric parameters derived from two techniques is strikingly similar indicating that the high degree of synchronization between them. This has a practical applicability by allowing calculating the error in one technique by comparing with other. Keywords: Ionosphere, Ionosonde, GPS, foF2, TEC.

Evaluation of different approaches to modeling the second-order ionospheric delay on GPS measurements

NASA Astrophysics Data System (ADS)

Garcia-Fernandez, M.; Desai, S. D.; Butala, M. D.; Komjathy, A.

2013-12-01

This work evaluates various approaches to compute the second order ionospheric correction (SOIC) to Global Positioning System (GPS) measurements. When estimating the reference frame using GPS, applying this correction is known to primarily affect the realization of the origin of the Earth's reference frame along the spin axis (Z coordinate). Therefore, the Z translation relative to the International Terrestrial Reference Frame 2008 is used as the metric to evaluate various published approaches to determining the slant total electron content (TEC) for the SOIC: getting the slant TEC from GPS measurements, and using the vertical total electron content (TEC) given by a Global Ionospheric Model (GIM) to transform it to slant TEC via a mapping function. All of these approaches agree to 1 mm if the ionospheric shell height needed in GIM-based approaches is set to 600 km. The commonly used shell height of 450 km introduces an offset of 1 to 2 mm. When the SOIC is not applied, the Z axis translation can be reasonably modeled with a ratio of +0.23 mm/TEC units of the daily median GIM vertical TEC. Also, precise point positioning (PPP) solutions (positions and clocks) determined with and without SOIC differ by less than 1 mm only if they are based upon GPS orbit and clock solutions that have consistently applied or not applied the correction, respectively. Otherwise, deviations of few millimeters in the north component of the PPP solutions can arise due to inconsistencies with the satellite orbit and clock products, and those deviations exhibit a dependency on solar cycle conditions.

Salient features of the dayside low latitude ionospheric response to the main phase step-I of the 17 March 2015 geomagnetic storm

NASA Astrophysics Data System (ADS)

Bagiya, Mala S.; Sunil, A. S.; Chakrabarty, D.; Sunda, Surendra

2017-10-01

Based on TEC observations by India's GPS Aided GEO Augmented Navigation (GAGAN) GPS network, we report the dayside low latitude ionospheric variations over the Indian region during the moderate main phase step-I of the 17 March 2015 geomagnetic storm. In addition, we assess the efficacy of GPS inferred TEC maps by International GNSS service (IGS) in capturing large scale diurnal features of equatorial ionization anomaly (EIA) over the Indian region during this period. Following the prompt penetration electric field (PPE) at ∼0605 UT, equatorial electrojet (EEJ) enhances by ∼55 nT over 75 ± 3oE longitudes where main phase step-I is coincided with local noon. Initial moderate EIA gradually strengthens with the storm commencement. Although GAGAN TEC exhibits more intense EIA evolution compare to IGS TEC maps, latitudinal extent of EIA are comparable in both. The enhanced EEJ reverses by ∼0918 UT under the effect of overshielding electric field, the later is accompanied by northward turning of interplanetary magnetic field (IMF) Bz. The weakening of well evolved EIA reflects in IGS TEC maps after ∼45 min of the overshielding occurrence. In contrary, GAGAN TEC shows the corresponding feature after ∼0115 h. Resurgence of EIA, following the PPE ∼1115 UT, shows up in GAGAN TEC but IGS TEC maps fails in capturing this feature. The observed low latitude TEC variations and EIA modulations are explained in terms of the varying storm time disturbance electric fields. The anomalies between the GAGAN TEC and IGS TEC maps are discussed in terms of the possible limitations of the IGS TEC maps in capturing storm time EIA variability over the Indian region.

Statistical characteristics of seismo-ionospheric GPS TEC disturbances prior to global Mw ≥ 5.0 earthquakes (1998-2014)

NASA Astrophysics Data System (ADS)

Shah, Munawar; Jin, Shuanggen

2015-12-01

Pre-earthquake ionospheric anomalies are still challenging and unclear to obtain and understand, particularly for different earthquake magnitudes and focal depths as well as types of fault. In this paper, the seismo-ionospheric disturbances (SID) related to global earthquakes with 1492 Mw ≥ 5.0 from 1998 to 2014 are investigated using the total electron content (TEC) of GPS global ionosphere maps (GIM). Statistical analysis of 10-day TEC data before global Mw ≥ 5.0 earthquakes shows significant enhancement 5 days before an earthquake of Mw ≥ 6.0 at a 95% confidence level. Earthquakes with a focal depth of less than 60 km and Mw ≥ 6.0 are presumably the root of deviation in the ionospheric TEC because earthquake breeding zones have gigantic quantities of energy at shallower focal depths. Increased anomalous TEC is recorded in cumulative percentages beyond Mw = 5.5. Sharpness in cumulative percentages is evident in seismo-ionospheric disturbance prior to Mw ≥ 6.0 earthquakes. Seismo-ionospheric disturbances related to strike slip and thrust earthquakes are noticeable for magnitude Mw6.0-7.0 earthquakes. The relative values reveal high ratios (up to 2) and low ratios (up to -0.5) within 5 days prior to global earthquakes for positive and negative anomalies. The anomalous patterns in TEC related to earthquakes are possibly due to the coupling of high amounts of energy from earthquake breeding zones of higher magnitude and shallower focal depth.

Pre-earthquake signatures in atmosphere/ionosphere and their potential for short-term earthquake forecasting. Case studies for 2015

NASA Astrophysics Data System (ADS)

Ouzounov, Dimitar; Pulinets, Sergey; Davidenko, Dmitry; Hernández-Pajares, Manuel; García-Rigo, Alberto; Petrrov, Leonid; Hatzopoulos, Nikolaos; Kafatos, Menas

2016-04-01

We are conducting validation studies on temporal-spatial pattern of pre-earthquake signatures in atmosphere and ionosphere associated with M>7 earthquakes in 2015. Our approach is based on the Lithosphere Atmosphere Ionosphere Coupling (LAIC) physical concept integrated with Multi-sensor-networking analysis (MSNA) of several non-correlated observations that can potentially yield predictive information. In this study we present two type of results: 1/ prospective testing of MSNA-LAIC for M7+ in 2015 and 2:/ retrospective analysis of temporal-spatial variations in atmosphere and ionosphere several days before the two M7.8 and M7.3 in Nepal and M8.3 Chile earthquakes. During the prospective test 18 earthquakes M>7 occurred worldwide, from which 15 were alerted in advance with the time lag between 2 up to 30 days and with different level of accuracy. The retrospective analysis included different physical parameters from space: Outgoing long-wavelength radiation (OLR obtained from NPOES, NASA/AQUA) on the top of the atmosphere, Atmospheric potential (ACP obtained from NASA assimilation models) and electron density variations in the ionosphere via GPS Total Electron Content (GPS/TEC). Concerning M7.8 in Nepal of April 24, rapid increase of OLR reached the maximum on April 21-22. GPS/TEC data indicate maximum value during April 22-24 periods. Strong negative TEC anomaly was detected in the crest of EIA (Equatorial Ionospheric Anomaly) on April 21st and strong positive on April 24th, 2015. For May 12 M7.3 aftershock similar pre- earthquake patterns in OLR and GPS/TEC were observed. Concerning the M8.3 Chile of Sept 16, the OLR strongest transient feature was observed of Sept 12. GPS/TEC analysis data confirm abnormal values on Sept 14. Also on the same day the degradation of EIA and disappearance of the crests of EIA as is characteristic for pre-dawn and early morning hours (11 LT) was observed. On Sept 16 co-seismic ionospheric signatures consistent with defined circular acoustic-gravity wave and different shock-acoustic waves was also observed. The spatial characteristics of pre-earthquake transient behavior in atmosphere and ionosphere were associated with large area but inside the preparation region estimated by Dobrovolsky ratio. Our analysis of simultaneous space measurements associated with 2015 M>7 earthquakes suggest that they follow a general temporal-spatial evolution pattern, which has been seen in other large earthquakes worldwide

LISN: Measurement of TEC values, and TID characteristics over South and Central America (Invited)

NASA Astrophysics Data System (ADS)

Valladares, C. E.

2013-12-01

The Low-latitude Ionospheric Sensor Network (LISN) is a distributed observatory designed to provide the climatology and weather of the low latitude ionosphere over the South American continent. Presently, the LISN observatory consists of 47 GPS receivers able to transmit TEC and scintillation values to a central server in a real-time basis. Historical TEC values from these receivers and from about 300 other GPSs that operated in South and Central America between 2008 and 2012 were used to derive regional maps of TEC and TIDs. A prominent feature of the TEC maps is the intense day-to-day variability that is observed during all seasons and under quiet and active magnetic conditions. To assess the TEC dependencies a non-linear least-square fit was conducted to simultaneously extract the solar flux, magnetic and seasonal variability for each square cell of the TEC maps and for each 30-min local time sector. It was found that TEC values and the anomaly intensity increase as a function of the solar flux. The latitudinal separation increases with magnetic activity, and TEC values in Central America become the largest when Kp is equal to 5o or more. TIDs are seen quite frequently over the Caribbean region and in the northern part of South America. To calculate the TIDs travel velocities, their propagation direction, and the scale-size of the disturbances a multi-site multi-dimension cross-correlation method was applied to the TEC database. Phase velocities of order 150 m/s and scale sizes between 100 and 400 km were typically observed. This paper will present the morphology and statistics of TIDs as a function of latitude, longitude, local time and season. It is also introduced the results of an investigation to correlate the appearance, phase velocity and angle of propagation of TIDs and tropospheric phenomena observed with the TRMM satellite.

A single-station empirical model for TEC over the Antarctic Peninsula using GPS-TEC data

NASA Astrophysics Data System (ADS)

Feng, Jiandi; Wang, Zhengtao; Jiang, Weiping; Zhao, Zhenzhen; Zhang, Bingbing

2017-02-01

Compared with regional or global total electron content (TEC) empirical models, single-station TEC empirical models may exhibit higher accuracy in describing TEC spatial and temporal variations for a single station. In this paper, a new single-station empirical total electron content (TEC) model, called SSM-month, for the O'Higgins Station in the Antarctic Peninsula is proposed by using Global Positioning System (GPS)-TEC data from 01 January 2004 to 30 June 2015. The diurnal variation of TEC in the O'Higgins Station may have changing features in different months, sometimes even in opposite forms, because of ionospheric phenomena, such as the Mid-latitude Summer Nighttime Anomaly (MSNA). To avoid the influence of different diurnal variations, the concept of monthly modeling is proposed in this study. The SSM-month model, which is established by month (including 12 submodels that correspond to the 12 months), can effectively describe the diurnal variation of TEC in different months. Each submodel of the SSM-month model exhibits good agreement with GPS-TEC input data. Overall, the SSM-month model fits the input data with a bias of 0.03 TECU (total electron content unit, 1 TECU = 1016 el m-2) and a standard deviation of 2.78 TECU. This model, which benefits from the modeling method, can effectively describe the MSNA phenomenon without implementing any modeling correction. TEC data derived from Center for Orbit Determination in Europe global ionosphere maps (CODE GIMs), International Reference Ionosphere 2012 (IRI2012), and NeQuick are compared with the SSM-month model in the years of 2001 and 2015-2016. Result shows that the SSM-month model exhibits good consistency with CODE GIMs, which is better than that of IRI2012 and NeQuick, in the O'Higgins Station on the test days.

Global Ionosphere Perturbations Monitored by the Worldwide GPS Network

NASA Technical Reports Server (NTRS)

Ho, C. M.; Manucci, A. T.; Lindqwister, U. J.; Pi, X.

1996-01-01

For the first time, measurements from the Global Positioning System (GPS) worldwide network are employed to study the global ionospheric total electron content(TEC) changes during a magnetic storm (November 26, 1994). These measurements are obtained from more than 60 world-wide GPS stations which continuously receive dual-frequency signals. Based on the delays of the signals, we have generated high resolution global ionospheric maps (GIM) of TEC at 15 minute intervals. Using a differential method comparing storm time maps with quiet time maps, we find that significant TEC increases (the positive effect ) are the major feature in the winter hemisphere during this storm (the maximum percent change relative to quiet times is about 150 percent).

Precise measurement method for ionospheric total electron content using signals from GPS satellites

NASA Technical Reports Server (NTRS)

Imae, Michito; Kiuchi, Hitoshi; Kaneko, Akihiro; Hama, Shinichi; Miki, Chihiro

1990-01-01

A GPS codeless receiver called GTR-2 was for measuring total electron content (TEC) along the line of sight to the GPS satellite by using the cross correlation amplitude of the received P-code signals carried by L1(1575.42 MHz) and L2(1227.6 MHz). This equipment has the performance of uncertainty in the measurement of TEC of about 2 X 10(exp 16) electrons/sq m when a 10 dBi gain antenna was used. To increase the measurement performance, an upper version of GTR-2 called GTR-3 is planned which uses the phase information of the continuous signals obtained by making a cross correlation or multiplication of the received L1 and L2 P-code signals. By using the difference of these measured phases values, the ionospheric delay with the ambiguities of the periods of L1+L2 and L1-L2 signals can be estimated.

Simultaneous ground-satellite observations of daytime traveling ionospheric disturbances over Japan using the GPS-TEC network and the CHAMP satellite

NASA Astrophysics Data System (ADS)

Moral, A. C.; Shiokawa, K.; Otsuka, Y.; Liu, H.; Nishioka, M.; Tsugawa, T.

2017-12-01

We report results of simultaneous ground-satellite measurements of daytime travelling ionospheric disturbances (TIDs) over Japan by using the GEONET GPS receiver network and the CHAMP satellite. For the two years of 2002 and 2008, we examined GPS measurements of TEC (Total Electron Content) and neutral and electron densities measured by CHAMP satellite. Total of fifteen TID events with clear southward moving structures in the GPS-TEC measurements are found by simultaneous ground-satellite measurements. On 2002, simultaneous events are only observed in January (1 event) and February (4 events). On 2008, ten events are observed around winter months (January (3 events), February (5), March (1), and October (1)). Neutral and electron densities measured by CHAMP show quasi-periodic fluctuations throughout the passages for all events. The CHAMP satellite crossed at least one clear TID phase front for all the events. We fitted a sinusoidal function to both ground and satellite data to obtain the frequencies and phase of the observed variations. We calculated the corresponding phase relationships between TEC variations and neutral and electron densities measured by CHAMP to categorize the events. In the presentations we report correspondence of these TID structures seen in the simultaneous ground-satellite observations by GPS-TEC and CHAMP, and discuss their phase relationship to identify the source of the daytime TIDs and specify how much of the observed variations are showing clear frequencies/or not in the nature at middle latitudes.

The dynamics and spectral characteristics of the GPS TEC wave packets excited by the solar terminator

NASA Astrophysics Data System (ADS)

Afraimovich, E. L.; Edemsky, I. K.; Voeykov, S. V.; Yasukevich, Y. V.; Zhivetiev, I. V.

2009-04-01

The great variety of solar terminator (ST) -linked phenomena in the atmosphere gave rise to a num¬ber of studies on the analysis of ionosphere parameter variations obtained by different ionosphere sounding methods. Main part of experimental data was obtained using methods for analyzing the spectrum of ionosphere parameter variations in separate local points. To identify ST-generated wave disturbances it is necessary to measure the dynamic and spectral characteristics of the wave disturbances and to compare it with spatial-temporal characteristics of ST. Using TEC measurements from the dense network of GPS sites GEONET (Japan), we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the solar terminator. We use two known forms of the 2D GPS-TEC image for our presentation of the space structure of ST-generated MS TWP: 1) - the diagram "distance-time"; 2) - the 2D-space distribution of the values of filtered TEC series dI (λ, φ, t) on the latitude φ and longitude λ for each 30-sec TEC counts. We found that the time period and wave-length of ST-generated wave packets are about 10-20 min and 200-300 km, respectively. Dynamic images analysis of dI (λ, φ, t) gives precise estimation of velocity and azimuth of TWP wave front propagation. We use the method of determining velocity of traveling ionosphere disturbances (SADM-GPS), which take into account the relative moving of subionosphere points. We found that the velocity of the TWP phase front, traveling along GEONET sites, varies in accordance with the velocity of the ST line displacement. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km. The TWP wave front extends along the ST line with the angular shift of about 20°. The hypothesis on the connection between the TWP generation and the solar terminator can be tested in the terminator local time (TLT) system: dT=TOBS-TST, where ТOBS is the observation time at the given point; TST is the arrival time of ST at the altitude of H over this point. The time delay dT of TWP appearance varies from 2.5 hrs at 30°N to 6 hrs at 45°N. We acknowledge the GEONET scientific group for providing GPS data used in this study. The work was supported by the SB RAS and FEB RAS collaboration project N 3.24, the RFBR-GFEN grant N 06-05-39026 and RFBR grant 07-05-00127.

Ionospheric perturbations due to earthquakes as determined from VLF and GPS-TEC data analysis at Agra, India

NASA Astrophysics Data System (ADS)

Singh, Dhananjali; Singh, Birbal; Pundhir, Devbrat

2018-04-01

Employing SoftPAL receiver, amplitude variations of VLF transmitter signals NWC (19.8 kHz) and NPM (21.4 kHz) are analyzed at Agra station in India (Geograph. lat. 27.2°N, long. 78°E) ±15 days from five major earthquakes of magnitude M = 6.9-8.5 occurred in Indian subcontinent during the years 2011-2013. We apply nighttime fluctuation (NF) method and show that in almost all cases the trend decreases and dispersion and NF increase on the same days corresponding to each earthquake about 11-15 days prior to the main shock. Assuming that the ionospheric perturbations are caused by atmospheric gravity waves (AGW), we also calculate AGW modulation index for each case and find its values increased on the days amplitude fluctuations take place. Its value is decreased in one case only where the perturbations may be attributed to penetration of seismogenic electric field. In order to support the above results we also present GPS-TEC data analyzed by us corresponding to three of the above earthquakes. We study the TEC anomalies (unusual enhancements) and find that in one case the precursory period is almost the same as that found in NF method.

Tsallis non-extensive statistical mechanics in the ionospheric detrended total electron content during quiet and storm periods

NASA Astrophysics Data System (ADS)

Ogunsua, B. O.; Laoye, J. A.

2018-05-01

In this paper, the Tsallis non-extensive q-statistics in ionospheric dynamics was investigated using the total electron content (TEC) obtained from two Global Positioning System (GPS) receiver stations. This investigation was carried out considering the geomagnetically quiet and storm periods. The micro density variation of the ionospheric total electron content was extracted from the TEC data by method of detrending. The detrended total electron content, which represent the variation in the internal dynamics of the system was further analyzed using for non-extensive statistical mechanics using the q-Gaussian methods. Our results reveals that for all the analyzed data sets the Tsallis Gaussian probability distribution (q-Gaussian) with value q > 1 were obtained. It was observed that there is no distinct difference in pattern between the values of qquiet and qstorm. However the values of q varies with geophysical conditions and possibly with local dynamics for the two stations. Also observed are the asymmetric pattern of the q-Gaussian and a highly significant level of correlation for the q-index values obtained for the storm periods compared to the quiet periods between the two GPS receiver stations where the TEC was measured. The factors responsible for this variation can be mostly attributed to the varying mechanisms resulting in the self-reorganization of the system dynamics during the storm periods. The result shows the existence of long range correlation for both quiet and storm periods for the two stations.

ISKANDARnet IOMOS: Near real-time equatorial space weather monitoring and alert system in Peninsular Malaysia

NASA Astrophysics Data System (ADS)

Musa, Tajul Ariffin; Leong, Shien Kwun; Abdullah, Khairul Anuar; Othman, Rusli

2012-11-01

This work proposes ISKANDARnet Ionospheric Outburst MOnitoring and alert System (IOMOS), along with Ionospheric Outburst Index (IOX) to develop an operational near real-time space weather service for Malaysia. The IOMOS is based on Global Positioning System (GPS) Network-based Real-Time Kinematic (NRTK) concept which is by nature for atmospheric (ionosphere and troposphere) modeling within the network coverage. The elegance of this solution lies in the fact that IOMOS utilize differential ionospheric residual from network of GPS baselines which incur no additional cost for operation. Users will be informed about the ionospheric perturbation through Short Message Service (SMS), email or Twitter®. This approach will ultimately beneficial for the navigation and satellite positioning communities, particularly during the coming Solar Cycle 24. In addition, a combination of local and global GPS network has been employed to study the equatorial ionosphere geomorphology and climatology in the Malaysian sector. Equatorial Total Electron Content (TEC) over Malaysia shows semi-annual, annual, and seasonal variations with maximum values appearing during equinoctial months and minimum during solstices months. The TEC value during vernal equinox is about 21% higher than autumnal equinox, and December solstice exceeds that at the June solstice by around 14%. It is also found that semi-annual variation is present at all levels of solar activity, whereas June solstice predominates December solstice during high solar activity for annual and seasonal variations. In near future, a near real-time TEC derivation system will be developed to support equatorial ionosphere modeling to enhance space weather service for Malaysia.

Relative amplitude of medium-scale traveling ionospheric disturbances as deduced from global GPS network

NASA Astrophysics Data System (ADS)

Voeykov, S. V.; Afraimovich, E. L.; Kosogorov, E. A.; Perevalova, N. P.; Zhivetiev, I. V.

We worked out a new method for estimation of relative amplitude dI I of total electron content TEC variations corresponding to medium-scale 30-300 km traveling ionospheric disturbances MS TIDs Daily and latitudinal dependences of dI I and dI I probability distributions are obtained for 52 days of 1999-2005 with different level of geomagnetic activity Statistical estimations were obtained for the analysis of 10 6 series of TEC with 2 3-hour duration To obtain statistically significant results three latitudinal regions were chosen North America high-latitudinal region 50-80 r N 200-300 r E 59 GPS receivers North America mid-latitudinal region 20-50 r N 200-300 r E 817 receivers equatorial belt -20 20 r N 0-360 r E 76 receivers We found that average daily value of the relative amplitude of TEC variations dI I changes from 0 3 to 10 proportionally to the value of geomagnetic index Kp This dependence is strong at high latitudes dI I 0 37 cdot Kp 1 5 and it is some weaker at mid latitudes dI I 0 2 cdot Kp 0 35 At the equator belt we found the weakest dependence dI I on the geomagnetic activity level dI I 0 1 cdot Kp 0 6 The most important and the most interesting result of our work is that during geomagnetic quiet conditions the relative amplitude of TEC variations at night considerably exceeds daily values by 3-5 times at equatorial and at high latitudes and by 2 times at mid latitudes But during strong magnetic storms the relative amplitude dI I at high

Multi-instrument observations of the ionospheric and plasmaspheric density structure

NASA Astrophysics Data System (ADS)

Yizengaw, E.; Moldwin, M. B.

2008-05-01

: The density within the ionosphere and plasmasphere can be monitored using a combination of techniques that use both ground- and space-based instruments. We are combining diagnostic observations of everything, but the kitchen sink. These include observations of GPS TEC, TOPEX and JASON TEC, IMAGE EUV and FUV, GUVI composition data, ULF resonances, and many other multi-satellite data sets such as DMSP in situ observations. The dramatically growing number of GPS receivers on the ground and onboard Low-Earth-Orbit (LEO) satellites offers an excellent opportunity for remote sensing and monitoring of the ionospheric and plasmaspheric density structure using GPS TEC tomographic reconstruction technique. This allows us to clearly quantify magnetosphere-ionosphere (M-I) coupling dynamics, as well as confirm the long-standing conjecture that the mid-latitude trough and plasmapause are on the same field line. This has been demonstrated globally, for the first time, using a combination of data from IMAGE EUV and ground- and space-based GPS receivers. The two dimensional tomographic image of the ionosphere and plasmasphere, using data from the GPS receiver onboard LEO satellites, such as FedSat, CHAMP, COSMIC, etc, also provides a new ability to image the flux tube structure of ionospheric ion outflows, tracking flux tube structure up to 3.17Re (20,200 km) altitude for the first time. The combination of data from the altimeter on JASON and ground-based GPS network also provides an excellent opportunity to experimentally estimate the plasmaspheric density contribution to the ground-based GPS TEC and thus to the degradation of navigation and communication accuracy.

Anomalous Variation in GPS TEC, Land and Ocean Parameters Prior to 3 Earthquakes

NASA Astrophysics Data System (ADS)

Yadav, Kunvar; Karia, Sheetal P.; Pathak, Kamlesh N.

2016-02-01

The present study reports the analysis of GPS TEC prior to 3 earthquakes ( M > 6.0). The earthquakes are: (1) Loyalty Island (22°36'S, 170°54'E) on 19 January 2009 ( M = 6.6), (2) Samoa Island (15°29'S, 172°5'W) on 30 August 2009 ( M = 6.6), and (3) Tohoku (38°19'N, 142°22'E) on 11 March 2011 ( M = 9.0). In an effort to search for a precursory signature we analysed the land and ocean parameters prior to the earthquakes, namely SLHF (Land) and SST (Ocean). The GPS TEC data indicate an anomalous behaviour from 1-13 days prior to earthquakes. The main purpose of this study was to explore and demonstrate the possibility of any changes in TEC, SST, and SLHF before, during and after the earthquakes which occurred near or beneath an ocean. This study may lead to better understanding of response of land, ocean, and ionosphere parameters prior to seismic activities.

A regional ionospheric TEC mapping technique over China and adjacent areas on the basis of data assimilation

NASA Astrophysics Data System (ADS)

Aa, Ercha; Huang, Wengeng; Yu, Shimei; Liu, Siqing; Shi, Liqin; Gong, Jiancun; Chen, Yanhong; Shen, Hua

2015-06-01

In this paper, a regional total electron content (TEC) mapping technique over China and adjacent areas (70°E-140°E and 15°N-55°N) is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service. The regional TEC maps can be generated accordingly with the spatial and temporal resolution being 1°×1° and 5 min, respectively. The accuracy and quality of the TEC mapping technique have been validated through the comparison with GNSS observations, the International Reference Ionosphere model values, the global ionosphere maps from Center for Orbit Determination of Europe, and the Massachusetts Institute of Technology Automated Processing of GPS TEC data from Madrigal database. The verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model, which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric TEC over China and adjacent areas.

Invesion of tsunami height using GPS TEC data. The case of the 2012 Haida Gwaii tsunami and Earthquake.

NASA Astrophysics Data System (ADS)

Rakoto, V.; Lognonne, P. H.; Rolland, L. M.

2015-12-01

Large earthquakes (i.eM>6) and tsunamis associated are responsible for ionospheric perturbations. These perturbations can be observed in the total electron content (TEC) measured from multi- frequency Global Navigation Satellite systems (GNSS) data (e.g GPS). We will focus on the studies of the Haïda Gwaii earthquake and tsunami case. It happened the 28 october 2012 along the Queen Charlotte fault of the Canada Western Coast. First, we compare GPS data of perturbation TEC to our model. We model the TEC perturbation in several steps. (1) First, we compute tsunami normal modes modes in atmosphere in using PREM model with 4.7km of oceanic layer. (2) We sum all the tsunami modes to obtain the neutral displacement. (3) We couple the ionosphere with the neutral atmosphere. (4) We integrate the perturbed electron density along each satellite station line of sight. At last, we present first results of TEC inversion in order to retrieve the waveform of the tsunami. This inversion has been done on synthetics data assuming Queen Charlotte Earthquake and Tsunami can be considered as a point source in far field.

Near-Real Time Monitoring of TEC Over Japan at NICT (RWC Tokyo OF ISES)

NASA Astrophysics Data System (ADS)

Miyake, W.; Jin, H.

2010-05-01

The world wide use of global navigation satellite systems such as GPS offers unique opportunities for a permanent monitoring of the total electron content (TEC) of the ionosphere. We have developed a system of the rapid derivation of TEC from GEONET (a dense GPS receiver network in Japan). In addition to a previous plot of TEC temporal variation over Japan, we have recently developed a near-real-time two-dimensional TEC map and have used it for the daily operation of Space Weather Forecast Center at NICT (Regional Warning Center Tokyo of International Space Environment Service). The TEC map can be used to continuously monitor the ionospheric disturbances over Japan, including spatial and temporal development of ionospheric storms, large-amplitude traveling ionospheric disturbances, and plasma bubbles intruding over Japan, with high time resolution. The development of the real-time monitoring system of TEC enables us to monitor large ionospheric disturbances, ranging from global- to small-scale disturbances, expected in the next solar maximum. The plot and maps are open to the public and are available on http://wdc.nict.go.jp/IONO/index_E.html.

Seismo-ionospheric Precursors in the GPS Total Electron Content of the 16 October 1999 Mw7.1 Hector Mine Earthquake

NASA Astrophysics Data System (ADS)

Tsai, H.; Su, Y.; Liu, J. G.; Chen, S.; Chen, M.

2013-12-01

In this paper, temporal and spatial analyses are employed to detect seismo-ionospheric precursors (SIPs) in the ionospheric total electron content (TEC) during 16 October 1999 Mw7.1 Hector Mine earthquake. To discriminate anomalies caused by global effects, such as solar radiations, magnetic storms, etc., and local effects, such as earthquake, we cross-examine the GPS TECs and their gradients in the eastward and northward directions at epicenter/centers of the Hector Mine area and the other two reference areas at similar magnetic latitudes in Europe and Japan. Temporal variations of the northward TEC gradient suggest SIPs most likely appearing day 6-5 before the earthquake. A global search by using the TEC of GIM (global ionosphere map) shows that the TEC increase and decrease anomalies continuously and specifically appear around the epicenter day 5 before the earthquake.

Regional And Seasonal Aspects Of Within-The-Hour Tec Statistics

NASA Astrophysics Data System (ADS)

Koroglu, Ozan; Arikan, Feza; Koroglu, Meltem

2015-04-01

Ionosphere is one of the atmosphere layers which has a plasma structure. Several mechanisms originating from both space and earth itself governs this plasma layer such as solar radiation and geomagnetic effects. Ionosphere plays important role for HF and satellite communication, and space based positioning systems. Therefore, the determination of statistical behavior of ionosphere has utmost importance. The variability of the ionosphere has complex spatio-temporal characteristics, which depends on solar, geomagnetic, gravitational and seismic activities. Total Electron Content (TEC) is one of the major observables for investigating and determining this variability. In this study, spatio-temporal within-the-hour statistical behavior of TEC is determined for Turkey, which is located in mid-latitude, using the TEC estimates from Turkish National Permanent GPS Network (TNPGN)-Active between the years 2009 and 2012. TEC estimates are obtained as IONOLAB-TEC which is developed by IONOLAB group (www.ionolab.org) from Hacettepe University. IONOLAB-TEC for each station in TNPGN-Active is organized in a database and grouped with respect to years, ionospheric seasons, hours and regions 2 degree by 3 degree, in latitude and longitude, respectively. The data sets are used to calculate within-the-hour parametric Probability Density Functions (PDF). For every year, every region and every hour, a representative PDF is determined. It is observed that TEC values have a strong hourly, seasonal and positional dependence on east-west direction, and the growing trend shifts according to sunrise and sunset times. It is observed that the data are distributed predominantly as Lognormal and Weibull. The averages and standard deviations of the chosen distributions follow the trends in 24 hour diurnal and 11 year solar cycle periods. The regional and seasonal behavior of PDFs are investigated using a representative GPS station within each region. Within-the-hour PDF estimates are grouped into ionospheric seasons as Winter, Summer, March equinox and September equinox. In winter and summer seasons, Lognormal distribution is observed. During equinox seasons, Weibull distribution is observed more frequently. Furthermore, all hourly TEC values in same region are combined in order to improve the reliability and accuracy of the probability density function estimates. It is observed that as being in mid-latitude region, the ionosphere over Turkey has robust characteristics that are distributed as Lognormal and Weibull. Statistical observations on PDF estimates of TEC of the ionosphere over Turkey will contribute to developing a regional and seasonal random field model, which will further contribute to HF channel characterization. This study is supported by a joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

Global Positioning System Total Electron Content Variation over King Sejong Station in Antarctic under the Solar Minimum Condition Between 2005 and 2009

NASA Astrophysics Data System (ADS)

Chung, Jong-Kyun; Jee, Geonhwa; Lee, Chi-Na

2011-12-01

The total electron content (TEC) using global positioning system (GPS) is analyzed to see the characteristics of ionosphere over King Sejong station (KSJ, geographic latitude 62°13' S, longitude 58° 47' W, corrected geomagnetic latitude 48° S) in Antarctic. The GPS operational ratio during the observational period between 2005 and 2009 is 90.1%. The annual variation of the daily mean TEC decreases from January 2005 to February 2009, but increase from the June 2009. In summer (December-February), the seasonal mean TEC values have the maximum of 26.2 ± 2.4 TEC unit (TECU) in 2005 and the minimum of 16.5 ± 2.8 TECU in 2009, and the annual differences decrease from 3.0 TECU (2005-2006) to 1.4 TECU (2008-2009). However, on November 2010, it significantly increases to 22.3 ± 2.8 TECU which is up to 5.8 TECU compared with 2009 in summer. In winter (June-August), the seasonal mean TEC slightly decreases from 13.7 ± 4.5 TECU in 2005 to 8.9 ± 0.6 TECU in 2008, and the a! nnual difference is constantly about 1.6 TECU, and increases to 10.3 ± 1.8 TECU in 2009. The annual variations of diurnal amplitude show the seasonal features that are scattered in summer and the enhancements near equinoxes are apparent in the whole years. In contrast, the semidiurnal amplitudes show the disturbed annual peaks in winter and its enhancements near equinoxes are unapparent. The diurnal phases are not constant in winter and show near 12 local time (LT). The semidiurnal phases have a seasonal pattern between 00 LT and 06 LT. Consequently, the KSJ GPS TEC variations show the significant semidiurnal variation in summer from December to February under the solar minimum between 2005 and 2009. The feature is considered as the Weddell Sea anomaly of larger nighttime electron density than a daytime electron density that has been observed around the Antarctica peninsula.

A two-step ionospheric modeling algorithm considering the impact of GLONASS pseudo-range inter-channel biases

NASA Astrophysics Data System (ADS)

Zhang, Rui; Yao, Yi-bin; Hu, Yue-ming; Song, Wei-wei

2017-12-01

The Global Navigation Satellite System presents a plausible and cost-effective way of computing the total electron content (TEC). But TEC estimated value could be seriously affected by the differential code biases (DCB) of frequency-dependent satellites and receivers. Unlike GPS and other satellite systems, GLONASS adopts a frequency-division multiplexing access mode to distinguish different satellites. This strategy leads to different wavelengths and inter-frequency biases (IFBs) for both pseudo-range and carrier phase observations, whose impacts are rarely considered in ionospheric modeling. We obtained observations from four groups of co-stations to analyze the characteristics of the GLONASS receiver P1P2 pseudo-range IFB with a double-difference method. The results showed that the GLONASS P1P2 pseudo-range IFB remained stable for a period of time and could catch up to several meters, which cannot be absorbed by the receiver DCB during ionospheric modeling. Given the characteristics of the GLONASS P1P2 pseudo-range IFB, we proposed a two-step ionosphere modeling method with the priori IFB information. The experimental analysis showed that the new algorithm can effectively eliminate the adverse effects on ionospheric model and hardware delay parameters estimation in different space environments. During high solar activity period, compared to the traditional GPS + GLONASS modeling algorithm, the absolute average deviation of TEC decreased from 2.17 to 2.07 TECu (TEC unit); simultaneously, the average RMS of GPS satellite DCB decreased from 0.225 to 0.219 ns, and the average deviation of GLONASS satellite DCB decreased from 0.253 to 0.113 ns with a great improvement in over 55%.

Mobile Devices and GPU Parallelism in Ionospheric Data Processing

NASA Astrophysics Data System (ADS)

Mascharka, D.; Pankratius, V.

2015-12-01

Scientific data acquisition in the field is often constrained by data transfer backchannels to analysis environments. Geoscientists are therefore facing practical bottlenecks with increasing sensor density and variety. Mobile devices, such as smartphones and tablets, offer promising solutions to key problems in scientific data acquisition, pre-processing, and validation by providing advanced capabilities in the field. This is due to affordable network connectivity options and the increasing mobile computational power. This contribution exemplifies a scenario faced by scientists in the field and presents the "Mahali TEC Processing App" developed in the context of the NSF-funded Mahali project. Aimed at atmospheric science and the study of ionospheric Total Electron Content (TEC), this app is able to gather data from various dual-frequency GPS receivers. It demonstrates parsing of full-day RINEX files on mobile devices and on-the-fly computation of vertical TEC values based on satellite ephemeris models that are obtained from NASA. Our experiments show how parallel computing on the mobile device GPU enables fast processing and visualization of up to 2 million datapoints in real-time using OpenGL. GPS receiver bias is estimated through minimum TEC approximations that can be interactively adjusted by scientists in the graphical user interface. Scientists can also perform approximate computations for "quickviews" to reduce CPU processing time and memory consumption. In the final stage of our mobile processing pipeline, scientists can upload data to the cloud for further processing. Acknowledgements: The Mahali project (http://mahali.mit.edu) is funded by the NSF INSPIRE grant no. AGS-1343967 (PI: V. Pankratius). We would like to acknowledge our collaborators at Boston College, Virginia Tech, Johns Hopkins University, Colorado State University, as well as the support of UNAVCO for loans of dual-frequency GPS receivers for use in this project, and Intel for loans of smartphones.

Characteristics of equatorial ionization anomaly (EIA) in relation to transionospheric satellite links around the northern crest in the Indian longitude sector

NASA Astrophysics Data System (ADS)

Das, A.; Paul, K. S.; Halder, S.; Basu, K.; Paul, A.

2014-02-01

The poleward gradient of the equatorial ionization anomaly (EIA) introduces more intense propagation effects on transionospheric satellite links in comparison to the equatorward gradient. Characterization of the poleward gradient was performed during March-April, August-October 2011 and March-April 2012 using GPS total electron content (TEC) recorded from a chain of stations located more or less along the same meridian (88.5° E) at Calcutta, Baharampore, Farakka and Siliguri. The poleward gradients calculated on magnetically quiet days at elevation in excess of 50° at 14:00, 15:00 and 16:00 LT were found to have a strong correlation with GPS S4 observed from Calcutta during post-sunset-to-midnight hours. A threshold value of poleward TEC gradient is calculated above which there is a probability of scintillation at Calcutta with S4 ≥ 0.4.

Application of Geostationary GNSS and SBAS Satellites for Studying Ionospheric TEC Disturbances of Geomagnetic and Meteorological Origin

NASA Astrophysics Data System (ADS)

Padokhin, A. M.; Kurbatov, G. A.; Yasyukevich, Y.; Yasyukevich, A.

2017-12-01

With the development of GNSS and SBAS constellations, the coherent multi-frequency L band transmissions are now available from a number of geostationary satellites. These signals can be used for ionospheric TEC estimations in the same way as widely used GPS/GLONASS signals. In this work, we compare noise patterns in TEC estimations based on different geostationary satellites data: augmentation systems (Indian GAGAN, European EGNOS and American WAAS), and Chinese COMPASS/Beidou navigation system. We show that noise level in geostationary COMPASS/Beidou TEC estimations is times smaller than noise in SBAS TEC estimation and corresponds to those of GPS/GLONASS at the same elevation angles. We discuss the capabilities of geostationary TEC data for studying ionospheric variability driven by space weather and meteorological sources at different time scales. Analyzing data from IGS/MGEX receivers we present geostationary TEC response on X-class Solar flares of current cycle, moderate and strong geomagnetic storms, including G4 St. Patrick's day Storm 2015 and recent G3 storm of the end of May 2017. We also discuss geostationary TEC disturbances in near equatorial ionosphere caused by two SSW events (minor and major final warming of 2015-2016 winter season) as well as geostationary TEC response on typhoons activity near Taiwan in autumn 2016. Our results show large potential of geostationary TEC estimations with GNSS and SBAS signals for continuous ionospheric monitoring.

Quantitative Evaluation of Ionosphere Models for Reproducing Regional TEC During Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Shim, J. S.; Kuznetsova, M.; Rastaetter, L.; Bilitza, D.; Codrescu, M.; Coster, A. J.; Emery, B.; Foster, B.; Fuller-Rowell, T. J.; Goncharenko, L. P.; Huba, J.; Mitchell, C. N.; Ridley, A. J.; Fedrizzi, M.; Scherliess, L.; Schunk, R. W.; Sojka, J. J.; Zhu, L.

2015-12-01

TEC (Total Electron Content) is one of the key parameters in description of the ionospheric variability that has influence on the accuracy of navigation and communication systems. To assess current TEC modeling capability of ionospheric models during geomagnetic storms and to establish a baseline against which future improvement can be compared, we quantified the ionospheric models' performance by comparing modeled vertical TEC values with ground-based GPS TEC measurements and Multi-Instrument Data Analysis System (MIDAS) TEC. The comparison focused on North America and Europe sectors during selected two storm events: 2006 AGU storm (14-15 Dec. 2006) and 2013 March storm (17-19 Mar. 2013). The ionospheric models used for this study range from empirical to physics-based, and physics-based data assimilation models. We investigated spatial and temporal variations of TEC during the storms. In addition, we considered several parameters to quantify storm impacts on TEC: TEC changes compared to quiet time, rate of TEC change, and maximum increase/decrease during the storms. In this presentation, we focus on preliminary results of the comparison of the models performance in reproducing the storm-time TEC variations using the parameters and skill scores. This study has been supported by the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center. Model outputs and observational data used for the study will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) for the space science communities to use.

Derivation of GPS TEC and receiver bias for Langkawi station in Malaysia

NASA Astrophysics Data System (ADS)

Teh, W. L.; Chen, W. S.; Abdullah, M.

2017-05-01

This paper presents the polynomial-type TEC model to derive total electron content (TEC) and receiver bias for Langkawi (LGKW) station in Malaysia at geographic latitude of 6.32° and longitude of 99.85°. The model uses a polynomial function of coordinates of the ionospheric piercing point to describe the TEC distribution in space. In the model, six polynomial coefficients and a receiver bias are unknown which can be solved by the least squares method. A reasonable agreement is achieved for the derivation of TEC and receiver bias for IENG station in Italy, as compared with that derived by the IGS analysis center, CODE. We process one year of LGKW data in 2010 and show the monthly receiver bias and the seasonal TEC variation. The monthly receiver bias varies between -48 and -24 TECu (1016 electrons/m2), with the mean value at -37 TECu. Large variations happen in the monthly receiver biases due to the low data coverage of high satellite elevation angle (60° < α ≤ 90°). Post-processing TEC approach is implemented which can resolve the wavy pattern of the monthly TEC baseline resulted from the large variation of the receiver bias. The seasonal TEC variation at LGKW exhibits a semi-annual variation, where the peak occurs during equinoctial months, and the trough during summer and winter months.

Assessment of Modeling Capability for Reproducing Storm Impacts on TEC

NASA Astrophysics Data System (ADS)

Shim, J. S.; Kuznetsova, M. M.; Rastaetter, L.; Bilitza, D.; Codrescu, M.; Coster, A. J.; Emery, B. A.; Foerster, M.; Foster, B.; Fuller-Rowell, T. J.; Huba, J. D.; Goncharenko, L. P.; Mannucci, A. J.; Namgaladze, A. A.; Pi, X.; Prokhorov, B. E.; Ridley, A. J.; Scherliess, L.; Schunk, R. W.; Sojka, J. J.; Zhu, L.

2014-12-01

During geomagnetic storm, the energy transfer from solar wind to magnetosphere-ionosphere system adversely affects the communication and navigation systems. Quantifying storm impacts on TEC (Total Electron Content) and assessment of modeling capability of reproducing storm impacts on TEC are of importance to specifying and forecasting space weather. In order to quantify storm impacts on TEC, we considered several parameters: TEC changes compared to quiet time (the day before storm), TEC difference between 24-hour intervals, and maximum increase/decrease during the storm. We investigated the spatial and temporal variations of the parameters during the 2006 AGU storm event (14-15 Dec. 2006) using ground-based GPS TEC measurements in the selected 5 degree eight longitude sectors. The latitudinal variations were also studied in two longitude sectors among the eight sectors where data coverage is relatively better. We obtained modeled TEC from various ionosphere/thermosphere (IT) models. The parameters from the models were compared with each other and with the observed values. We quantified performance of the models in reproducing the TEC variations during the storm using skill scores. This study has been supported by the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center. Model outputs and observational data used for the study will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) for the space science communities to use.

Monitoring Shuttle Burns and Rocket Launches with GPS

NASA Astrophysics Data System (ADS)

Coster, A. J.; Bhatt, A.; O'Hanlon, B.; Rideout, W.

2009-12-01

We report on different GPS analysis techniques that can be used to examine the effects of rocket exhaust on the upper atmosphere. GPS observations of artificially produced electron density holes created by chemical releases from Space Shuttle Orbital Maneuvering System (OMS) engine burns will be discussed. The percentage drop in total electron content (TEC) and the temporal and spatial scales observed in the electron density hole for different Shuttle burn experiments will be compared. We will also report on observations of TEC depletions associated with Titan rocket launches on 8 April 2003 and on 19 October 2005. Finally we will discuss the use of GPS measurements of precipitable water vapor from time periods before, during, and after Shuttle burns.

Handling cycle slips in GPS data during ionospheric plasma bubble events

NASA Astrophysics Data System (ADS)

Banville, S.; Langley, R. B.; Saito, S.; Yoshihara, T.

2010-12-01

During disturbed ionospheric conditions such as the occurrence of plasma bubbles, the phase and amplitude of the electromagnetic waves transmitted by GPS satellites undergo rapid fluctuations called scintillation. When this phenomenon is observed, GPS receivers are more prone to signal tracking interruptions, which prevent continuous measurement of the total electron content (TEC) between a satellite and the receiver. In order to improve TEC monitoring, a study was conducted with the goal of reducing the effects of signal tracking interruptions by correcting for "cycle slips," an integer number of carrier wavelengths not measured by the receiver during a loss of signal lock. In this paper, we review existing cycle-slip correction methods, showing that the characteristics associated with ionospheric plasma bubbles (rapid ionospheric delay fluctuations, data gaps, increased noise, etc.) prevent reliable correction of cycle slips. Then, a reformulation of the "geometry-free" model conventionally used for ionospheric studies with GPS is presented. Geometric information is used to obtain single-frequency estimates of TEC variations during momentary L2 signal interruptions, which also provides instantaneous cycle-slip correction capabilities. The performance of this approach is assessed using data collected on Okinawa Island in Japan during a plasma bubble event that occurred on 23 March 2004. While an improvement in the continuity of TEC time series is obtained, we question the reliability of any cycle-slip correction technique when discontinuities on both GPS legacy frequencies occur simultaneously for more than a few seconds.

Longitudinal dependence of the seasonal variations of the topside ionospheric and plasmaspheric electron content: observations and model results

NASA Astrophysics Data System (ADS)

Zhang, Man-Lian; Liu, Libo; Ning, Baiqi; Wan, Weixing

2016-07-01

Radio signals transmitted from GPS satellite going through the ionization zone above the Earth will be refracted by the ionized components in the ionosphere and the plasmasphere, which would produce additional transfer delay and generate extra errors in satellite navigation and positioning, etc. These errors have strong relation with the total electron content (TEC) along the signal's travelling path. Therefore TEC is one of the most important parameters required by many users for different modern usage purposes. The topside ionospheric and plasmaspheric electron content makes a large contribution to TEC. In the present study, data for the year 2008 of the topside ionospheric and plasmaspheric electron content (PEC) between the height of 800-20200km above the Earth derived from the upward-looking TEC measurements of the precise orbit determination antenna on board the COSMIC low Earth orbit (LEO) satellites to the GPS signals are used to study the longitudinal dependence of the seasonal variations of PEC. A comparison study of the observed PEC with the IZMIRAN_Plas model results is also made. Our study showed that PEC shows different seasonal variations at different longitudinal sectors: for the 240°E-60°E longitudinal sector, PEC shows a strong annual variation with lowest value in the June solstice and highest value in the December solstice months; In contrast, very weak seasonal variations are observed for PEC at 60°E-240°E longitudinal sector; Comparison study showed that this longitudinal dependence feature of the observed PEC's seasonal variation is not well captured by the IZMIRAN_Plas model result. Acknowledgments This research was supported by the National Natural Science Foundation of China (NSFC No. 41274163)

The influence of grounding on GPS receiver differential code biases

NASA Astrophysics Data System (ADS)

Choi, Byung-Kyu; Lee, Sang Jeong

2018-07-01

The Global Positioning System (GPS) has become an effective tool for estimating ionospheric total electron content (TEC). One of the critical factors affecting ionospheric TEC estimation from GPS data is the differential code biases (DCBs) inherent in both GPS receivers and satellites. To investigate the factor that affects the receiver DCB, we consider the relationship between the receiver DCB and the grounding of an antenna. GPS data from 9 stations in South Korea from three periods (the years 2009, 2014, and 2017) were used in the analysis. It was found that a significant jump (∼8-13 ns, or ∼ 23-37 TECU) in hourly DCB time series occurred simultaneously at the two different sites when an antenna is changed from a grounded to the non-grounded state. Thus, our study clearly identifies that the grounding of GPS equipment is a factor of the receiver DCB changes.

Short Term Single Station GNSS TEC Prediction Using Radial Basis Function Neural Network

NASA Astrophysics Data System (ADS)

Muslim, Buldan; Husin, Asnawi; Efendy, Joni

2018-04-01

TEC prediction models for 24 hours ahead have been developed from JOG2 GPS TEC data during 2016. Eleven month of TEC data were used as a training model of the radial basis function neural network (RBFNN) and 1 month of last data (December 2016) is used for the RBFNN model testing. The RBFNN inputs are the previous 24 hour TEC data and the minimum of Dst index during the previous 24 hours. Outputs of the model are 24 ahead TEC prediction. Comparison of model prediction show that the RBFNN model is able to predict the next 24 hours TEC is more accurate than the TEC GIM model.

Seasonal variations of the ionospheric total electron content in Asian equatorial anomaly regions

NASA Astrophysics Data System (ADS)

Tsai, Ho-Fang; Liu, Jann-Yenq; Tsai, Wei-Hsiung; Liu, Chao-Han; Tseng, Ching-Liang; Wu, Chin-Chun

2001-12-01

The ionospheric total electron contents (TEC) in both northern and southern equatorial anomaly regions are examined by using the Global Positioning System (GPS) in Asian area. The TEC contour charts obtained at YMSM (25.2°N, 121.6°E 14.0°N geomagnetic) and DGAR (7.3°S, 72.4°E 16.2°S geomagnetic) stations in 1997, solar minimum, are investigated. It is found that the ionospheric crests manifest remarkable seasonal variations. The TEC values on both northern and southern equatorial anomaly crests yield their maximum values during the vernal and autumnal months, but the winter anomaly does not appear in the southern region. Results show that both crests are fully developed around midday in winter, postnoon in equinoxes and late afternoon in summer, and the two crests move significantly equatorward in winter but slightly poleward in summer and autumn. These phenomena can be fully explained by a combined theory of the transequatorial neutral wind, the subsolar point, and the auroral equatorward wind.

USC/JPL GAIM: A Real-Time Global Ionospheric Data Assimilation Model

NASA Astrophysics Data System (ADS)

Mandrake, L.; Wilson, B. D.; Hajj, G.; Wang, C.; Pi, X. `; Iijima, B.

2004-12-01

We are in the midst of a revolution in ionospheric remote sensing driven by the illuminating powers of ground and space-based GPS receivers, new UV remote sensing satellites, and the advent of data assimilation techniques for space weather. The University of Southern Califronia (USC) and the Jet Propulsion Laboratory (JPL) have jointly developed a Global Assimilative Ionospheric Model (GAIM) to monitor space weather, study storm effects, and provide ionospheric calibration for DoD customers and NASA flight projects. GAIM is a physics-based 3D data assimilation model that uses both 4DVAR and Kalman filter techniques to solve for the ion & electron density state and key drivers such as equatorial electrodynamics, neutral winds, and production terms. GAIM accepts as input ground GPS TEC data from 900+ sites, occultation links from CHAMP, SAC-C, IOX, and the coming COSMIC constellation, UV limb and nadir scans from the TIMED and DMSP satellites, and in situ data from a variety of satellites (C/NOFS & DMSP). GAIM can ingest multiple data sources in real time, updates the 3D electron density grid every 5 minutes, and solves for improved drivers every 1-2 hours. GAIM density retrievals have been validated by comparisons to vertical TEC measurements from TOPEX & JASON, slant TEC measurements from independent GPS sites, density profiles from ionosondes & incoherent scatter radars, and alternative tomographic retrievals. Daily USC/JPL GAIM runs have been operational since March 2003 using 100-200 ground GPS sites as input and TOPEX/JASON and ionosondes for daily validation. A prototype real-time GAIM system has been running since May 2004. RT GAIM ingests TEC data from 77+ streaming GPS sites every 5 minutes, adds more TEC for better global coverage every hour from hourly GPS sites, and updates the ionospheric state every 5 minutes using the Kalman filter. We plan to add TEC links from COSMIC occultations and UV radiance data from the DMSP satellites, when they become available, to the daily and RT GAIM runs. Our presentation will include results from numerous validation case studies and one year of JASON validation statistics. Customers are currently evaluating the accuracy of USC/JPL GAIM "nowcasts" for ray tracing applications and trans-ionospheric path delay calibration.

Investigation of the TEC Changes in the vicinity of the Earthquake Preparation Zone

NASA Astrophysics Data System (ADS)

Ulukavak, Mustafa; Yalcinkaya, Mualla

2016-04-01

Recently, investigation of the anomalies in the ionosphere before the earthquake has taken too much attention. The Total Electron Content (TEC) data has been used to monitor the changes in the ionosphere. Hence, researchers use the TEC changes before the strong earthquakes to monitor the anomalies in the ionosphere. In this study, the GPS-TEC variations, obtained from the GNSS stations in the vicinity of the earthquake preparation zone, was investigated. Nidra earthquake (M6.5), which was occurred on the north-west of Greece on November 17th, 2015 (38.755°N, 20.552°E), was selected for this study. First, the equation proposed by Dobrovolsky et al. (1979) was used to calculate the radius of the earthquake preparation zone. International GNSS Service (IGS) stations in the region were classified with respect to the radius of the earthquake preparation zone. The observation data of each station was obtained from the Crustal Dynamics Data and Information System (CDDIS) archive to estimate GPS-TEC variations between 16 October 2015 and 16 December 2015. Global Ionosphere Maps (GIM) products, obtained from the IGS, was used to check the robustness of the GPS-TEC variations. Possible anomalies were analyzed for each GNSS station by using the 15-day moving median method. In order to analyze these pre-earthquake ionospheric anomalies, we investigated three indices (Kp, F10.7 and Dst) related to the space weather conditions between 16 October 2015 and 16 December 2015. Solar and geomagnetic indices were obtained from The Oceanic and Atmospheric Administration (NOAA), The Canadian Space Weather Forecast Centre (CSWFC), and the Data Analysis Center for Geomagnetism and Space Magnetism Graduate School of Science, Kyoto University (WDC). This study aims at investigating the possible effects of the earthquake on the TEC variations.

Detection of the Equatorial Ionospheric Irregularities Using the POD GPS Measurements

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Astafyeva, E.; Cherniak, I.

2015-12-01

By making use of GPS measurements from Precise Orbit Determination (POD) GPS antenna onboard Low Earth Orbit (LEO) satellites we present results of the equatorial irregularities/plasma bubbles detection. For a given research we use data from a multi-satellite constellation consisting of the three Swarm satellites and the TerraSAR-X satellite. The major advantage of such LEO constellation is rather similar orbit altitude of ~500 km. The GPS-based indices, characterizing the occurrence and the strength of the ionospheric irregularities, were derived from the LEO GPS observations of a zenith-looking onboard GPS antenna. To study GPS fluctuation activity at the topside equatorial ionosphere we used TEC-based indices ROT (rate of TEC change) and ROTI (rate of TEC Index), proposed by Pi et al. (1997). We demonstrate a successful implementation of this technique for several case studies of the equatorial plasma bubbles occurrence in the post-midnight and morning LT hours during the year 2014. The ionospheric irregularities detected with GPS technique in Swarm/TerrasSAR-X data are consistent with the in situ plasma density variations registered by the three Swarm satellites (PLP measurements), as well as by three DMSP satellites at ~840 km orbital height, which indicate a large altitudinal extent of the observed phenomenon. Also we analyzed the global/seasonal distribution of the ionospheric irregularities at the topside equatorial region caused the phase fluctuations in GPS measurements onboard LEO satellite. We demonstrate that ROT/ROTI technique can be applied to LEO GPS data for geomagnetically quiet and disturbed conditions, as well as detection of the storm-induced equatorial irregularities in the morning local time.

Ionospheric corrections to precise time transfer using GPS

NASA Technical Reports Server (NTRS)

Snow, Robert W.; Osborne, Allen W., III; Klobuchar, John A.; Doherty, Patricia H.

1994-01-01

The free electrons in the earth's ionosphere can retard the time of reception of GPS signals received at a ground station, compared to their time in free space, by many tens of nanoseconds, thus limiting the accuracy of time transfer by GPS. The amount of the ionospheric time delay is proportional to the total number of electrons encountered by the wave on its path from each GPS satellite to a receiver. This integrated number of electrons is called Total Electron Content, or TEC. Dual frequency GPS receivers designed by Allen Osborne Associates, Inc. (AOA) directly measure both the ionospheric differential group delay and the differential carrier phase advance for the two GPS frequencies and derive from this the TEC between the receiver and each GPS satellite in track. The group delay information is mainly used to provide an absolute calibration to the relative differential carrier phase, which is an extremely precise measure of relative TEC. The AOA Mini-Rogue ICS-4Z and the AOA TurboRogue ICS-4000Z receivers normally operate using the GPS P code, when available, and switch to cross-correlation signal processing when the GPS satellites are in the Anti-Spoofing (A-S) mode and the P code is encrypted. An AOA ICS-Z receiver has been operated continuously for over a year at Hanscom AFB, MA to determine the statistics of the variability of the TEC parameter using signals from up to four different directions simultaneously. The 4-channel ICS-4Z and the 8-channel ICS-4000Z, have proven capabilities to make precise, well calibrated, measurements of the ionosphere in several directions simultaneously. In addition to providing ionospheric corrections for precise time transfer via satellite, this dual frequency design allows full code and automatic codeless operation of both the differential group delay and differential carrier phase for numerous ionospheric experiments being conducted. Statistical results of the data collected from the ICS-4Z during the initial year of ionospheric time delay in the northeastern U.S., and initial results with the ICS-4000Z, will be presented.

The mapping of ionospheric TEC for central Russian and European regions on the base of GPS and GLONASS measurements

NASA Astrophysics Data System (ADS)

Shagimuratov, Irk; Cherniak, Iurii; Zakharenkova, Irina; Ephishov, Ivan; Krankowski, Andrzej; Radievsky, Alexander

2014-05-01

The total electron content (TEC) is a key parameter not only for space radio communication but also for addressing the fundamental problems of the ionosphere physics and near Earth space. Currently, the main sources of information on the TEC in the global scale are GNSS signals measurements. The spatial-temporal behavior of the ionosphere can be most effectively analyzed using TEC maps. To date, global IGS global ionospheric maps with a resolution of 2.5 degree in latitude and 5 in longitude and a time resolution of 2 h are most widely used. To study the detailed structure of the ionospheric gradients and rapid process as well as for precise positioning task it is necessary to use more precise regional TEC maps. The Regional TEC maps are currently constructed by different research groups for different regions: USA, Europe, Japan etc. The West Department of IZMIRAN research group is a one in Russia who works on the task of regional ionosphere mapping since 2000. It was developed the methodology for obtaining information on the spatial TEC distribution, TEC maps of the ionosphere on the basis of the algorithm for multi-station processing of GNSS observations. Using a set of algorithms and programs, regional TEC maps with a spatial resolution of 1° and a time resolution up to 15 min can be produced. Here is developed the approach to establish the regular online internet service for regional ionosphere mapping of the Western Russia and Eastern Europe. Nowadays the development of GLONASS navigation system is completely finished and it consists of a constellation of more than 24 satellites. It is good perspective for investigations of the ionosphere structure and dynamics on the base of the simultaneous observations of GPS and GLONASS systems. The GLONASS satellites have the inclination about 64 degrees as against GPS satellites with 56. So the GLONASS provides opportunity to study the high latitude ionosphere. The different scale electron density irregularities, presented in high latitude ionosphere, can complicate phase ambiguity resolution. As known the strong gradients are observed in polar ionosphere near equator and polar walls of the main ionospheric trough. At high latitudes GLONASS satellites are observed on higher elevations that decrease the influence of horizontal ionospheric gradients and as consequence enable represent with more true Total Electron Content over individual high latitude station. In the report we discuss the features determining TEC from GLONASS observations and demonstrate its advantages for the high latitude ionosphere's studies. A comparison with TEC measurements from GPS/GLONASS for quiet and disturbed geomagnetic conditions is also presented. This work is supported by RFBR grant 14-07-00512.

Improvement of Klobuchar model for GNSS single-frequency ionospheric delay corrections

NASA Astrophysics Data System (ADS)

Wang, Ningbo; Yuan, Yunbin; Li, Zishen; Huo, Xingliang

2016-04-01

Broadcast ionospheric model is currently an effective approach to mitigate the ionospheric time delay for real-time Global Navigation Satellite System (GNSS) single-frequency users. Klobuchar coefficients transmitted in Global Positioning System (GPS) navigation message have been widely used in various GNSS positioning and navigation applications; however, this model can only reduce the ionospheric error by approximately 50% in mid-latitudes. With the emerging BeiDou and Galileo, as well as the modernization of GPS and GLONASS, more precise ionospheric correction models or algorithms are required by GNSS single-frequency users. Numerical analysis of the initial phase and nighttime term in Klobuchar algorithm demonstrates that more parameters should be introduced to better describe the variation of nighttime ionospheric total electron content (TEC). In view of this, several schemes are proposed for the improvement of Klobuchar algorithm. Performance of these improved Klobuchar-like models are validated over the continental and oceanic regions during high (2002) and low (2006) levels of solar activities, respectively. Over the continental region, GPS TEC generated from 35 International GNSS Service (IGS) and the Crust Movement Observation Network of China (CMONOC) stations are used as references. Over the oceanic region, TEC data from TOPEX/Poseidon and JASON-1 altimeters are used for comparison. A ten-parameter Klobuchar-like model, which describes the nighttime term as a linear function of geomagnetic latitude, is finally proposed for GNSS single-frequency ionospheric corrections. Compared to GPS TEC, while GPS broadcast model can correct for 55.0% and 49.5% of the ionospheric delay for the year 2002 and 2006, respectively, the proposed ten-parameter Klobuchar-like model can reduce the ionospheric error by 68.4% and 64.7% for the same period. Compared to TOPEX/Poseidon and JASON-1 TEC, the improved ten-parameter Klobuchar-like model can mitigate the ionospheric delay by 61.1% and 64.3% in 2002 and 2006, respectively.

Study of ionospheric disturbances over the China mid- and low-latitude region with GPS observations

NASA Astrophysics Data System (ADS)

Ning, Yafei; Tang, Jun

2018-01-01

Ionospheric disturbances constitute the main restriction factor for precise positioning techniques based on global positioning system (GPS) measurements. Simultaneously, GPS observations are widely used to determine ionospheric disturbances with total electron content (TEC). In this paper, we present an analysis of ionospheric disturbances over China mid- and low-latitude area before and during the magnetic storm on 17 March 2015. The work analyses the variation of magnetic indices, the amplitude of ionospheric irregularities observed with four arrays of GPS stations and the influence of geomagnetic storm on GPS positioning. The results show that significant ionospheric TEC disturbances occurred between 10:30 and 12:00 UT during the main phase of the large storm, and the static position reliability for this period are little affected by these disturbances. It is observed that the positive and negative disturbances propagate southward along the meridian from mid-latitude to low-latitude regions. The propagation velocity is from about 200 to 700 m s-1 and the amplitude of ionospheric disturbances is from about 0.2 to 0.9 TECU min-1. Moreover, the position dilution of precession (PDOP) with static precise point positioning (PPP) on storm and quiet days is 1.8 and 0.9 cm, respectively. This study is based on the analysis of ionospheric variability with differential rate of vertical TEC (DROVT) and impact of ionospheric storm on positioning with technique of GPS PPP.

Investigations of the Nature and Behavior of Plasma-Density Disturbances That May Impact GPS and Other Transionospheric Systems

DTIC Science & Technology

2002-10-31

association with the High-frequency Active Auroral Research Program ( HAARP ). In addition to a classic riometer and a GPS Total Electron Content (TEC...sensor previously operating at the HAARP site, NWRA also operates a set of Transit receivers for measurements of TEC and scintillation at VHF and UHF...supplementing the receiver at HAARP with a receiver north of the site and an additional receiver installed south of the HAARP site.

Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Multi-Instrument Space-Borne and Ground Observations. Preliminary Results

NASA Technical Reports Server (NTRS)

Ouzounov, Dimitar; Pulinets, Sergey; Romanov, Alexey; Romanov, Alexander; Tsbulya, Konstantin; Davidenko, Dmitri; Kafatos, Menas; Taylor, Patrick

2011-01-01

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. Data include outgoing long wave radiation (OLR), GPS/TEC, Low-Earth orbit ionospheric tomography and critical frequency foF2. Our first results show that on March 8th 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 on this day in the lower ionospheric there was also confirmed an abnormal TEC variation over the epicenter. From March 3-11 a large increase in electron concentration was recorded at all four Japanese ground based ionosondes, which returned to normal after the main earthquake The joined 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.

Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary Results

NASA Technical Reports Server (NTRS)

Ouzounov, Dimitar; Pulinets, Sergey; Romanov, Alexey; Tsybulya, Konstantin; Davidenko, Dimitri; Kafatos, Menas; Taylor, Patrick

2011-01-01

The recent M9 Tohoku Japan earthquake of March 11, 2011 was the largest recorded earthquake ever to hit this nation. We retrospectively analyzed the temporal and spatial variations of four different physical parameters - outgoing long wave radiation (OLR), GPS/TEC, Low-Earth orbit tomography and critical frequency foF2. These changes characterize the state of the atmosphere and ionosphere several days before the onset of this earthquake. Our first results show that on March 8th 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 on this day in the lower ionospheric there was also confirmed an abnormal TEC variation over the epicenter. From March 3-11 a large increase in electron concentration was recorded at all four Japanese ground based ionosondes, which return to normal after the main earthquake. We found a positive correlation between the atmospheric and ionospheric anomalies and the Tohoku earthquake. This study may lead to a better understanding of the response of the atmosphere/ionosphere to the Great Tohoku earthquake.

On the reported ionospheric precursor of the 1999 Hector Mine, California earthquake

USGS Publications Warehouse

Thomas, Jeremy N.; Love, Jeffrey J.; Komjathy, Attila; Verkhoglyadova, Olga P.; Butala, Mark; Rivera, Nicholas

2012-01-01

Using Global Positioning System (GPS) data from sites near the 16 Oct. 1999 Hector Mine, California earthquake, Pulinets et al. (2007) identified anomalous changes in the ionospheric total electron content (TEC) starting one week prior to the earthquake. Pulinets (2007) suggested that precursory phenomena of this type could be useful for predicting earthquakes. On the other hand, and in a separate analysis, Afraimovich et al. (2004) concluded that TEC variations near the epicenter were controlled by solar and geomagnetic activity that were unrelated to the earthquake. In an investigation of these very different results, we examine TEC time series of long duration from GPS stations near and far from the epicenter of the Hector Mine earthquake, and long before and long after the earthquake. While we can reproduce the essential time series results of Pulinets et al., we find that the signal they identify as anomalous is not actually anomalous. Instead, it is just part of normal global-scale TEC variation. We conclude that the TEC anomaly reported by Pulinets et al. is unrelated to the Hector Mine earthquake.

On the reported ionospheric precursor of the Hector Mine, California earthquake

USGS Publications Warehouse

Thomas, J.N.; Love, J.J.; Komjathy, A.; Verkhoglyadova, O.P.; Butala, M.; Rivera, N.

2012-01-01

Using Global Positioning System (GPS) data from sites near the 16 Oct. 1999 Hector Mine, California earthquake, Pulinets et al. (2007) identified anomalous changes in the ionospheric total electron content (TEC) starting one week prior to the earthquake. Pulinets (2007) suggested that precursory phenomena of this type could be useful for predicting earthquakes. On the other hand, and in a separate analysis, Afraimovich et al. (2004) concluded that TEC variations near the epicenter were controlled by solar and geomagnetic activity that were unrelated to the earthquake. In an investigation of these very different results, we examine TEC time series of long duration from GPS stations near and far from the epicenter of the Hector Mine earthquake, and long before and long after the earthquake. While we can reproduce the essential time series results of Pulinets et al., we find that the signal they identified as being anomalous is not actually anomalous. Instead, it is just part of normal global-scale TEC variation. We conclude that the TEC anomaly reported by Pulinets et al. is unrelated to the Hector Mine earthquake.

Quantifications of Geomagnetic Storm Impact on TEC and NmF2 during 2013 Mar. event

NASA Astrophysics Data System (ADS)

Shim, J. S.; Tsagouri, I.; Goncharenko, L. P.; Mays, M. L.; Taktakishvili, A.; Rastaetter, L.; Kuznetsova, M. M.

2016-12-01

We investigate the ionospheric response to 2013 Mar. geomagnetic storm event using GPS TEC, ISR and ionosonde observations in North American sector. In order to quantify variations of TEC and NmF2 (or foF2) due to the storm, we remove the background quiet-time values (e.g., TEC of one day prior to the storm, NmF2 median and average of five quietest days for 30 days prior to the storm). In addition, in order to assess modeling capability of reproducing storm impacts on TEC and NmF2, we compare the observations with various model simulations, which are obtained from empirical, physics-based, and data assimilation models. Further, we investigate how uncertainty in the interplanetary magnetic field (IMF) impacts on TEC and NmF2 during the geomagnetic storm event. For this uncertainty study, we use a physics-based coupled ionosphere-thermosphere model, CTIPe, and solar wind parameters obtained from ensemble of WSA-ENLIL+Cone model simulations. This study has been supported by the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center. Model outputs and observational data used for the study will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) for the space science communities to use.

Swarm Utilisation Analysis: LEO satellite observations for the ESA's SSA Space Weather network

NASA Astrophysics Data System (ADS)

Kervalishvili, Guram; Stolle, Claudia; Rauberg, Jan; Olsen, Nils; Vennerstrøm, Susanne; Gullikstad Johnsen, Magnar; Hall, Chris

2017-04-01

ESA's (European Space Agency) constellation mission Swarm was successfully launched on 22 November 2013. The three satellites achieved their final constellation on 17 April 2014 and since then Swarm-A and Swarm-C orbiting the Earth at about 470 km (flying side-by-side) and Swarm-B at about 520 km altitude. Each of Swarm satellite carries instruments with high precision to measure magnetic and electric fields, neutral and plasma densities, and TEC (Total Electron Content) for which a dual frequency GPS receiver is used. SUA (Swarm Utilisation Analysis) is a project of the ESA's SSA (Space Situational Awareness) SWE (Space Weather) program. Within this framework GFZ (German Research Centre for Geosciences, Potsdam, Germany) and DTU (National Space Institute, Kongens Lyngby, Denmark) have developed two new Swarm products ROT (Rate Of change of TEC) and PEJ (Location and intensity level of Polar Electrojets), respectively. ROT is derived as the first time derivative from the Swarm measurements of TEC at 1 Hz sampling. ROT is highly relevant for users in navigation and communications: strong plasma gradients cause GPS signal degradation or even loss of GPS signal. Also, ROT is a relevant space weather asset irrespective of geomagnetic activity, e.g., high amplitude values of ROT occur during all geomagnetic conditions. PEJ is derived from the Swarm measurements of the magnetic field strength at 1 Hz sampling. PEJ has a high-level importance for power grid companies since the polar electrojet is a major cause for ground-induced currents. ROT and PEJ together with five existing Swarm products TEC, electron density, IBI (Ionospheric Bubble Index), FAC (Field-Aligned Current), and vector magnetic field build the SUA service prototype. This prototype will be integrated into ESA's SSA Space Weather network as a federated service and will be available soon from ESA's SSA SWE Ionospheric Weather and Geomagnetic Conditions Expert Service Centres (ESCs).

Monitoring of ionospheric irregularities with multi-GNSS observations: a new ionosphere activity index and product services

NASA Astrophysics Data System (ADS)

Wang, Ningbo; Li, Zishen; Yuan, Yunbin; Yuan, Hong

2017-04-01

Key words: Ionospheric irregularity, Rate of TEC (ROT), Rate of ROT index (RROT), GPS and GLONASS The ionospheric irregularities have a strong impact on many applications of Global Navigation Satellite Systems (GNSS) and other space-based radio systems. The rate of ionospheric total electron content (TEC) change index (ROTI, TECu/min), defined as the standard deviation of rate of TEC change (ROT) within a short time (e.g. 5 minutes), has been developed to describe the ionospheric irregularities and associated scintillations. However, ROT parameter may still contain the trend term of ionospheric TEC in spite of small-scale fluctuations. On the basis of single-differenced ROT (dROT) values, we develop a new ionosphere activity index, rate of ROT change index (RROT, TECu/min), to characterize the irregularity degree of the ionosphere. To illustrate the use of the index, we investigated the consistency between ROTI and RROT indexes, through the analysis of GPS data and S4 observations collected at two high-latitude stations of the northern hemisphere. It is confirmed that the correlation coefficients between RROT and S4 are higher than those between ROTI and S4 for the test period, meaning that the proposed RROT index is applicable to monitor the ionospheric irregularities and associated scintillations. RROT index can be easily calculated from dual-frequency GNSS signals (like GPS L1 and L2 carrier phase measurements). On the basis of GPS and GLONASS data provided by the IGS, ARGN, EPN and USCORS tracking networks (more than 1500 stations per day), absolute ROT (AROT), gradient of TEC index (GOTI), ROTI and RROT maps are generated to reflect the ionospheric irregularity activities. These maps are provided in an IONEX-like format on a global scale with a temporal resolution of 15 minutes and a spatial resolution of 5 and 2.5 degrees in longitude and latitude, respectively, and the maps with high spatial resolution (2x2 degrees) are also generated for European, Australia and North American regions. The product files are produced on a daily basis with a latency of 3 days. Users now can access these products from the ftp archive of the Chinese Academy of Sciences (CAS, ftp://ftp.gipp.org.cn/product/). These maps can be used for ionospheric weather services, ionospheric irregularity modeling and foresting, as well as other GNSS applications. Although they are provided in a post-processing mode at present, it is expected that the near real-time services will be available since the availability of real-time data streams from the IGS.

Temporal-Spatial Variation of Global GPS-Derived Total Electron Content, 1999–2013

PubMed Central

Guo, Jinyun; Li, Wang; Liu, Xin; Kong, Qiaoli; Zhao, Chunmei; Guo, Bin

2015-01-01

To investigate the temporal-spatial distribution and evolutions of global Total Electron Content (TEC), we estimate the global TEC data from 1999 to 2013 by processing the GPS data collected by the International Global Navigation Satellite System (GNSS) Service (IGS) stations, and robustly constructed the TEC time series at each of the global 5°×2.5° grids. We found that the spatial distribution of the global TEC has a pattern where the number of TECs diminishes gradually from a low-latitude region to high-latitude region, and anomalies appear in the equatorial crest and Greenland. Temporal variations show that the peak TEC appears in equinoctial months, and this corresponds to the semiannual variation of TEC. Furthermore, the winter anomaly is also observed in the equatorial area of the northern hemisphere and high latitudes of the southern hemisphere. Morlet wavelet analysis is used to determine periods of TEC variations and results indicate that the 1-day, 26.5-day, semi-annual and annual cycles are the major significant periods. The fitting results of a quadratic polynomial show that the effect of solar activity on TEC is stronger in low latitudes than in mid-high latitudes, and stronger in the southern hemisphere than in the northern hemisphere. But the effect in low latitudes in the northern hemisphere is stronger than that in low latitudes in the southern hemisphere. The effect of solar activity on TECs was analyzed with the cross wavelet analysis and the wavelet coherence transformation, and we found that there appears to be a strong coherence in the period of about 27 days. So the sunspot as one index of solar activity seriously affects the TEC variations with the sun’s rotation. We fit the TEC data with the least squares spectral analysis to study the periodic variations of TEC. The changing trend of TEC is generally -0.08 TECu per year from 1999 to 2013. So TECs decrease over most areas year by year, but TECs over the Arctic around Greenland maintained a rising trend during these 15 years. PMID:26193101

Automated daily processing of more than 1000 ground-based GPS receivers for studying intense ionospheric storms

NASA Technical Reports Server (NTRS)

Komjathy, Attila; Sparks, Lawrence; Wilson, Brian D.; Mannucci, Anthony J.

2005-01-01

To take advantage of the vast amount of GPS data, researchers use a number of techniques to estimate satellite and receiver interfrequency biases and the total electron content (TEC) of the ionosphere. Most techniques estimate vertical ionospheric structure and, simultaneously, hardware-related biases treated as nuisance parameters. These methods often are limited to 200 GPS receivers and use a sequential least squares or Kalman filter approach. The biases are later removed from the measurements to obtain unbiased TEC. In our approach to calibrating GPS receiver and transmitter interfrequency biases we take advantage of all available GPS receivers using a new processing algorithm based on the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This new capability is designed to estimate receiver biases for all stations. We solve for the instrumental biases by modeling the ionospheric delay and removing it from the observation equation using precomputed GIM maps. The precomputed GIM maps rely on 200 globally distributed GPS receivers to establish the ''background'' used to model the ionosphere at the remaining 800 GPS sites.

Detection of Natural Hazards Generated TEC Perturbations and Related New Applications

NASA Astrophysics Data System (ADS)

Komjathy, A.; Yang, Y.; Langley, R. B.

2013-12-01

Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcanic eruptions, and tsunamis. Research at the University of New Brunswick (UNB) laid the foundations to model the three-dimensional ionosphere at NASA's Jet Propulsion Laboratory by ingesting ground- and space-based GPS measurements into the state-of-the-art Global Assimilative Ionosphere Modeling (GAIM) software. As an outcome of the UNB and NASA research, new and innovative GPS applications have been invented including the use of ionospheric measurements to detect tiny fluctuations in the GPS signals between the spacecraft and GPS receivers caused by natural hazards occurring on or near the Earth's surface. This continuing research is expected to provide early warning for tsunamis, earthquakes, volcanic eruptions, and meteor impacts, for example, using GPS and other global navigation satellite systems. We will demonstrate new and upcoming applications including recent natural hazards and artificial explosions that generated TEC perturbations to perform state-of-the-art imaging and modeling of earthquakes, tsunamis and meteor impacts. By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage.

Recent Progress in Understanding Natural-Hazards-Generated TEC Perturbations: Measurements and Modeling Results

NASA Astrophysics Data System (ADS)

Komjathy, A.; Yang, Y. M.; Meng, X.; Verkhoglyadova, O. P.; Mannucci, A. J.; Langley, R. B.

2015-12-01

Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcanic eruptions, and tsunamis. Research at the University of New Brunswick (UNB) laid the foundations to model the three-dimensional ionosphere at NASA's Jet Propulsion Laboratory by ingesting ground- and space-based GPS measurements into the state-of-the-art Global Assimilative Ionosphere Modeling (GAIM) software. As an outcome of the UNB and NASA research, new and innovative GPS applications have been invented including the use of ionospheric measurements to detect tiny fluctuations in the GPS signals between the spacecraft and GPS receivers caused by natural hazards occurring on or near the Earth's surface.We will show examples for early detection of natural hazards generated ionospheric signatures using ground-based and space-borne GPS receivers. We will also discuss recent results from the U.S. Real-time Earthquake Analysis for Disaster Mitigation Network (READI) exercises utilizing our algorithms. By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage. It is also expected that ionospheric monitoring of TEC perturbations might become an integral part of existing natural hazards warning systems.

Statistical seismo-ionospheric precursors of M7.0+ earthquakes in Circum-Pacific seismic belt by GPS TEC measurements

NASA Astrophysics Data System (ADS)

Li, Wang; Yue, Jianping; Guo, Jinyun; Yang, Yang; Zou, Bin; Shen, Yi; Zhang, Kefei

2018-03-01

The Circum-Pacific seismic belt is the region heavily affected by earthquakes in the world. The relationship between earthquake (e.g., the geographic location, occurrence time, magnitude, and focal depth) and ionospheric anomalies in the belt was investigated using 100 M7.0+ earthquakes during 2006-2015. The ground-based GPS measurements and global ionosphere map (GIM) data were used for the analyses of the ionospheric variations preceding the earthquakes. The results indicated that the occurrence rate of total electron content (TEC) anomalies was proportional to the magnitude and inversely proportional to the focal depth to a certain degree, and the occurrence frequency of anomalies had a rising trend with the days getting close to the main shock. The occurrence rate of TEC anomalies in the Southern hemisphere was larger than that in the Northern hemisphere. Besides, the spatial characteristics of TEC anomalies showed that the anomalies in low-middle latitudes did not coincide with the epicenter, sometimes the anomalies were also observed in the corresponding conjugated region. However, the TEC anomalies in the high latitude usually appeared around the epicenter and within the seismogenic zone while no TEC anomalies appeared in the conjugated area. These results may have potential applications to the earthquake prediction in the Circum-Pacific seismic belt.

Code and codeless ionospheric measurements with NASA's Rogue GPS Receiver

NASA Technical Reports Server (NTRS)

Srinivasan, Jeff M.; Meehan, Tom K.; Young, Lawrence E.

1989-01-01

The NASA/JPL Rogue Receiver is an 8-satellite, non-multiplexed, highly digital global positioning system (GPS) receiver that can obtain dual frequency data either with or without knowledge of the P-code. In addition to its applications for high accuracy geodesy and orbit determination, the Rogue uses GPS satellite signals to measure the total electron content (TEC) of the ionosphere along the lines of sight from the receiver to the satellites. These measurements are used by JPL's Deep Space Network (DSN) for calibrating radiometric data. This paper will discuss Rogue TEC measurements, emphasizing the advantages of a receiver that can use the P-code, when available, but can also obtain reliable dual frequency data when the code is encrypted.

Ionospheric effects over Europe during the solar eclipse on 20 March 2015

NASA Astrophysics Data System (ADS)

Hoque, Mainul; Jakowski, Norbert; Berdermann, Jens

2017-04-01

A total solar eclipse occurred on March 20, 2015 moving from the North-West Europe towards the North-East. Due to strong solar radiation changes dynamic processes were initiated in the atmosphere and ionosphere causing a measurable impact e.g. on the temperature and ionization during the eclipse. We analyzed the 20 March 2015 solar eclipse effects on the ionospheric structure over Europe using multi-sensor observations such as vertical sounding (VS) and Global Positioning System (GPS) measurements. Whereas the VS measurements are used to provide peak electron density information at the ionospheric F2, F1 and E layers over selected ionosonde stations, a dense network of GPS stations is used to provide high spatial resolution of the total electron content (TEC) estimates over Europe. We reconstructed the TEC maps with 5 minutes time resolution and thus investigated the original TEC maps and differential TEC maps obtained by subtracting 27 days medians from the actual TEC map values on 20 March 2015. By combining VS and GPS measurements the equivalent slab thickness has been estimated over several ionosonde stations to get information how the shape of the vertical electron density profile changes during the eclipse. The analysis of the solar eclipse on 20 March 2015 presented here will contribute to understand the ionospheric response on solar eclipses occurring at different latitudes. The observations indicate that a number of competitive processes initiated by an eclipse are often enhanced by dynamic forces associated with large scale geophysical conditions not directly impacted by the solar eclipse. Our TEC estimation shows that the total ionization reduces up to 60% (after bias correction 40%) as a function of obscuration. Since the 20 March 2015 eclipse occurred during the negative phase of a severe geomagnetic storm on 17 March 2015, the observed TEC depletion is higher than those reported earlier for 1999 and 2005 eclipses. Thus, a negative bias of up to 20% was observed over Northern Europe already before the eclipse occurred. Moreover, the eclipse path of the solar eclipse in 2015 is traced at higher latitudes compared with eclipses observed in the years 1999 and 2005. The ionospheric response to the obscuration function is delayed up to 40 minutes decreasing with growing distance from the totality zone and increasing with altitude. The increasing delay with altitude is in agreement with earlier findings for other eclipses. The equivalent slab thickness was found to increase by approximately 80 -100 km during the solar eclipse on 20 March 2015 showing evidence for a pronounced loss in the bottomside ionosphere causing a delayed depletion of the topside ionosphere.

Remote Sensing of the Ionosphere and Plasmasphere from Space Using Radiowaves

NASA Technical Reports Server (NTRS)

Mannucci, Anthony J.

2008-01-01

Topics include the scientific context, trans-ionospheric and sounding, small-scale structure, plasmasphere, fast and slow tomography, and pseudo-imaging. Individual slides focus on where geospace science stands today, variability in inner magnetosphere electric fields, Appleton-Hartree formula, phase and range ionospheric observables, examples of leveling, large ionization changes during storms, new mid-latitude phenomena, ionospheric sounding, COSMIC CERTO/Tri-band beacon, LEO-ground radio tomography, irregularity measurements, COSMIC, critical sensor data from COSMIC GPS limb sounding, occultation geometry, comparison of calibrated slant TEC measurements for 26 June 2006, historic examples of Abel electron density profiles, comparison of UCAR and JPL Able profiles of 26 June 2006, validating UCAR and JPL Abel profiles using Arecibo ISR measurements for 26 June 2006, E-region from GPS/MET 1995, Abel versus gradient assisted retrieval, 3000 profiles/day, plasmasphere, JASON TEC above satellite, GPS equatorial plasmasphere measurements, April 2002 geomagnetic storm, and space-based GPS tomography.

Transient Effects in Atmosphere and Ionosphere preceding the two 2015 M7.8 and M7.3 Earthquakes in Nepal

NASA Astrophysics Data System (ADS)

Ouzounov, D.; Pulinets, S. A.; Hernandez-Pajares, M.; Alberto Garcia Rigo, A. G.; Davidenko, D.; Hatzopoulos, N.; Kafatos, M.

2015-12-01

The recent M7.8 Nepal earthquake of April 25, 2015 was the largest recorded earthquake event to hit this nation since 1934. We prospectively and retrospectively analyzed the transient variations of three different physical parameters - outgoing earth radiation (OLR), GPS/TEC and the thermodynamic proprieties in the lower atmosphere. These changes characterize the state of the atmosphere and ionosphere several days before the onset of this earthquake. Our preliminary results show that in mid March 2015 a rapid increase of emitted infrared radiation was observed from the satellite data and an anomaly near the epicenter reached the maximum on April 21-22. The ongoing analysis of satellite radiation revealed another transient anomaly on May 3th, probably associated with the M7.3 of May 12, 2015. The analysis of air temperature form ground stations show similar patterns of rapid increases offset 1-2 days earlier to the satellite transient anomalies.The GPS/TEC data indicate an increase and variation in electron density reaching a maximum value during April 22-24. We found a strong negative TEC anomaly in the crest of EIA (Equatorial Ionospheric Anomaly) on April 21st and strong positive on April 24th, 2015. Our results show strong ionospheric effects not only in the changes of the EIA intensity but also within the latitudinal movements of the crests of EIA.

Spatial and temporal analysis of the total electron content over China during 2011-2014

NASA Astrophysics Data System (ADS)

Zheng, Jianchang; Zhao, Biqiang; Xiong, Bo; Wan, Weixing

2016-06-01

In the present work we investigate variations of ionospheric total electron content (TEC) with empirical orthogonal function (EOF) analysis, the four-year TEC data are derived from ∼250 GPS observations of the crustal movement observation network of China (CMONOC) over East Asian area (30-55°N, 70-140°E) during the period from 2011, January to 2014, December. The first two EOF components together account for ∼93.78% of total variance of the original TEC data set, and it is found that the first EOF component represents a spatial variability of semi-annual variation and the second EOF component exhibits pronounced east-west longitudinal difference with respect to zero valued geomagnetic declination line. In addition, climatology of the vertical plasma drift velocity vdz induced by HWM zonal wind field (∼300 km) are studied in the paper. Results shows vdz displays significant east-west longitudinal difference at 10:00 LT and 20:00 LT, and its daytime temporal variation is consistent with the second EOF principal component, which suggests that the east-west longitudinal variability is partly caused by the thermospheric zonal wind and geomagnetic declination. It is expected that with this dense GPS network, local ionospheric variability can be described more accurately and a more realistic ionospheric model can be constructed and used for the satellite navigation and radio propagation.

The August 21, 2017 American total solar eclipse through the eyes of GPS

NASA Astrophysics Data System (ADS)

Kundu, Bhaskar; Panda, Dibyashakti; Gahalaut, Vineet K.; Catherine, J. K.

2018-04-01

We explored spatio-temporal variation in Total Electron Contents (TEC) in the ionosphere caused by the recent August 21, 2017 total solar eclipse, which was observed over the United States of America. The path of total solar eclipse passes through the continental parts of the United States of America, starting in the northwestern state of Oregon and ending in the southeastern state of South Carolina, approximately covering 4000 km length. Across this length EarthScope Plate Boundary Observatory (PBO) has been operating a dense cGPS/GNSS networks. During the course of passage of the solar eclipse, the sudden decline in solar radiation by temporarily obscuration by the Moon caused a drop of ˜6-9 × 1016 electrons/m2in the ionosphere with time-delay at the cGPS sites. The significant drop in TEC at cGPS sites captured the average migration velocity of shadow along the eclipse path (0.74 km/s), from which we estimated the Moon's orbital velocity (˜1 km/s). Further, this event also caused some marginal increase in TEC during the eclipse in the Earth's ionosphere in the magnetically conjugate region at the tip of South America and Antarctica, consistent with the model predictions of SAMI3 by Naval Research Laboratory.

Empirical Orthogonal Function (EOF) Analysis of Storm-Time GPS Total Electron Content Variations

NASA Astrophysics Data System (ADS)

Thomas, E. G.; Coster, A. J.; Zhang, S.; McGranaghan, R. M.; Shepherd, S. G.; Baker, J. B.; Ruohoniemi, J. M.

2016-12-01

Large perturbations in ionospheric density are known to occur during geomagnetic storms triggered by dynamic structures in the solar wind. These ionospheric storm effects have long attracted interest due to their impact on the propagation characteristics of radio wave communications. Over the last two decades, maps of vertically-integrated total electron content (TEC) based on data collected by worldwide networks of Global Positioning System (GPS) receivers have dramatically improved our ability to monitor the spatiotemporal dynamics of prominent storm-time features such as polar cap patches and storm enhanced density (SED) plumes. In this study, we use an empirical orthogonal function (EOF) decomposition technique to identify the primary modes of spatial and temporal variability in the storm-time GPS TEC response at midlatitudes over North America during more than 100 moderate geomagnetic storms from 2001-2013. We next examine the resulting time-varying principal components and their correlation with various geophysical indices and parameters in order to derive an analytical representation. Finally, we use a truncated reconstruction of the EOF basis functions and parameterization of the principal components to produce an empirical representation of the geomagnetic storm-time response of GPS TEC for all magnetic local times local times and seasons at midlatitudes in the North American sector.

Comparison of IRI-Plas and IONOLAB Slant Total Electron Content for Disturbed Days of Ionosphere

NASA Astrophysics Data System (ADS)

Shukurov, Seymur; Gulyaeva, Tamara; Arikan, Feza; Necat Deviren, M.; Tuna, Hakan; Arikan, Orhan

Variabilities due to geomagnetic, and seismic activities in ionosphere can be observed by using Total Electron Content (TEC). TEC estimated on a path between a dual-frequency Global Positioning System (GPS) receiver and a GPS satellite at a given date and time is called Slant TEC (STEC). STEC contains the variability of ionosphere on a given path, therefore it is a useful variable to identify the anisotropicity. IONOLAB group has developed a novel method for STEC estimation (IONOLAB-STEC) from GPS phase delay recordings resolving the phase ambiguity and calculating IONOLAB-BIAS as receiver interfrequency bias. International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) is the standard climatic model of ionosphere. IONOLAB group automatized the computation of STEC between a GPS satellite and receiver for a given date. In this study, IRI-Plas-STEC and IONOLAB-STEC are compared for geomagnetically active storm days and for the days prior to earthquakes over Turkey using Symmetric Kullback-Liebler Distance (SKLD). It is observed that IRI-Plas-STEC and IONOLAB-STEC are very similar for magnetically quiet days, and IRI-Plas-STEC provides a background ionosphere. This study is supported by the joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

Characterization of Ionospheric Dynamics Over The East African Dip Equatorial Region Using GPS-Derived Total Electron Content.

NASA Astrophysics Data System (ADS)

Olwendo, J. O.

2016-12-01

Through a linear combination of GPS satellite range and phase measurement observed on two carrier frequencies by terrestrial based GPS receivers, the ionospheric total electron content (TEC) along oblique GPS signal path can be quantified. Using Adjusted Spherical Harmonic (ASHA) expansion, regional TEC maps over the East Africa sector has been achieved. The observed TEC has been used to evaluate the performance of IRI2007 and NeQuick 2 models over the region. Ionospheric irregularities have been measured and the plasma drift velocity and the East-West extent of the irregularities have also been analyzed by using a Very High Frequency (VHF) receiver system that is closely spaced. The hourly TEC images developed have shown that the Southern Equatorial Ionization Anomaly (EIA) crest over the East African sector lies within the Kenyan region, and the occurrence of scintillation is dependent on how well the anomaly crest forms. Scintillation occurrences are intense at and around the edges of EIA crest due to the presence of high ambient electron densities and sharp TEC depletions. Simultaneous recording of amplitude scintillations at VHF and L-band frequencies reveal two distinct types of scintillation namely; the Plasma Bubble Induced (PBI) and the Bottom Side Sinusoidal (BSS). The PBI scintillations are characterized by high intensity during the post-sunset hours of the equinoctial months and appear at both VHF and L-band frequencies. The BSS type are associated with VHF scintillation and are characterized by long duration patches and often exhibit Fresnel oscillation on the roll portion of the power spectrum, which suggest a weak scattering from thin screen irregularities. The occurrence of post-midnight L-band scintillation events which are not linked to pre-midnight scintillation observations raises fundamental question on the mechanism and source of electric fields driving the plasma depletion under conditions of very low background electron density.

Real-time reconstruction of topside ionosphere scale height from coordinated GPS-TEC and ionosonde observations

NASA Astrophysics Data System (ADS)

Gulyaeva, Tamara; Poustovalova, Ljubov

The International Reference Ionosphere model extended to the plasmasphere, IRI-Plas, has been recently updated for assimilation of total electron content, TEC, derived from observations with Global Navigation Satellite System, GNSS. The ionosonde products of the F2 layer peak density (NmF2) and height (hmF2) ensure true electron density maximum at the F2 peak. The daily solar and magnetic indices used by IRI-Plas code are compiled in data files including the 3-hour ap and kp magnetic index from 1958 onward, 12-monthly smoothed sunspot number R12 and Global Electron Content GEC12, daily solar radio flux F10.7 and daily sunspot number Ri. The 3-h ap-index is available in Real Time, RT, mode from GFZ, Potsdam, Germany, daily update of F10.7 is provided by Space Weather Canada service, and daily estimated international sunspot number Ri is provided by Solar Influences Data Analysis Center, SIDC, Belgium. For IRI-Plas-RT operation in regime of the daily update and prediction of the F2 layer peak parameters, the proxy kp and ap forecast for 3 to 24 hours ahead based on data for preceding 12 hours is applied online at http://www.izmiran.ru/services/iweather/. The topside electron density profile of IRI-Plas code is expressed with complementary half-peak density anchor height above hmF2 which corresponds to transition O+/H+ height. The present investigation is focused on reconstruction of topside ionosphere scale height using vertical total electron content (TEC) data derived from the Global Positioning System GPS observations and the ionosonde derived F2 layer peak parameters from 25 observatories ingested into IRI-Plas model. GPS-TEC and ionosonde measurements at solar maximum (September, 2002, and October, 2003) for quiet, positively disturbed, and negatively disturbed days of the month are used to obtain the topside scale height, Htop, representing the range of altitudes from hmF2 to the height where NmF2 decay by e times occurs. Mapping of the F2 layer peak parameters and TEC allows interpolate these parameters at coordinated grid sites from independent GPS receivers and ionosondes data. Exponential scale height Htop exceeds scale height HT of the α-Chapman layer by 3 times - the latter refers to a narrow altitude range from hmF2 to the height of 1.2 times decay of NmF2. While typical quiet daytime value of the topside scale height is around 200 km, it can be enhanced by 2-3 times during the negative phase of the ionospheric storm as it is captured by IRI-Plas-RT model ingesting the F2 peak and TEC data. This study is supported by the joint grant of RFBR 13-02-91370-CT_a and TUBITAK 112E568.

Variations of ionospheric plasma at different altitudes before the 2005 Sumatra Indonesia Ms 7.2 earthquake

NASA Astrophysics Data System (ADS)

Liu, Jing; Zhang, Xuemin; Novikov, Victor; Shen, Xuhui

2016-09-01

In recent years, many researchers pay more attention to abnormities before earthquake, and in this study, seismo-ionospheric synchronous disturbances at different altitudes by GPS and satellite observations were first studied around one Sumatra Indonesia Ms 7.2 earthquake that occurred on 5 July 2005. By using the same temporal and spatial methods, data of GPS-total electron content (TEC) from Jet Propulsion Laboratory, electron density (Ne) from Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions, and ion density (Ni) from Defense Meteorological Satellite Program were deeply analyzed. The ionospheric plasma disturbances in GPS-TEC and increasement of Ne at 710 km were found on 4 July, and plasma density at the three altitudes has all increased on 7 July after the earthquake. All the disturbances were not just above the epicenter. TEC perturbations have happened at the east of the epicenter for the two days, and electron density enhancement at 710 km has moved to west of the TEC perturbations at the same time on 4 July, which may be caused by E × B drift. The moving direction of upgoing plasma was simulated using SAMI2 model. The results have shown that the plasma will move to higher altitude along the geomagnetic force line, which could exactly account for the plasma density enhancement in the northern direction of the geomagnetic south latitude earthquake.

Comparison of GPS receiver DCB estimation methods using a GPS network

NASA Astrophysics Data System (ADS)

Choi, Byung-Kyu; Park, Jong-Uk; Min Roh, Kyoung; Lee, Sang-Jeong

2013-07-01

Two approaches for receiver differential code biases (DCB) estimation using the GPS data obtained from the Korean GPS network (KGN) in South Korea are suggested: the relative and single (absolute) methods. The relative method uses a GPS network, while the single method determines DCBs from a single station only. Their performance was assessed by comparing the receiver DCB values obtained from the relative method with those estimated by the single method. The daily averaged receiver DCBs obtained from the two different approaches showed good agreement for 7 days. The root mean square (RMS) value of those differences is 0.83 nanoseconds (ns). The standard deviation of the receiver DCBs estimated by the relative method was smaller than that of the single method. From these results, it is clear that the relative method can obtain more stable receiver DCBs compared with the single method over a short-term period. Additionally, the comparison between the receiver DCBs obtained by the Korea Astronomy and Space Science Institute (KASI) and those of the IGS Global Ionosphere Maps (GIM) showed a good agreement at 0.3 ns. As the accuracy of DCB values significantly affects the accuracy of ionospheric total electron content (TEC), more studies are needed to ensure the reliability and stability of the estimated receiver DCBs.

GPS, BDS and Galileo ionospheric correction models: An evaluation in range delay and position domain

NASA Astrophysics Data System (ADS)

Wang, Ningbo; Li, Zishen; Li, Min; Yuan, Yunbin; Huo, Xingliang

2018-05-01

The performance of GPS Klobuchar (GPSKlob), BDS Klobuchar (BDSKlob) and NeQuick Galileo (NeQuickG) ionospheric correction models are evaluated in the range delay and position domains over China. The post-processed Klobuchar-style (CODKlob) coefficients provided by the Center for Orbit Determination in Europe (CODE) and our own fitted NeQuick coefficients (NeQuickC) are also included for comparison. In the range delay domain, BDS total electrons contents (TEC) derived from 20 international GNSS Monitoring and Assessment System (iGMAS) stations and GPS TEC obtained from 35 Crust Movement Observation Network of China (CMONC) stations are used as references. Compared to BDS TEC during the short period (doy 010-020, 2015), GPSKlob, BDSKlob and NeQuickG can correct 58.4, 66.7 and 54.7% of the ionospheric delay. Compared to GPS TEC for the long period (doy 001-180, 2015), the three ionospheric models can mitigate the ionospheric delay by 64.8, 65.4 and 68.1%, respectively. For the two comparison cases, CODKlob shows the worst performance, which only reduces 57.9% of the ionospheric range errors. NeQuickC exhibits the best performance, which outperforms GPSKlob, BDSKlob and NeQuickG by 6.7, 2.1 and 6.9%, respectively. In the position domain, single-frequency stand point positioning (SPP) was conducted at the selected 35 CMONC sites using GPS C/A pseudorange with and without ionospheric corrections. The vertical position error of the uncorrected case drops significantly from 10.3 m to 4.8, 4.6, 4.4 and 4.2 m for GPSKlob, CODKlob, BDSKlob and NeQuickG, however, the horizontal position error (3.2) merely decreases to 3.1, 2.7, 2.4 and 2.3 m, respectively. NeQuickG outperforms GPSKlob and BDSKlob by 5.8 and 1.9% in vertical component, and by 25.0 and 3.2% in horizontal component.

Study of ionospheric precursors using GPS and GIM-TEC data related to earthquakes occurred on 16 April and 24 September, 2013 in Pakistan region

NASA Astrophysics Data System (ADS)

Pundhir, Devbrat; Singh, Birbal; Singh, O. P.; Gupta, Saral Kumar; Karia, S. P.; Pathak, K. N.

2017-11-01

In this paper, we have examined the diurnal variations of GPS-TEC observed at two Indian stations of Agra (27.2°N, 78°E) and Surat (21.16°N, 72.78°E) and global ionospheric maps data (GIM-TEC) for the months of April and September 2013 in search of ionospheric precursors of three major earthquakes (M > 6.5) that occurred in these months. The well-established quartile based statistical technique is adopted for the analysis of TEC data. The results show two kinds of anomalies, one in which simultaneous enhancements in TEC occurred in the three sets of data, 1-9 days and 3 days before the main shock in the two months respectively, and another in which anomalies occurred 15 days before in April, and 21 days before in September at Surat respectively. The depletions have also been found in three data sets but they are not significant. These anomalies are unlikely be influenced by geomagnetic parameters due to quiet magnetic conditions. The effect of also solar activity have also been considered and examined very precisely. The results are interpreted in terms of Lithosphere-Atmosphere-Ionosphere coupling (LAIC) mechanisms available in the literature.

Collocated ionosonde and dense GPS/GLONASS network measurements of midlatitude MSTIDs

NASA Astrophysics Data System (ADS)

Sherstyukov, R. O.; Akchurin, A. D.; Sherstyukov, O. N.

2018-04-01

To analyze midlatitude medium-scale travelling ionospheric disturbances (MSTIDs) over Kazan (55.5°N, 49°E), Russia, the sufficiently dense network of GNSS receivers (more than 150 ground-based stations) were used. For the first time, daytime MSTIDs in the form of their main signature (band structure) on high-resolution two-dimensional maps of the total electron content perturbation (TEC maps) are compared with ionosonde data with a high temporal resolution. For a pair of events, a relationship between southwestward TEC perturbations and evolution of F2 layer traces was established. So F2 peak frequency varied in antiphase to TEC perturbations. The ionograms show that during the movement of plasma depletion band (overhead ionosonde) the F2 peak frequency is the highest, and vice versa, for the plasma enhancement band, the F2 peak frequency is the lowest. One possible explanation may be a greater inclination of the radio beam from the vertical during the placement of a plasma enhancement band above the ionosonde, as evidenced by the absence of multiple reflections and the increased occurrence rate of additional cusp trace. Another possible explanation may be the redistribution of the electron content in the topside ionosphere with a small decrease in the F peak concentration of the layer with a small increase in TEC along the line-of-sight. Analysis of F2 peak frequency variation shows that observed peak-to-peak values of TEC perturbation equal to 0.4 and 1 TECU correspond to the values of ΔN/N equal to 13% and 28%. The need for further research is evident.

Space Weather Activities of IONOLAB Group: TEC Mapping

NASA Astrophysics Data System (ADS)

Arikan, F.; Yilmaz, A.; Arikan, O.; Sayin, I.; Gurun, M.; Akdogan, K. E.; Yildirim, S. A.

2009-04-01

Being a key player in Space Weather, ionospheric variability affects the performance of both communication and navigation systems. To improve the performance of these systems, ionosphere has to be monitored. Total Electron Content (TEC), line integral of the electron density along a ray path, is an important parameter to investigate the ionospheric variability. A cost-effective way of obtaining TEC is by using dual-frequency GPS receivers. Since these measurements are sparse in space, accurate and robust interpolation techniques are needed to interpolate (or map) the TEC distribution for a given region in space. However, the TEC data derived from GPS measurements contain measurement noise, model and computational errors. Thus, it is necessary to analyze the interpolation performance of the techniques on synthetic data sets that can represent various ionospheric states. By this way, interpolation performance of the techniques can be compared over many parameters that can be controlled to represent the desired ionospheric states. In this study, Multiquadrics, Inverse Distance Weighting (IDW), Cubic Splines, Ordinary and Universal Kriging, Random Field Priors (RFP), Multi-Layer Perceptron Neural Network (MLP-NN), and Radial Basis Function Neural Network (RBF-NN) are employed as the spatial interpolation algorithms. These mapping techniques are initially tried on synthetic TEC surfaces for parameter and coefficient optimization and determination of error bounds. Interpolation performance of these methods are compared on synthetic TEC surfaces over the parameters of sampling pattern, number of samples, the variability of the surface and the trend type in the TEC surfaces. By examining the performance of the interpolation methods, it is observed that both Kriging, RFP and NN have important advantages and possible disadvantages depending on the given constraints. It is also observed that the determining parameter in the error performance is the trend in the Ionosphere. Optimization of the algorithms in terms of their performance parameters (like the choice of the semivariogram function for Kriging algorithms and the hidden layer and neuron numbers for MLP-NN) mostly depend on the behavior of the ionosphere at that given time instant for the desired region. The sampling pattern and number of samples are the other important parameters that may contribute to the higher errors in reconstruction. For example, for all of the above listed algorithms, hexagonal regular sampling of the ionosphere provides the lowest reconstruction error and the performance significantly degrades as the samples in the region become sparse and clustered. The optimized models and coefficients are applied to regional GPS-TEC mapping using the IONOLAB-TEC data (www.ionolab.org). Both Kriging combined with Kalman Filter and dynamic modeling of NN are also implemented as first trials of TEC and space weather predictions.

Where does the plasmasphere begin? Revisit to topside ionospheric profiles in comparison with plasmaspheric TEC from Jason-1

NASA Astrophysics Data System (ADS)

Lee, Han-Byul; Kim, Yong Ha; Kim, Eunsol; Hong, Junseok; Kwak, Young-Sil

2016-10-01

Topside ionospheric profiles have been measured by Alouette 1 and ISIS 1/2 in the periods of 1962-1972 and 1972-1979, respectively. The profiles cover from the orbital altitude of 1000 km to the F2 peak and show large variations over local time, latitude, and seasons. We here analyze these variations in comparison with plasmaspheric total electron contents (pTECs) that were measured by Jason-1 satellite from the altitude of 1336 km to 20,200 km (GPS orbit). The scale heights of the profiles are generally smaller in the daytime than nighttime but show large day-to-day variations, implying that the ionospheric profiles at 1000 km are changing dynamically, rather than being in diffusive equilibrium. We also derived transition heights between O+ and H+, which show a clear minimum at dawn for low-latitude profiles due to decreasing O+ density at night. To compare with pTEC, we compute topside ionospheric total electron content (tiTEC) by integrating over 800-1336 km using the slope of the profiles. The tiTEC varies in a clear diurnal pattern from 0.3 to 1 and 3 total electron content unit (TECU, 1 TECU = 1016 el m-2) for low and high solar activity, respectively, whereas Jason-1 pTEC values are distributed over 2-6 TECU and 4-8 TECU for low and high solar activity, respectively, with no apparent diurnal modulation. Latitudinal variations of tiTEC show distinctive hemispheric asymmetry while that of Jason-1 pTEC is closely symmetric about the magnetic equator. The local time and latitudinal variations of tiTEC basically resemble those of the ionosphere but are characteristically different from those of Jason-1 pTEC. Based on the difference between tiTEC and pTEC variations, we propose that the region above 1300 km should be considered as the plasmasphere. Lower altitudes for the base of "plasmaspheric TEC," as used in some studies, would cause contamination of ionospheric influence.

Longitudinal study of the ionospheric response to the geomagnetic storm of 15 May 2005 and manifestation of TADs

NASA Astrophysics Data System (ADS)

Sharma, S.; Galav, P.; Dashora, N.; Pandey, R.

2011-06-01

Response of low latitude ionosphere to the geomagnetic storm of 15 May 2005 has been studied using total electron content (TEC) data, obtained from three GPS stations namely, Yibal, Udaipur and Kunming situated near the northern crest of equatorial ionization anomaly at different longitudes. Solar wind parameters, north-south component of the interplanetary magnetic field (IMF Bz) and AE index data have been used to infer the strength of the geomagnetic storm. A large value of eastward interplanetary electric field at 06:15 UT, during the time of maximum southward IMF Bz has been used to infer the transmission of an eastward prompt penetration electric field (PPEF) which resulted in a peak in TEC at 07:45 UT due to the local uplift of plasma in the low latitudes near the anomaly crest over a wide range of longitudes. Wave-like modulations superposed over the second enhancement in TEC between 09:15 UT to 10:30 UT have been observed at all the three stations. The second enhancement in TEC along with the modulations of up to 5 TECU have been attributed to the combined effect of super plasma fountain and traveling atmospheric disturbances (TAD). Observed large enhancements in TEC are a cause of concern for satellite based navigation and ground positioning. Increased [O/N2] ratio between 09:15 UT to 10:15 UT when modulations in TEC have been also observed, confirms the presence of TADs over a wide range of longitudes.

A Regional GPS Receiver Network For Monitoring Mid-latitude Total Electron Content During Storms

NASA Astrophysics Data System (ADS)

Vernon, A.; Cander, Lj. R.

A regional GPS receiver network has been used for monitoring mid-latitude total elec- tron content (TEC) during ionospheric storms at the current solar maximum. Differ- ent individual storms were examined to study how the temporal patterns of changes develop and how they are related to solar and geomagnetic activity for parameter de- scriptive of plasmaspheric-ionospheric ionisation. Use is then made of computer con- touring techniques to produce snapshot maps of TEC for different study cases. Com- parisons with the local ionosonde data at different phases of the storms enable the storm developments to be studied in detail.

Tomography Reconstruction of Ionospheric Electron Density with Empirical Orthonormal Functions Using Korea GNSS Network

NASA Astrophysics Data System (ADS)

Hong, Junseok; Kim, Yong Ha; Chung, Jong-Kyun; Ssessanga, Nicholas; Kwak, Young-Sil

2017-03-01

In South Korea, there are about 80 Global Positioning System (GPS) monitoring stations providing total electron content (TEC) every 10 min, which can be accessed through Korea Astronomy and Space Science Institute (KASI) for scientific use. We applied the computerized ionospheric tomography (CIT) algorithm to the TEC dataset from this GPS network for monitoring the regional ionosphere over South Korea. The algorithm utilizes multiplicative algebraic reconstruction technique (MART) with an initial condition of the latest International Reference Ionosphere-2016 model (IRI-2016). In order to reduce the number of unknown variables, the vertical profiles of electron density are expressed with a linear combination of empirical orthonormal functions (EOFs) that were derived from the IRI empirical profiles. Although the number of receiver sites is much smaller than that of Japan, the CIT algorithm yielded reasonable structure of the ionosphere over South Korea. We verified the CIT results with NmF2 from ionosondes in Icheon and Jeju and also with GPS TEC at the center of South Korea. In addition, the total time required for CIT calculation was only about 5 min, enabling the exploration of the vertical ionospheric structure in near real time.

The Ionosphere and Ocean Altimetry

NASA Technical Reports Server (NTRS)

Lindqwister, Ulf J.

1999-01-01

The accuracy of satellite-based single-frequency radar ocean altimeters benefits from calibration of the total electron content (TEC) of the ionosphere below the satellite. Data from the global network of Global Positioning System (GPS) receivers provides timely, continuous, and globally well-distributed measurements of ionospheric electron content. We have created a daily automated process called Daily Global Ionospheric Map (Daily-GIM) whose primary purpose is to use global GPS data to provide ionospheric calibration data for the Geosat Follow-On (GFO) ocean altimeter. This process also produces an hourly time-series of global maps of the electron content of the ionosphere. This system is designed to deliver "quick-look" ionospheric calibrations within 24 hours with 90+% reliability and with a root-mean-square accuracy of 2 cm at 13.6 GHz. In addition we produce a second product within 72 hours which takes advantage of additional GPS data which were not available in time for the first process. The diagram shows an example of a comparison between TEC data from the Topographic Experiment (TOPEX) ocean altimeter and Daily-GIM. TEC are displayed in TEC units, TECU, where 5 TECU is 1 cm at 13.6 GHz. Data from a single TOPEX track is shown. Also shown is the Bent climatological model TEC for the track. Although the GFO satellite is not yet in its operational mode, we have been running Daily-GIM reliably (much better than 90%) with better than 2-cm accuracy (based on comparisons against TOPEX) for several months. When timely ephemeris files for the European Remote Sensing Satellite 2 (ERS-2) are available, daily ERS-2 altimeter ionospheric calibration files are produced. When GFO ephemeris files are made available to us, we produce GFO ionosphere calibration files. Users of these GFO ionosphere calibration files find they are a great improvement over the alternative International Reference Ionosphere 1995 (IRI-95) climatological model. In addition, the TOPEX orbit determination team at JPL has been using the global ionospheric maps to calibrate the single frequency GPS data from the TOPEX receiver, and report highly significant improvements in the ephemeris. The global ionospheric maps are delivered daily to the International GPS Service (IGS), making them available to the scientific community. Additional information is contained in the original.

Earthquake-Ionosphere Coupling Processes

NASA Astrophysics Data System (ADS)

Kamogawa, Masashi

After a giant earthquake (EQ), acoustic and gravity waves are excited by the displacement of land and sea surface, propagate through atmosphere, and then reach thermosphere, which causes ionospheric disturbances. This phenomenon was detected first by ionosonde and by HF Doppler sounderin the 1964 M9.2 Great Alaskan EQ. Developing Global Positioning System (GPS), seismogenic ionospheric disturbance detected by total electron content (TEC) measurement has been reported. A value of TEC is estimated by the phase difference between two different carrier frequencies through the propagation in the dispersive ionospheric plasma. The variation of TEC is mostly similar to that of F-region plasma. Acoustic-gravity waves triggered by an earthquake [Heki and Ping, EPSL, 2005; Liu et al., JGR, 2010] and a tsunami [Artu et al., GJI, 2005; Liu et al., JGR, 2006; Rolland, GRL, 2010] disturb the ionosphere and travel in the ionosphere. Besides the traveling ionospheric disturbances, ionospheric disturbances excited by Rayleigh waves [Ducic et al, GRL, 2003; Liu et al., GRL, 2006] as well as post-seismic 4-minute monoperiodic atmospheric resonances [Choosakul et al., JGR, 2009] have been observed after the large earthquakes. Since GPS Earth Observation Network System (GEONET) with more than 1200 GPS receiving points in Japan is a dense GPS network, seismogenic ionospheric disturbance is spatially observed. In particular, the seismogenic ionospheric disturbance caused by the M9.0 off the Pacific coast of Tohoku EQ (henceforth the Tohoku EQ) on 11 March 2011 was clearly observed. Approximately 9 minutes after the mainshock, acoustic waves which propagated radially emitted from the tsunami source area were observed through the TEC measurement (e. g., Liu et al. [JGR, 2011]). Moreover, there was a depression of TEC lasting for several tens of minutes after a huge earthquake, which was a large-scale phenomenon extending to a radius of a few hundred kilometers. This TEC depression may be an ionospheric phenomenon attributed to tsunami, termed tsunamigenic ionospheric hole (TIH) [Kakinami and Kamogwa et al., GRL, 2012]. After the TEC depression accompanying a monoperiodic variation with approximately 4-minute period as an acoustic resonance between the ionosphere and the solid earth, the TIH gradually recovered. In addition, geomagnetic pulsations with the periods of 150, 180 and 210 seconds were observed on the ground in Japan approximately 5 minutes after the mainshock. Since the variation with the period of 180 seconds was simultaneously detected at the magnetic conjugate of points of Japan, namely Australia, field aligned currents along the magnetic field line were excited. The field aligned currents might be excited due to E and F region dynamo current caused by acoustic waves originating from the tsunami. This result implies that a large earthquake generates seismogenic field aligned currents. Furthermore, monoperiodical geomagnetic oscillation pointing to the epicenter of which velocity corresponds to Rayleigh waves occurs. This may occur due to seismogenic arc-current in E region. Removing such magnetic oscillations from the observed data, clear tsunami dynamo effect was found. This result implies that a large EQ generates seismogenic field aligned currents, seismogenic arc-current and tsunami dynamo current which disturb geomagnetic field. Thus, we found the complex coupling process between a large EQ and an ionosphere from the results of Tohoku EQ.

PPS GPS: What Is It? And How Do I Get It

DTIC Science & Technology

1994-06-01

Positioning Service, Selective Availabilit B.PRICE CODIE 17. SECURITY CLASSIFICATION II. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20...the TEC Water Detection Response Team which operates in remote areas of the world. These activities, require the GPS receiver to be capable of removing

Ionospheric Modeling: Development, Verification and Validation

DTIC Science & Technology

2005-09-01

facilitate the automated processing of a large network of GPS receiver data. 4.; CALIBRATION AND VALIDATION OF IONOSPHERIC SENSORS We have been...NOFS Workshop, Estes Park, CO, January 2005. W. Rideout, A. Coster, P. Doherty, MIT Haystack Automated Processing of GPS Data to Produce Worldwide TEC

Tsunami Wave Height Estimation from GPS-Derived Ionospheric Data

NASA Astrophysics Data System (ADS)

Rakoto, Virgile; Lognonné, Philippe; Rolland, Lucie; Coïsson, P.

2018-05-01

Large underwater earthquakes (Mw>7) can transmit part of their energy to the surrounding ocean through large seafloor motions, generating tsunamis that propagate over long distances. The forcing effect of tsunami waves on the atmosphere generates internal gravity waves that, when they reach the upper atmosphere, produce ionospheric perturbations. These perturbations are frequently observed in the total electron content (TEC) measured by multifrequency Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS, and, in the future, Galileo. This paper describes the first inversion of the variation in sea level derived from GPS TEC data. We used a least squares inversion through a normal-mode summation modeling. This technique was applied to three tsunamis in far field associated to the 2012 Haida Gwaii, 2006 Kuril Islands, and 2011 Tohoku events and for Tohoku also in close field. With the exception of the Tohoku far-field case, for which the tsunami reconstruction by the TEC inversion is less efficient due to the ionospheric noise background associated to geomagnetic storm, which occurred on the earthquake day, we show that the peak-to-peak amplitude of the sea level variation inverted by this method can be compared to the tsunami wave height measured by a DART buoy with an error of less than 20%. This demonstrates that the inversion of TEC data with a tsunami normal-mode summation approach is able to estimate quite accurately the amplitude and waveform of the first tsunami arrival.

Mapping the total electron content over Malaysia using Spherical Cap Harmonic Analysis

NASA Astrophysics Data System (ADS)

Bahari, S.; Abdullah, M.; Bouya, Z.; Musa, T. A.

2017-12-01

The ionosphere over Malaysia is unique because of her location which is in close proximity to the geomagnetic equator and is in the equatorial regions. In this region, the magnetic field is horizontally oriented from south to north and field aligned direction is in the meridional plane (ExB) which becomes the source of equatorial ionospheric anomaly occurrence such as plasma bubble, fountain effects and others. Until today, there is no model that has been developed over Malaysia to study the ionosphere. Due to that, the main objective of this paper is to develop a new technique for mapping the total electron content (TEC) from GPS measurements. Data by myRTKnet network of GPS receiver over Malaysia were used in this study. A new methodology, based on modified spherical cap harmonic analysis (SCHA), was developed to estimate diurnal vertical TEC over the region using GPS observations. The SCHA model is based on longitudinal expansion in Fourier series and fractional Legendre co-latitudinal functions over a spherical cap-like region. The TEC map with spatial resolution of 0.15 ° x 0.15 ° in latitude and longitude with the time resolution of 30 seconds are derived. TEC maps from the SCHA model were compared with the global ionospheric map and other regional models. Result shows that during low solar activity, SCHA model had a better mapping with the accuracy of less than 1 TECU compared to other regional models.

The study of variability of TEC over mid-latitude American regions during the ascending phase of solar cycle 24 (2009-2011)

NASA Astrophysics Data System (ADS)

Asmare Tariku, Yekoye

2016-08-01

This paper deals with the pattern of the variability of the Global Positioning System vertical total electron content (GPS VTEC) and the modeled vertical total electron content (IRI 2012 TEC) over American mid-latitude regions during the rising phase of solar cycle 24 (2009-2011). This has been conducted employing ground-based dual frequency GPS receiver installed at Mississippi County Airport (geographic lat. 36.85°N and long. 270.64°E). In this work, the monthly and seasonal variations in the measured VTEC have been analyzed and compared with the VTEC inferred from IRI-2012 model. It has been shown that the monthly and seasonal mean VTEC values get decreased mostly between 05:00 and 10:00 UT and reach their minimal nearly at around 10:00 UT for both the experimental and the model. The VTEC values then get increased and reach the peak values at around 20:00 UT and decrease again. Moreover, it is depicted that the model better estimates both the monthly and seasonal mean hourly VTEC values mostly between 15:00 and 20:00 UT. The modeled monthly and seasonal VTEC values are smaller than the corresponding measured values as the solar activity decreases when all options for the topside electron density are used. However, as the Sun goes from a very low to a high solar activity, the overestimation performance of the VTEC values derived from the model increases. The overall results show that it is generally better to use the model with IRI-2000 option for the topside electron density in estimating the monthly and seasonal VTEC variations, especially when the activity of the Sun decreases.

GPS TEC near the crest of the EIA at 95°E during the ascending half of solar cycle 24 and comparison with IRI simulations

NASA Astrophysics Data System (ADS)

Bhuyan, Pradip Kumar; Hazarika, Rumajyoti

2013-10-01

Total electron content (TEC) data obtained from GPS dual frequency measurements during the ascending half of the solar cycle 24 from 2009 to 2012 over Dibrugarh (27.5°N, 94.9°E; 17.6°N MLAT) have been used to study the diurnal, seasonal, annual and solar cycle variation of TEC. The measurements reported here are for the first time from the location situated at the poleward edge of the northern equatorial ionization anomaly (EIA) and within the peak region of the longitudinal wave number 4 (WN4) structure in EIA crest TEC. TEC exhibits a minimum around 0600 LT and diurnal maximum around 1300-1600 LT. In the low and moderate solar activity years 2009-2010 and 2010-2011, average daytime (1000-1600 LT) TEC in summer was higher (25.4 and 36.6 TECU) compared to that in winter (21.5 and 26.1 TECU). However, at the peak of the solar cycle in 2011-2012, reversal in the level of ionization between winter and summer takes place and winter TEC becomes higher (50.6 TECU) than that in summer (45.0 TECU). Further, TEC in spring (34.1, 49.9 and 63.3 TECU respectively in 2009-10, 2010-11 and 2011-12) is higher than that in autumn (24.2, 32.3 and 51.9 TECU respectively) thus showing equinoctial asymmetry in all the years of observation. The winter anomaly in high solar activity years and equinoctial asymmetry all throughout may be largely attributed to changes in the thermospheric O/N2 density ratio. A winter to summer delay of ˜1 h in the time of occurrence of the diurnal maximum has also been observed. Daytime maximum TEC bears a nonlinear relationship with F10.7 cm solar flux. TEC increases linearly with F10.7 cm solar flux initially up to about 140 sfu (1 sfu = 10-22 W m-2 Hz-1) after which it tends to saturate. On the contrary, TEC increases linearly with solar EUV flux (photons cm-2 s-1, 0.5-50 nm) during the same period. TEC predicted by the IRI 2012 are lower than the measured TEC for nearly 90% of the time.

Ionospheric disturbances detected by high-resolution GPS-TEC observations after an earthquake and a tornado

NASA Astrophysics Data System (ADS)

Tsugawa, Takuya; Otsuka, Yuichi; Saito, Akinori; Ishii, Mamoru; Nishioka, Michi

Ionospheric disturbances following the 2011 Tohoku earthquake and the 2013 Moore tornado were observed by high-resolution GPS total electron content (TEC) observations using dense GPS receiver networks. After the 2011 Tohoku earthquake, concentric waves with short propagation distance propagated in the radial direction in the propagation velocity of 3,457, 783, 423 m/s for the first, second, third peak, respectively. Following these waves, concentric waves with long propagation distance appeared to propagate at the velocity of 138-288 m/s. In the vicinity of the epicenter, sudden TEC depletions and short-period oscillations with a period of approximately 4 minutes were also observed. The center of these ionospheric variations, termed the "ionospheric epicenter", corresponded to the tsunami source. Comparing to the results of a numerical simulation using non-hydrostatic compressible atmosphere-ionosphere model, the first peak of circular wave would be caused by the acoustic waves generated from the propagating Rayleigh wave. The second and third waves would be caused by atmospheric gravity waves excited in the lower ionosphere due to the acoustic wave propagations from the tsunami source. The fourth and following waves are considered to be caused by the atmospheric gravity waves induced by the wavefronts of traveling tsunami. After the EF5 tornado hit Moore, Oklahoma, USA, on 20 May 2013, clear concentric waves and short-period oscillations were observed. These concentric waves were non-dispersive waves with a horizontal wavelength of approximately 120 km and a period of approximately 13 minutes. They were observed for more than seven hours throughout North America. TEC oscillations with a period of approximately 4 minutes were also observed in the south of Moore for more than eight hours. Comparison between the GPS-TEC observations and the infrared cloud images from the GOES satellite indicates that the concentric waves and the short-period oscillations would be caused by supercell-induced atmospheric gravity waves and acoustic resonances, respectively. In this presentation, we will introduce the observational results of these ionospheric disturbances and discuss about the mechanism of concentric waves and short-period oscillations observed in both events.

Verification of the modelling of the main ionospheric trough by the Electron Density Assimilative Model (EDAM)

NASA Astrophysics Data System (ADS)

Parker, James; Pryse, Eleri; Jackson-Booth, Natasha

2017-04-01

The main ionospheric trough is a large-scale spatial depletion in the ionospheric electron density that commonly separates the auroral and mid-latitude regions. The feature covers several degrees in latitude and is extended in longitude. It exhibits substantial day-to-day variability in both the location of its minimum ionisation density and in its latitudinal structure. Observations from the UK have shown the trough to be a night-time feature, appearing in early evening to the north of the mainland and progressing equatorward during the course of the night. At dawn, photoionisation fills in the feature. Under increasing levels of geomagnetic activity, the trough moves progressively to lower latitudes. Steep gradients on the trough walls and their variability can cause problems for radio applications. EDAM can be used to model the ionosphere at the trough latitudes by assimilating ionospheric observations from this region into the International Reference Ionosphere (IRI). In this study troughs modelled by EDAM, assimilating data for a period from September to December 2002, are presented and are verified by comparisons with independent observations. Measurements of slant total electron content (sTEC) between GPS satellites and forty ground receivers in Europe were assimilated into EDAM to model the ionospheric electron density. The Vertical Total Electron Content (VTEC) was then calculated through the model, with the values at the longitude of 0.0E considered to obtain statistical characteristics of identified troughs parameters. Comparisons of the parameters with those obtained previously, using transmissions from the satellites of NIMS (Navy Ionospheric Monitoring System) orbiting at altitudes lower than GPS, revealed consistent results. Further support for the EDAM trough was obtained by comparisons of the model with independent GPS measurements. For this a GPS ground station not used in the assimilation was used to observe the sTEC to this "truth" station. Comparisons of these independent truth data with sTEC calculated through the model were used to determine the accuracy of EDAM in the vicinity of the trough.

Preliminary Investigation of Longitudinal Differences in TEC and Scintillation at Transition Latitudes

DTIC Science & Technology

1991-04-04

AIR. j NO ABSOLUTE TEC. C: NEW SATELITE WINDOWS INSERTED. j - IAPEDRIVE PROBLEM. D: SOME DATA ON CHART NOT RECORDED ON TAPE. H = NPIB INTERFASE...PROBLEM. E: SOME DATA BROKEN UP. V 2 FLOPPY DISK/DRIVE PROBLEM. F: TAPE CHANGE. W - WRONG SATELITE WINDOWS. TOTAL HOURS OF ACTIVITY LEVEL 1:300 P - POWER...0 1 0 31 1 COMMENT’S: ADDITIONAL COMMENT’S. A: TAPE STOP * L1/L2 SCINTILLATION. B: GPS SYSTEM OFF THE AIR. O= N ABSOLUTE TEC. C: NEW SATELITE WINDOWS

A possible space-based tsunami early warning system using observations of the tsunami ionospheric hole.

PubMed

Kamogawa, Masashi; Orihara, Yoshiaki; Tsurudome, Chiaki; Tomida, Yuto; Kanaya, Tatsuya; Ikeda, Daiki; Gusman, Aditya Riadi; Kakinami, Yoshihiro; Liu, Jann-Yenq; Toyoda, Atsushi

2016-12-01

Ionospheric plasma disturbances after a large tsunami can be detected by measurement of the total electron content (TEC) between a Global Positioning System (GPS) satellite and its ground-based receivers. TEC depression lasting for a few minutes to tens of minutes termed as tsunami ionospheric hole (TIH) is formed above the tsunami source area. Here we describe the quantitative relationship between initial tsunami height and the TEC depression rate caused by a TIH from seven tsunamigenic earthquakes in Japan and Chile. We found that the percentage of TEC depression and initial tsunami height are correlated and the largest TEC depressions appear 10 to 20 minutes after the main shocks. Our findings imply that Ionospheric TEC measurement using the existing ground receiver networks could be used in an early warning system for near-field tsunamis that take more than 20 minutes to arrive in coastal areas.

A possible space-based tsunami early warning system using observations of the tsunami ionospheric hole

PubMed Central

Kamogawa, Masashi; Orihara, Yoshiaki; Tsurudome, Chiaki; Tomida, Yuto; Kanaya, Tatsuya; Ikeda, Daiki; Gusman, Aditya Riadi; Kakinami, Yoshihiro; Liu, Jann-Yenq; Toyoda, Atsushi

2016-01-01

Ionospheric plasma disturbances after a large tsunami can be detected by measurement of the total electron content (TEC) between a Global Positioning System (GPS) satellite and its ground-based receivers. TEC depression lasting for a few minutes to tens of minutes termed as tsunami ionospheric hole (TIH) is formed above the tsunami source area. Here we describe the quantitative relationship between initial tsunami height and the TEC depression rate caused by a TIH from seven tsunamigenic earthquakes in Japan and Chile. We found that the percentage of TEC depression and initial tsunami height are correlated and the largest TEC depressions appear 10 to 20 minutes after the main shocks. Our findings imply that Ionospheric TEC measurement using the existing ground receiver networks could be used in an early warning system for near-field tsunamis that take more than 20 minutes to arrive in coastal areas. PMID:27905487

Estimate of higher order ionospheric errors in GNSS positioning

NASA Astrophysics Data System (ADS)

Hoque, M. Mainul; Jakowski, N.

2008-10-01

Precise navigation and positioning using GPS/GLONASS/Galileo require the ionospheric propagation errors to be accurately determined and corrected for. Current dual-frequency method of ionospheric correction ignores higher order ionospheric errors such as the second and third order ionospheric terms in the refractive index formula and errors due to bending of the signal. The total electron content (TEC) is assumed to be same at two GPS frequencies. All these assumptions lead to erroneous estimations and corrections of the ionospheric errors. In this paper a rigorous treatment of these problems is presented. Different approximation formulas have been proposed to correct errors due to excess path length in addition to the free space path length, TEC difference at two GNSS frequencies, and third-order ionospheric term. The GPS dual-frequency residual range errors can be corrected within millimeter level accuracy using the proposed correction formulas.

An Initial Investigation of Ionospheric Gradients for Detection of Ionospheric Disturbances over Turkey

NASA Astrophysics Data System (ADS)

Koroglu, Meltem; Arikan, Feza; Koroglu, Ozan

2015-04-01

Ionosphere is an ionized layer of earth's atmosphere which affect the propagation of radio signals due to highly varying electron density structure. Total Electron Content (TEC) and Slant Total Electron Content (STEC) are convenient measures of total electron density along a ray path. STEC model is given by the line integral of the electron density between the receiver and GPS satellite. TEC and STEC can be estimated by observing the difference between the two GPS signal time delays that have different frequencies L1 (1575 MHz) and L2 (1227 MHz). During extreme ionospheric storms ionospheric gradients becomes larger than those of quiet days since time delays of the radio signals becomes anomalous. Ionosphere gradients can be modeled as a linear semi-infinite wave front with constant propagation speed. One way of computing the ionospheric gradients is to compare the STEC values estimated between two neighbouring GPS stations. In this so-called station-pair method, ionospheric gradients are defined by dividing the difference of the time delays of two receivers, that see the same satellite at the same time period. In this study, ionospheric gradients over Turkey are computed using the Turkish National Permanent GPS Network (TNPGN-Active) between May 2009 and September 2012. The GPS receivers are paired in east-west and north-south directions with distances less than 150 km. GPS-STEC for each station are calculated using IONOLAB-TEC and IONOLAB-BIAS softwares (www.ionolab.org). Ionospheric delays are calculated for each paired station for both L1 and L2 frequencies and for each satellite in view with 30 s time resolution. During the investigation period, different types of geomagnetic storms, Travelling Ionospheric Disturbances (TID), Sudden Ionospheric Disturbances (SID) and various earthquakes with magnitudes between 3 to 7.4 have occured. Significant variations in the structure of station-pair gradients have been observed depending on location of station-pairs, the path of the satellites, strength of the geomagnetic storms and type, depth and magnitude of the earthquakes. For a typical geomagnetic storm the gradients can get as high as 30 mm/km. For the earthquakes, both the magnitude and the structure of the ionospheric delay gradients exhibit strong variability. This study forms a basis for a comprehensive understanding of ionospheric variability for midlatitude GBAS and SBAS systems. This study is supported by a joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

Dual-band beacon experiment over Southeast Asia for ionospheric irregularity analysis

NASA Astrophysics Data System (ADS)

Watthanasangmechai, K.; Yamamoto, M.; Saito, A.; Saito, S.; Maruyama, T.; Tsugawa, T.; Nishioka, M.

2013-12-01

An experiment of dual-band beacon over Southeast Asia was started in March 2012 in order to capture and analyze ionospheric irregularities in equatorial region. Five GNU Radio Beacon Receivers (GRBRs) were aligned along 100 degree geographic longitude. The distances between the stations reach more than 500 km. The field of view of this observational network covers +/- 20 degree geomagnetic latitude including the geomagnetic equator. To capture ionospheric irregularities, the absolute TEC estimation technique was developed. The two-station method (Leitinger et al., 1975) is generally accepted as a suitable method to estimate TEC offsets of dual-band beacon experiment. However, the distances between the stations directly affect on the robustness of the technique. In Southeast Asia, the observational network is too sparse to attain a benefit of the classic two-station method. Moreover, the least-squares approch used in the two-station method tries too much to adjust the small scales of the TEC distribution which are the local minima. We thus propose a new technique to estimate the TEC offsets with the supporting data from absolute GPS-TEC from local GPS receivers and the ionospheric height from local ionosondes. The key of the proposed technique is to utilize the brute-force technique with weighting function to find the TEC offset set that yields a global minimum of RMSE in whole parameter space. The weight is not necessary when the TEC distribution is smooth, while it significantly improves the TEC estimation during the ESF events. As a result, the latitudinal TEC shows double-hump distribution because of the Equatorial Ionization Anomaly (EIA). In additions, the 100km-scale fluctuations from an Equatorial Spread F (ESF) are captured at night time in equinox seasons. The plausible linkage of the meridional wind with triggering of ESF is under invatigating and will be presented. The proposed method is successful to estimate the latitudinal TEC distribution from dual-band frequency beacon data for the sparse observational network in Southeast Asia which may be useful for other equatorial sectors like Affrican region as well.

Solar activity indices as a proxy for the variation of ionospheric Total Electron Content (TEC) over Bahir Dar, Ethiopia during the year 2010-2014

NASA Astrophysics Data System (ADS)

Kassa, Tsegaye; Tilahun, Samson; Damtie, Baylie

2017-09-01

This paper was aimed at investigating the solar variations of vTEC as a function of solar activity parameters, EUV and F10.7 radio flux. The daily values of ionospheric vertical Total Electron Content (vTEC) were observed using a dual frequency GPS receiver deployed at Bahir Dar (11.6°N and 37.36°E), Ethiopia. Measurements were taken during the period of 2010-2014 for successive five years and analysis was done on only quiet day observations. A quadratic fit was used as a model to describe the daily variation of vTEC in relation to solar parameters. Linear and non-linear coefficients of the vTEC variations were calculated in order to capture the trend of the variation. The variation of vTEC have showed good agreement with the trend of solar parameters in almost all of the days we consider during the period of our observations. We have explicitly observed days with insignificant TECU deviation (eg. modeling with respect to EUV, DOY = 49 in 2010 and modeling with respect to F10.7, DOY = 125 in 2012 and the like) and days with maximum deviation (about 50 TECU). A maximum deviation were observed, on average, during months of equinox whereas minimum during solstice months. This implies that there is a need to consider more parameters, including EUV and F10.7, that can affect the variation of vTEC during equinox seasons. Relatively, small deviations was observed in modeling vTEC as a function of EUV compared to that of the variation due to F10.7 cm flux. This may also tell us that EUV can be more suitable in modeling the solar variation of vTEC especially for longterm trends. Even though, the linear trend of solar variations of vTEC was frequently observed, significant saturation and amplification trends of the solar variations of vTEC were also observed to some extent across the months of the years we have analyzed. This mixed trend of the solar variation of vTEC implies the need for thorough investigation on the effect of solar parameters on TEC. However, based on long-term dataset, we came to conclude that the solar variations of vTEC is dominated by its linear pattern.

Application of Modified Particle Swarm Optimization Method for Parameter Extraction of 2-D TEC Mapping

NASA Astrophysics Data System (ADS)

Toker, C.; Gokdag, Y. E.; Arikan, F.; Arikan, O.

2012-04-01

Ionosphere is a very important part of Space Weather. Modeling and monitoring of ionospheric variability is a major part of satellite communication, navigation and positioning systems. Total Electron Content (TEC), which is defined as the line integral of the electron density along a ray path, is one of the parameters to investigate the ionospheric variability. Dual-frequency GPS receivers, with their world wide availability and efficiency in TEC estimation, have become a major source of global and regional TEC modeling. When Global Ionospheric Maps (GIM) of International GPS Service (IGS) centers (http://iono.jpl.nasa.gov/gim.html) are investigated, it can be observed that regional ionosphere along the midlatitude regions can be modeled as a constant, linear or a quadratic surface. Globally, especially around the magnetic equator, the TEC surfaces resemble twisted and dispersed single centered or double centered Gaussian functions. Particle Swarm Optimization (PSO) proved itself as a fast converging and an effective optimization tool in various diverse fields. Yet, in order to apply this optimization technique into TEC modeling, the method has to be modified for higher efficiency and accuracy in extraction of geophysical parameters such as model parameters of TEC surfaces. In this study, a modified PSO (mPSO) method is applied to regional and global synthetic TEC surfaces. The synthetic surfaces that represent the trend and small scale variability of various ionospheric states are necessary to compare the performance of mPSO over number of iterations, accuracy in parameter estimation and overall surface reconstruction. The Cramer-Rao bounds for each surface type and model are also investigated and performance of mPSO are tested with respect to these bounds. For global models, the sample points that are used in optimization are obtained using IGS receiver network. For regional TEC models, regional networks such as Turkish National Permanent GPS Network (TNPGN-Active) receiver sites are used. The regional TEC models are grouped into constant (one parameter), linear (two parameters), and quadratic (six parameters) surfaces which are functions of latitude and longitude. Global models require seven parameters for single centered Gaussian and 13 parameters for double centered Gaussian function. The error criterion is the normalized percentage error for both the surface and the parameters. It is observed that mPSO is very successful in parameter extraction of various regional and global models. The normalized reconstruction error varies from 10-4 for constant surfaces to 10-3 for quadratic surfaces in regional models, sampled with regional networks. Even for the cases of a severe geomagnetic storm that affects measurements globally, with IGS network, the reconstruction error is on the order of 10-1 even though individual parameters have higher normalized errors. The modified PSO technique proved itself to be a useful tool for parameter extraction of more complicated TEC models. This study is supported by TUBITAK EEEAG under Grant No: 109E055.

On the problem of detection of seismo-ionospheric phenomena by multi-instrumental radiophysical observations

NASA Astrophysics Data System (ADS)

Cherniak, Iurii; Zakharenkova, Irina; Shagimuratov, Irk; Suslova, Olga

2012-07-01

Analysis of the previous works on lithosphere-ionosphere interactions confirmed the necessity to use simultaneous observations from several independent diagnostics tools in order to raise the reliability of the observed seismo-ionospheric effects. The influence on the ionosphere from below is weaker in comparison with effects of solar or geomagnetic origin. Due to this reason it is very actual the problem of detection of seismo-ionospheric anomalies on the background of strong regular and quasi-regular variation of space weather parameters. For the given research we use integrated processing of the ionospheric data from different sources: total electron content (TEC) data obtained on the basis of regular GPS observations of IGS stations located in Sakhalin and Japan regions, ionospheric E and F2 layers peak parameters, derived from data of Japan ionosonde network and electron density profiles, obtained by FORMOSAT-3/COSMIC radio occultation measurements. As a case-study it was analyzed the Nevelsk earthquake (M 6.2) that took place at the Far East of Russian Federation on August 2, 2007. On July 29, 2007, several days prior to earthquake, the characteristic anomaly was found out as the day-time significant enhancement of TEC at the vicinity of earthquake. This enhancement reached the maximal value of 4-6 TECU in absolute values, that is 40-50% to the background conditions, and it was situated very close to the epicenter position. The noticeable enhancement of F2 peak critical frequency (foF2) was observed over Wakkanai ionosonde. For the evening hours (19-22 LT) it reached the value of 6.8-7.7 MHz whereas monthly median was 5.3-5.7 MHz. This foF2 increase was coincided in time with the appearance of TEC anomaly in TEC maps over the considered region (taken from GIMs IONEX). In order to separate seismo-ionospheric perturbations from geomagnetic disturbances it was done the comparative analysis of the revealed ionospheric effect possibly related with seismic activity and ionosphere changes during geomagnetic storms which took place during July and August of 2007. We acknowledge the University Corporation for Atmospheric Research (UCAR) for providing the COSMIC data, IGS community for GPS permanent data and WDC for Ionosphere, Tokyo, National Institute of Information and Communications Technology (NICT) for ionosonde data. This work was supported by Russian Federation President grant MK-2058.2011.5.

Calculating Total Electron Content under the presence of the Aurora Borealis in Fairbanks, Alaska, and Kiruna, Sweden.

NASA Astrophysics Data System (ADS)

Ahmad, H.; Ehteshami, A.; Edgar, B.

2015-12-01

With the presence of the ionosphere and plasmasphere interacting with geomagnetic storms, scattering effects can be seen by the signals sent to and by GPS/GLONASS satellites. To quantify this dispersive effect, scientists look into what the culprit is that causes this signal bias on an atomic level. Results have shown that the concentration of oscillating electrons is directly proportional to the amount of bias the signal from a point on earth to a GPS satellite witnesses. This is called the Total Electron Content (TEC) of a specified path, measured in electrons per meters squared (. In this project, the process of collecting and analyzing TEC units was kept the same as the previous methods while keeping the cost below $3,000. Using a dual-frequency GNSS receiver from Javad, Triumph-2, the project team recorded a series of 24 hour interval data logs as the receiver stored incoming signals from any reachable satellite. Because of the dispersive media in the ionosphere, the signal witnesses a bend in its path causing a delay, called the Slant TEC (sTEC). Using libraries from GPStk and TEQC, we analyzed RINEX files to view the differential phase and differential pseudorange frequency to compute slant TEC units (sTECU). Using the obtained data, we analyzed the difference between the sTEC units collected in Houston, Texas to the ones collected in Fairbanks, Alaska. Afterwards, the project will continue on another balloon in Kiruna, Sweden at the Esrange Space Center. The receiver will be in flight this time on a 48 hour flight.

Regional TEC dynamic modeling based on Slepian functions

NASA Astrophysics Data System (ADS)

Sharifi, Mohammad Ali; Farzaneh, Saeed

2015-09-01

In this work, the three-dimensional state of the ionosphere has been estimated by integrating the spherical Slepian harmonic function and Kalman filter. The spherical Slepian harmonic functions have been used to establish the observation equations because of their properties in local modeling. Spherical harmonics are poor choices to represent or analyze geophysical processes without perfect global coverage but the Slepian functions afford spatial and spectral selectivity. The Kalman filter has been utilized to perform the parameter estimation due to its suitable properties in processing the GPS measurements in the real-time mode. The proposed model has been applied to the real data obtained from the ground-based GPS observations across some portion of the IGS network in Europe. Results have been compared with the estimated TECs by the CODE, ESA, IGS centers and IRI-2012 model. The results indicated that the proposed model which takes advantage of the Slepian basis and Kalman filter is efficient and allows for the generation of the near-real-time regional TEC map.

Inversion of the perturbation GPS-TEC data induced by tsunamis in order to estimate the sea level anomaly.

NASA Astrophysics Data System (ADS)

Rakoto, Virgile; Lognonné, Philippe; Rolland, Lucie; Coïsson, Pierdavide; Drilleau, Mélanie

2017-04-01

Large underwater earthquakes (Mw > 7) can transmit part of their energy to the surrounding ocean through large sea-floor motions, generating tsunamis that propagate over long distances. The forcing effect of tsunami waves on the atmosphere generate internal gravity waves which produce detectable ionospheric perturbations when they reach the upper atmosphere. Theses perturbations are frequently observed in the total electron content (TEC) measured by the multi-frequency Global navigation Satellite systems (GNSS) data (e.g., GPS,GLONASS). In this paper, we performed for the first time an inversion of the sea level anomaly using the GPS TEC data using a least square inversion (LSQ) through a normal modes summation modeling technique. Using the tsunami of the 2012 Haida Gwaii in far field as a test case, we showed that the amplitude peak to peak of the sea level anomaly inverted using this method is below 10 % error. Nevertheless, we cannot invert the second wave arriving 20 minutes later. This second wave is generaly explain by the coastal reflection which the normal modeling does not take into account. Our technique is then applied to two other tsunamis : the 2006 Kuril Islands tsunami in far field, and the 2011 Tohoku tsunami in closer field. This demonstrates that the inversion using a normal mode approach is able to estimate fairly well the amplitude of the first arrivals of the tsunami. In the future, we plan to invert in real the TEC data in order to retrieve the tsunami height.

Relative importance of horizontal and vertical transports to the formation of ionospheric storm-enhanced density and polar tongue of ionization

NASA Astrophysics Data System (ADS)

Liu, Jing; Wang, Wenbin; Burns, Alan; Solomon, Stanley C.; Zhang, Shunrong; Zhang, Yongliang; Huang, Chaosong

2016-08-01

There are still uncertainties regarding the formation mechanisms for storm-enhanced density (SED) in the high and subauroral latitude ionosphere. In this work, we deploy the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) and GPS total electron content (TEC) observations to identify the principle mechanisms for SED and the tongue of ionization (TOI) through term-by-term analysis of the ion continuity equation and also identify the advantages and deficiencies of the TIEGCM in capturing high-latitude and subauroral latitude ionospheric fine structures for the two geomagnetic storm events occurring on 17 March 2013 and 2015. Our results show that in the topside ionosphere, upward E × B ion drifts are most important in SED formation and are offset by antisunward neutral winds and downward ambipolar diffusion effects. In the bottomside F region ionosphere, neutral winds play a major role in generating SEDs. SED signature in TEC is mainly caused by upward E × B ion drifts that lift the ionosphere to higher altitudes where chemical recombination is slower. Horizontal E × B ion drifts play an essential role in transporting plasma from the dayside convection throat region to the polar cap to form TOIs. Inconsistencies between model results and GPS TEC data were found: (1) GPS relative TEC difference between storm time and quiet time has "holes" in the dayside ion convection entrance region, which do not appear in the model results. (2) The model tends to overestimate electron density enhancements in the polar region. Possible causes for these inconsistencies are discussed in this article.

Comparative analysis of GPS-derived TEC estimates and foF2 observations during storm conditions towards the expansion of ionospheric forecasting capabilities over Europe

NASA Astrophysics Data System (ADS)

Tsagouri, Ioanna; Belehaki, Anna; Elias, Panagiotis

2017-04-01

This paper builts the discussion on the comparative analysis of the variations in the peak electron density at F2 layer and the TEC parameter during a significant number of geomagnetic storm events that occurred in the present solar cycle 24. The ionospheric disturbances are determined through the comparison of actual observations of the foF2 critical frequency and GPS-TEC estimates obtained over European locations with the corresponding median estimates, and they are analysed in conjunction to the solar wind conditions at L1 point that are monitored by the ACE spacecraft. The quantification of the storm impact on the TEC parameter in terms of possible limitations introduced by different TEC derivation methods is carefully addressed.The results reveal similarities and differences in the response of the two parameters with respect to the solar wind drivers of the storms, as well as the local time and the latitude of the observation point. The aforementioned dependences drive the storm-time forecasts of the SWIF model (Solar Wind driven autorgressive model for Ionospheric short-term Forecast), which is operationally implemented in the DIAS system (http://dias.space.noa.gr) and extensively tested in performance at several occassions. In its present version, the model provides alerts and warnings for upcoming ionospheric disturbances, as well as single site and regional forecasts of the foF2 characteristic over Europe up to 24 hours ahead based on the assesment of the solar wind conditions at ACE location. In that respect, the results obtained above support the upgrade of the SWIF's modeling technique in forecasting the storm-time TEC variation within an operational environment several hours in advance. Preliminary results on the evaluation of the model's efficiency in TEC prediction are also discussed, giving special attention in the assesment of the capabilities through the TEC-derivation uncertanties for future discussions.

Detection and Characterization of Traveling Ionospheric Disturbances (TIDs) with GPS and HF sensors

NASA Astrophysics Data System (ADS)

Groves, K. M.; Paznukhov, V.; Bullett, T. W.; Mackenzie, E.

2014-12-01

Recently there has been increasing interest and awareness in the coupling between the neutral atmosphere and the ionosphere and specifically in processes that cause wave-like non-stationary perturbations in the bottom-side of the F-region. A class of these perturbations having periods greater than about five minutes and wavelengths greater than a kilometer or so are believed to occur routinely and propagate throughout the ionosphere; they are known as traveling ionospheric disturbances (TIDs). In this study we investigate ground-based techniques for detecting and characterizing TIDs with periods ranging from 30-90 minutes and wavelengths of 10s of km or more. These waves are believed to affect the Doppler and propagation angles of high frequency (HF) radio waves refracting through the affected regions. Wave-like perturbations are also commonly observed in GPS total electron content (TEC) data. In the current study we monitor a number of different commercial HF broadcast transmitters from a station in Wallops Island, VA and collect GPS TEC data from numerous stations along the path between the HF receiver at Wallops and specific HF transmitters. The objective is to understand the relationship between TID signatures on HF and GPS sensors and to possibly characterize TIDs using such observations, including propagation velocity, amplitude, wavelength and potentially source. Given that GPS TEC data are now relatively abundant around the globe, establishing a reliable technique for quantifying TIDs with these measurements would yield an important new technique towards developing a global TID monitoring capability that could support ionosphere-thermosphere coupling science as well as potential monitoring capabilities for natural disasters (e.g., earthquakes, tsunamis, volcanic eruptions) with significant TID signatures.

Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) resulting from Chelyabinsk Meteor Blast

NASA Astrophysics Data System (ADS)

Sheeks, B. J.; Warren, N.; Coster, A. J.

2013-12-01

A global network of GPS receivers continuously make line-of-sight (LOS) measurements of the total electron content (TEC) of the ionosphere. This TEC measurement data can be analyzed to 'persistently monitor' natural and man-made activity in the atmosphere (such as volcanic eruptions, earthquakes, rocket launches, etc) which propagate into the ionosphere to produce TIDs (Traveling Ionospheric Disturbances). As an example we have analyzed in detail the TIDs resulting from the 15 Feb 2013 Chelyabinsk meteor blast as observed by the Artu GPS receiver site in Arti, Russia close to the event. Seven of the GPS satellite measurements with LOS pierce points within 1000 km of the blast show disturbances. Four of these clearly show VTEC oscillations with ~12 minute periods. The other three show much weaker responses, but their LOS pierce points are far from the blast and their aspects between the geomagnetic field & blast propagation vector are unfavorable (near broadside). By fitting all seven measurements we estimate a propagation speed of ~380 m/s for these medium-scale TIDs. As future 'persistent surveillance' efforts we intend to investigate the observability of man-made activities such as static rocket engine firings in TEC measurements. Analysis of MSTIDs resulting from the Chelyabinsk meteor blast

Ionospheric Scintillation Induced by Solar Wind Dynamic Pressure Enhancements in the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Coppeans, T.; Zou, S.; Weatherwax, A. T.; Coster, A. J.

2017-12-01

Ionospheric scintillation is the random fluctuation in GPS signal radio waves passing through the ionosphere, a phenomenon that can result in the loss of GPS tracking, but can also reveal information about plasma structures in the ionosphere. Sudden compression of the Earth's magnetosphere by a solar wind dynamic pressure enhancement can cause dramatic changes in the E and F region ionospheric plasma. In this study, we investigate the possible ionospheric scintillation induced by solar wind pressure enhancements using ground-based scintillation receivers located at the McMurdo station and the South Pole station in Antarctica. Various studies of scintillation effects have been carried out, mainly in the northern hemisphere, while the southern hemisphere remains less studied. A pool of storm sudden commencements occurring between Jan. 2011 and Dec. 2014 were sorted based on solar wind dynamic pressure enhancement, background conditions, availability of data, and magnitude of scintillation response. Among the 89 events examined, 14 of them exhibited enhanced scintillation and were selected for detailed examination. Besides the scintillation receivers, other datasets have also been used to carry out the above study, including field-aligned currents from AMPERE, and global GPS TEC. Effects of FACs and TEC/TEC gradients on the generation of these scintillations are studied.

Automated daily processing of more than 1000 ground-based GPS receivers for studying intense ionospheric storms

NASA Astrophysics Data System (ADS)

Komjathy, Attila; Sparks, Lawrence; Wilson, Brian D.; Mannucci, Anthony J.

2005-12-01

As the number of ground-based and space-based receivers tracking the Global Positioning System (GPS) satellites steadily increases, it is becoming possible to monitor changes in the ionosphere continuously and on a global scale with unprecedented accuracy and reliability. As of August 2005, there are more than 1000 globally distributed dual-frequency GPS receivers available using publicly accessible networks including, for example, the International GPS Service and the continuously operating reference stations. To take advantage of the vast amount of GPS data, researchers use a number of techniques to estimate satellite and receiver interfrequency biases and the total electron content (TEC) of the ionosphere. Most techniques estimate vertical ionospheric structure and, simultaneously, hardware-related biases treated as nuisance parameters. These methods often are limited to 200 GPS receivers and use a sequential least squares or Kalman filter approach. The biases are later removed from the measurements to obtain unbiased TEC. In our approach to calibrating GPS receiver and transmitter interfrequency biases we take advantage of all available GPS receivers using a new processing algorithm based on the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This new capability is designed to estimate receiver biases for all stations. We solve for the instrumental biases by modeling the ionospheric delay and removing it from the observation equation using precomputed GIM maps. The precomputed GIM maps rely on 200 globally distributed GPS receivers to establish the "background" used to model the ionosphere at the remaining 800 GPS sites.

Ionospheric Anomalies on the day of the Devastating Earthquakes during 2000-2012

NASA Astrophysics Data System (ADS)

Su, Fanfan; Zhou, Yiyan; Zhu, Fuying

2013-04-01

The study of the ionospheric abnormal changes during the large earthquakes has attracted much attention for many years. Many papers have reported the deviations of Total Electron Content (TEC) around the epicenter. The statistical analysis concludes that the anomalous behavior of TEC is related with the earthquakes with high probability[1]. But the special cases have different features[2][3]. In this study, we carry out a new statistical analysis to investigate the nature of the ionospheric anomalies during the devastating earthquakes. To demonstrate the abnormal changes of the ionospheric TEC, we have examined the TEC database from the Global Ionosphere Map (GIM). The GIM ( ftp://cddisa.gsfc.nasa.gov/pub/gps/products/ionex) includes about 200 of worldwide ground-based receivers of the GPS. The TEC data with resolution of 5° longitude and 2.5° latitude are routinely published in a 2-h time interval. The information of earthquakes is obtained from the USGS ( http://earthquake.usgs.gov/earthquakes/eqarchives/epic/). To avoid the interference of the magnetic storm, the days with Dst≤-20 nT are excluded. Finally, a total of 13 M≥8.0 earthquakes in the global area during 2000-2012 are selected. The 27 days before the main shock are treated as the background days. Here, 27-day TEC median (Me) and the standard deviation (σ) are used to detect the variation of TEC. We set the upper bound BU = Me + 3*σ, and the lower bound BL = Me - 3*σ. Therefore the probability of a new TEC in the interval (BL, BU) is approximately 99.7%. If TEC varies between BU and BL, the deviation (DTEC) equals zero. Otherwise, the deviations between TEC and bounds are calculated as DTEC = BU/BL - TEC. From the deviations, the positive and negative abnormal changes of TEC can be evaluated. We investigate temporal and spatial signatures of the ionospheric anomalies on the day of the devastating earthquakes(M≥8.0). The results show that the occurrence rates of positive anomaly and negative anomaly are almost equal. The most significant anomaly on the day may occur at the time very close to the main shock, but sometimes it is not the case. The positions of the maximal deviations always deviate from the epicenter. The direction may be southeast, southwest, northeast or northwest with the almost equal probability. The anomalies may move to the epicenter, deviate to any direction, or stay at the same position and gradually fade out. There is no significant feature, such as occurrence time, position, or motion, and so on, which can indicate the source of the anomalies. References: [1].Le, H., J. Y. Liu, et al. (2011). "A statistical analysis of ionospheric anomalies before 736 M6.0+earthquakes during 2002-2010." J. Geophys. Res. 116. [2].Liu, J. Y., Y. I. Chen, et al. (2009). "Seismoionospheric GPS total electron content anomalies observed before the 12 May 2008 Mw7.9 Wenchuan earthquake." J. Geophys. Res. 114. [3].Rolland, L. M., P. Lognonne, et al. (2011). "Detection and modeling of Rayleigh wave induced patterns in the ionosphere." J. Geophys. Res. 116.

Assessment of IRI-2012, NeQuick-2 and IRI-Plas 2015 models with observed equatorial ionization anomaly in Africa during 2009 sudden stratospheric warming event

NASA Astrophysics Data System (ADS)

Bolaji, O. S.; Oyeyemi, E. O.; Adewale, A. O.; Wu, Q.; Okoh, D.; Doherty, P. H.; Kaka, R. O.; Abbas, M.; Owolabi, C.; Jidele, P. A.

2017-11-01

In Africa, we assessed the performance of all the three options of International Reference Ionosphere 2012, IRI-2012 (i.e. IRI-2001, IRI-2001COR and IRI-NeQuick), NeQuick-2 and IRI-Plas 2015 models prior to and during 2009 sudden stratospheric warming (SSW) event to predict equatorial ionization anomaly (EIA) crest locations and their magnitudes using total electron content (TEC) from experimental records of Global Positioning System (GPS). We confirmed that the IRI-Plas 2015 that appeared as the best compared to all of the models as regard prediction of the EIA crest locations in the northern hemisphere of Africa is due to discontinuities in the GPS data between ∼8° N and 22° N. As regard the predictions of EIA crest magnitudes and the location of EIA crests in the southern hemisphere of Africa, they are not present in all the models. The NeQuick-2 model does not have the capability to predict either the EIA crest location in the northern or southern hemisphere. The SSW effect on the low latitude was able to modify a single EIA crest to pre-noon and post noon EIA crests in the northern hemisphere during the SSW peak phase and significantly reduced the GPS TEC magnitudes over the hemispheres as well. These SSW effects and delays of plasma transportation to higher latitudes in GPS TEC were absent in all the models. For future improvements of IRI-2012, NeQuick-2 and IRI-Plas 2015 models, SSW conditions should be included in order to characterize the effect of lower atmosphere on the ionosphere. The EIA trough modeling is only present in IRI-2001COR and IRI-2001NeQuick options. In the middle latitude, all the model could not predict the location of highest TEC magnitudes found at RBAY (Richardsbay, South Africa).

C/NOFS, SWARM, and LISN Observations of Equatorial Plasma Bubbles

NASA Astrophysics Data System (ADS)

Valladares, C. E.; Coisson, P.; Buchert, S. C.; Huang, C.; Sheehan, R.

2017-12-01

We have used Langmuir Probe densities measured during the early commissioning phase of the SWARM mission and simultaneous number densities recorded with the PLP instrument on board the C/NOFS satellite to investigate the geometric characteristics of equatorial plasma bubbles (EPB). The SWARM satellites orbit in a polar orbit and the C/NOFS satellite has a near equatorial trajectory making it possible to precisely measure the north-south and the east-west width of plasma depletions. This unique satellite database is complemented with TEC values collected with hundreds of GPS receivers that belong to LISN and other networks that operate in South and Central America. The GPS receivers provide multiple and almost concurrent observations of the TEC depletions that are required to calculate the velocity of plasma bubbles as a function of time, latitude, and longitude. The bubble velocity field commonly decreases through the night from 150 to 0 m/s and from low to higher latitudes at a rate equal to 5 m/s/degree. This bubble velocity field is used to trace backward and forward in time the satellite and GPS observations and reconstruct plasma depletions in 3 dimensions. The 3-D geometry indicates that in December 2013, the EPBs most of the time correspond to a series of embedded shells that drift eastward with velocities that vary between 125 and 20 m/s. The 3-D reconstructed EPBs can be used to perform close comparisons with results of numerical simulations and 2-D observations conducted with coherent radars or imagers.

Statistical Analysis of the Ionosphere based on Singular Value Decomposition

NASA Astrophysics Data System (ADS)

Demir, Uygar; Arikan, Feza; Necat Deviren, M.; Toker, Cenk

2016-07-01

Ionosphere is made up of a spatio-temporally varying trend structure and secondary variations due to solar, geomagnetic, gravitational and seismic activities. Hence, it is important to monitor the ionosphere and acquire up-to-date information about its state in order both to better understand the physical phenomena that cause the variability and also to predict the effect of the ionosphere on HF and satellite communications, and satellite-based positioning systems. To charaterise the behaviour of the ionosphere, we propose to apply Singular Value Decomposition (SVD) to Total Electron Content (TEC) maps obtained from the TNPGN-Active (Turkish National Permanent GPS Network) CORS network. TNPGN-Active network consists of 146 GNSS receivers spread over Turkey. IONOLAB-TEC values estimated from each station are spatio-temporally interpolated using a Universal Kriging based algorithm with linear trend, namely IONOLAB-MAP, with very high spatial resolution. It is observed that the dominant singular value of TEC maps is an indicator of the trend structure of the ionosphere. The diurnal, seasonal and annual variability of the most dominant value is the representation of solar effect on ionosphere in midlatitude range. Secondary and smaller singular values are indicators of secondary variation which can have significance especially during geomagnetic storms or seismic disturbances. The dominant singular values are related to the physical basis vectors where ionosphere can be fully reconstructed using these vectors. Therefore, the proposed method can be used both for the monitoring of the current state of a region and also for the prediction and tracking of future states of ionosphere using singular values and singular basis vectors. This study is supported by by TUBITAK 115E915 and Joint TUBITAK 114E092 and AS CR14/001 projects.

Multi-dimensional distribution of near-field ionospheric disturbances produced by the 2015 Mw7.8 Nepal earthquake

NASA Astrophysics Data System (ADS)

Tang, Jun; Yuan, Yunbin

2017-10-01

Ionospheric anomalies possibly associated with large earthquakes, particularly coseismic ionospheric disturbances, have been detected by global positioning system (GPS). A large Nepal earthquake with magnitude Mw7.8 occurred on April 25, 2015. In this paper, we investigate the multi-dimensional distribution of near-field coseismic ionospheric disturbances (CIDs) using total electron content (TEC) and computerized ionospheric tomography (CIT) from regional GPS observational data. The results show significant ionospheric TEC disturbances and interesting multi-dimensional structures around the main shock. Regarding the TEC changes, coseismic ionospheric disturbances occur approximately 10-20 min after the earthquake northeast and northwest of epicentre. The maximum ridge-to-trough amplitude of CIDs is up to approximately 0.90 TECU/min. Propagation velocities of the TEC disturbances are 1.27 ± 0.06 km/s and 1.91 ± 0.38 km/s. It is believed that the ionospheric disturbances are triggered by acoustic and Rayleigh waves. Tomographic results show that the three-dimensional distribution of ionospheric disturbances obviously increases at an altitude of 300 km above the surrounding epicentre, predominantly in the entire region between 200 km and 400 km. Significant ionospheric disturbances appear at 06:30 UT from tomographic images. This study reveals characteristics of an ionospheric anomaly caused by the Nepal earthquake.

Observation of subsecond variations in auroral region total electron content using 100 Hz sampling of GPS observables

NASA Astrophysics Data System (ADS)

McCaffrey, A. M.; Jayachandran, P. T.

2017-06-01

First ever auroral region total electron content (TEC) measurements at 100 Hz using a Septentrio PolaRxS Pro receiver are analyzed to discover ionospheric signatures which would otherwise be unobtainable with the frequently used lower sampling rates. Two types of variations are observed: small-magnitude (amplitude) variations, which are present consistently throughout the data set, and larger-magnitude (amplitude) variations, which are less frequent. Small-amplitude TEC fluctuations are accounted for by the receiver phase jitter. However, estimated secondary ionospheric effects in the calculation of TEC and the receiver phase jitter were unable to account for the larger-amplitude TEC fluctuations. These variations are also accompanied by fluctuations in the magnetic field, which seems to indicate that these fluctuations are real and of geophysical significance. This paper presents a technique and the capability of high-rate TEC measurements in the study of auroral dynamics. Further detailed study is needed to identify the cause of these subsecond TEC fluctuations and associated magnetic field fluctuations.

Seismo-Ionospheric Precursor in the GIM TEC of the 24 August 2014 M6 Napa Earthquake

NASA Astrophysics Data System (ADS)

Wu, T. Y.; Liu, T. J. Y.; Liu, J. Y.

2015-12-01

This study examines seismo-ionospheric precursors (SIPs) in the global ionosphere map (GIM) of the total electron content (TEC) associated with the 24 August 2014 M6 South Napa earthquake and statistical evidence of SIPs of the GPS TEC in western USA during 2000-2014. The temporal SIP in the GIM TEC around the epicenter significantly decreasing (negative anomaly) on 22 August. To discriminate the global effect, such as solar flares, magnetic storms, etc., and the local effect, such as earthquakes, 5183 lattices on the GIM are employed to conduct a global search of the SIP distribution. Anomalies of both GIM TEC and associated gradients specifically and continuously appearing over the epicenter suggest that the SIP relate to the 2014 South Napa earthquake. A simulation is further carried out to produce the SIP in GIM TEC before the earthquake. Results indicate that the eastward electric field generated over the epicenter area during the earthquake preparation period to be essential.

Space-borne Observations of Atmospheric Pre-Earthquake Signals in Seismically Active Areas: Case Study for Greece 2008-2009

NASA Technical Reports Server (NTRS)

Ouzounov, D. P.; Pulinets, S. A.; Davidenko, D. A.; Kafatos, M.; Taylor, P. T.

2013-01-01

We are conducting theoretical studies and practical validation of atm osphere/ionosphere phenomena preceding major earthquakes. Our approach is based on monitoring of two physical parameters from space: outgoi ng long-wavelength radiation (OLR) on the top of the atmosphere and e lectron and electron density variations in the ionosphere via GPS Tot al Electron Content (GPS/TEC). We retrospectively analyzed the temporal and spatial variations of OLR an GPS/TEC parameters characterizing the state of the atmosphere and ionosphere several days before four m ajor earthquakes (M>6) in Greece for 2008-2009: M6.9 of 02.12.08, M6. 2 02.20.08; M6.4 of 06.08.08 and M6.4 of 07.01.09.We found anomalous behavior before all of these events (over land and sea) over regions o f maximum stress. We expect that our analysis reveal the underlying p hysics of pre-earthquake signals associated with some of the largest earthquakes in Greece.

TEC variations over Mediteranean before and during the strong earthquake (M=6.2) of 12th October 2013 in Crete, Greece

NASA Astrophysics Data System (ADS)

Contadakis, Michael; Arabelos, Dimitrios; Vergos, Georgios; Spatalas, Spyridon

2014-05-01

In this paper the Total Electron Content (TEC) data of 9 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations over Mediteranean before and during the strong earthquake of 12th of October 2013, Which occur in western of Crete, Greece. In accordance to the results of similar analysis on the occasion of earthquakes in the area (Contadakis et al 2008, 2012a,2012b) the main conclusions of this analysis are the following. (a) TEC oscillations in a broad range of frequencies occur randomly over a broad area of several hundred km from the earthquake and (b) high frequency oscillations (f ≥ 0.0003Hz, periods T ≤ 60m) seems to point to the location of the earthquake with a questionable accuracy but the fractal characteristics of the frequencies distribution, points to the locus of the earthquake with a rather higher accuracy. We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology. Key words: GPS network, ionospheric total electron content, wavelet analysis References Contadakis, M.E., Arabelos, D.N. G. Asteriadis, S.D. Spatalas and Ch. Pikridas, 2008. TEC variations over the Mediterranean during the seismic activity period of the last quarter of 2005 in the area of Greece, Nat. Hazards Earth Syst. Sci., 8, 1267-1276 M.E. Contadakis, D.N. Arabelos, Ch. Pikridas and S.D. Spatalas, 2012a,TEC variations over Southern Europe before and during the M6.3 Abruzzo earthquake of 6th April 2009, Annals of Geophysics, Vol.55,1, p.83-93 M.E.Contadakis, D.N.Arabelos, and G.Vergos, 2012b, TEC variations over North-western Balkan peninsula before and during the seismic activity of 24th May 2009, EGU GA, Geoph. Res. Abs., Vol. 14, EGU2012-2319-2

Inversion of tsunami height using ionospheric observations. The case of the 2012 Haida Gwaii tsunami

NASA Astrophysics Data System (ADS)

Rakoto, V.; Lognonne, P. H.; Rolland, L.

2014-12-01

Large and moderate tsunamis generate atmospheric internal gravity waves that are detectable using ionospheric monitoring. Indeed tsunamis of height 2cm and more in open ocean were detected with GPS (Rolland et al. 2010). We present a new method to retrieve the tsunami height from GPS-derived Total Electron Content observations. We present the case of the Mw 7.8 Haida Gwaii earthquake that occured the 28 october 2012 offshore the Queen Charlotte island near the canadian west coast. This event created a moderate tsunami of 4cm offshore the Hawaii archipelago. Equipped with more than 50 receivers it was possible to image the tsunami-induced ionospheric perturbation. First, our forward model leading to the TEC perturbation follows three steps : (1) 3D modeling of the neutral atmosphere perturbation by summation of tsunami-induced gravity waves normal modes. (2) Coupling of the neutral atmosphere perturbation with the ionosphere to retrieve the electron density perturbation. (3) Integration of the electron density perturbation along each satellite-station ray path. Then we compare this results to the data acquired by the Hawaiian GPS network. Finally, we examine the possibility to invert the TEC data in order to retrieve the tsunami height and waveform. For this we investigate the link between the height of tsunamis and the perturbed TEC in the ionosphere.

Low latitude ionospheric TEC responses to dynamical complexity quantifiers during transient events over Nigeria

NASA Astrophysics Data System (ADS)

Ogunsua, Babalola

2018-04-01

In this study, the values of chaoticity and dynamical complexity parameters for some selected storm periods in the year 2011 and 2012 have been computed. This was done using detrended TEC data sets measured from Birnin-Kebbi, Torro and Enugu global positioning system (GPS) receiver stations in Nigeria. It was observed that the significance of difference (SD) values were mostly greater than 1.96 but surprisingly lower than 1.96 in September 29, 2011. The values of the computed SD were also found to be reduced in most cases just after the geomagnetic storm with immediate recovery a day after the main phase of the storm while the values of Lyapunov exponent and Tsallis entropy remains reduced due to the influence of geomagnetic storms. It was also observed that the value of Lyapunov exponent and Tsallis entropy reveals similar variation pattern during storm period in most cases. Also recorded surprisingly were lower values of these dynamical quantifiers during the solar flare event of August 8th and 9th of the year 2011. The possible mechanisms responsible for these observations were further discussed in this work. However, our observations show that the ionospheric effects of some other possible transient events other than geomagnetic storms can also be revealed by the variation of chaoticity and dynamical complexity.

Greenland Network (GNET) observations of Polar cap Patches and Arcs

NASA Astrophysics Data System (ADS)

Cesar, V. E.; Pradipta, R.; Pedersen, T.

2017-12-01

TEC values collected with the Greenland Network (GNET) of GPS/GNSS receivers and 630.0 nm airglow emissions recorded with an all-sky imager located at Qaanaaq in Greenland are used to investigate the relationship between the appearance and evolution of polar cap patches (PCP) and Sun-aligned arcs (S-AA) and the characteristics of the solar wind. Both PCP and S-AA produce TEC enhancements, but the PCP velocity is 10 times larger than the S-AA's drift. In addition, PCP move anti-sunwardly and the S-AA move in the dawn-dusk direction. We use these properties of PCPs and S-AAs and calculate the velocity of the TEC enhancements to identify and discriminate between patches and arcs. The physical location of the boundary of the polar cap is based on DMSP observations of particle precipitation. The IMF and other solar wind parameters are gathered with the ACE satellite that is positioned at the L1 point. Our observations indicate that during December 2009, TEC enhancements occur in the polar cap almost every day, but only when the solar wind velocity exceeds 290 km/s. PCPs appear almost immediately after the Bz turns southward; however, the S-AAs develop a few hours after Bz points northward. These conclusions demonstrate the ability of GNET continuous measurements over Greenland to conduct investigations of the formation and evolution of polar cap patches and arcs.

Comparison between IRI-2012 and GPS-TEC observations over the western Black Sea

NASA Astrophysics Data System (ADS)

Inyurt, Samed; Yildirim, Omer; Mekik, Cetin

2017-07-01

The ionosphere is a dynamic layer which generally changes according to radiation emitted by the sun, the movement of the earth around the sun, and sunspot activity. Variations can generally be categorized as regular or irregular variations. Both types of variation have a huge effect on radio wave propagation. In this study, we have focused on the seasonal variation effect, which is one of the regular forms of variation in terms of the ionosphere. We examined the seasonal variation over the ZONG station in Turkey for the year 2014. Our analysis results and IRI-2012 present different ideas about ionospheric activity. According to our analysed results, the standard deviation reached a maximum value in April 2014. However, the maximum standard deviation obtained from IRI-2012 was seen in February 2014. Furthermore, it is clear that IRI-2012 underestimated the VTEC values when compared to our results for all the months analysed. The main source of difference between the two models is the IRI-2012 topside ionospheric representation. IRI-2012 VTEC has been produced as a result of the integration of an electron density profile within altitudinal limits of 60-2000 km. In other words, the main problem with regard to the IRI-2012 VTEC representation is not being situated in the plasmaspheric part of the ionosphere. Therefore we propose that the plasmaspheric part should be taken into account to calculate the correct TEC values in mid-latitude regions, and we note that IRI-2012 does not supply precise TEC values for use in ionospheric studies.

Ionospheric TEC, thermospheric cooling and Σ[O/N2] compositional changes during the 6-17 March 2012 magnetic storm interval (CAWSES II)

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Tsurutani, B. T.; Mannucci, A. J.; Mlynczak, M. G.; Hunt, L. A.; Paxton, L. J.

2014-08-01

A series of four geomagnetic storms (the minimum SYM-H~-148 nT) occurred during the March 6-17, 2012 in the ascending phase of the solar cycle 24. This interval was selected by CAWSES II for its campaign. The GPS total electron content (TEC) database and JPL's Global Ionospheric Maps (GIM) were used to study vertical TEC (VTEC) for different local times and latitude ranges. The largest response to geomagnetic activity is shown in increases of the low-latitude dayside VTEC. Several GPS sites feature post-afternoon VTEC “bite-outs”. During Sudden Impulse (SI+) event on March 8th a peak daytime VTEC restores to about quiet-time values. It is shown that the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation correlates well with auroral heating. A factor of ~5 cooling increase is noted in some storms. The cooling radiation intensifies in the auroral zone and spreads towards the equator. Effects of the storm appear at lower latitudes ~18.6 h later. The column density ratio Σ[O/N2] is analyzed based on TIMED/GUVI measurements. Both increases (at low latitudes) and decreases (from auroral to middle latitudes) in the ratio occurs during the geomagnetic storms. We suggest that the column density ratio could be enhanced at low to middle latitudes on the dayside partially due to the superfountain effect (atomic oxygen uplift due to ion-neutral drag). It is suggested that decreases in the Σ[O/N2] ratio at high to middle-latitudes may be caused by high thermospheric temperatures. During SI+s, there is an increase in Σ[O/N2] ratio at auroral latitudes.

Evaluation of long term solar activity effects on GPS derived TEC

NASA Astrophysics Data System (ADS)

Mansoori, Azad A.; Khan, Parvaiz A.; Ahmad, Rafi; Atulkar, Roshni; M, Aslam A.; Bhardwaj, Shivangi; Malvi, Bhupendra; Purohit, P. K.; Gwal, A. K.

2016-10-01

The solar activity hence the solar radiance follows a long term periodic variability with eleven years periodicity, known as solar cycle. This drives the long term variability of the ionosphere. In the present problem we investigate the long term behaviour of the ionosphere with the eleven year cyclic solar activity. Under the present study we characterize the ionospheric variability by Total Electron Content (TEC) using measurements made by Global Positioning System (GPS) and solar cycle variability by various solar activity indices. We make use of five solar activity indices viz. sunspot number (Rz), solar radio Flux (F10.7 cm), EUV Flux (26-34 nm), flare index and CME occurrences. The long term variability of these solar activity indices were then compared and correlated with the variability of ionospheric TEC, at a mid latitude station, Usuda (36.13N, 138.36E), of Japan, during the solar cycle 23 and ascending phase of cycle 24. From our study, we found that long term changes in the ionospheric TEC vary synchronously with corresponding changes in the solar activity indices. The correlation analysis shows that all the solar activity indices exhibit a very strong correlation with TEC (R =0.76 -0.99). Moreover the correlation between the two is stronger in the descending phase of the solar cycle. The correlation is found to be remarkably strongest during the deep minimum of the solar cycle 24 i.e. between 2007- 2009. Also we noticed a hysteresis effect exists with solar radio flux (F10.7 cm) and solar EUV flux (26-34 nm). This effect is absent with other parameters.

Validation of ionospheric electron density profiles inferred from GPS occultation observations of the GPS/MET experiment

NASA Astrophysics Data System (ADS)

Kawakami, Todd Mori

In April of 1995, the launch of the GPS Meteorology Experiment (GPS/MET) onboard the Orbview-1 satellite, formerly known as Microlab-1, provided the first technology demonstration of active limb sounding of the Earth's atmosphere with a low Earth orbiting spacecraft utilizing the signals transmitted by the satellites of the Global Positioning System (GPS). Though the experiment's primary mission was to probe the troposphere and stratosphere, GPS/MET was also capable of making radio occultation observations of the ionosphere. The application of the GPS occultation technique to the upper atmosphere created a unique opportunity to conduct ionospheric research with an unprecedented global distribution of observations. For operational support requirements, the Abel transform could be employed to invert the horizontal TEC profiles computed from the L1 and L2 phase measurements observed by GPS/MET into electron density profiles versus altitude in near real time. The usefulness of the method depends on how effectively the TEC limb profiles can be transformed into vertical electron density profiles. An assessment of GPS/MET's ability to determine electron density profiles needs to be examined to validate the significance of the GPS occultation method as a new and complementary ionospheric research tool to enhance the observational databases and improve space weather modeling and forecasting. To that end, simulations of the occultation observations and their inversions have been conducted to test the Abel transform algorithm and to provide qualitative information about the type and range of errors that might be experienced during the processing of real data. Comparisons of the electron density profiles inferred from real GPS/MET observations are then compared with coincident in situ measurements from the satellites of Defense Meteorological Satellite Program (DMSP) and ground-based remote sensing from digisonde and incoherent scatter radar facilities. The principal focus of this study is the validation of the electron density profiles inferred from GPS occultation observations using the Abel transform.

Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: A Preliminary Feasibility Demonstration

NASA Astrophysics Data System (ADS)

Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Mazzoni, Augusto; Crespi, Mattia; Wei, Yong; Mannucci, Anthony J.

2017-04-01

It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves.

Latitudinal and Seasonal Investigations of Storm-Time TEC Variation

NASA Astrophysics Data System (ADS)

Adimula, I. A.; Oladipo, O. A.; Adebiyi, S. J.

2016-07-01

The ionosphere responds markedly and unpredictably to varying magnetospheric energy inputs caused by solar disturbances on the geospace. Knowledge of the impact of the space weather events on the ionosphere is important to assess the environmental effect on the operations of ground- and space-based technologies. Thus, global positioning system (GPS) measurements from the international GNSS service (IGS) database were used to investigate the ionospheric response to 56 geomagnetic storm events at six different latitudes comprising the northern and southern hemispheres in the Afro-European sector. Statistical distributions of total electron content (TEC) response show that during the main phase of the storms, enhancement of TEC is more pronounced in most of the seasons, regardless of the latitude and hemisphere. However, a strong seasonal dependence appears in the TEC response during the recovery phase. Depletion of TEC is majorly observed at the high latitude stations, and its appearance at lower latitudes is seasonally dependent. In summer hemisphere, the depletion of TEC is more pronounced in nearly all the latitudinal bands. In winter hemisphere, enhancement as well as depletion of TEC is observed over the high latitude, while enhancement is majorly observed over the mid and low latitudes. In equinoxes, the storm-time TEC distribution shows a fairly consistent characteristic with the summer distribution, particularly in the northern hemisphere.

Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: A Preliminary Feasibility Demonstration

PubMed Central

Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Mazzoni, Augusto; Crespi, Mattia; Wei, Yong; Mannucci, Anthony J.

2017-01-01

It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves. PMID:28429754

Real-Time Detection of Tsunami Ionospheric Disturbances with a Stand-Alone GNSS Receiver: A Preliminary Feasibility Demonstration.

PubMed

Savastano, Giorgio; Komjathy, Attila; Verkhoglyadova, Olga; Mazzoni, Augusto; Crespi, Mattia; Wei, Yong; Mannucci, Anthony J

2017-04-21

It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves.

Total electron content disturbances during minor sudden stratospheric warming, over the Brazilian region: A case study during January 2012

NASA Astrophysics Data System (ADS)

Vieira, F.; Fagundes, P. R.; Venkatesh, K.; Goncharenko, L. P.; Pillat, V. G.

2017-02-01

The effects of sudden stratospheric warming (SSW) on ionosphere have been investigated by several scientists, using different observational techniques and model simulations. However, the minor SSW event during January 2012 is one of those that are less studied. Influences of several types of possible drivers—minor SSW event, changing solar flux, moderate geomagnetic storm on 22-25 January, and one of the largest solar proton events on 23-30 January—make it a challenging period to interpret. In the present study, the GPS-total electron content (TEC) measurements from a network of 72 receivers over the Brazilian region are considered. This network of 72 GPS-TEC locations lies between 5°N and 30°S (35°) latitudes and 35°W and 65°W (30°) longitudes. Further, two chains of GPS receivers are used to study the response of the equatorial ionization anomaly (EIA) in the Brazilian eastern and western sectors, as well as its day-to-day variability before and during the SSW-2012. It was noted that the TEC is depleted to the order of 30% all over the Brazilian region, from equator to beyond the EIA regions and from east to west sectors. It is also noticed that the EIA strengths at the east and west sectors were weakened during the SSW-2012. However, the Brazilian eastern sector was found to be more disturbed compared to the western sector during this SSW-2012 event.

GPS Array as a Sensor of Lithosphere, Troposphere and Ionosphere

NASA Astrophysics Data System (ADS)

Heki, K.

2011-12-01

The Japanese dense array of GPS receivers (GEONET) started operation in 1993, and is currently composed of ~1200 stations. GPS (or GNSS in general) receivers can be compared to a Swiss army knife: it could be used not only for positioning (a knife) but also for various purposes, e.g. remote sensing of tropospheric water vapor or ionospheric electrons (screw driver, tin opener etc). Dense GPS arrays have been found extremely useful for variety of geophysical studies. In this lecture, I briefly review their historical achievements, recent highlights, and future perspectives. In Japan, first generation GPS stations were implemented in 1993 (the Kanto-Tokai region) and 1994 (nationwide) by GSI, Japan. Shortly after the launch, they successfully caught coseismic crustal movement of several major earthquakes, the 1994 October Shikotan (Mw8.3), the 1994 December Sanriku (Mw7.6), and the 1995 January Kobe (Mw7.0) earthquakes. These earthquakes accelerated the densification of the GPS network, achieving 1000 in the number of stations within the following 2-3 years. In addition to coseismic jumps, important discoveries continued in 1990s, e.g. large-scale afterslip of interplate thrust earthquakes and slow slip events (SSE). Later it was shown that tilt- and strainmeter can better observe short-term SSEs, and InSAR can draw more detailed maps of coseismic crustal movements. Now GPS array is recognized as a good tool to measure crustal movement with high temporal resolution and stability and with moderate sensitivity and spatial resolution. GPS data are also useful to study hydrosphere. Seasonal crustal movements in Japan mainly reflect changes in hydrological loads. Multipath signatures in GPS data also provide useful information on the environment around the antenna, e.g. soil moisture, snow depth and vegetation. I will compare the snow depth record over a winter inferred by analyzing GPS multipath signatures, and observed by a conventional apparatus. GPS can also measure precipitable water vapor (PWV) of troposphere. After intense feasibility studies of GPS meteorology in 1990s, PWV information from GEONET has been routinely assimilated in the operational mesoscale model of the Japan Meteorological Agency since 2009. It is found useful in predicting localized heavy rainfalls that often attack Japan in summer. It is fairly easy to measure ionospheric total electron content (TEC) by using phase differences between L1 and L2 carriers from GPS satellites. Applications of GPS for upper atmospheric studies started for ionospheric disturbances of space weather origins. In 2003, clear coseismic ionospheric disturbances of the Tokachi-Oki earthquake were found, and the GPS-TEC technique has been extensively used to study ionospheric disturbances of solid earth origins, e.g. earthquakes and volcanic eruptions. There are also several recent examples of artificial ionospheric disturbances caused by rocket launches and passage of ballistic missiles from North Korea above NE Japan. In the last part of the lecture, I summarize what the GPS array saw before, during and after the 2011 Tohoku-Oki earthquake. The topic covers not only pre-, co- and postseismic crustal movements, but also results of high-rate sampling, and possible detection of precursory changes in ionospheric TEC immediately before the earthquake.

Multi-instrument observations of pre-earthquake transient signatures associated with 2015 M8.3 Chile earthquake

NASA Astrophysics Data System (ADS)

Ouzounov, D.; Pulinets, S. A.; Hernandez-Pajares, M.; Garcia-Rigo, A.; De Santis, A.; Pavón, J.; Liu, J. Y. G.; Chen, C. H.; Cheng, K. C.; Hattori, K.; Stepanova, M. V.; Romanova, N.; Hatzopoulos, N.; Kafatos, M.

2016-12-01

We are conducting multi parameter validation study on lithosphere/atmosphere /ionosphere transient phenomena preceding major earthquakes particularly for the case of M8.3 of Sept 16th, 2015 in Chile. Our approach is based on monitoring simultaneously a series of different physical parameters from space: 1/Outgoing long-wavelength radiation (OLR obtained from NOAA/AVHRR); 2/ electron and electron density variations in the ionosphere via GPS Total Electron Content (GPS/TEC), and 3/geomagnetic field and plasma density variation (Swarm); and from ground: 3/ GPS crustal deformation and 4/ground-based magnetometers. The time and location of main shock was prospectively alerted in advance using the Multi Sensor Networking Approach (MSNA-LAIC) approach. We analyzed retrospectively several physical observations characterizing the state of the lithosphere, atmosphere and ionosphere several days before, during and after the M8.3 earthquakes in Illapel. Our continuous satellite monitoring of long-wave (LW) data over Chile, shows a rapid increase of emitted radiation during the end of August 2015 and an anomaly in the atmosphere was detected at 19 LT on Sept 1st, 2015, over the water near to the epicenter. On Sept 2nd Swarm magnetic measurements show an anomalous signature over the epicentral region. GPS/TEC analysis revealed an anomaly on Sept 14th and on the same day the degradation of Equatorial Ionospheric Anomaly (EIA) and disappearance of the crests of EIA as is characteristic for pre-dawn and early morning hours (11 LT) was observed. On Sept 16th co-seismic ionospheric signatures consistent with defined circular acoustic-gravity wave and different shock-acoustic waves were also observed. GPS TEC and deformation studies were computed from 48 GPS stations (2013-2015) of National Seismological Center of Chile (CSN) GPS network. A transient signal of deformation has been observed a week in advance correlated with ground-based magnetometers ULF signal fluctuation from closest to the epicenter station from the SAMBA-AMBER network. The characteristics of the observed pre-, and co - seismic transient signals associated with the M8.3 of Illapel, Chile 2015 earthquake suggested that they follow general temporal-spatial evolution pattern, which has been seen in other large earthquakes worldwide.

Response of lightning energy and total electron content with sprites over Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Suparta, W.; Yusop, N.

2017-05-01

This paper investigates the response of the lightning energy with the total electron content (TEC) derived from GPS over Antarctic Peninsula during St Patrick’s geomagnetic storm. During this event, sprite as one of the mesospheric transient luminous events (TLEs) associated with positive cloud-to-ground (+CG) lightning discharges can be generated. In this work, GPS and lightning data for the period from 14 to 20 March 2015 is analyzed. Geomagnetic activity and electric field data are also processed to relate the geomagnetic storm and lightning. Results show that during St Patrick’s geomagnetic storm, the lighting energy was produced up to ∼257 kJ. The ionospheric TEC was obtained 60 TECU, 38 TECU and 78 TECU between 18:00 and 21:00 UT for OHI3, PALV and ROTH stations, respectively. The peak of lightning energy was observed 14 hours after peaked of TEC. Sprite possibly generated through the electrical coupling process between the top cloud, middle and upper atmosphere with the DC electric field found to be ∼10 mVm-1 which leading to the sprite generation after the return strokes on 18 March 2015.

Modeling the plasmasphere based on LEO satellites onboard GPS measurements

NASA Astrophysics Data System (ADS)

Chen, Peng; Yao, Yibin; Li, Qinzheng; Yao, Wanqiang

2017-01-01

The plasmasphere, which is located above the ionosphere, is a significant component of Earth's atmosphere. A global plasmaspheric model was constructed using the total electron content (TEC) along the signal propagation path calculated using onboard Global Positioning System observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and MetOp-A, provided by the COSMIC Data Analysis and Archive Center (CDAAC). First, the global plasmaspheric model was established using only COSMIC TEC, and a set of MetOp-A TEC provided by CDAAC served for external evaluation. Results indicated that the established model using only COSMIC data is highly accurate. Then, COSMIC and MetOp-A TEC were combined to produce a new global plasmaspheric model. Finally, the variational characteristics of global plasmaspheric electron content with latitude, local time, and season were investigated using the global plasmaspheric model established in this paper.

Vertical structure of medium-scale traveling ionospheric disturbances

NASA Astrophysics Data System (ADS)

Ssessanga, Nicholas; Kim, Yong Ha; Kim, Eunsol

2015-11-01

We develop an algorithm of computerized ionospheric tomography (CIT) to infer information on the vertical and horizontal structuring of electron density during nighttime medium-scale traveling ionospheric disturbances (MSTIDs). To facilitate digital CIT we have adopted total electron contents (TEC) from a dense Global Positioning System (GPS) receiver network, GEONET, which contains more than 1000 receivers. A multiplicative algebraic reconstruction technique was utilized with a calibrated IRI-2012 model as an initial solution. The reconstructed F2 peak layer varied in altitude with average peak-to-peak amplitude of ~52 km. In addition, the F2 peak layer anticorrelated with TEC variations. This feature supports a theory in which nighttime MSTID is composed of oscillating electric fields due to conductivity variations. Moreover, reconstructed TEC variations over two stations were reasonably close to variations directly derived from the measured TEC data set. Our tomographic analysis may thus help understand three-dimensional structure of MSTIDs in a quantitative way.

Use of Total Electron Content data to analyze ionosphere electron density gradients

NASA Astrophysics Data System (ADS)

Nava, B.; Radicella, S. M.; Leitinger, R.; Coisson, P.

In presence of electron density gradients the thin shell approximation for the ionosphere used together with a simple mapping function to convert slant Total Electron Content TEC to vertical TEC could lead to TEC conversion errors Therefore these mapping function errors can be used to identify the effects of the electron density gradients in the ionosphere In the present work high precision GPS derived slant TEC data have been used to investigate the effects of the electron density gradients in the middle and low latitude ionosphere under geomagnetic quiet and disturbed conditions In particular the data corresponding to the geographic area of the American sector for the days 5-7 April 2000 have been used to perform a complete analysis of mapping function errors based on the coinciding pierce point technique The results clearly illustrate the electron density gradient effects according to the locations considered and to the actual levels of disturbance of the ionosphere

GPS & GLONASS Observations of Large-Scale Traveling Ionospheric Disturbances during the 2015 St. Patrick's Day Storm

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Astafyeva, E.; Cherniak, I.

2016-12-01

We investigate signatures of the large-scale travelling ionospheric disturbances (LSTIDs) that they leave in the ground-based total electron content (TEC) during the 2015 St. Patrick's Day Storm. We take advantage of a large number of the ground-based GPS/GNSS receivers to analyze simultaneous LSTIDs propagation in different sectors from very dense and multipoint observations. The region of interest includes the both Northern and Southern American sectors, as well as the whole European sector. We use measurements derived from more than 5000 GPS/GNSS receivers of numerous global and regional GNSS networks. We considerably increase number of available observations by processing signals from not only GPS but also from GLONASS. We retrieve a perturbation component of the resulted TEC maps constructed with high spatial and temporal resolution. LSTIDs originating in the auroral oval and propagating equatorward were clearly identified in both hemispheres. In this report we discuss features of the observed LSTIDs, in particular, 1) similarities and differences of their simultaneous propagation over American and European sectors ; 2) interhemispheric LSTIDs propagation in the American sector; 3) dependence of the LSTIDs characteristic parameters (velocity, wavelength) on the intensification of the auroral activity during the main phase of this storm.

GPS-TEC of the Ionospheric Disturbances as a Tool for Early Tsunami Warning

NASA Astrophysics Data System (ADS)

Kunitsyn, Viacheslav E.; Nesterov, Ivan A.; Shalimov, Sergey L.; Krysanov, Boris Yu.; Padokhin, Artem M.; Rekenthaler, Douglas

2013-04-01

Recently, the GPS measurements were used for retrieving the information on the various types of ionospheric responses to seismic events (earthquakes, seismic Rayleigh waves, and tsunami) which generate atmospheric waves propagating up to the ionospheric altitudes where the collisions between the neutrals and charge particles give rise to the motion of the ionospheric plasma. These experimental results can well be used in architecture of the future tsunami warning system. The point is an earlier (in comparison with seismological methods) detection of the ionospheric signal that can indicate the moment of tsunami generation. As an example we consider the two-dimensional distributions of the vertical total electron content (TEC) variations in the ionosphere both close to and far from the epicenter of the Japan undersea earthquake of March 11, 2011 using radio tomographic (RT) reconstruction of high-temporal-resolution (2-minute) data from the Japan and the US GPS networks. Near-zone TEC variations shows a diverging ionospheric perturbation with multi-component spectral composition emerging after the main shock. The initial phase of the disturbance can be used as an indicator of the tsunami generation and subsequently for the tsunami early warning. Far-zone TEC variations reveals distinct wave train associated with gravity waves generated by tsunami. According to observations tsunami arrives at Hawaii and further at the coast of Southern California with delay relative to the gravity waves. Therefore the gravity wave pattern can be used in the early tsunami warning. We support this scenario by the results of modeling with the parameters of the ocean surface perturbation corresponding to the considered earthquake. In addition it was observed in the modeling that at long distance from the source the gravity wave can pass ahead of the tsunami. The work was supported by the Russian Foundation for Basic Research (grants 11-05-01157 and 12-05-33065).

Real time validation of GPS TEC precursor mask for Greece

NASA Astrophysics Data System (ADS)

Pulinets, Sergey; Davidenko, Dmitry

2013-04-01

It was established by earlier studies of pre-earthquake ionospheric variations that for every specific site these variations manifest definite stability in their temporal behavior within the time interval few days before the seismic shock. This self-similarity (characteristic to phenomena registered for processes observed close to critical point of the system) permits us to consider these variations as a good candidate to short-term precursor. Physical mechanism of GPS TEC variations before earthquakes is developed within the framework of Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model. Taking into account the different tectonic structure and different source mechanisms of earthquakes in different regions of the globe, every site has its individual behavior in pre-earthquake activity what creates individual "imprint" on the ionosphere behavior at every given point. Just this so called "mask" of the ionosphere variability before earthquake in the given point creates opportunity to detect anomalous behavior of electron concentration in ionosphere basing not only on statistical processing procedure but applying the pattern recognition technique what facilitates the automatic recognition of short-term ionospheric precursors of earthquakes. Such kind of precursor mask was created using the GPS TEC variation around the time of 9 earthquakes with magnitude from M6.0 till M6.9 which took place in Greece within the time interval 2006-2011. The major anomaly revealed in the relative deviation of the vertical TEC was the positive anomaly appearing at ~04PM UT one day before the seismic shock and lasting nearly 12 hours till ~04AM UT. To validate this approach it was decided to check the mask in real-time monitoring of earthquakes in Greece starting from the 1 of December 2012 for the earthquakes with magnitude more than 4.5. During this period (till 9 of January 2013) 4 cases of seismic shocks were registered, including the largest one M5.7 on 8 of January. For all of them the mask confirmed its validity and 6 of December event was predicted in advance.

An Analysis on the TEC Variability and Ionospheric Scintillation at Los Alamos, New Mexico Derived from FORTE-Received LAPP Signals

NASA Astrophysics Data System (ADS)

Huang, Z.; Roussel-Dupre, R.

2003-12-01

The total electron content (TEC) of ionosphere and its electron density irregularities (scintillation) have effects of degradation and disruption on radio signals passed between ground stations and orbiting man-made satellites. With the rapid increase in operational reliance on UHF/VHF satellite communication, it is desirable to obtain understandings of ionosphere TEC variability and scintillation characteristics to improve our ability of predicting satellite communication outages. In this work, data collected from FORTE satellite received LAPP (Los Alamos Portable Pulser) signals during 1998-2002 are used to derive TEC and ionospheric scintillation index at Los Alamos, New Mexico. To characterize in-situ TEC variability at Los Alamos, the FORTE-LAPP derived TECs are analyzed against diurnal, seasonal, solar activity, magnetic storm, and stratospheric warming. The results are also compared with the TEC estimates from the Los Alamos ionospheric transfer function (ITF) implemented with the global ionospheric models (IRI, PIM), and GPS -derived TEC maps. The FORTE-LAPP signals are also analyzed against two important measures of the effect of scintillation on broadband signals, the mean time delay and the time delay jitter. The results are used to examine coherence frequency bandwidth and compared with the predictions from a global scintillation model (WBMOD). The FORTE-LAPP analyzed and WBMOD predicted scintillation characteristics are used to investigate temporal and seasonal behavior of scintillation at Los Alamos.

A method of estimating GPS instrumental biases with a convolution algorithm

NASA Astrophysics Data System (ADS)

Li, Qi; Ma, Guanyi; Lu, Weijun; Wan, Qingtao; Fan, Jiangtao; Wang, Xiaolan; Li, Jinghua; Li, Changhua

2018-03-01

This paper presents a method of deriving the instrumental differential code biases (DCBs) of GPS satellites and dual frequency receivers. Considering that the total electron content (TEC) varies smoothly over a small area, one ionospheric pierce point (IPP) and four more nearby IPPs were selected to build an equation with a convolution algorithm. In addition, unknown DCB parameters were arranged into a set of equations with GPS observations in a day unit by assuming that DCBs do not vary within a day. Then, the DCBs of satellites and receivers were determined by solving the equation set with the least-squares fitting technique. The performance of this method is examined by applying it to 361 days in 2014 using the observation data from 1311 GPS Earth Observation Network (GEONET) receivers. The result was crosswise-compared with the DCB estimated by the mesh method and the IONEX products from the Center for Orbit Determination in Europe (CODE). The DCB values derived by this method agree with those of the mesh method and the CODE products, with biases of 0.091 ns and 0.321 ns, respectively. The convolution method's accuracy and stability were quite good and showed improvements over the mesh method.

Ionospheric response to the 2006 sudden stratospheric warming event over the equatorial and low latitudes in the Brazilian sector using GPS observations

NASA Astrophysics Data System (ADS)

de Jesus, R.; Batista, I. S.; Fagundes, P. R.; Venkatesh, K.; de Abreu, A. J.

2017-02-01

The main purpose of this paper is to study the response of the ionospheric F-region using GPS-TEC measurements at equatorial and low latitude regions over the Brazilian sector during an sudden stratospheric warming (SSW) event in the year 2006. In this work, we present vertical total electron content (VTEC) and phase fluctuations derived from GPS network in Brazil. The continuous wavelet transform (CWT) was employed to check the periodicities of the ΔVTEC during the SSW event. The results show a strong decrease in VTEC and ΔVTEC values in the afternoon over low latitudes from DOY 05-39 (during the SSW event) mainly after the second SSW temperature peak. The ionospheric ΔVTEC pattern over Brazilian sector shows diurnal and semidiurnal oscillations during the 2006 SSW event. In addition, for the first time, variations in ΔVTEC (low latitude stations) with periods of about 02-08 day have been reported during an SSW event. Using GPS stations located in the Brazilian sector, it is reported for the first time that equatorial ionospheric irregularities were not suppressed by the SSW event.

Local time, seasonal, and solar cycle dependency of longitudinal variations of TEC along the crest of EIA over India

NASA Astrophysics Data System (ADS)

Sunda, Surendra; Vyas, B. M.

2013-10-01

global wave number 4 structure in the Indian longitudinal region spanning from ~70 to 95°E forming the upward slope of the peak in the total electron content (TEC) are reported along the crest of equatorial ionization anomaly (EIA). The continuous and simultaneous measurements from five GPS stations of GPS Aided Geo Augmented Navigation (GAGAN) network are used in this study. The long-term database (2004-2012) is utilized for examining the local time, seasonal, and solar cycle dependency on the longitudinal variations of TEC. Our results confirm the existence of longitudinal variations of TEC in accordance with wave number 4 longitudinal structure including its strength. The results suggest that these variations, in general, start to develop at ~09 LT, achieve maximum strength at 12-15 LT, and decay thereafter, the decay rate depending on the season. They are more pronounced in equinoctial season followed by summer and winter. The longitudinal variations persist beyond midnight in equinox seasons, whereas in winter, they are conspicuously absent. Interestingly, they also exhibit significant solar cycle dependence in the solstices, whereas in the equinoxes, they are independent of solar activity. The comparison of crest-to-trough ratio (CTR) in the eastern (92°E) and western (72°E) extreme longitudes reveals higher CTR on the eastern side than over the western extreme, suggesting the role of nonmigrating tides in modulating the ExB vertical drift and the consequential EIA crest formation.

Recent Advances in Remote Sensing of Natural Hazards-Induced Atmospheric and Ionospheric Perturbations

NASA Astrophysics Data System (ADS)

Yang, Y. M.; Komjathy, A.; Meng, X.; Verkhoglyadova, O. P.; Langley, R. B.; Mannucci, A. J.

2015-12-01

Traveling ionospheric disturbances (TIDs) induced by acoustic-gravity waves in the neutral atmosphere have significant impact on trans-ionospheric radio waves such as Global Navigation Satellite System (GNSS, including Global Position System (GPS)) measurements. Natural hazards and solid Earth events, such as earthquakes, tsunamis and volcanic eruptions are actual sources that may trigger acoustic and gravity waves resulting in traveling ionospheric disturbances (TIDs) in the upper atmosphere. Trans-ionospheric radio wave measurements sense the total electron content (TEC) along the signal propagation path. In this research, we introduce a novel GPS-based detection and estimation technique for remote sensing of atmospheric wave-induced TIDs including space weather phenomena induced by major natural hazard events, using TEC time series collected from worldwide ground-based dual-frequency GNSS (including GPS) receiver networks. We demonstrate the ability of using ground- and space-based dual-frequency GPS measurements to detect and monitor tsunami wave propagation from the 2011 Tohoku-Oki earthquake and tsunami. Major wave trains with different propagation speeds and wavelengths were identified through analysis of the GPS remote sensing observations. Dominant physical characteristics of atmospheric wave-induced TIDs are found to be associated with specific tsunami propagations and oceanic Rayleigh waves. In this research, we compared GPS-based observations, corresponding model simulations and tsunami wave propagation. Results are shown to lead to a better understanding of the tsunami-induced ionosphere responses. Based on current distribution of Plate Boundary Observatory GPS stations, the results indicate that tsunami-induced TIDs may be detected about 60 minutes prior to tsunamis arriving at the U.S. west coast. It is expected that this GNSS-based technology will become an integral part of future early-warning systems.

Online, automatic, ionospheric maps: IRI-PLAS-MAP

NASA Astrophysics Data System (ADS)

Arikan, F.; Sezen, U.; Gulyaeva, T. L.; Cilibas, O.

2015-04-01

Global and regional behavior of the ionosphere is an important component of space weather. The peak height and critical frequency of ionospheric layer for the maximum ionization, namely, hmF2 and foF2, and the total number of electrons on a ray path, Total Electron Content (TEC), are the most investigated and monitored values of ionosphere in capturing and observing ionospheric variability. Typically ionospheric models such as International Reference Ionosphere (IRI) can provide electron density profile, critical parameters of ionospheric layers and Ionospheric electron content for a given location, date and time. Yet, IRI model is limited by only foF2 STORM option in reflecting the dynamics of ionospheric/plasmaspheric/geomagnetic storms. Global Ionospheric Maps (GIM) are provided by IGS analysis centers for global TEC distribution estimated from ground-based GPS stations that can capture the actual dynamics of ionosphere and plasmasphere, but this service is not available for other ionospheric observables. In this study, a unique and original space weather service is introduced as IRI-PLAS-MAP from http://www.ionolab.org

Regional TEC model under quiet geomagnetic conditions and low-to-moderate solar activity based on CODE GIMs

NASA Astrophysics Data System (ADS)

Feng, Jiandi; Jiang, Weiping; Wang, Zhengtao; Zhao, Zhenzhen; Nie, Linjuan

2017-08-01

Global empirical total electron content (TEC) models based on TEC maps effectively describe the average behavior of the ionosphere. However, the accuracy of these global models for a certain region may not be ideal. Due to the number and distribution of the International GNSS Service (IGS) stations, the accuracy of TEC maps is geographically different. The modeling database derived from the global TEC maps with different accuracy is likely one of the main reasons that limits the accuracy of the new models. Moreover, many anomalies in the ionosphere are geographic or geomagnetic dependent, and as such the accuracy of global models can deteriorate if these anomalies are not fully incorporated into the modeling approach. For regional models built in small areas, these influences on modeling are immensely weakened. Thus, the regional TEC models may better reflect the temporal and spatial variations of TEC. In our previous work (Feng et al., 2016), a regional TEC model TECM-NEC is proposed for northeast China. However, this model is only directed against the typical region of Mid-latitude Summer Nighttime Anomaly (MSNA) occurrence, which is meaningless in other regions without MSNA. Following the technique of TECM-NEC model, this study proposes another regional empirical TEC model for other regions in mid-latitudes. Taking a small area BeiJing-TianJin-Tangshan (JJT) region (37.5°-42.5° N, 115°-120° E) in China as an example, a regional empirical TEC model (TECM-JJT) is proposed using the TEC grid data from January 1, 1999 to June 30, 2015 provided by the Center for Orbit Determination in Europe (CODE) under quiet geomagnetic conditions. The TECM-JJT model fits the input CODE TEC data with a bias of 0.11TECU and a root mean square error of 3.26TECU. Result shows that the regional model TECM-JJT is consistent with CODE TEC data and GPS-TEC data.

Statistical evidence of seismo-ionospheric precursors of the GPS total electron content in China

NASA Astrophysics Data System (ADS)

Chen, Yuh-Ing; Huang, Chi-Shen; Liu, Jann-Yenq

2015-04-01

Evidence of the seismo-ionospheric precursor (SIP) is reported by statistically investigating the relationship between the total electron content (TEC) in global ionosphere map (GIM) and 56 M≥6.0 earthquakes during 1998-2013 in China. A median-based method together with the z test is employed to examine the TEC variations 30 days before and after the earthquake. It is found that the TEC significantly decreases 0600-1000 LT 1-6 days before the earthquake, and anomalously increases in 3 time periods of 1300-1700 LT 12-15 days; 0000-0500 LT 15-17 days; and 0500-0900 LT 22-28 days before the earthquake. The receiver operating characteristic (ROC) curve is then used to evaluate the efficiency of TEC for predicting M≥6.0 earthquakes in China during a specified time period. Statistical results suggest that the SIP is the significant TEC reduction in the morning period of 0600-1000 LT. The SIP is further confirmed since the area under the ROC curve is positively associated with the earthquake magnitude.

Statistical evidences of seismo-ionospheric precursors applying receiver operating characteristic (ROC) curve on the GPS total electron content in China

NASA Astrophysics Data System (ADS)

Chen, Yuh-Ing; Huang, Chi-Shen; Liu, Jann-Yenq

2015-12-01

Evidence of the seismo-ionospheric precursor (SIP) is reported by statistically investigating the relationship between the total electron content (TEC) in global ionosphere map (GIM) and 56 M ⩾ 6.0 earthquakes during 1998-2013 in China. A median-based method together with the z test is employed to examine the TEC variations 30 days before and after the earthquake. It is found that the TEC significantly decreases 0600-1000 LT 1-6 days before the earthquake, and anomalously increases in 3 time periods of 1300-1700 LT 12-15 days; 0000-0500 LT 15-17 days; and 0500-0900 LT 22-28 days before the earthquake. The receiver operating characteristic (ROC) curve is then used to evaluate the efficiency of TEC for predicting M ⩾ 6.0 earthquakes in China during a specified time period. Statistical results suggest that the SIP is the significant TEC reduction in the morning period of 0600-1000 LT. The SIP is further confirmed since the area under the ROC curve is positively associated with the earthquake magnitude.

Multi-instrumental Study of Storm-induced Ionospheric Irregularities at Midlatitudes

NASA Astrophysics Data System (ADS)

Cherniak, I.; Zakharenkova, I.; Sokolovskiy, S. V.

2017-12-01

We present multi-instrumental analysis of the unusually intense plasma density irregularities occurred over European midlatitudes during geomagnetic storm of 22-23 June 2015. We combine GPS/GLONASS observations derived from the dense ground-based networks ( 1500 stations) with in situ plasma density onboard Swarm and DMSP satellites and COSMIC Radio Occultation (RO) ionospheric electron density profiles. During this geomagnetic storm, the strong ionospheric irregularities of auroral origin were registered over the Northern Europe sub-auroral and midlatitudes. Meanwhile, another kind of ionospheric irregularities of equatorial origin reached European midlatitudes from the south. The prompt penetration electric fields caused the occurrence of plasma bite-outs in the post-sunset sector over the Western Africa low latitudes and extension of the large-scale plasma bubbles toward Europe. Using GPS/GLONASS observations, the plasma bubble signatures were mapped in Europe. They were observed for more than 8 h (20-04 UT) and covered a broad area within 30o-40o N and 20o W-10o E. In this region, the steep plasma gradients, as large as 5-10 TECU/degree, and numerous embedded deep plasma depletions were developed on the background of high plasma density. For low latitude region, the bite-out signature was recognized in the form of the significantly modified shape of the COSMIC-derived ionospheric electron density profiles. These unique results were confirmed by the in situ density and upward-looking GPS data onboard the Swarm satellites at 500 km altitude, in situ density measured by DMSP and ground-based absolute TEC observations. It was found that close similarity between in situ Ne and Swarm-derived topside vertical TEC suggests that plasma density enhancements and depletions are developed in the topside ionosphere (>500 km). The intensity of plasma gradients at different altitudes was also estimated by COSMIC-based measurements of GPS signal intensity and phase fluctuations as well as by rate of TEC changes on COSMIC-GPS links. Occurrence of the plasma bubbles in Europe affected GNSS measurements over number of reference stations and led to performance degradation of SBAS EGNOS.

Dynamics of total electron content distribution during strong geomagnetic storms

NASA Astrophysics Data System (ADS)

Astafyeva, E. I.; Afraimovich, E. L.; Kosogorov, E. A.

We worked out a new method of mapping of total electron content TEC equal lines displacement velocity The method is based on the technique of global absolute vertical TEC value mapping Global Ionospheric Maps technique GIM GIM with 2-hours time resolution are available from Internet underline ftp cddisa gsfc nasa gov in standard IONEX-files format We determine the displacement velocity absolute value as well as its wave vector orientation from increments of TEC x y derivatives and TEC time derivative for each standard GIM cell 5 in longitude to 2 5 in latitude Thus we observe global traveling of TEC equal lines but we also can estimate the velocity of these line traveling Using the new method we observed anomalous rapid accumulation of the ionosphere plasma at some confined area due to the depletion of the ionization at the other spacious territories During the main phase of the geomagnetic storm on 29-30 October 2003 very large TEC enhancements appeared in the southwest of North America TEC value in that area reached up to 200 TECU 1 TECU 10 16 m -2 It was found that maximal velocity of TEC equal lines motion exceeded 1500 m s and the mean value of the velocity was about 400 m s Azimuth of wave vectors of TEC equal lines were orientated toward the center of region with anomaly high values of TEC the southwest of North America It should be noted that maximal TEC values during geomagnetically quiet conditions is about 60-80 TECU the value of TEC equal lines

Response of data-driven artificial neural network-based TEC models to neutral wind for different locations, seasons, and solar activity levels from the Indian longitude sector

NASA Astrophysics Data System (ADS)

Sur, D.; Haldar, S.; Ray, S.; Paul, A.

2017-07-01

The perturbations imposed on transionospheric signals by the ionosphere are a major concern for navigation. The dynamic nature of the ionosphere in the low-latitude equatorial region and the Indian longitude sector has some specific characteristics such as sharp temporal and latitudinal variation of total electron content (TEC). TEC in the Indian longitude sector also undergoes seasonal variations. The large magnitude and sharp variation of TEC cause large and variable range errors for satellite-based navigation system such as Global Positioning System (GPS) throughout the day. For accurate navigation using satellite-based augmentation systems, proper prediction of TEC under certain geophysical conditions is necessary in the equatorial region. It has been reported in the literature that prediction accuracy of TEC has been improved using measured data-driven artificial neural network (ANN)-based vertical TEC (VTEC) models, compared to standard ionospheric models. A set of observations carried out in the Indian longitude sector have been reported in this paper in order to find the amount of improvement in performance accuracy of an ANN-based VTEC model after incorporation of neutral wind as model input. The variations of this improvement in prediction accuracy with respect to latitude, longitude, season, and solar activity have also been reported in this paper.

A nonlinear background removal method for seismo-ionospheric anomaly analysis under a complex solar activity scenario: A case study of the M9.0 Tohoku earthquake

NASA Astrophysics Data System (ADS)

He, Liming; Wu, Lixin; Pulinets, Sergey; Liu, Shanjun; Yang, Fan

2012-07-01

A precise determination of ionospheric total electron content (TEC) anomaly variations that are likely associated with large earthquakes as observed by global positioning system (GPS) requires the elimination of the ionospheric effect from irregular solar electromagnetic radiation. In particular, revealing the seismo-ionospheric anomalies when earthquakes occurred during periods of high solar activity is of utmost importance. To overcome this constraint, a multiresolution time series processing technique based on wavelet transform applicable to global ionosphere map (GIM) TEC data was used to remove the nonlinear effect from solar radiation for the earthquake that struck Tohoku, Japan, on 11 March, 2011. As a result, it was found that the extracted TEC have a good correlation with the measured solar extreme ultraviolet flux in 26-34 nm (EUV26-34) and the 10.7 cm solar radio flux (F10.7). After removing the influence of solar radiation origin in GIM TEC, the analysis results show that the TEC around the forthcoming epicenter and its conjugate were significantly enhanced in the afternoon period of 8 March 2011, 3 days before the earthquake. The spatial distributions of the TEC anomalous and extreme enhancements indicate that the earthquake preparation process had brought with a TEC anomaly area of size approximately 1650 and 5700 km in the latitudinal and longitudinal directions, respectively.

(abstract) Application of the GPS Worldwide Network in the Study of Global Ionospheric Storms

NASA Technical Reports Server (NTRS)

Ho, C. M.; Mannucci, A. J.; Lindqwister, U. J.; Pi, X.; Sparks, L. C.; Rao, A. M.; Wilsion, B. D.; Yuan, D. N.; Reyes, M.

1997-01-01

Ionospheric storm dynamics as a response to the geomagnetic storms is a very complicated global process involving many different mechanisms. Studying ionospheric storms will help us to understand the energy coupling process between the Sun and Earth and possibly also to effectively forecast space weather changes. Such a study requires a worldwide monitoring system. The worldwide GPS network, for the first time, makes near real-time global ionospheric TEC measurements a possibility.

Real-time Scintillation Monitoring in Alaska from a Longitudinal Chain of ASTRA's SM-211 GPS TEC and Scintillation Receivers

NASA Astrophysics Data System (ADS)

Crowley, G.; Azeem, S. I.; Reynolds, A.; Santana, J.; Hampton, D. L.

2013-12-01

Amplitude and phase scintillation can cause serious difficulties for GPS receivers. Intense scintillation can cause loss of lock. High latitude studies generally show that phase scintillation can be severe, but the amplitude scintillation tends to be small. The reason for this is not yet understood. Furthermore, the actual causes of the ionospheric irregularities that produce high latitude scintillation are not well understood. While the gradient drift instability is thought to be important in the F-region, there may be other structures present in either the E- or F-regions. The role of particle precipitation is also not well understood. Four of ASTRA's CASES GPS receivers were deployed in Alaska to demonstrate our ability to map scintillation in realtime, to provide space weather services to GPS users, and to initiate a detailed investigation of these effects. These dual-frequency GPS receivers measure total electron content (TEC) and scintillation. The scintillation monitors were deployed in a longitudinal chain at sites in Kaktovic, Fort Yukon, Poker Flat, and Gakona. Scintillation statistics show phase scintillations to be largest at Kaktovic and smallest at Gakona. We present GPS phase scintillation and auroral emission results from the Alaska chain to characterize the correspondence between scintillation and auroral features, and to investigate the role of high latitude auroral features in driving the phase scintillations. We will also present data showing how phase scintillation can cause other GPS receivers to lose lock. The data and results are particularly valuable because they illustrate some of the challenges of using GPS systems for positioning and navigation in an auroral region like Alaska. These challenges for snowplough drivers were recently highlighted, along with the CASES SM-211 space weather monitor, in a special video in which ASTRA and three other small businesses were presented with an entrepreneurial award from William Shatner (http://youtu.be/bIVKEQH_YPk).

Ionospheric response to infrasonic-acoustic waves generated by natural hazard events

NASA Astrophysics Data System (ADS)

Zettergren, M. D.; Snively, J. B.

2015-09-01

Recent measurements of GPS-derived total electron content (TEC) reveal acoustic wave periods of ˜1-4 min in the F region ionosphere following natural hazard events, such as earthquakes, severe weather, and volcanoes. Here we simulate the ionospheric responses to infrasonic-acoustic waves, generated by vertical accelerations at the Earth's surface or within the lower atmosphere, using a compressible atmospheric dynamics model to perturb a multifluid ionospheric model. Response dependencies on wave source geometry and spectrum are investigated at middle, low, and equatorial latitudes. Results suggest constraints on wave amplitudes that are consistent with observations and that provide insight on the geographical variability of TEC signatures and their dependence on the geometry of wave velocity field perturbations relative to the ambient geomagnetic field. Asymmetries of responses poleward and equatorward from the wave sources indicate that electron perturbations are enhanced on the equatorward side while field aligned currents are driven principally on the poleward side, due to alignments of acoustic wave velocities parallel and perpendicular to field lines, respectively. Acoustic-wave-driven TEC perturbations are shown to have periods of ˜3-4 min, which are consistent with the fraction of the spectrum that remains following strong dissipation throughout the thermosphere. Furthermore, thermospheric acoustic waves couple with ion sound waves throughout the F region and topside ionosphere, driving plasma disturbances with similar periods and faster phase speeds. The associated magnetic perturbations of the simulated waves are calculated to be observable and may provide new observational insight in addition to that provided by GPS TEC measurements.

Inter-Disciplinary Validation of Pre Earthquake Signals. Case Study for Major Earthquakes in Asia (2004-2010) and for 2011 Tohoku Earthquake

NASA Technical Reports Server (NTRS)

Ouzounov, D.; Pulinets, S.; Hattori, K.; Liu, J.-Y.; Yang. T. Y.; Parrot, M.; Kafatos, M.; Taylor, P.

2012-01-01

We carried out multi-sensors observations in our investigation of phenomena preceding major earthquakes. Our approach is based on a systematic analysis of several physical and environmental parameters, which we found, associated with the earthquake processes: thermal infrared radiation, temperature and concentration of electrons in the ionosphere, radon/ion activities, and air temperature/humidity in the atmosphere. We used satellite and ground observations and interpreted them with the Lithosphere-Atmosphere- Ionosphere Coupling (LAIC) model, one of possible paradigms we study and support. We made two independent continues hind-cast investigations in Taiwan and Japan for total of 102 earthquakes (M>6) occurring from 2004-2011. We analyzed: (1) ionospheric electromagnetic radiation, plasma and energetic electron measurements from DEMETER (2) emitted long-wavelength radiation (OLR) from NOAA/AVHRR and NASA/EOS; (3) radon/ion variations (in situ data); and 4) GPS Total Electron Content (TEC) measurements collected from space and ground based observations. This joint analysis of ground and satellite data has shown that one to six (or more) days prior to the largest earthquakes there were anomalies in all of the analyzed physical observations. For the latest March 11 , 2011 Tohoku earthquake, our analysis shows again the same relationship between several independent observations characterizing the lithosphere /atmosphere coupling. On March 7th we found a rapid increase of emitted infrared radiation observed from satellite data and subsequently an anomaly developed near the epicenter. The GPS/TEC data indicated an increase and variation in electron density reaching a maximum value on March 8. Beginning from this day we confirmed an abnormal TEC variation over the epicenter in the lower ionosphere. These findings revealed the existence of atmospheric and ionospheric phenomena occurring prior to the 2011 Tohoku earthquake, which indicated new evidence of a distinct coupling between the lithosphere and atmosphere/ionosphere.

Ionospheric total electron content anomalies due to Typhoon Nakri on 29 May 2008: A nonlinear principal component analysis

NASA Astrophysics Data System (ADS)

Lin, Jyh-Woei

2012-09-01

This paper uses Nonlinear Principal Component Analysis (NLPCA) and Principal Component Analysis (PCA) to determine Total Electron Content (TEC) anomalies in the ionosphere for the Nakri Typhoon on 29 May, 2008 (UTC). NLPCA, PCA and image processing are applied to the global ionospheric map (GIM) with transforms conducted for the time period 12:00-14:00 UT on 29 May 2008 when the wind was most intense. Results show that at a height of approximately 150-200 km the TEC anomaly using NLPCA is more localized; however its intensity increases with height and becomes more widespread. The TEC anomalies are not found by PCA. Potential causes of the results are discussed with emphasis given to vertical acoustic gravity waves. The approximate position of the typhoon's eye can be detected if the GIM is divided into fine enough maps with adequate spatial-resolution at GPS-TEC receivers. This implies that the trace of the typhoon in the regional GIM is caught using NLPCA.

TEC variations over North-western Balkan Peninsula before and during the seismic activity of 24th May 2009

NASA Astrophysics Data System (ADS)

Contadakis, M. E.; Arabelos, D. N.; Vergos, G.

2012-04-01

In this paper the Total Electron Content (TEC) data of 8 Global Positioning System (GPS) stations of the EUREF network, 4 close and 4 remote to EQ epicentre stations, which are being provided by IONOLAB (Turkey), were analysed using wavelet analysis and Discrete Fourier Analysis in order to investigate the TEC variations over North-western Balkan Peninsula before and during the seismic activity of 24th of May, 2009. The main conclusions of this analysis are the following. (a) TEC oscillations in a broad range of frequencies occur randomly over a broad area of several hundred km from the earthquake and (b) high frequency oscillations (f ≥ 0.0003Hz, periods T ≤ 60m) seems to point to the location of the earthquake with a questionable accuracy but the fractal characteristics of the frequencies distribution, points to the locus of the earthquake with a rather higher accuracy. We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology.

TEC variations over the Mediterranean before and during the strong earthquake (M = 6.5) of 12th October 2013 in Crete, Greece

NASA Astrophysics Data System (ADS)

Contadakis, M. E.; Arabelos, D. N.; Vergos, G.; Spatalas, S. D.; Skordilis, M.

In this paper, the total electron content (TEC) data from eight global positioning system (GPS) stations of the EUREF network, provided by IONOLAB (Turkey), were analyzed using discrete Fourier analysis to investigate the TEC variations over the Mediterranean before and during the strong earthquake of 12th October 2013, which occurred west of Crete, Greece. In accordance with the results of similar analyses in the area, the main conclusions of this study are the following: (a) TEC oscillations in a broad range of frequencies occur randomly over an area of several hundred km from the earthquake and (b) high frequency oscillations (f ⩾ 0.0003 Hz, periods T ⩽ 60 m) may point to the location of the earthquake with questionable accuracy. The fractal characteristics of the frequency distribution may point to the locus of the earthquake with higher accuracy. We conclude that the lithosphere-atmosphere-ionosphere coupling (LAIC) mechanism through acoustic or gravity waves could explain this phenomenology.

Use of total electron content data to analyze ionosphere electron density gradients

NASA Astrophysics Data System (ADS)

Nava, B.; Radicella, S. M.; Leitinger, R.; Coïsson, P.

In the presence of electron density gradients the thin shell approximation for the ionosphere, used together with a simple mapping function to convert slant total electron content (TEC) to vertical TEC, could lead to TEC conversion errors. These "mapping function errors" can therefore be used to detect the electron density gradients in the ionosphere. In the present work GPS derived slant TEC data have been used to investigate the effects of the electron density gradients in the middle and low latitude ionosphere under geomagnetic quiet and disturbed conditions. In particular the data corresponding to the geographic area of the American Sector for the days 5-7 April 2000 have been used to perform a complete analysis of mapping function errors based on the "coinciding pierce point technique". The results clearly illustrate the electron density gradient effects according to the locations considered and to the actual levels of disturbance of the ionosphere. In addition, the possibility to assess an ionospheric shell height able to minimize the mapping function errors has been verified.

Assessing the Performance of GPS Precise Point Positioning Under Different Geomagnetic Storm Conditions during Solar Cycle 24.

PubMed

Luo, Xiaomin; Gu, Shengfeng; Lou, Yidong; Xiong, Chao; Chen, Biyan; Jin, Xueyuan

2018-06-01

The geomagnetic storm, which is an abnormal space weather phenomenon, can sometimes severely affect GPS signal propagation, thereby impacting the performance of GPS precise point positioning (PPP). However, the investigation of GPS PPP accuracy over the global scale under different geomagnetic storm conditions is very limited. This paper for the first time presents the performance of GPS dual-frequency (DF) and single-frequency (SF) PPP under moderate, intense, and super storms conditions during solar cycle 24 using a large data set collected from about 500 international GNSS services (IGS) stations. The global root mean square (RMS) maps of GPS PPP results show that stations with degraded performance are mainly distributed at high-latitude, and the degradation level generally depends on the storm intensity. The three-dimensional (3D) RMS of GPS DF PPP for high-latitude during moderate, intense, and super storms are 0.393 m, 0.680 m and 1.051 m, respectively, with respect to only 0.163 m on quiet day. RMS errors of mid- and low-latitudes show less dependence on the storm intensities, with values less than 0.320 m, compared to 0.153 m on quiet day. Compared with DF PPP, the performance of GPS SF PPP is inferior regardless of quiet or disturbed conditions. The degraded performance of GPS positioning during geomagnetic storms is attributed to the increased ionospheric disturbances, which have been confirmed by our global rate of TEC index (ROTI) maps. Ionospheric disturbances not only lead to the deteriorated ionospheric correction but also to the frequent cycle-slip occurrence. Statistical results show that, compared with that on quiet day, the increased cycle-slip occurrence are 13.04%, 56.52%, and 69.57% under moderate, intense, and super storms conditions, respectively.

An Interdisciplinary Approach at Studying the Earth-Sun System with GPS/GNSS and GPS-like Signals

NASA Technical Reports Server (NTRS)

Zuffada, Cinzia; Hajj, George; Mannucci, Anthony J.; Chao, Yi; Ao, Chi; Zumberge, James

2005-01-01

The value of Global Positioning Satellites (GPS) measurements to atmospheric science, space physics, and ocean science, is now emerging or showing a potential to play a major role in the evolving programs of NASA, NSF and NOAA. The objective of this communication is to identify and articulate the key scientific questions that are optimally, or perhaps uniquely, addressed by GPS or GPS-like observations, and discuss their relevance to existing or planned national Earth-science research programs. The GPS-based ocean reflection experiments performed to date have demonstrated the precision and spatial resolution suitable to altimetric applications that require higher spatial resolution and more frequent repeat than the current radar altimeter satellites. GPS radio occultation is promising as a climate monitoring tool because of its benchmark properties: its raw observable is based on extremely accurate timing measurements. GPS-derived temperature profiles can provide meaningful climate trend information over decadal time scales without the need for overlapping missions or mission-to-mission calibrations. By acquiring data as GPS satellites occult behind the Earth's limb, GPS also provides high vertical resolution information on the vertical structure of electron density with global coverage. New experimental techniques will create more comprehensive TEC maps by using signals reflected from the oceans and received in orbit. This communication will discuss a potential future GNSS Earth Observing System project which would deploy a constellation of satellites using GPS and GPS-like measurements, to obtain a) topography measurements based on GPS reflections with an accuracy and horizontal resolution suitable for eddy monitoring, and h) climate-records quality atmospheric temperature profiles. The constellation would also provide for measurements of ionospheric elec tron density. This is a good example of an interdisciplinary mission concept, with broad science objectives of high societal relevance, al l resting on common cost-effective technology.

Forecasting Space Weather-Induced GPS Performance Degradation Using Random Forest

NASA Astrophysics Data System (ADS)

Filjar, R.; Filic, M.; Milinkovic, F.

2017-12-01

Space weather and ionospheric dynamics have a profound effect on positioning performance of the Global Satellite Navigation System (GNSS). However, the quantification of that effect is still the subject of scientific activities around the world. In the latest contribution to the understanding of the space weather and ionospheric effects on satellite-based positioning performance, we conducted a study of several candidates for forecasting method for space weather-induced GPS positioning performance deterioration. First, a 5-days set of experimentally collected data was established, encompassing the space weather and ionospheric activity indices (including: the readings of the Sudden Ionospheric Disturbance (SID) monitors, components of geomagnetic field strength, global Kp index, Dst index, GPS-derived Total Electron Content (TEC) samples, standard deviation of TEC samples, and sunspot number) and observations of GPS positioning error components (northing, easting, and height positioning error) derived from the Adriatic Sea IGS reference stations' RINEX raw pseudorange files in quiet space weather periods. This data set was split into the training and test sub-sets. Then, a selected set of supervised machine learning methods based on Random Forest was applied to the experimentally collected data set in order to establish the appropriate regional (the Adriatic Sea) forecasting models for space weather-induced GPS positioning performance deterioration. The forecasting models were developed in the R/rattle statistical programming environment. The forecasting quality of the regional forecasting models developed was assessed, and the conclusions drawn on the advantages and shortcomings of the regional forecasting models for space weather-caused GNSS positioning performance deterioration.

The spatio-temporal characteristics of the wave structure excited by the solar terminator as deduced from TEC measurements at the global GPS network

NASA Astrophysics Data System (ADS)

Afraimovich, E.

2009-04-01

Recent investigations have shown that movement of the solar terminator (ST) causes generation of acoustic-gravity waves (AGW), turbulence and instabilities in the ionosphere plasma. Among all the sources of gravity waves, the moving ST has a special status, since it is a predictable phenomenon, whose characteristics are well known. Considering the ST as a stable and repetitive source of AGW, one can derive information about atmospheric conditions from the response of the medium to this input. The great variety of ST-linked phenomena in the atmosphere gave rise to a number of studies on the analysis of ionosphere parameter variations obtained by different ionosphere sounding methods. However, virtually all experimental data were obtained using indirect methods for analyzing the spectrum of ionosphere parameter variations, which can result from a number of factors. This causes difficulties in the reliable identification of ST-linked AGW, because in general case AGW can be generated by different sources either of natural or of anthropogenic origin. To identify ST-generated wave disturbances it is insufficient to register the time dependence of ionosphere parameters or their spectrum. It is necessary to measure the spatial structure of these disturbances and to compare it with spatial-temporal characteristics of ST. Another important requirement implies the continuous, global character of observations. Using long-term (1998-2007) total electron content (TEC) measurements from the IGS GPS global network and dense networks of GPS sites in USA (CORS) and Japan (GEONET), we have obtained the first evidence for the wave structure excited by the solar terminator (ST). We have found two main types of the observed TEC disturbances: large-scale (LS) 60-min variations with amplitude of about 0.5-1 TECU and medium-scale (MS) 15-min variations with amplitude of about 0.05-0.1 TECU. The first type of disturbances was predicted in theoretical investigations and registered earlier using different methods of ionosphere radio sounding. The second type of the observed TEC disturbances is MS traveling wave packets (MS TWP) generated when the time derivative of TEC amount to its maximum. That ST-generated wave packets have been found for the first time. We have obtained the first data regarding the spatio-temporal characteristics and the statistics of MS TWP. There is no correlation between TWP amount and Dst-index value. We found that ST-generated wave packets have duration of about 1-2 hours and time shift of about 1.5-6 hours after the ST appearance at the altitude of 300 km. The TWP wave front extends almost along ST-line. The wavelength of ST-generated wave packets is about 100-300 km. The space image of MS TWP is characterized by pronounced anisotropy (the ratio between lengthwise and transversal scales exceeds 10) and high coherence over a long distance of about 2000 km. The work was supported by the SB RAS and FEB RAS collaboration project N 3.24, the RFBR-GFEN grant N 06-05-39026 and RFBR grant 07-05-00127.

The Scaling Law of The Near-Field Coseismic Ionospheric Disturbances

NASA Astrophysics Data System (ADS)

Cahyadi, M.; Heki, K.

2013-12-01

Coseismic ionospheric disturbances (CIDs) appear shortly after relatively large earthquakes as a result of ionospheric irregularity associated with passing atmospheric waves excited by the earthquakes. CIDs appearing approximately 10 minutes after earthquakes are caused by acoustic waves generated by coseismic vertical movements of the crust or the sea surface, and they propagate as fast as ~1 km/second over the distance of hundreds of kilometres. Here we collected past examples of CID detected in Total Electron Content (TEC) by GPS observations for 21 earthquakes 1994-2012 distributed worldwide. Their moment magnitudes (Mw) range from 6.6 to 9.2, and include two normal fault earthquakes that occurred in the outer rise region of the trenches (2007 January central Kuril earthquake, and 2012 December Tohoku-oki earthquake), and two strike-slip earthquakes (the main shock and the largest aftershock of the 2012 North Sumatra earthquakes). The rest are all reverse-fault earthquakes. We tried to select the pair of GPS satellite and station showing the largest CID amplitudes. Due to the directivity, the ionospheric piercing point (IPP) of line-of-sight (LOS) should be on the southern/northern side for earthquakes in the northern/southern hemisphere. We also selected GPS stations lying on the same side of IPP and located farther than IPP, to enable shallow-angle LOS penetration with the CID wavefront. We also selected CIDs with (1) appearance time not later than 15 minutes after earthquakes, and (2) sharp peaks. The first ensures that IPPs are close to the epicentres and geometric decays are insignificant. The second condition is the manifestation of the shallow angle penetration of LOS. The peak amplitudes were derived by (1) finding the peak TEC value, (2) going back in time from the peak by 90 seconds, and (3) calculating the TEC difference at the two epochs. We also obtained background vertical TEC from Global Ionospheric Maps (GIM), and expressed the CID amplitudes as percents relative to the background TEC. When we plot relative CID amplitudes as a function of seismic moment in the double logarithmic plot, data are distributed roughly around a line, suggesting that they obey a certain scaling law. The slope of the line shows that the CID amplitudes increase by two orders of magnitude as Mw increases by three. We speculate that this reflects the scaling law governing the maximum uplift in relatively large shallow-angle reverse faultings. This scaling law and its empirical factor-two uncertainty in CID amplitude imply that we can determine Mw with an uncertainty of ×0.45 by measuring CID amplitudes. This is useful for early warning in a region where tsunamis arrive at the coast later than acoustic waves arrive at the ionospheric F layer, and this is the case for the Pacific coast of NE Japan. There are two earthquakes deviating negatively beyond the factor 2 uncertainty. They are the 2012 North Sumatra earthquake (Mw8.6), the largest strike-slip earthquakes ever recorded, and its largest aftershock (Mw8.1). This negative deviation would possibly reflect the smaller vertical crustal movements in strike-slip earthquakes than dip-slip events.

Ionospheric variations during sudden stratospheric warming in the high- and mid-latitude regions

NASA Astrophysics Data System (ADS)

Yasyukevich, Anna; Voeykov, Sergey; Mylnikova, Anna

2017-04-01

The ionospheric dynamic in the high- and middle-latitude regions during the periods of sudden stratospheric warmings (SSW) was studied by using the international network of phase dual-frequency GPS/GLONASS receivers and the vertical sounding data. Twelve SSW events that occurred in the Northern Hemisphere 2006 through 2013 were considered. In order to identify the possible response of the ionosphere to SSW events, we carried out the analysis of the total electron (TEC) and the F2-layer maximum electron density (NmF2) deviations from the background level. We have also studied changes of the level of total electron content (TEC) wave-like variations characterized by a special index WTEC. The index reflects the intensity of medium- and large-scale traveling ionospheric disturbances. The dynamics of the high- and middle-latitude ionosphere at the points near the SSW areas was found to differ from the regular. For a large number of events, it is shown that, despite quiet geomagnetic conditions, a noticeable decrease in the NmF2 and TEC values (by 5-10% relative to the background level) is observed during the SSW evolution and maximum stages. On the contrary, for 10-20 days after the SSW maxima, NmF2 and TEC significantly exceed the monthly averaged values. Moreover, these electron density changes are observed for both strong and weak stratospheric warmings, and are recorded mainly during daytime. The observed SSW effects in the polar and mid-latitude ionosphere are assumed to be probably associated with the changes in the neutral composition at the thermospheric heights that affect the F2-layer electron density. The study is supported by the Russian Foundation for Basic Research under Grant No. 16-35-60018, as well as by the RF President Grant of Public Support for RF Leading Scientific Schools (NSh-6894.2016.5).

Global Ionospheric Perturbations Monitored by the Worldwide GPS Network

NASA Technical Reports Server (NTRS)

Ho, C. M.; Mannucci, A. T.; Lindqwister, U. J.; Pi, X. Q.

1996-01-01

Based on the delays of these (Global Positioning System-GPS)signals, we have generated high resolution global ionospheric TEC (Total Electronic Changes) maps at 15-minute intervals. Using a differential method comparing storm time maps with quiet time maps, we find that the ionopshere during this time storm has increased significantly (the percentage change relative to quiet times is greater than 150 percent) ...These preliminary results (those mentioned above plus other in the paper)indicate that the differential maping method, which is based on GPS network measurements appears to be a useful tool for studying the global pattern and evolution process of the entire ionospheric perturbation.

An Ionospheric Response to the 2013 Moore EF5 Tornad, Detected By High-Resolution GPS-TEC Observations

NASA Astrophysics Data System (ADS)

Kubota, M.; Nishioka, M.; Tsugawa, T.; Ishii, M.

2014-12-01

We observed clear concentric waves and short-period oscillations in the ionosphere after the EF5 tornado hit Moore, Oklahoma, USA, on 20 May 2013 using a dense wide-coverage ionospheric total electron content (TEC) observation in North America. These concentric waves were non-dispersive waves with a horizontal wavelength of ~120 km and a period of ~13 minutes. They were observed for more than seven hours throughout North America. TEC oscillations with a period of ~4 minutes were also observed in the south of Moore for more than eight hours. Comparison between the TEC observation and the infrared cloud image from the GOES satellite indicates that the concentric waves were caused by supercells rather than the tornados themselves. Backward ray-tracing analysis suggests that the leaking of atmospheric waves in a thermal duct excited AGWs in the ionosphere. The short-period TEC oscillation could be explained by the acoustic resonance triggered by strong long-lasting supercells. This observational result provides the first clear evidence of a severe meteorological event causing atmospheric waves propagating upward in the upper atmosphere and reaching the ionosphere.

Investigation of ionospheric scintillation at UKM station, Malaysia during low solar activity

NASA Astrophysics Data System (ADS)

Seif, Aramesh; Abdullah, Mardina; Marie Hasbi, Alina; Zou, Yuhua

2012-12-01

In this paper the investigation of the occurrence of ionospheric scintillation with S4≥0.2 was conducted by using a dual-frequency GISTM (GPS Ionospheric Scintillation and TEC monitor) at Universiti Kebangsaan Malaysia station, Malaysia (2.55°N, 101.46°E; geomagnetic: 7.39°S, 173.63°E) between September 2009 and December 2010. The study shows that significant nighttime amplitude scintillation event with 0.4≤S4<0.6 mainly occurred in the months of March, September and October, while significant daytime amplitude scintillation activity took place in November and December with 0.3≤S4<0.5. Moreover, nighttime amplitude scintillation observed at UKM station always occurred with phase scintillations, total electron content (TEC) depletions, rate of change of TEC (ROT) fluctuations and the enhancement of rate of TEC index (ROTI). Nevertheless, during daytime amplitude scintillation, TEC depletions and ROT fluctuations were much weaker than those that occurred during nighttime and this may be caused by small scale irregularities in the E region, called sporadic-E (Es), while the occurrences of nighttime amplitude scintillation maybe caused by the ionospheric irregularities in the F region.

Assimilation of DMSP/SSUSI UV data into IDA4D

NASA Astrophysics Data System (ADS)

Gelinas, L. J.; Bust, G. S.; Brinkman, D. G.; Straus, P. R.; Swartz, R. L.

2014-12-01

Ionospheric Data Assimilation Four-Dimensional (IDA4D) is a continuous-time, three-dimensional imaging algorithm that can produce 4D electron density specifications for various science investigations [e.g., Bust et al., 2007]. IDA4D is based on three-dimensional variational (3DVAR) data assimilation [Daley and Barker, 2001]. The algorithm combines various data sources and their associated error covariances with a background model (in this case the IRI) and its covariances to produce an ionospheric specification with formal uncertainties. IDA4D employs a Gauss- Markov Kalman filter technique similar to that used by operational assimilation models. The model can ingest a broad spectrum of data types that are either linearly or non-linearly related to electron density, including ground-based TEC, space-based TEC as measured by GPS occultation sensors and UV emissions associated with nightside recombination of O+. IDA4D has been undergoing testing at The Aerospace Corporation to determine its performance with respect to combinations of input data sets under different conditions (solar minimum, solar maximum, geomagnetic activity). The results presented here summarize the performance of IDA4D when UV data is ingested, both with and without additional TEC measurements. The UV data used in the study summarized here are 135.6 nm emissions measured the SSUSI instruments on F16 and F18 DMSP. We discuss the process by which UV data is ingested into IDA4D, including data binning, error estimation and correction of 135.6 nm contamination from mutual neutralization of O+ and O-. Model performance is then assessed using comparisons to various ground truth data, including ISR data, Jason VTEC, CNOF/S in-situ plasma density and ionosonde-derived NmF2 values. The results of this study show that UV data improves model performance, particularly when TEC data coverage is sparse. Bust, G. S., G. Crowley, T. W. Garner, T. L. Gaussiran II, R. W. Meggs, C. N. Mitchell, P. S. J. Spencer, P. Yin, and B. Zapfe (2007) ,Four Dimensional GPS Imaging of Space-Weather Storms, Space Weather, 5, S02003, doi:10.1029/2006SW000237. Daley, R. & Barker, E., NAVDAS: Formulation and Diagnostics. Monthly Weather Review 129, 869 (2001).

Utilizing new GNSS capabilities for exploring Geospace

NASA Astrophysics Data System (ADS)

Coster, A. J.

2015-12-01

In 2000 the density of GPS receivers across the continental United States increased to the point that strictly data-driven regional maps of total electron content (TEC) could be constructed. These data-driven maps allowed the TEC to be monitored throughout the course of geomagnetic storms and to observe the progression of traveling ionospheric disturbances. This allowed studies of the development of storm enhanced density plumes in both hemispheres and of the dynamic changes in the equatorial TEC following stratospheric warming events. Currently, GPS TEC maps have become recognized as one of the premier tools to monitor coupling of atmospheric regions from both below and above the ionosphere. The number of available scientific dual-frequency receivers across the globe now exceeds 3000. However this number is anticipated to increase rapidly in part due to the numerous arrays being fielded for commercial applications such as precision farming and highway surveying. In addition, there will be a rapid increase in the number of GNSS signals available in the near future. Besides GPS, the European Union is building a system named GALILEO, which will consist of a 30-satellite constellation. The Russians have a system based on a 24-satellite constellation named GLONASS. The Chinese are developing a system called Beidou, which means "stars of the Big Dipper". The Beidou system will consist of 35 satellites. By 2023, there will be more than 160 GNSS satellites and 400 signals. Multi-constellation, multi-band GNSS will be a major enabler for space weather studies. This talk will focus on the potential of using the multiple new GNSS signals and the new higher density receiver arrays for measurements of plasma drift, detailed studies of traveling ionospheric disturbances (TIDS) and expanded studies of atmospheric coupling. We will conclude by describing the tremendous potential of merging GNSS observations with observations collected by arrays of low-cost, low-power, and small form factor ionosondes. In the future, we predict that new ionosonde and GNSS receiver networks will enable unprecedented mesoscale real-time tomographic observations of the ionosphere.

Classification of Regional Ionospheric Disturbances Based on Support Vector Machines

NASA Astrophysics Data System (ADS)

Begüm Terzi, Merve; Arikan, Feza; Arikan, Orhan; Karatay, Secil

2016-07-01

Ionosphere is an anisotropic, inhomogeneous, time varying and spatio-temporally dispersive medium whose parameters can be estimated almost always by using indirect measurements. Geomagnetic, gravitational, solar or seismic activities cause variations of ionosphere at various spatial and temporal scales. This complex spatio-temporal variability is challenging to be identified due to extensive scales in period, duration, amplitude and frequency of disturbances. Since geomagnetic and solar indices such as Disturbance storm time (Dst), F10.7 solar flux, Sun Spot Number (SSN), Auroral Electrojet (AE), Kp and W-index provide information about variability on a global scale, identification and classification of regional disturbances poses a challenge. The main aim of this study is to classify the regional effects of global geomagnetic storms and classify them according to their risk levels. For this purpose, Total Electron Content (TEC) estimated from GPS receivers, which is one of the major parameters of ionosphere, will be used to model the regional and local variability that differs from global activity along with solar and geomagnetic indices. In this work, for the automated classification of the regional disturbances, a classification technique based on a robust machine learning technique that have found wide spread use, Support Vector Machine (SVM) is proposed. SVM is a supervised learning model used for classification with associated learning algorithm that analyze the data and recognize patterns. In addition to performing linear classification, SVM can efficiently perform nonlinear classification by embedding data into higher dimensional feature spaces. Performance of the developed classification technique is demonstrated for midlatitude ionosphere over Anatolia using TEC estimates generated from the GPS data provided by Turkish National Permanent GPS Network (TNPGN-Active) for solar maximum year of 2011. As a result of implementing the developed classification technique to the Global Ionospheric Map (GIM) TEC data which is provided by the NASA Jet Propulsion Laboratory (JPL), it will be shown that SVM can be a suitable learning method to detect the anomalies in Total Electron Content (TEC) variations. This study is supported by TUBITAK 114E541 project as a part of the Scientific and Technological Research Projects Funding Program (1001).

A method for separating seismo-ionospheric TEC outliers from heliogeomagnetic disturbances by using nu-SVR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pattisahusiwa, Asis; Liong, The Houw; Purqon, Acep

Seismo-Ionospheric is a study of ionosphere disturbances associated with seismic activities. In many previous researches, heliogeomagnetic or strong earthquake activities can caused the disturbances in the ionosphere. However, it is difficult to separate these disturbances based on related sources. In this research, we proposed a method to separate these disturbances/outliers by using nu-SVR with the world-wide GPS data. TEC data related to the 26th December 2004 Sumatra and the 11th March 2011 Honshu earthquakes had been analyzed. After analyzed TEC data in several location around the earthquake epicenter and compared with geomagnetic data, the method shows a good result inmore » the average to detect the source of these outliers. This method is promising to use in the future research.« less

US EPA GEOSPATIAL QUALITY COUNCIL: ENSURING QUALITY GEOSPATIAL SOLUTIONS

EPA Science Inventory

This presentation will discuss the history, strategy, products, and future plans of the EPA Geospatial Quality Council (GQC). A topical review of GQC products will be presented including:

o Guidance for Geospatial Data Quality Assurance Project Plans.

o GPS - Tec...

Phase and amplitude Variation of Weddell Sea Anomaly at King Sejong Station in Antarctic between 2005 and 2009

NASA Astrophysics Data System (ADS)

Chung, J.; Lee, C.; Jee, G.

2011-12-01

The Weddell Sea Anomaly (WSA) in ionosphere has been defined by higher electron density at nighttime than during the daytime on summer season near the region of the Weddell Sea.Recent studies show the WSA is an extreme case of longitudinal variation and occurrs all of season except for winter when F10.7 is high. We examine the temporal variation of the WSA using the ground-based GPS TEC measured King Sejong station (geographic latitude 62.2°S, longitude 58.5°W, corrected geomagnetic latitude 48°S) in Antarctic between 2005 and 2009 in condition of solar minimum. We analyze the characteristics of diurnal and semi-diurnal variation for all of years and examine the yearly and seasonal variation of phase and amplitude of the WSA. Our results of local time GPS TEC variation show the amplitudes of the WSA are significant in the summer and its phases appear to be changed according to the season.

A Real-Time Earthquake Precursor Detection Technique Using TEC from a GPS Network

NASA Astrophysics Data System (ADS)

Alp Akyol, Ali; Arikan, Feza; Arikan, Orhan

2016-07-01

Anomalies have been observed in the ionospheric electron density distribution prior to strong earthquakes. However, most of the reported results are obtained by earthquake analysis. Therefore, their implementation in practice is highly problematic. Recently, a novel earthquake precursor detection technique based on spatio-temporal analysis of Total Electron Content (TEC) data obtained from Turkish National Permanent GPS Network (TNPGN) is developed by IONOLAB group (www.ionolab.org). In the present study, the developed detection technique is implemented in a causal setup over the available data set in test phase that enables the real time implementation. The performance of the developed earthquake prediction technique is evaluated by using 10 fold cross validation over the data obtained in 2011. Among the 23 earthquakes that have magnitudes higher than 5, the developed technique can detect precursors of 14 earthquakes while producing 8 false alarms. This study is supported by TUBITAK 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

(abstract) Using GPS Measurements to Identify Global Ionospheric Storms in Near Real-Time

NASA Technical Reports Server (NTRS)

Ho, C. M.; Mannucci, A. J.; Lindqwister, U. J.; Rao, A. M.; Pi, X.; Wilson, B. D.; Yuan, D. N.; Reyes, M.

1996-01-01

The solar wind interacts with the Earth's magnetosphere, eventually dissipating energy into the ionosphere and atmosphere. As a terminator, the ionosphere responds to magnetic storms, which is very important in understanding the energy coupling process between the Sun and the Earth and in forecasting space weather changes.The worldwide GPS network, for the first time, makes near real-time global ionospheric TEC measurements a possibility. Based on these measurements, global ionospheric TEC maps are generated with time resolution of from 5 minutes to hours. Using these maps, we can analyze the global evolution of ionospheric storms on temporal and spatial scales, which have been dificult to study before. We find that for certain types of storms (such as TID-driven), it is possible to identify them near onset and issue warning signals during the early stages. Main attention has been paid on northern hemispheric winter storms. Their common features and physical mechanisms are being investigated.

Validation of foF2 and TEC Modeling During Geomagnetic Disturbed Times: Preliminary Outcomes of International Forum for Space Weather Modeling Capabilities Assessment

NASA Astrophysics Data System (ADS)

Shim, J. S.; Tsagouri, I.; Goncharenko, L. P.; Kuznetsova, M. M.

2017-12-01

To address challenges of assessment of space weather modeling capabilities, the CCMC (Community Coordinated Modeling Center) is leading the newly established "International Forum for Space Weather Modeling Capabilities Assessment." This presentation will focus on preliminary outcomes of the International Forum on validation of modeled foF2 and TEC during geomagnetic storms. We investigate the ionospheric response to 2013 Mar. geomagnetic storm event using ionosonde and GPS TEC observations in North American and European sectors. To quantify storm impacts on foF2 and TEC, we first quantify quiet-time variations of foF2 and TEC (e.g., the median and the average of the five quietest days for the 30 days during quiet conditions). It appears that the quiet time variation of foF2 and TEC are about 10% and 20-30%, respectively. Therefore, to quantify storm impact, we focus on foF2 and TEC changes during the storm main phase larger than 20% and 50%, respectively, compared to 30-day median. We find that in European sector, both foF2 and TEC response to the storm are mainly positive phase with foF2 increase of up to 100% and TEC increase of 150%. In North America sector, however, foF2 shows negative effects (up to about 50% decrease), while TEC shows positive response (the largest increase is about 200%). To assess modeling capability of reproducing the changes of foF2 and TEC due to the storm, we use various model simulations, which are obtained from empirical, physics-based, and data assimilation models. The performance of each model depends on the selected metrics, therefore, only one metrics is not enough to evaluate the models' predictive capabilities in capturing the storm impact. The performance of the model also varies with latitude and longitude.

Capabilities of SWACI as an essential component of EURIPOS

NASA Astrophysics Data System (ADS)

Borries, C.; Jakowski, N.; Mayer, C.; Wilken, V.; Missling, K. D.; Barkmann, H.; Mielich, J.

2009-04-01

EURIPOS as a European research network of an ionospheric and plamaspheric observation system relies on the well established European vertical sounding network and an equivalent network of numerous receivers of signals from Global Navigation Satellite Systems (GNSS) such as GPS and Galileo. According to this base line EURIPOS is assisted by current ionospheric services such as DIAS (Digital Upper Atmosphere Server) and SWACI (Space Weather Application Center Ionosphere) operated by NOA and DLR, respectively. This paper shall demonstrate the capabilities of SWACI providing an essential basis for supporting the enhanced service by EURIPOS. The current SWACI service operates a powerful data processing system working both in real-time and post-processing modes in order to provide actual information to the customers (http://w3swaci.dlr.de). Typical data products include ground based GNSS derived European maps of the Total Electron Content (TEC) and corresponding derivatives such as latitudinal and longitudinal gradients and rate of change, updated every 5 minutes. Space based retrievals include radio occultation data as well as a 3D reconstruction of the topside ionosphere between CHAMP orbit and GPS satellite orbit height. The different types of products are described and discussed in relation to EURIPOS requirements and objectives. Emphasis is given to new products which may be created by combining vertical sounding and TEC data. The resulting equivalent slab thickness is discussed by combining ionosonde data from Juliusruh with corresponding TEC data extracted from the TEC maps. EURIPOS shall provide this valuable shape parameter in near real time at several vertical sounding stations. The dynamics of the profile shape is important for studying ionospheric storms. The capabilities of SWACI for monitoring and studying ionospheric storms observed since 2000 will be demonstrated.

High-Latitude Ionospheric Imaging using Canadian High Arctic Ionospheric Network (CHAIN)

NASA Astrophysics Data System (ADS)

Meziane, K.; Jayachandran, P. T.; Hamza, A. M.; MacDougall, J. W.

2013-12-01

Understanding the polar cap dynamics is a fundamental problem in solar-terrestrial physics; any breakthroughs would have to take into account the interactions that take place at the interfaces between the Solar Wind and the Magnetosphere and between the latter and the ionosphere, respectively. Over the past decade a significant number of ground-based GPS receivers and digital ionosondes have been deployed in the polar cap and auroral region. This deployment has allowed the harvest of much needed data, otherwise not available, which in turn helps understand the dynamics of the polar ionospheric regions. A technique, used consistently by researchers in the field, consists of inverting the Total Electron Content (TEC) along the ray path obtained from a system of GPS receivers. In the present study, a combination of tomography and ionosonde data from the CHAIN network is used to examine the dynamics of polar cap patches. First, the TEC derived from GPS receivers through tomographic reconstruction is directly compared with ionosonde data. The comparison includes periods of quite and disturbed geomagnetic activity. We then use the vertical density profiles derived from the CHAIN ionosondes as initial seeds for the reconstruction of the tomographic images of the polar cap regions. Precise electron density peaks obtained through the tomographic reconstruction fall within a range that is consistent with direct CHAIN measurements when certain conditions are met. An assessment of the performance of the resulting combination of GPS and ionosonde data is performed, and conclusions are presented.

Review of variations in Mw < 7 earthquake motions on position and TEC (Mw = 6.5 Aegean Sea earthquake sample)

NASA Astrophysics Data System (ADS)

Yildirim, Omer; Inyurt, Samed; Mekik, Cetin

2016-02-01

Turkey is a country located in the middle latitude zone, where tectonic activity is intensive. Recently, an earthquake of magnitude 6.5 Mw occurred offshore in the Aegean Sea on 24 May 2014 at 09:25 UTC, which lasted about 40 s. The earthquake was also felt in Greece, Romania, and Bulgaria in addition to Turkey. In recent years, ionospheric anomaly detection studies have been carried out because of seismicity with total electron content (TEC) computed from the global navigation satellite system's (GNSS) signal delays and several interesting findings have been published. In this study, both TEC and positional variations have been examined separately following a moderate size earthquake in the Aegean Sea. The correlation of the aforementioned ionospheric variation with the positional variation has also been investigated. For this purpose, a total of 15 stations was used, including four continuously operating reference stations in Turkey (CORS-TR) and stations in the seismic zone (AYVL, CANA, IPSA, and YENC), as well as international GNSS service (IGS) and European reference frame permanent network (EPN) stations. The ionospheric and positional variations of the AYVL, CANA, IPSA, and YENC stations were examined using Bernese v5.0 software. When the precise point positioning TEC (PPP-TEC) values were examined, it was observed that the TEC values were approximately 4 TECU (total electron content unit) above the upper-limit TEC value at four stations located in Turkey, 3 days before the earthquake at 08:00 and 10:00 UTC. At the same stations, on the day before the earthquake at 06:00, 08:00, and 10:00 UTC, the TEC values were approximately 5 TECU below the lower-limit TEC value. The global ionosphere model TEC (GIM-TEC) values published by the Centre for Orbit Determination in Europe (CODE) were also examined. Three days before the earthquake, at all stations, it was observed that the TEC values in the time period between 08:00 and 10:00 UTC were approximately 2 TECU above the upper-limit TEC value; 1 day before the earthquake at 06:00, 08:00, and 10:00 UTC, the TEC values were approximately 4 TECU below the lower-limit TEC value. Again, by using the same 15 stations, positional variation investigation for before and after the earthquake was undertaken for the AYVL, CANA, IPSA, and YENC stations. As a result of the conducted analysis, positional displacements were seen before and after the earthquake at the CANA station, which is the nearest station to the earthquake centre. Before and after the earthquake, positional displacements were observed as 10 and 3 cm respectively.

Observation of medium-scale traveling ionospheric disturbances over Peninsular Malaysia based on IPP trajectories

NASA Astrophysics Data System (ADS)

Husin, Asnawi; Abdullah, M.; Momani, M. A.

2011-04-01

Using vertical total electron content (VTEC) data that were derived from the Malaysia Real Time Kinematic GPS network (MyRTKnet), we analyzed the time variation of the VTEC with the occurrence of medium-scale traveling ionospheric disturbances (MSTIDs) based on ionospheric pierce point (IPP) trajectories. MSTIDs are known as ionospheric disturbance phenomena that generally induce perturbations in important ionospheric parameters such as the ionospheric total electron content (TEC). A method was developed to detect the existence of MSTIDs by identifying rapid fluctuations in the TEC by subjecting the TEC data time series to high-pass filtering. Data were evaluated using the GPS MyRTKnet network over Peninsular Malaysia in the month of September 2007 (a time period with relatively low geomagnetic activity). Two-dimensional maps over Peninsular Malaysia were constructed based on the IPP trajectories. Analysis of the cross correlation of detrended VTEC data from six MyRTKnet stations (PASP, KRAI, GMUS, CAME, TLKI and SBKB) yielded MSTID velocities of around 100 ± 50 m s-1 in the daytime and 60 ± 30 m s-1 in the nighttime, with occurrences of 17.6% and 13.7%, respectively. The results show that although the MSTID wave structure propagates southwestward, some waves also move northward. These waves were connected to the effect of the meridional neutral wind in the upper regions of the ionosphere (400 km).

Observation and Modeling of Storm Generated Acoustic Waves in the Ionosphere Revealed in a Dense Network of GPS Receivers

NASA Astrophysics Data System (ADS)

Walterscheid, R. L.; Azeem, S. I.

2017-12-01

Acoustic waves generated in the lower atmosphere may become an important source of variably in the upper atmosphere. Although they are excited with small amplitudes they are minimally subject to viscous dissipation and may reach significant amplitudes at F-region altitudes. A number of studies in the 1970s showed clear signatures in ionosonde data in the infrasonic period range attributable to thunder storm activity. We have examined Total Electron Content data from a dense network of over 4000 ground-based GPS receivers over the continental United States during an outbreak of severe weather, including tornados, over Kansas in May 2015. A sequence of GPS TEC images showed clear Traveling Ionospheric Disturbances (TIDs) in the form of concentric rings moving outward from the center of the storm region. The characteristics of the disturbance (phase speed and frequency) were consistent with acoustic waves in the infrasonic range. We have modeled the disturbance by including a tropospheric heat source representing latent heat release from a large thunderstorm. The disturbance at ionospheric altitudes resembles the observed disturbance in terms of phase speed, frequency and horizontal wavelength. We conclude that the observed TIDs in TEC were caused by an acoustic wave generated by deep convection.

INEGI's Network of GPS permanent stations in Mexico

NASA Astrophysics Data System (ADS)

Gonzalez Franco, G. A.

2013-05-01

The Active National Geodetic Network administered by INEGI (Instituto Nacional de Estadística y Geografía) is a set of 24 GPS permanent stations in Mexico that was established in 1993 for a national rural cadastral project, its has been mainly used for geodetic surveys through Mexico including international borders, and has been progressing to contribute to national, regional and international reference frames through the delivering of GPS data or coordinate solutions from INEGI Processing Center to SIRGAS and NAREF. Recently GAMIT/GLOBK Processing of permanent stations in Mexico was realized from 2007-2011 to determine station's velocity. Related to natural hazards, a subset of INEGI network contributes to the project Real Time Integrated Atmosferic Water Wapor and TEC from GPS. The GPS network planned evolution consider changing to a GNSS network, adding stations to IGS, maintain the services of the present, and contribute to multidisciplinary geodetic studies through data publicly available.

Comparing GNSS Total Electron Content of Sonmiani, Pakistan with NeQuick-2 & IRI-2012 during July 2014 - June 2015

NASA Astrophysics Data System (ADS)

Ayyaz Ameen, Muhammad; Ghafoor, Memoona; Weimin, Zhen

2016-07-01

Total Electron Content (TEC) data acquired by an in-house fabricated GNSS receiver (by China Research Institute of Radiowave Propagation, CRIRP) working with NovaTel antenna installed at Sonmiani (geograph. 24.95°N, 67.14°E) is being reported for the first time. The period under study is one year (July 2014 to June 2015) which is based upon the hourly instantaneous TEC values of 120 days (10 international quietest days, IQD per month). The data confirms the annual variation of TEC at the station which lies at the northern crest of equatorial ionization anomaly (EIA) region. GNSS TEC values in general are then compared with NeQuick-2 and IRI-2012. Model comparison shows that NeQuick-2 predicts the TEC with greater confidence whereas IRI-2012 shows larger discrepancies with respect to the data. Seasonal variation shows the highest TEC values during equinox months. December solstice values of TEC are higher than the June solstice values, this confirms that the seasonal anomaly is dominating in the region during the course of study.

Variations of total electron content during geomagnetic disturbances: A model/observation comparison

NASA Technical Reports Server (NTRS)

Roble, G. Lu X. Pi A. D. Richmond R. G.

1997-01-01

This paper studies the ionospheric response to major geomagnetic storm of October 18-19, 1995, using the thermosphere-ionosphere electrodynamic general circulation model (TIE-GCM) simulations and the global ionospheric maps (GIM) of total electron content (TEC) observations from the Global Positioning System (GPS) worldwide network.

Stormtime Magnetosphere-Ionosphere-Thermosphere Interactions and Dynamics

DTIC Science & Technology

2013-03-13

1 2. BACKGROUND ... BACKGROUND The studies described in this report were performed in support of ongoing and planned space weather programs in the areas of Space Situational...Ionosphere The purpose of this effort was to initiate on-going analysis of COSMIC -GPS measurements of total electron content (TEC) in the dayside

Precise Ionosphere Monitoring via a DSFH Satellite TT&C Link

NASA Astrophysics Data System (ADS)

Chen, Xiao; Li, Guangxia; Li, Zhiqiang; Yue, Chao

2014-11-01

A phase-coherent and frequency-hopped PN ranging system was developed, originally for the purpose of anti-jamming TT&C (tracking, telemetry and telecommand) of military satellites of China, including the Beidou-2 navigation satellites. The key innovation in the synchronization of this system is the unambiguous phase recovery of direct sequence and frequency hopping (DSFH) spread spectrum signal and the correction of frequency-dependent phase rotation caused by ionosphere. With synchronization achieved, a TEC monitoring algorithm based on maximum likelihood (ML) principle is proposed and its measuring precision is analyzed through ground simulation, onboard confirmation tests will be performed when transionosphere DSFH links are established in 2014. The measuring precision of TEC exceeds that obtained from GPS receiver data because the measurement is derived from unambiguous carrier phase estimates, not pseudorange estimates. The observation results from TT&C stations can provide real time regional ionosphere TEC estimation.

Global Ionospheric and Plasmaspheric Monitoring With FORMOSAT-3/COSMIC and Ground GPS Observables

NASA Astrophysics Data System (ADS)

Tsai, H.; Ho, T.; Cheng, M.; Hsu, B.; Liu, J. G.

2011-12-01

The global ionosphere map (GIM) provides instantaneous "snapshots" of the global total electron content (TEC) distribution by interpolating the ground-based GPS observables, which include the ionospheric and plasmaspheric content. The increasing use of the FORMOSAT-3/COSMIC (F3/C) satellites provides a change to monitor the global ionospheric and plasmaspheric content individually. The global plasmasphere map (GPM) is constructed by the F3/C non-radio occultation (RO) data in 3-hour snapshot, while the re-defined GIM in narrow sense is contructed with the blending of F3/C RO, the ground GPS observables, and the GPM. The result can be used to study the interaction between ionosphere and plasmasphere.

Methodology and consistency of slant and vertical assessments for ionospheric electron content models

NASA Astrophysics Data System (ADS)

Hernández-Pajares, Manuel; Roma-Dollase, David; Krankowski, Andrzej; García-Rigo, Alberto; Orús-Pérez, Raül

2017-12-01

A summary of the main concepts on global ionospheric map(s) [hereinafter GIM(s)] of vertical total electron content (VTEC), with special emphasis on their assessment, is presented in this paper. It is based on the experience accumulated during almost two decades of collaborative work in the context of the international global navigation satellite systems (GNSS) service (IGS) ionosphere working group. A representative comparison of the two main assessments of ionospheric electron content models (VTEC-altimeter and difference of Slant TEC, based on independent global positioning system data GPS, dSTEC-GPS) is performed. It is based on 26 GPS receivers worldwide distributed and mostly placed on islands, from the last quarter of 2010 to the end of 2016. The consistency between dSTEC-GPS and VTEC-altimeter assessments for one of the most accurate IGS GIMs (the tomographic-kriging GIM `UQRG' computed by UPC) is shown. Typical error RMS values of 2 TECU for VTEC-altimeter and 0.5 TECU for dSTEC-GPS assessments are found. And, as expected by following a simple random model, there is a significant correlation between both RMS and specially relative errors, mainly evident when large enough number of observations per pass is considered. The authors expect that this manuscript will be useful for new analysis contributor centres and in general for the scientific and technical community interested in simple and truly external ways of validating electron content models of the ionosphere.

Seismo-Ionospheric Coupling as Intensified EIA Observed by Satellite Electron Density and GPS-TEC Data

NASA Astrophysics Data System (ADS)

Ryu, K.; Jangsoo, C.; Kim, S. G.; Jeong, K. S.; Parrot, M.; Pulinets, S. A.; Oyama, K. I.

2014-12-01

Examples of intensified EIA features temporally and spatially related to large earthquakes observed by satellites and GPS-TEC are introduced. The precursory, concurrent, and ex-post enhancements of EIA represented by the equatorial electron density, which are thought to be related to the M8.7 Northern Sumatra earthquake of March 2005, the M8.0 Pisco earthquake of August 2007, and the M7.9 Wenchuan Earthquake of 12 May 2008, are shown with space weather condition. Based on the case studies, statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions satellite (DEMETER) over a period of 2005-2010 was executed in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the EIA intensity indices were performed for each region with excluding the possible effects from the geomagnetic and solar activity. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 7.0 in the low latitude region can accompany observable seismo-ionospheric coupling phenomena in the form of EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling to explain the observation and the possibility of earthquake prediction using the EIA intensity variation are discussed.

A new electron density model of the plasmasphere for operational applications and services

NASA Astrophysics Data System (ADS)

Jakowski, Norbert; Hoque, Mohammed Mainul

2018-03-01

The Earth's plasmasphere contributes essentially to total electron content (TEC) measurements from ground or satellite platforms. Furthermore, as an integral part of space weather, associated plasmaspheric phenomena must be addressed in conjunction with ionosphere weather monitoring by operational space weather services. For supporting space weather services and mitigation of propagation errors in Global Navigation Satellite Systems (GNSS) applications we have developed the empirical Neustrelitz plasmasphere model (NPSM). The model consists of an upper L shell dependent part and a lower altitude dependent part, both described by specific exponential decays. Here the McIllwain parameter L defines the geomagnetic field lines in a centered dipole model for the geomagnetic field. The coefficients of the developed approaches are successfully fitted to numerous electron density data derived from dual frequency GPS measurements on-board the CHAMP satellite mission from 2000 to 2005. The data are utilized for fitting up to the L shell L = 3 because a previous validation has shown a good agreement with IMAGE/RPI measurements up to this value. Using the solar radio flux index F10.7 as the only external parameter, the operation of the model is robust, with 40 coefficients fast and sufficiently accurate to be used as a background model for estimating TEC or electron density profiles in near real time GNSS applications and services. In addition to this, the model approach is sensitive to ionospheric coupling resulting in anomalies such as the Nighttime Winter Anomaly and the related Mid-Summer Nighttime Anomaly and even shows a slight plasmasphere compression of the dayside plasmasphere due to solar wind pressure. Modelled electron density and TEC values agree with estimates reported in the literature in similar cases.

Using Global Total Electron Content to Understand Interminimum Changes in Solar EUV Irradiance and Thermospheric Composition

NASA Astrophysics Data System (ADS)

McDonald, S. E.; Emmert, J. T.; Krall, J.; Mannucci, A. J.; Vergados, P.

2017-12-01

To understand how and why the distribution of geospace plasma in the ionosphere/plasmasphere is evolving over multi-decadal time scales in response to solar, heliospheric and atmospheric forcing, it is critically important to have long-term, stable datasets. In this study, we use a newly constructed dataset of GPS-based total electron content (TEC) developed by JPL. The JPL Global Ionosphere Mapping (GIM) algorithm was used to generate a 35-station dataset spanning two solar minimum periods (1993-2014). We also use altimeter-derived TEC measurements from TOPEX-Poseidon and Jason-1 to construct a continuous dataset for the 1995-2014 time period. Both longterm datasets are compared to each other to study interminimum changes in the global TEC (during 1995-1995 and 2008-2009). We use the SAMI3 physics-based model of the ionosphere to compare the simulations of 1995-2014 with the JPL TEC and TOPEX/Jason-1 datasets. To drive SAMI3, we use the Naval Research Laboratory Solar Spectral Irradiance (NRLSSI) model to specify the EUV irradiances, and NRLMSIS to specify the thermosphere. We adjust the EUV irradiances and thermospheric constituents to match the TEC datasets and draw conclusions regarding sources of the differences between the two solar minimum periods.

Building resilience of the Global Positioning System to space weather

NASA Astrophysics Data System (ADS)

Fisher, Genene; Kunches, Joseph

2011-12-01

Almost every aspect of the global economy now depends on GPS. Worldwide, nations are working to create a robust Global Navigation Satellite System (GNSS), which will provide global positioning, navigation, and timing (PNT) services for applications such as aviation, electric power distribution, financial exchange, maritime navigation, and emergency management. The U.S. government is examining the vulnerabilities of GPS, and it is well known that space weather events, such as geomagnetic storms, contribute to errors in single-frequency GPS and are a significant factor for differential GPS. The GPS industry has lately begun to recognize that total electron content (TEC) signal delays, ionospheric scintillation, and solar radio bursts can also interfere with daily operations and that these threats grow with the approach of the next solar maximum, expected to occur in 2013. The key challenges raised by these circumstances are, first, to better understand the vulnerability of GPS technologies and services to space weather and, second, to develop policies that will build resilience and mitigate risk.

Unbiased total electron content (UTEC), their fluctuations, and correlation with seismic activity over Japan

NASA Astrophysics Data System (ADS)

Cornely, Pierre-Richard; Hughes, John

2018-02-01

Earthquakes are among the most dangerous events that occur on earth and many scientists have been investigating the underlying processes that take place before earthquakes occur. These investigations are fueling efforts towards developing both single and multiple parameter earthquake forecasting methods based on earthquake precursors. One potential earthquake precursor parameter that has received significant attention within the last few years is the ionospheric total electron content (TEC). Despite its growing popularity as an earthquake precursor, TEC has been under great scrutiny because of the underlying biases associated with the process of acquiring and processing TEC data. Future work in the field will need to demonstrate our ability to acquire TEC data with the least amount of biases possible thereby preserving the integrity of the data. This paper describes a process for removing biases using raw TEC data from the standard Rinex files obtained from any global positioning satellites system. The process is based on developing an unbiased TEC (UTEC) data and model that can be more adaptable to serving as a precursor signal for earthquake forecasting. The model was used during the days and hours leading to the earthquake off the coast of Tohoku, Japan on March 11, 2011 with interesting results. The model takes advantage of the large amount of data available from the GPS Earth Observation Network of Japan to display near real-time UTEC data as the earthquake approaches and for a period of time after the earthquake occurred.

Origin of the ahead of tsunami traveling ionospheric disturbances during Sumatra tsunami and offshore forecasting

NASA Astrophysics Data System (ADS)

Bagiya, Mala S.; Kherani, E. A.; Sunil, P. S.; Sunil, A. S.; Sunda, S.; Ramesh, D. S.

2017-07-01

The presence of ionospheric disturbances associated with Sumatra 2004 tsunami that propagated ahead of tsunami itself has previously been identified. However, their origin remains unresolved till date. Focusing on their origin mechanism, we document these ionospheric disturbances referred as Ahead of tsunami Traveling Ionospheric Disturbances (ATIDs). Using total electron content (TEC) data from GPS Aided GEO Augmented Navigation GPS receivers located near the Indian east coast, we first confirm the ATIDs presence in TEC that appear 90 min ahead of the arrival of tsunami at the Indian east coast. We propose here a simulation study based on tsunami-atmospheric-ionospheric coupling that considers tsunamigenic acoustic gravity waves (AGWs) to excite these disturbances. We explain the ATIDs generation based on the dissipation of transverse mode of the primary AGWs. The simulation corroborates the excitation of ATIDs with characteristics similar to the observations. Therefore, we offer an alternative theoretical tool to monitor the offshore ATIDs where observations are either rare or not available and could be potentially important for the tsunami early warning.

Ionospheric observations using GPS radio occultation from a nanosat platform

NASA Astrophysics Data System (ADS)

Bishop, R. L.; Redding, M.; Straus, P. R.

2012-12-01

The Compact Total Electron Content Sensor (CTECS) is a GPS radio occultation instrument designed for cubesat platforms that utilizes a COTS receiver, modified firmware, and a custom designed antenna. CTECS was placed on the Pico Satellite Solar Cell Testbed 2 (PSSC2) nanosat that was installed on the Space Shuttle Atlantis (STS-135). PSSC2 was successfully released from the shuttle on 20 July 2011 near 380 km altitude. Because of attitude control and power issues, only 13.5 hours of data was collected during its approximately 5-month mission life. Total Electron Content (TEC) observations were obtained and this presentation will present a summary of all TEC data analyzed from the mission. We will discuss the instrument challenges encountered, data issues, and future planned improvements to CTECS. Two CTECS flight units were delivered in the spring of 2012 for integration on the SMC/XR Space Environment NanoSatellite Experiment (SENSE) spacecrafts that are scheduled for launch in the second half of 2013. We will present a summary of the SENSE mission, performance of the improved CTECS sensors, and the results of ground and day-in-the-life testing.

Review of variations in Mw < 7 earthquake motions on position and tec (Mw = 6.5 aegean sea earthquake sample)

NASA Astrophysics Data System (ADS)

Yildirim, O.; Inyurt, S.; Mekik, C.

2015-10-01

Turkey is a country located in Middle Latitude zone and in which tectonic activity is intensive. Lastly, an earthquake of magnitude 6.5Mw occurred at Aegean Sea offshore on date 24 May 2014 at 12:25 UTC and it lasted approximately 40 s. The said earthquake was felt also in Greece, Romania and Bulgaria in addition to Turkey. In recent years seismic origin ionospheric anomaly detection studies have been done with TEC (Total Electron Contents) generated from GNSS (Global Navigation Satellite System) signals and the findings obtained have been revealed. In this study, TEC and positional variations have been examined seperately regarding the earthquake which occurred in the Aegean Sea. Then The correlation of the said ionospheric variation with the positional variation has been investigated. For this purpose, total fifteen stations have been used among which the data of four numbers of CORS-TR stations in the seismic zone (AYVL, CANA, IPSA, YENC) and IGS and EUREF stations are used. The ionospheric and positional variations of AYVL, CANA, IPSA and YENC stations have been examined by Bernese 5.0v software. When the (PPP-TEC) values produced as result of the analysis are examined, it has been understood that in the four stations located in Turkey, three days before the earthquake at 08:00 and 10:00 UTC, the TEC values were approximately 4 TECU above the upper limit TEC value. Still in the same stations, one day before the earthquake at 06:00, 08:00 and 10:00 UTC, it is being shown that the TEC values were approximately 5 TECU below the lower limit TEC value. On the other hand, the GIM-TEC values published by the CODE center have been examined. Still in all stations, it has been observed that three days before the earthquake the TEC values in the time portions of 08:00 and 10:00 UTC were approximately 2 TECU above, one day before the earthquake at 06:00, 08:00 and 10:00 UTC, the TEC values were approximately 4 TECU below the lower limit TEC value. Again, by using the same fifteen numbers of stations, positional variation investigation before and after the earthquake has been made for AYVL, CANA, IPSA and YENC stations. As result of the analysis made, positional displacements has been seen before and after earthquake at CANA station which is the nearest station to earthquake center. It is about 10 and 3 cm before three days and one day earthquake.

Atmospheric gravity wave detection following the 2011 Tohoku earthquakes combining COSMIC occultation and GPS observations

NASA Astrophysics Data System (ADS)

Yan, X.; Tao, Y.; Xia, C.; Qi, Y.; Zuo, X.

2017-12-01

Several studies have reported the earthquake-induced atmospheric gravity waves detected by some new technologies such as airglow (Makela et al., 2011), GOCE (Garcia et al., 2013), GRACE (Yang et al., 2014), F3/C radio occultation sounding (Coïsson et al., 2015). In this work, we collected all occultation events on 11 March, and selected four events to analyze at last. The original and filtered podTEC is represented as function of the altitude of the impact parameter and UT of the four events. Then, the travel time diagrams of filtered podTEC derived from the events were analyzed. The occultation signal from one event (marked as No.73) is consistent with the previous results reported by Coïsson. 2015, which is corresponds to the ionospheric signal induced from tsunami gravity wave. What is noticeable, in this work, is that three occultation events of No.403, 77 and 118 revealed a disturbance of atmospheric gravity wave with velocity 300m/s, preceding the tsunami. It would probably be correspond to the gravity waves caused by seismic rupture but not tsunami. In addition, it can be seen that the perturbation height of occultation observation TEC is concentrated at 200-400km, corresponding ionosphere F region. The signals detected above are compared with GPS measurements of TEC from GEONET and IGS. From GPS data, traveling ionospheric disturbances were observed spreading out from the epicenter as a quasi-circular propagation pattern with the time. Exactly, we observed an acoustic wave coupled with Rayleigh wave starting from the epicenter with a speed of 3.0km/s and a superimposed acoustic-gravity wave moving with a speed of 800m/s. The acoustic-gravity wave generated at the epicenter and gradually attenuated 800km away, then it is replaced by a gravity wave coupled with the tsunami that moves with a speed of between 100 and 300m/s. It is necessary to confirm the propagation process of the waves if we attempt to evaluate the use of ionospheric seismology as a potential support for future earthquake and tsunami warning systems. Acknowledgement: This work is supported by NSFC (41604135), China Postdoctoral Science Foundation funded project (1231703), State Key Laboratory of Earthquake Dynamics (LED2015B04), Key Laboratory of Earth and Planetary Physics, Hubei Subsurface Multi-scale Imaging Key Laboratory.

Earthquake- and tsunami-induced ionospheric disturbances detected by GPS total electron content observation

NASA Astrophysics Data System (ADS)

Tsugawa, T.; Nishioka, M.; Matsumura, M.; Shinagawa, H.; Maruyama, T.; Ogawa, T.; Saito, A.; Otsuka, Y.; Nagatsuma, T.; Murata, T.

2012-12-01

Ionospheric disturbances induced by the 2011 Tohoku earthquake and tsunami were studied by the high-resolution GPS total electron content (TEC) observation in Japan and in the world. The initial ionospheric disturbance appeared as sudden depletions by about 6 TEC unit (20%) about seven minutes after the earthquake onset, near the epicenter. From 06:00UT to 06:15UT, circular waves with short propagation distance propagated in the radial direction in the propagation velocity of 3,457, 783, 423 m/s for the first, second, third peak, respectively. Following these waves, concentric waves with long propagation distance appeared to propagate at the velocity of 138-288 m/s. In the vicinity of the epicenter, shortperiod oscillations with period of about 4 minutes were observed after 06:00 UT for 3 hours or more. We focus on the the circular and concentric waves in this paper. The circular or concentric structures indicate that these ionospheric disturbances had a point source. The center of these structures, termed as "ionospheric epicenter", was located around 37.5 deg N of latitude and 144.0 deg E of longitude, 170 km far from the epicenter to the southeast direction, and corresponded to the tsunami source. Comparing to the results of a numerical simulation using non-hydrostatic compressible atmosphere-ionosphere model, the first peak of circular wave would be caused by the acoustic waves generated from the propagating Rayleigh wave. The second and third waves would be caused by atmospheric gravity waves excited in the lower ionosphere due to the acoustic wave propagations from the tsunami source. The fourth and following waves are considered to be caused by the atmospheric gravity waves induced by the wavefronts of traveling tsunami. Long-propagation of these TEC disturbances were studied also using high-resolution GPS-TEC data in North America and Europe. Medium-scale wave structures with wavelengths of several 100 km appeared in the west part of North America at the almost same time as the tsunami arrival. On the other hand, no remarkable wave structure was observed in Europe. We will introduce these observational results and discuss about the generation and propagation mechanisms of the ionospheric disturbances induced by the earthquake and tsunami.

A comparison of TEC fluctuations and scintillations at Ascension Island

NASA Astrophysics Data System (ADS)

Basu, S.; Groves, K. M.; Quinn, J. M.; Doherty, P.

1999-11-01

With increasing reliance on space-based platforms for global navigation and communication, concerns about the impact of ionospheric scintillation on these systems have become a high priority. Recently, the Air Force Research Laboratory (AFRL) performed amplitude scintillation measurements of L1 (1.575 MHz) signals from GPS satellites at Ascension Island (14.45° W, 7.95° S; magnetic latitude 16° S) during February-April, 1998, to compare amplitude scintillations with fluctuations of the total electron content (TEC). Ascension Island is located in the South Atlantic under the southern crest of the equatorial anomaly of F2 ionization where scintillations will be much enhanced during the upcoming solar maximum period. Ascension Island is included in the global network of the International GPS Service (IGS) and the GPS receivers in this network report the carrier to noise (C/N) ratio, the dual frequency carrier phase and pseudorange data at 30-s intervals. Such data with a sampling interval of 30 s were analyzed to determine TEC, the rate of change of TEC (ROT) and also ROTI, defined as the standard deviation of ROT. The spatial scale of ROTI, sampled at 30 s interval, will correspond to 6 km when the vector sum of the ionospheric projection of the satellite velocity and the irregularity drift orthogonal to the propagation path is of the order of 100 m/s. On the other hand, the scale-length of the amplitude scintillation index corresponds to the Fresnel dimension which is about 400 m for the GPS L1 frequency and an ionospheric height of 400 km. It is shown that, in view of the co-existence of large and small scale irregularities in equatorial irregularity structures, during the early evening hours, and small magnitude of irregularity drifts, ROTI measurements can be used to predict the presence of scintillation causing irregularities. The quantitative relationship between ROTI and S4, however, varies considerably due to variations of the ionospheric projection of the satellite velocity and the ionospheric irregularity drift. During the post-midnight period, due to the decay of small scale irregularities leading to a steepening of irregularity power spectrum, ROTI, on occasions, may not be associated with detectable levels of scintillation. In view of the power law type of irregularity power spectrum, ROTI will, in general, be larger than S4 and the ratio, ROTI/S4, in the present dataset is found to vary between 2 and 10. At high latitudes, where the ionospheric motion, driven by large electric fields of magnetospheric origin, is much enhanced during magnetically active periods, ROTI/S4 may be considerably larger than that in the equatorial region.

Validation of a Global Ionospheric Data Assimilation Model

NASA Astrophysics Data System (ADS)

Wilson, B.; Hajj, G.; Wang, C.; Pi, X.; Rosen, I.

2003-04-01

As the number of ground and space-based receivers tracking the global positioning system (GPS) steadily increases, and the quantity of other ionospheric remote sensing data such as measurements of airglow also increases, it is becoming possible to monitor changes in the ionosphere continuously and on a global scale with unprecedented accuracy and reliability. However, in order to make effective use of such a large volume of data for both ionospheric specification and forecast, it is important to develop a data- driven ionospheric model that is consistent with the underlying physical principles governing ionosphere dynamics. A fully 3-dimensional Global Assimilative Ionosphere Model (GAIM) is currently being developed by a joint University of Southern California and Jet Propulsion Laboratory team. GAIM uses a first-principles ionospheric physics model (“forward” model) and Kalman filtering and 4DVAR techniques to not only solve for densities on a 3D grid but also estimate key driving forces which are inputs to the theoretical model, such as the ExB drift, neutral wind, and production terms. The driving forces are estimated using an “adjoint equation” to compute the required partial derivatives, thereby greatly reducing the computational demands compared to other techniques. For estimation of the grid densities, GAIM uses an approximate Kalman filter implementation in which the portions of the covariance matrix that are retained (the off-diagonal elements) are determined by assumed but physical correlation lengths in the ionosphere. By selecting how sparse or full the covariance matrix is over repeated Kalman filter runs, one can fully investigate the tradeoff between estimation accuracy and computational speed. Although GAIM will ultimately use multiple datatypes and many data sources, we have performed a first study of quantitative accuracy by ingesting GPS-derived TEC observations from ground and space-based receivers and nighttime UV radiance data from the LORAAS limb scanner on ARGOS, and then comparing the retrieved density field to independent ionospheric observations. A series of such GAIM retrievals will be presented and validated by comparisons to: vertical TEC data from the TOPEX altimeter, slant TEC data from ground GPS sites that were not included in the assimilation runs, and global ionosonde data (F0F2, HMF2, and bottom-side profiles where available). By presenting animated movies of the GAIM densities and vertical TEC maps, and their errors computed as differences from the independent observations, we will demonstrate the reasonableness and physicality of the climatology derived from the GAIM forward model, examine the consistency of the GPS and UV datatypes, and characterize the quantitative accuracy of the ionospheric “weather” specification provided by the assimilation retrievals.

Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

NASA Astrophysics Data System (ADS)

Dashora, N.; Sharma, S.; Dabas, R. S.; Alex, S.; Pandey, R.

2009-05-01

Results pertaining to the response of the equatorial and low latitude ionosphere to a major geomagnetic storm that occurred on 15 May 2005 are presented. These results are also the first from the Indian zone in terms of (i) GPS derived total electron content (TEC) variations following the storm (ii) Local low latitude electrodynamics response to penetration of high latitude convection electric field (iii) effect of storm induced traveling atmospheric disturbances (TAD's) on GPS-TEC in equatorial ionization anomaly (EIA) zone. Data set comprising of ionospheric TEC obtained from GPS measurements, ionograms from an EIA zone station, New Delhi (Geog. Lat. 28.42° N, Geog. Long. 77.21° E), ground based magnetometers in equatorial and low latitude stations and solar wind data obtained from Advanced Composition Explorer (ACE) has been used in the present study. GPS receivers located at Udaipur (Geog. Lat. 24.73° N, Geog. Long. 73.73° E) and Hyderabad (Geog. Lat. 17.33° N, Geog. Long. 78.47° E) have been used for wider spatial coverage in the Indian zone. Storm induced features in vertical TEC (VTEC) have been obtained comparing them with the mean VTEC of quiet days. Variations in solar wind parameters, as obtained from ACE and in the SYM-H index, indicate that the storm commenced on 15 May 2005 at 02:39 UT. The main phase of the storm commenced at 06:00 UT on 15 May with a sudden southward turning of the Z-component of interplanetary magnetic field (IMF-Bz) and subsequent decrease in SYM-H index. The dawn-to-dusk convection electric field of high latitude origin penetrated to low and equatorial latitudes simultaneously as corroborated by the magnetometer data from the Indian zone. Subsequent northward turning of the IMF-Bz, and the penetration of the dusk-to-dawn electric field over the dip equator is also discernible. Response of the low latitude ionosphere to this storm may be characterized in terms of (i) enhanced background level of VTEC as compared to the mean VTEC, (ii) peaks in VTEC and foF2 within two hours of prompt penetration of electric field and (iii) wave-like modulations in VTEC and sudden enhancement in hmF2 within 4-5 h in to the storm. These features have been explained in terms of the modified fountain effect, local low latitude electrodynamic response to penetration electric field and the TIDs, respectively. The study reveals a strong positive ionospheric storm in the Indian zone on 15 May 2005. Consequences of such major ionospheric storms on the systems that use satellite based navigation solutions in low latitude, are also discussed.

Equatorial Ionospheric Anomaly (EIA) and comparison with IRI model during descending phase of solar activity (2005-2009)

NASA Astrophysics Data System (ADS)

Kumar, Sanjay; Singh, A. K.; Lee, Jiyun

2014-03-01

The ionospheric variability at equatorial and low latitude region is known to be extreme as compared to mid latitude region. In this study the ionospheric total electron content (TEC), is derived by analyzing dual frequency Global Positioning System (GPS) data recorded at two stations separated by 325 km near the Indian equatorial anomaly region, Varanasi (Geog latitude 25°, 16/ N, longitude 82°, 59/ E, Geomagnetic latitude 16°, 08/ N) and Kanpur (Geog latitude 26°, 18/ N, longitude 80°, 12/ E, Geomagnetic latitude 17°, 18/ N). Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the descending phase of solar activity from 2005 to 2009. It is found that the maximum TEC (EIA) near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semi-annual variation is seen with two maxima occurring in both spring and autumn. Results also showed the presence of winter anomaly or seasonal anomaly in the EIA crest throughout the period 2005-2009 only except during the deep solar minimum year 2007-2008. The correlation analysis indicate that the variation of EIA crest is more affected by solar activity compared to geomagnetic activity with maximum dependence on the solar EUV flux, which is attributed to direct link of EUV flux on the formation of ionosphere and main agent of the ionization. The statistical mean occurrence of EIA crest in TEC during the year from 2005 to 2009 is found to around 12:54 LT hour and at 21.12° N geographic latitude. The crest of EIA shifts towards lower latitudes and the rate of shift of the crest latitude during this period is found to be 0.87° N/per year. The comparison between IRI models with observation during this period has been made and comparison is poor with increasing solar activity with maximum difference during the year 2005.

Ionospheric variation observed in Oregon Real-time GNSS network during the total eclipse of 21 August 2017

NASA Astrophysics Data System (ADS)

Shahbazi, A.; Park, J.; Kim, S.; Oberg, R.

2017-12-01

As the ionospheric behavior is highly related to the solar activity, the total eclipse passing across the North America on 21 August 2017 is expected to significantly affect the electron density in the ionosphere along the path. Taking advantage of GNSS capability for observing total electron content (TEC), this study demonstrates the impact of the total eclipse not only on the TEC variation during the period of the event but also on GNSS positioning. Oregon Department of Transportation (ODOT) runs a dense real time GNSS network, referred to as Oregon Real-time GNSS network (ORGN). From the dual frequency GPS and GLONASS observations in ORGN, the TEC over the network area can be extracted. We observe the vertical TEC (VTEC) from the ORGN for analyzing the ionospheric condition in the local area affected by the eclipse. To observe the temporal variation, we also observe the slant TEC (STEC) in each ray path and analyze the short term variation in different geometry of each ray path. Although the STEC is dependent quantity upon the changing geometry of a satellite, this approach provides insight to the ionospheric behavior of the total eclipse because the STEC does not involve the projection error, which is generated by VTEC computation. During the period of eclipse, the abnormal variations on VTEC and STEC are expected. The experimental results will be presented in time series plots for selected stations as well as the regional TEC map in Oregon. In addition to the TEC monitoring, we also test the positioning result of ORGN stations through Precise Point Positioning (PPP) and relative positioning. The expected result is that the both positioning results are degraded during the solar eclipse due to the instable ionospheric condition over short time.

Two-dimensional ionospheric tomography over the low-latitude Indian region: An intercomparison of ART and MART algorithms

NASA Astrophysics Data System (ADS)

Das, Sukanta Kumar; Shukla, Ashish Kumar

2011-04-01

Single-frequency users of a satellite-based augmentation system (SBAS) rely on ionospheric models to mitigate the delay due to the ionosphere. The ionosphere is the major source of range and range rate errors for users of the Global Positioning System (GPS) who require high-accuracy positioning. The purpose of the present study is to develop a tomography model to reconstruct the total electron content (TEC) over the low-latitude Indian region which lies in the equatorial ionospheric anomaly belt. In the present study, the TEC data collected from the six TEC collection stations along a longitudinal belt of around 77 degrees are used. The main objective of the study is to find out optimum pixel size which supports a better reconstruction of the electron density and hence the TEC over the low-latitude Indian region. Performance of two reconstruction algorithms Algebraic Reconstruction Technique (ART) and Multiplicative Algebraic Reconstruction Technique (MART) is analyzed for different pixel sizes varying from 1 to 6 degrees in latitude. It is found from the analysis that the optimum pixel size is 5° × 50 km over the Indian region using both ART and MART algorithms.

Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector

NASA Astrophysics Data System (ADS)

Sahai, Y.; Becker-Guedes, F.; Fagundes, P. R.; Lima, W. L. C.; Otsuka, Y.; Huang, C.-S.; Espinoza, E. S.; Pi, X.; de Abreu, A. J.; Bolzan, M. J. A.; Pillat, V. G.; Abalde, J. R.; Pimenta, A. A.; Bittencourt, J. A.

This paper presents an investigation of geomagnetic storm effects in the equatorial and low latitude F-region in the Brazilian sector during the intense geomagnetic storm on 18 August, 2003 (SSC 14:21 UT on 17/08; ΣKp = 52+; Ap = 108; ∣Dst∣ max = 168 at 1600 UT on 18/08). Simultaneous ionospheric sounding measurements from two stations, viz., Palmas (10.2°S, 48.2°W; dip latitude 5.7°S) and Sao Jose dos Campos (23.2°S, 45.9°W; dip latitude 17.6°S), Brazil, are presented for the nights of 16-17, 17-18 and 18-19 August, 2003 (quiet, disturbed and recovery phases). Both stations are equipped with the Canadian Advanced Digital Ionosonde (CADI). Quiet and disturbed conditions of the F-region ionosphere are compared using data collected from the two stations. The relationship between magnetospheric disturbance and low-latitude ionospheric dynamics, and generation of ionospheric irregularities are discussed. On the disturbed nights (17-18 and 18-19 August), the low latitude station S. J. Campos showed strong enhancements in the F-region critical frequency (foF2), whereas the near equatorial station Palmas showed strong uplifting of the F-layer about 1 h earlier. Normally during the June solstice months (May-August) in the Brazilian sector, large-scale ionospheric irregularities in form of plasma bubbles are rarely observed. On the night of 17-18 August, ionsospheric sounding observations at Palmas showed the presence of bottomside spread-F, whereas on the night of 18-19 August, the observations at Palmas and S. J. Campos showed the presence of plasma bubbles when the storm recovery phase had just started. The complementary GPS data available from several stations in the "Rede Brasileira de Monitoramento Continuo de GPS (Brazilian Network for Continuous GPS Monitoring)" are used to obtain the vertical total electron content (VTEC) and the rate of change of TEC per minute on UT days 18 and 19 August, 2003 and presented. Also, several global ionospheric TEC maps from the worldwide network of GPS receivers are presented, showing widespread latitudinal and longitudinal TEC changes during the different phases of the storm. All the observations (local ionospheric sounding and GPS network measurements, and global GPS measurements) presented in this investigation related to the geomagnetic storm on 18 August indicate that the equatorial and low latitude region in the Brazilian sector had much stronger effect during the recovery phase compared with the main phase. A comparison of the observed disturbance drifts with the Fejer-Scherliess storm-time model drifts indicate that the modeled drifts are not consistent with the present observations.

An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

NASA Astrophysics Data System (ADS)

Hajra, Rajkumar; Chakraborty, Shyamal Kumar; Tsurutani, Bruce T.; DasGupta, Ashish; Echer, Ezequiel; Brum, Christiano G. M.; Gonzalez, Walter D.; Sobral, José Humberto Andrade

2016-07-01

We present a geomagnetic quiet time (Dst > -50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980-1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58° N, 88.38° E geographic; 12.09° N, 160.46° E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89-0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of ~50-100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400-0500 LT) minimum and near-noon (1300-1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-σ range from the observed mean values.

Seasonal and solar cycle effects on TEC at 95°E in the ascending half (2009-2014) of the subdued solar cycle 24: Consistent underestimation by IRI 2012

NASA Astrophysics Data System (ADS)

Kakoti, Geetashree; Bhuyan, Pradip Kumar; Hazarika, Rumajyoti

2017-07-01

TEC measured at Dibrugarh (27.5°N, 94.9°E, 17.5°N Geomag.) from 2009 to 2014 is used to study its temporal characteristics during the ascending half of solar cycle 24. The measurements provide an opportunity to assess the diurnal, seasonal and longterm predictability of the IRI 2012 (with IRI Nequick, IRI01-corr, IRI 2001topside options) during this solar cycle which is distinctively low in magnitude compared to the previous cycles. The low latitude station Dibrugarh is normally located at the poleward edge of the northern EIA. A semi-annual variation in GPS TEC is observed with the peaks occurring in the equinoxes. The peak in spring (March, April) is higher than that in autumn (September, October) irrespective of the year of observation. The spring autumn asymmetry is also observed in IRI TEC. In contrast, the winter (November, December, January, February) anomaly is evident only in high activity years. TEC bears a distinct nonlinear relationship with 10.7 cm solar flux (F10.7). TEC increases linearly with F10.7 up to about 125 sfu beyond which it tends to saturate. The correlation between TEC and solar flux is found to be a function of local time and peaks at 10:00 LT. TEC varies nonlinearly with solar EUV flux similar to its variation with F10.7. The nonlinearity is well captured by the IRI. The saturation of TEC at high solar activity is attributed to the inability of the ionosphere to accommodate more ionization after it reaches the level of saturation ion pressure. Annual mean TEC increased from the minimum in 2009 almost linearly till 2012, remains at the same level in 2013 and then increased again in 2014. IRI TEC shows a linear increase from 2009 to 2014. IRI01-corr and IRI-NeQuick TEC are nearly equal at all local times, season and year of observation while IRI-2001 simulated TEC are always higher than that simulated by the other two versions. The IRI 2012 underestimates the TEC at about all local times except for a few hours in the midday in all season or year of observation. The discrepancy between model and measured TEC is high in spring and in the evening hours. The consistent underestimation of the TEC at this longitude by the IRI may be attributed to the inadequate ingestion of F region data from this longitude sector into the model and exclusion of the plasmaspheric content.

Ionospheric response to the total solar eclipse in India on 22 July, 2009

NASA Astrophysics Data System (ADS)

Chauhan, Vishal; Agrawal, Shikah; Singh, O. P.; Singh, Birbal

2010-05-01

The variations in total electron content (TEC) and amplitude of the fixed frequency VLF transmitter signals (f =19.8 kHz, NWC, Australia) are studied at Agra (Geographic lat. 27.20N, long. 780E), India during the total solar eclipse of 22 July, 2009 which was longest seen in India ever since 18 August, 1968. The equipments used for the study are a dual frequency GPS receiver (GSV 4004V). The data for a period of fifteen days (±7 days from the date of the event) are analysed and it is found that the TEC decreased by about 30% from normal days during the total solar eclipse. The period of the data analysis is characterised by a low level of geomagnetic activity, hence the decrease in TEC s is unlikely to be influenced by geomagnetic disturbances. The results are interpreted in terms of depression in electron densities at all ionospheric heights and are consistent with those obtained by earlier workers during similar eclipse events.

Statistical characteristics of locally generated ESF during equinoctial months over Sanya

NASA Astrophysics Data System (ADS)

Meng, Xing; Fang, Hanxian; Li, Guozhu; Weng, Libin

2018-05-01

Understanding the local generation rate of equatorial spread-F (ESF) is important for forecasting ionospheric scintillation. Using the GPS ionospheric scintillation/TEC and VHF radar data during March-April and September-October from 2010 to 2014, the occurrence of ionospheric scintillation, TEC fast fluctuation, and backscatter plume were studied. Through analyzing the simultaneous occurrence of ionospheric scintillation, TEC fast fluctuation and backscatter plume, the local generation rate of ESF over Sanya was investigated. The results show that the monthly generation rate varies between 0% and 68%. A significant equinoctial asymmetry of local generation rate of ESF can be found in 2010, 2013 and 2014. The local generation rate of ESF increases from 2010 to 2014 during March-April, while it does not have similar trend during September-October. The plasma vertical drift influenced by solar activity has a significant impact on the monthly generation rate. The equinoctial asymmetry of plasma vertical drift may contribute a lot to the equinoctial asymmetry of the generation rate of ESF.

SHPTS: towards a new method for generating precise global ionospheric TEC map based on spherical harmonic and generalized trigonometric series functions

NASA Astrophysics Data System (ADS)

Li, Zishen; Yuan, Yunbin; Wang, Ningbo; Hernandez-Pajares, Manuel; Huo, Xingliang

2015-04-01

To take maximum advantage of the increasing Global Navigation Satellite Systems (GNSS) data to improve the accuracy and resolution of global ionospheric TEC map (GIM), an approach, named Spherical Harmonic plus generalized Trigonometric Series functions (SHPTS), is proposed by integrating the spherical harmonic and the generalized trigonometric series functions on global and local scales, respectively. The SHPTS-based GIM from January 1st, 2001 to December 31st, 2011 (about one solar cycle) is validated by the ionospheric TEC from raw global GPS data, the GIM released by the current Ionospheric Associate Analysis Center (IAAC), the TOPEX/Poseidon satellite and the DORIS. The present results show that the SHPTS-based GIM over the area where no real data are available has the same accuracy level (approximately 2-6 TECu) to that released by the current IAAC. However, the ionospheric TEC in the SHPTS-based GIM over the area covered by real data is more accurate (approximately 1.5 TECu) than that of the GIM (approximately 3.0 TECu) released by the current IAAC. The external accuracy of the SHPTS-based GIM validated by the TOPEX/Poseidon and DORIS is approximately 2.5-5.5 and 1.5-4.5 TECu, respectively. In particular, the SHPTS-based GIM is the best or almost the best ranked, along with those of JPL and UPC, when they are compared with TOPEX/Poseidon measurements, and the best (in addition to UPC) when they are validated with DORIS data. With the increase in the number of GNSS satellites and contributing stations, the performance of the SHPTS-based GIM can be further improved. The SHPTS-based GIM routinely calculated using global GPS, GLONASS and BDS data will be found at the website http://www.gipp.org.cn.

Seismoionosphere Disturbances Above Mediterranean Region During 2000

NASA Astrophysics Data System (ADS)

Oraevsky, V. N.; Ruzhin, Yu. Ya.; Sinelnikov, V. M.; Shagimuratov, I. I.

The identical ionospheric anomalies or suspected seismoprecursors in TEC (total elec- tron content of ionosphere) were found (Oraevsky et.al., 2000) for two powerful (mag- nitude everyone was more than 7.5) earthquakes of 1999 which was having place in Turkey one after another during three months and apart less of 100 kilometers. For check and endorsements it, in the present work we spend the analysis of TEC behav- ior for the Mediterranean locale during long period (almost of year), to be exact: since February till December, 2000. For this time the total number in locale there were 87 earthquakes with magnitude M (on a Richter scale) more than 4 (M=4-4.5 is a thresh- old value for occurrence (or generation) noticeable seismogenic disturbances in an ionosphere). It has allowed, first of all, to investigate a background situation on season- diurnal TEC variations for detection seismogenic disturbances in an ionosphere. In process the data on TEC of all stations of a GPS network in locale are used, but we present outcomes of station Trabzon (40.0N/39.8E), as an example. Take in mind, that the TEC variations mirror a F2 layer state of an ionosphere, we have used, for compar- ison, the behavior of a critical frequency f0F2 (fundamental parameter of F2 plasma layer) for neighboring station of vertical ionosphere sounding (probing) in SOFIA. For different levels of geomagnetic activity is analysed in detail the spatialy-temporary pa- rameters of seismogenic ionosphere disturbances in dependence of mutual lay-out of earthquake epicenters and points of observation. Disturbances of an ionosphere, for which one can assign the properties of seismo- precursors, are found for the majority of the earthquakes which were having place in locale for indicated period. It is shown, that it is possible surely to select and distinguish them from background ionosphere variations which are generated by solar-earth couplings or gelio-geomagnetic activity. As a result, for range of magnitudes of M = 4.1-6.8 or for above-stated earthquakes, is found, that attitude, amplitude and size of seismogenic disturbance in an ionosphere are determined appreciably by energy and epicente position of the future earthquake.

Total electron content (TEC) variability at Los Alamos, New Mexico: A comparative study: FORTE-derived TEC analysis

NASA Astrophysics Data System (ADS)

Huang, Zhen; Roussel-Dupré, Robert

2005-12-01

Data collected from Fast On-Orbit Recording of Transient Events (FORTE) satellite-received Los Alamos Portable Pulser (LAPP) signals during 1997-2002 are used to derive the total electron content (TEC) at Los Alamos, New Mexico. The LAPP-derived TECs at Los Alamos are analyzed for diurnal, seasonal, interannual, and 27-day solar cycle variations. Several aspects in deriving TEC are analyzed, including slant to vertical TEC conversion, quartic effects on transionosperic signals, and geomagnetic storm effects on the TEC variance superimposed on the averaged TEC values.

Analysis of ionospheric TEC from GNSS observables over the Turkish region and predictability of IRI and SPIM models

NASA Astrophysics Data System (ADS)

Ansari, Kutubuddin; Corumluoglu, Ozsen; Panda, Sampad Kumar

2017-04-01

The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish Permanent GNSS Network (TPGN) and International GNSS Services (IGS) observations during the period from January 2015 to December 2015. The corresponding TEC predicted by the International Reference Ionosphere (IRI 2012) and Standard Plasmasphere-Ionosphere Model (SPIM), and interpolated from Global Ionosphere Maps (GIMs) are evaluated to realize their reliability over the region. We studied the diurnal and monthly behavior of TEC and the relative TEC deviations along with the upper and lower quartiles to represent its spatio-temporal variability. The diurnal variation of GNSS-derived TEC indicates its maximum peak value around 10.00 UT which decreases gradually to attain minimum value after midnight. The monthly maximum value of TEC is observed in March followed by May and August, and the lowest value is seen during September. Studies show that the monthly relative deviation of TEC variability lies in the range of -1 to 4 units for all stations with the maximum difference between positive and negative variability remaining around 5. The studies also cover seasonal variation, grand-mean of ionospheric TEC and TEC intensity from the TPGN. The seasonal ionospheric VTEC pattern over all stations depicts slight increment in VTEC distribution during March equinox compared to September equinox. The December solstice perceived relatively higher VTEC than June solstice. The overall of VTEC values enhanced at all stations towards end of the year 2015 compare to mid of year due the high solar activity. The maximum grand-mean of VTEC is registered in March equinox while the lowest value is seen in September irrespective of all stations. The measured grand-mean intensity variations of VTEC values are in ascending phase during March, May, August and November months, but in descending phase during February, April, June and September months. The latitudinal study shows daytime TEC slowly decreasing with latitudes with a latitudinal gradient range of 0.1-0.2 TECU/degree. Additionally, the TEC analysis during the strong geomagnetic storm period (07-11 September 2015; SYM-H -120 nT) infers relatively better predictability of the SPIM model compared to the IRI 2012 model. The outputs of this study would complement towards a complete understanding of the lower mid-latitude ionospheric dynamics and its effects on radio propagations, particularly over the Turkish region.

Local ionospheric electron density reconstruction from simultaneous ground-based GNSS and ionosonde measurements

NASA Astrophysics Data System (ADS)

Stankov, S. M.; Warnant, R.; Stegen, K.

2009-04-01

The purpose of the LIEDR (Local Ionospheric Electron Density Reconstruction) system is to acquire and process data from simultaneous ground-based GNSS TEC and digital ionosonde measurements, and subsequently to deduce the vertical electron density distribution in the local ionosphere. LIEDR is primarily designed to operate in real time for service applications, and, if sufficient data from solar and geomagnetic observations are available, to provide short-term forecast as well. For research applications and further development of the system, a post-processing mode of operation is also envisaged. In essence, the reconstruction procedure consists in the following. The high-precision ionosonde measurements are used for directly obtaining the bottom part of the electron density profile. The ionospheric profiler for the lower side (i.e. below the density peak height, hmF2) is based on the Epstein layer functions using the known values of the critical frequencies, foF2 and foE, and the propagation factor, M3000F2. The corresponding bottom-side part of the total electron content is calculated from this profile and is then subtracted from the GPS TEC value in order to obtain the unknown portion of the TEC in the upper side (i.e. above the hmF2). Ionosonde data, together with the simultaneously-measured TEC and empirically obtained O+/H+ ion transition level values, are all required for the determination of the topside electron density scale height. The topside electron density is considered as a sum of the constituent oxygen and hydrogen ion densities with unknown vertical scale heights. The latter are calculated by solving a system of transcendental equations that arise from the incorporation of a suitable ionospheric profiler (Chapman, Epstein, or Exponential) into formulae describing ionospheric conditions (plasma quasi-neutrality, ion transition level). Once the topside scale heights are determined, the construction of the vertical electron density distribution in the entire altitude range is a straightforward process. As a by-product of the described procedure, the value of the ionospheric slab thickness can be easily computed. To be able to provide forecast, additional information about the current solar and geomagnetic activity is needed. For the purpose, observations available in real time -- at the Royal Institute of Meteorology (RMI), the Royal Observatory of Belgium (ROB), and the US National Oceanic and Atmospheric Administration (NOAA) -- are used. Recently, a new hybrid model for estimating and predicting the local magnetic index K has been developed. This hybrid model has the advantage of using both, ground-based (geomagnetic field components) and space-based (solar wind parameters) measurements, which results in more reliable estimates of the level of geomagnetic activity - current and future. The described reconstruction procedure has been tested on actual measurements at the RMI Dourbes Geophysics Centre (coordinates: 50.1N, 4.6E) where a GPS receiver is collocated with a digital ionosonde (code: DB049, type: Lowell DGS 256). Currently, the nominal time resolution between two consecutive reconstructions is set to 15 minutes with a forecast horizon for each reconstruction of up to 60 minutes. Several applications are envisaged. For example, the ionospheric propagation delays can be estimated and corrected much easier if the electron density profile is available at a nearby location on a real-time basis. Also, both the input data and the reconstruction results can be used for validation purposes in ionospheric models, maps, and services. Recent studies suggest that such ionospheric monitoring systems can help research/services related to aircraft navigation, e.g. for development of the ‘ionospheric threat' methodology.

GPS Observations of Medium-Scale Traveling Ionospheric Disturbances over New Zealand

NASA Astrophysics Data System (ADS)

Otsuka, Y.; Lee, C.; Shiokawa, K.; Tsugawa, T.; Nishioka, M.

2014-12-01

Using the GPS data obtained from dual-frequency GPS receivers in New Zealand, we have made two-dimensional maps of total electron content (TEC) in 2012 in order to reveal statistical characteristics of MSTIDs at mid-latitudes in southern hemisphere. As of 2012, approximately 40 GPS receivers are in operation in New Zealand. We found that most of the MSITDs over New Zealand propagate northwestward during nighttime in summer and northeastward during daytime in winter. The propagation direction of the nighttime MSTIDs is consistent with the theory that polarization electric fields play an important role in the generating MSTIDs. Because the daytime MSTIDs propagate equatorward, we can speculate that they could be caused by atmospheric gravity waves in the thermosphere. The propagation direction of the daytime MSTIDs also has an eastward component in addition to the equatorward component. This feature is consistent with the daytime MSTIDs observed at mid-latitudes in both northern and southern hemispheres. By carrying out model calculations, we have shown that the eastward component of the MSTID propagation direction during daytime is attributed to an interaction of gravity waves to the background neutral winds. Because most of the daytime MSTIDs appear before 14 LT, the background neutral winds could blow westward. According to the dispersion relation for atmospheric gravity waves, vertical wavelength of the gravity waves becomes larger when the gravity wave propagates in the direction opposite to the background winds. Consequently, the gravity waves having an eastward component of the propagation direction could cause larger amplitude of TEC variations compared to the gravity waves propagating westward. This could be a reason why the propagation direction of the dime MSTIDs has an eastward component.

Imperfect coupling between northern and southern ionospheres: asymmetry in TEC anomalies before earthquakes

NASA Astrophysics Data System (ADS)

Jhuang, Hau-Kun; Ho, Yi-Ying; Lee, Lou-Chuang

2016-04-01

The northern ionosphere is coupled to the conjugate southern ionosphere through the highly conducting geomagenetic field lines. The coupling is very strong or "perfect" if the geomagnetic field lines are equipotential (the parallel electric field E||=0) and hence the perpendicular electric field (E⊥) at the conjugate sites of both ionospheres are equal. The coupling is "imperfect" if some of the geomagnetic field lines are non-equipotential (E||≠0). The field-aligned electric field E|| can be associated with electron inertia, pressure gradient and collisions appearing in the form of double layer, kinetic Alfvén waves and finite field-aligned conductivity σ||. We use the Global Ionospheric Maps (GIM) data to examine the conjugate effect of total electron content (TEC) for six significant earthquakes. The anomalous (ΔTEC)source in the source ionosphere and (ΔTEC)conjugate in the conjugate ionosphere are obtained for 85 events before the six earthquakes. The ΔTEC ratio β = (ΔTEC)conjugate / (ΔTEC)source is calculated for each anomaly. For a "perfect" coupling, β=1. There are 85 anomalous events before the six significant earthquakes, with 62 events occurring in the daytime (07-18 LT) and 23 events in the nighttime (19-06 LT). The average value of daytime (07-18 LT) TEC variations in the source ionosphere is |ΔTEC|source =20.13 TECu, while the average value in the nighttime (19-06 LT) ionosphere is |ΔTEC|source=14.43 TECu. The value of ΔTEC ratio β ranges from 0.05 (very weak coupling) to 0.98 (nearly perfect coupling) with an average of 0.52. There are 14 strong coupling cases with β ≥0.8, which take place from 11 LT to 19 LT. The daytime (07-18 LT) β average value is 0.57 and the nighttime (19-06 LT) β average is 0.37. The south-north ionosphere coupling is stronger (weaker) in the daytime (nighttime).

Temporal-Spatial Pattern of Pre-earthquake Signatures in Atmosphere and Ionosphere Associated with Major Earthquakes in Greece.

NASA Astrophysics Data System (ADS)

Calderon, I. S.; Ouzounov, D.; Anagnostopoulos, G. C.; Pulinets, S. A.; Davidenko, D.; Karastathis, V. K.; Kafatos, M.

2015-12-01

We are conducting validation studies on atmosphere/ionosphere phenomena preceding major earthquakes in Greece in the last decade and in particular the largest (M6.9) earthquakes that occurred on May 24, 2014 in the Aegean Sea and on February 14, 2008 in South West Peloponisos (Methoni). Our approach is based on monitoring simultaneously a series of different physical parameters from space: Outgoing long-wavelength radiation (OLR) on the top of the atmosphere, electron and electron density variations in the ionosphere via GPS Total Electron Content (GPS/TEC), and ULF radiation and radiation belt electron precipitation (RBEP) accompanied by VLF wave activity into the topside ionosphere. In particular, we analyzed prospectively and retrospectively the temporal and spatial variations of various parameters characterizing the state of the atmosphere and ionosphere several days before the two M6.9 earthquakes. Concerning the Methoni EQ, DEMETER data confirm an almost standard profile before large EQs, with TEC, ULF, VLF and RBEP activity preceding some (four) days the EQ occurrence and silence the day of EQ; furthermore, during the period before the EQ, a progressive concentration of ULF emission centers around the future epicenter was confirmed. Concerning the recent Greek EQ of May 24, 2014, thermal anomaly was discovered 30 days and TEC anomaly 38 hours in advance accordingly. The spatial characteristics of pre-earthquake anomalous behavior were associated with the epicentral region. Our analysis of simultaneous space measurements before the great EQs suggests that they follow a general temporal-spatial pattern, which has been seen in other large EQs worldwide.

Column-like EED extending from equatorial topside ionosphere toward plasmasphere retrieved from IGS and LEO/GPS observations with 3-D CT inversion

NASA Astrophysics Data System (ADS)

Xiao, R.; Ma, S. Y.; Xu, J. S.; Xiong, C.; Luehr, H.; Jakowski, N.

2010-05-01

The electron density distributions in the equatorial ionosphere are retrieved from GPS observations of joint ground-based IGS and onboard CHAMP/GRACE satellites during November 2004 super-storm by 3-D tomography technique. For LEO satellite-based GPS receiving, both the occultation TEC data and that along the radio propagation paths above the LEO are used and assimilated into the huge IGS TEC dataset. The electron density images are reconstructed for different sectors of America, Asia and Europe and produced for every hour. The retrieved electron densities are validated by satellite in situ measurements of CHAMP Langmuir probe and GRACE Ka-band SST (low-low satellite-to-satellite tracking) derived electron density averaged between the two satellites, as well as by numerical simulations. It reveals some very interesting storm-time structures of Ne distributions, such as top-hat-like F2-3 double layer and column-like enhanced electron densities (CEED). The CEED are found during the main phase of the storm near the minimum of Dst and in the longitudinal sector centered at 157E. They extend from the topside ionosphere toward to plasmasphere, reaching at least about 2000 km as high. The footprints of the CEED stand on the two peaks of the EIA. The forming mechanism of CEED and its relationship with SED and plasmaspheric plumes are worthy of further study. This work is supported by NSFC (No.40674078).

The origin of infrasonic ionosphere oscillations over tropospheric thunderstorms

NASA Astrophysics Data System (ADS)

Shao, Xuan-Min; Lay, Erin H.

2016-07-01

Thunderstorms have been observed to introduce infrasonic oscillations in the ionosphere, but it is not clear what processes or which parts of the thunderstorm generate the oscillations. In this paper, we present a new technique that uses an array of ground-based GPS total electron content (TEC) measurements to locate the source of the infrasonic oscillations and compare the source locations with thunderstorm features to understand the possible source mechanisms. The location technique utilizes instantaneous phase differences between pairs of GPS-TEC measurements and an algorithm to best fit the measured and the expected phase differences for assumed source positions and other related parameters. In this preliminary study, the infrasound waves are assumed to propagate along simple geometric raypaths from the source to the measurement locations to avoid extensive computations. The located sources are compared in time and space with thunderstorm development and lightning activity. Sources are often found near the main storm cells, but they are more likely related to the downdraft process than to the updraft process. The sources are also commonly found in the convectively quiet stratiform regions behind active cells and are in good coincidence with extensive lightning discharges and inferred high-altitude sprites discharges.

Measurements of the ionospheric reaction to exhaust from dedicated burns of the space shuttle’s orbital maneuvering system engines over Kwajalein

NASA Astrophysics Data System (ADS)

Caton, R. G.; Groves, K. M.; Pedersen, T. R.; Hysell, D. L.; Carrano, C. S.; Bernhardt, P. A.; Tsunoda, R. T.; Coster, A. J.

2009-12-01

In a continuation of the Shuttle Ionospheric Modification with Pulsed Localized Exhaust (SIMPLEX) experiment, a series of Orbiting Maneuver Subsystem (OMS) engine burns from the space shuttle have been carried out over Kwajalein Atoll in the Republic of the Marshall Islands. Exhaust from the shuttle’s two OMS engines consists of CO, CO2, H2, H20, and N2, each of which interact with the background ionosphere (predominately O+) through charge exchange resulting in electron “holes.” Such interactions have been detected from the ground with radars, optical imagers, and GPS TEC measurements and from space with satellites such as the Communication/Navigation Outage Forecasting System (C/NOFS) in the Shuttle Exhaust Ion Turbulence Experiment (SEITE). In this talk, we present signatures of ionospheric modification resulting from OMS burns during recent shuttle missions observed in incoherent scatter returns on the ARPA Long-range Tracking And Instrumentation Radar (ALTAIR) and in optical data from an All-Sky Imager. GPS TEC measurements are investigated for evidence of depletions resulting from post-burn molecular recombination. Space Shuttle OMS Engine Burn

GPS detection of ionospheric perturbation before the 13 February 2001, El Salvador earthquake

NASA Astrophysics Data System (ADS)

Plotkin, V. V.

A large earthquake of M6.6 occurred on 13 February 2001 at 14:22:05 UT in El Salvador. We detected ionospheric perturbation before this earthquake using GPS data received from CORS network. Systematic decreases of ionospheric total electron content during two days before the earthquake onset were observed at set of stations near the earthquake location and probably in region of about 1000 km from epicenter. This result is consistent with that of investigators, which studied these phenomena with several observational techniques. However it is possible, that such TEC changes are simultaneously accompanied by changes due to solar wind parameters and Kp -index.

Regional ionospheric TEC data assimilation and now-casting service

NASA Astrophysics Data System (ADS)

Aa, E.; Liu, S.; Wengeng, H.

2017-12-01

Ionospheric data assimilation is a now-casting technique to incorporate irregular ionospheric measurements into certain background model, which is an effective and efficient way to overcome the limitation of the unbalanced data distribution and to improve the accuracy of the model, so that the model and the data can be optimally combined with each other to produce a more reliable and reasonable system specification. In this study, a regional total electron content (TEC) now-casting system over China and adjacent areas (70E-140E and 15N-55N) is developed on the basis of data assimilation technique. The International Reference Ionosphere (IRI) is used here as background model, and the GNSS data are derived from both the Space Environment Monitoring Network of Chinese Academy of Sciences (SEMnet) and International GNSS Service (IGS) data. A Three-dimensional variation algorithm (3DVAR) combined with Gauss-Markov Kalman filter technique is used to implement the data assimilation. The regional gridded TEC maps and the position errors of single-frequency GPS receivers can be generated and publicized online (http://sepc.ac.cn/TEC_chn.php) in quasi-real time, which is updated for every 15 min. It is one of the ionospheric now-casting systems in China based on data assimilation algorithm, which can be used not only for real-time monitoring of ionosphere environment over China and adjacent areas, but also in providing accurate and effective specification of regional ionospheric TEC and error correction for satellite navigation, radar imaging, shortwave communication, and other relevant applications.

Observed TEC Anomalies by GNSS Sites Preceding the Aegean Sea Earthquake of 2014

NASA Astrophysics Data System (ADS)

Ulukavak, Mustafa; Yal&ccedul; ınkaya, Mualla

2016-11-01

In recent years, Total Electron Content (TEC) data, obtained from Global Navigation Satellites Systems (GNSS) receivers, has been widely used to detect seismo-ionospheric anomalies. In this study, Global Positioning System - Total Electron Content (GPS-TEC) data were used to investigate ionospheric abnormal behaviors prior to the 2014 Aegean Sea earthquake (40.305°N 25.453°E, 24 May 2014, 09:25:03 UT, Mw:6.9). The data obtained from three Continuously Operating Reference Stations in Turkey (CORS-TR) and two International GNSS Service (IGS) sites near the epicenter of the earthquake is used to detect ionospheric anomalies before the earthquake. Solar activity index (F10.7) and geomagnetic activity index (Dst), which are both related to space weather conditions, were used to analyze these pre-earthquake ionospheric anomalies. An examination of these indices indicated high solar activity between May 8 and 15, 2014. The first significant increase (positive anomalies) in Vertical Total Electron Content (VTEC) was detected on May 14, 2014 or 10 days before the earthquake. This positive anomaly can be attributed to the high solar activity. The indices do not imply high solar or geomagnetic activity after May 15, 2014. Abnormal ionospheric TEC changes (negative anomaly) were observed at all stations one day before the earthquake. These changes were lower than the lower bound by approximately 10-20 TEC unit (TECU), and may be considered as the ionospheric precursor of the 2014 Aegean Sea earthquake

Importance of Ionospheric Gradients for error Correction

NASA Astrophysics Data System (ADS)

Ravula, Ramprasad

Importance of Ionospheric Gradients for error Correction R. Ram Prasad1, P.Nagasekhar2 1Sai Spurthi Institute of Technology-JNTU Hyderabad,2Sai Spurthi Institute of Technology-JNTU Hyderabad Email ID:rams.ravula@gmail.com In India, Indian Space Research Organization (ISRO) has established with an objective to develop space technology and its application to various national tasks. To cater to the needs of civil aviation applications, GPS Aided Geo Augmented Navigation (GAGAN) system is being jointly implemented along with Airports Authority of India (AAI) over the Indian region. The most predominant parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of total number of electrons present in one square meter cylindrical cross sectional area in the line of site direction between the satellite and the user on the earth i.e. Total Electron Content (TEC).The irregular distribution of electron densities i.e. rate of TEC variation, causes Ionospheric gradients such as spatial gradients (Expressed in TECu/km) and temporal gradients (Expressed in TECu /minute). Among the satellite signals arriving to the earth in multiple directions, the signals which suffer from severe ionospheric gradients can be estimated i.e. Rate of TEC Index (ROTI) and Rate of TEC (ROT). These aspects which contribute to errors can be treated for improving GAGAN positional accuracy.

Unusual ionospheric variations before the strong Auckland Islands, New Zealand earthquake of 30th September, 2007

NASA Astrophysics Data System (ADS)

Ibanga, J. I.; Akpan, A. E.; George, N. J.; Ekanem, A. M.; George, A. M.

2018-06-01

Using the IAP experiment on board, the DEMETER and TEC from GPS data, unusual ionospheric variations have been observed some days before the 7.4 magnitude New Zealand earthquake. Both sets of data recorded perturbations 10 days before the earthquake at about the same time. The total ion density per centimeter cube (cm-3), recorded a variation of 6.94 while the differential total electron content (DTEC) in total electron content unit 1016 electron per metre square gave a value of 2.93TECU. The observed anomalies were screened for false alarm using the geomagnetic indices of Kernnifzer digit (Kp) and disturbance storm time (Dst.) It was however seen that the state of the ionosphere was geomagnetically quiet during this period; hence the observed variations were seismogenic.

Near Real-time GNSS-based Ionospheric Model using Expanded Kriging in the East Asia Region

NASA Astrophysics Data System (ADS)

Choi, P. H.; Bang, E.; Lee, J.

2016-12-01

Many applications which utilize radio waves (e.g. navigation, communications, and radio sciences) are influenced by the ionosphere. The technology to provide global ionospheric maps (GIM) which show ionospheric Total Electron Content (TEC) has been progressed by processing GNSS data. However, the GIMs have limited spatial resolution (e.g. 2.5° in latitude and 5° in longitude), because they are generated using globally-distributed and thus relatively sparse GNSS reference station networks. This study presents a near real-time and high spatial resolution TEC model over East Asia by using ionospheric observables from both International GNSS Service (IGS) and local GNSS networks and the expanded kriging method. New signals from multi-constellation (e.g,, GPS L5, Galileo E5) were also used to generate high-precision TEC estimates. The newly proposed estimation method is based on the universal kriging interpolation technique, but integrates TEC data from previous epochs to those from the current epoch to improve the TEC estimation performance by increasing ionospheric observability. To propagate previous measurements to the current epoch, we implemented a Kalman filter whose dynamic model was derived by using the first-order Gauss-Markov process which characterizes temporal ionospheric changes under the nominal ionospheric conditions. Along with the TEC estimates at grids, the method generates the confidence bounds on the estimates using resulting estimation covariance. We also suggest to classify the confidence bounds into several categories to allow users to recognize the quality levels of TEC estimates according to the requirements for user's applications. This paper examines the performance of the proposed method by obtaining estimation results for both nominal and disturbed ionospheric conditions, and compares these results to those provided by GIM of the NASA Jet propulsion Laboratory. In addition, the estimation results based on the expanded kriging method are compared to the results from the universal kriging method for both nominal and disturbed ionospheric conditions.

Effect of the X5.4 Class Solar Flare Event of Solar Cycle 24 ON the GPS Signal Reception in Peninsular Malaysia

NASA Astrophysics Data System (ADS)

Ismail, S.; Musa, T. A.; Aris, W. A. W.; Gopir, G.

2016-09-01

In this paper, we examine the effect of solar flare event on the Global Positioning System (GPS) signal reception in Peninsular Malaysia during the X5.4 class solar flare on 7th March 2012, 00:24 UT at active region AR1429. GPS data from six MyRTKnet stations that cover the northern, southern, western and eastern regions of Peninsular Malaysia were used, namely Langkawi (Kedah), Bandar Baharu (Pulau Pinang), Pekan (Pahang), Mersing (Johor), Tanjung Pengelih (Johor) and Malacca (Malacca). The total electron content (TEC) was estimated based on the single layer ionospheric model. Next, the ionospheric delay for each GPS frequency of L1 (1575.42 MHz), L2 (1227.60 MHz) and L5 (1176.45 MHz) was then calculated. The results show that solar flare event can influence the GPS signal reception in Peninsular Malaysia where the X5.4 class solar flare shows significant effect of the ionospheric delay within the range of 9 m - 20 m. These research findings will significantly contribute to space weather study and its effects on space-based positioning system such as the GPS.

Ionospheric Sensor Developments for the Year-2000 Solar Maximum

DTIC Science & Technology

2000-10-23

locations, work during the year enhanced and exploited several diagnostic instruments deployed for the High frequency Active Aurora Research Program ( HAARP ...Under HAARP , measurements employing both GPS and coherent VHF-UHF signals transmitted from satellites in low-earth polar orbit resulted in time...histories and latitudinal scans of absolute TEC over Maska, and enhanced operation of the HAARP classic riometer resulted in essentially continuous

Evaluation of the Klobuchar model in TaiWan

NASA Astrophysics Data System (ADS)

Li, Jinghua; Wan, Qingtao; Ma, Guanyi; Zhang, Jie; Wang, Xiaolan; Fan, Jiangtao

2017-09-01

Ionospheric delay is the mainly error source in Global Navigation Satellite System (GNSS). Ionospheric model is one of the ways to correct the ionospheric delay. The single-frequency GNSS users modify the ionospheric delay by receiving the correction parameters broadcasted by satellites. Klobuchar model is widely used in Global Positioning System (GPS) and COMPASS because it is simple and convenient for real-time calculation. This model is established on the observations mainly from Europe and USA. It does not describe the equatorial anomaly region. South of China is located near the north crest of the equatorial anomaly, where the ionosphere has complex spatial and temporal variation. The assessment on the validation of Klobuchar model in this area is important to improve this model. Eleven years (2003-2014) data from one GPS receiver located at Taoyuan Taiwan (121°E, 25°N) are used to assess the validation of Klobuchar model in Taiwan. Total electron content (TEC) from the dual-frequency GPS observations is calculated and used as the reference, and TEC based on the Klobuchar model is compared with the reference. The residual is defined as the difference between the TEC from Klobuchar model and the reference. It is a parameter to reflect the absolute correction of the model. RMS correction percentage presents the validation of the model relative to the observations. The residuals' long-term variation, the RMS correction percentage, and their changes with the latitudes are analyzed respectively to access the model. In some months the RMS correction did not reach the goal of 50% purposed by Klobuchar, especially in the winter of the low solar activity years and at nighttime. RMS correction did not depend on the 11-years solar activity, neither the latitudes. Different from RMS correction, the residuals changed with the solar activity, similar to the variation of TEC. The residuals were large in the daytime, during the equinox seasons and in the high solar activity years; they are small at night, during the solstice seasons, and in the low activity years. During 1300-1500 BJT in the high solar activity years, the mean bias was negative, implying the model underestimated TEC on average. The maximum mean bias was 33TECU in April 2014, and the maximum underestimation reached 97TECU in October 2011. During 0000-0200 BJT, the residuals had small mean bias, small variation range and small standard deviation. It suggested that the model could describe the TEC of the ionosphere better than that in the daytime. Besides the variation with the solar activity, the residuals also vary with the latitudes. The means bias reached the maximum at 20-22°N, corresponding to the north crest of the equatorial anomaly. At this latitude, the maximum mean bias was 47TECU lower than the observation in the high activity years, and 12TECU lower in the low activity years. The minimum variation range appeared at 30-32°N in high and low activity years. But the minimum mean bias was at different latitudes in the high and low activity years. In the high activity years, it appeared at 30-32°N, and in the low years it was at 24-26°N. For an ideal model, the residuals should have small mean bias and small variation range. Further study is needed to learn the distribution of the residuals and to improve the model.

Total Electron Content Retrieved From L-Band Radiometers and Potential Improvements to the IGS Model

NASA Astrophysics Data System (ADS)

Soldo, Yan; Hong, Liang; El-Nimri, Salem; Le Vine, David M.

2018-04-01

In recent years, several L-band microwave instruments have been launched into Earth's orbit to measure soil moisture and ocean salinity (e.g., Soil Moisture and Ocean Salinity [SMOS], Aquarius, and Soil Moisture Active/Passive [SMAP]). As the microwave signal travels through the ionosphere, the polarization vector rotates (Faraday rotation) and it is possible to estimate the total electron content (TEC) along the path by measuring this change. A comparison is presented of the TEC retrieved from Aquarius and SMAP over the ocean with the values provided by the IGS (International Global Navigation Satellite System Service (GNSS)). The TEC retrieved from Aquarius and SMAP measurements show good agreement with each other and, on a global scale, are in agreement with the TEC provided by the IGS. However, there are cases in which the TEC from the two satellite sensors are in good agreement with each other but differ significantly from the IGS TEC. The comparison suggests that the L-band instruments are a reliable source of TEC over the ocean and could be a valuable supplementary source of TEC values that could be assimilated in the IGS models, especially over the ocean, where GNSS ground stations are sparse.

The ionospheric disturbances caused by the explosion of the Mount Tongariro volcano in 2012

NASA Astrophysics Data System (ADS)

Po Cheng, C.; Lin, C.; Chang, L. C.; Chen, C.

2013-12-01

Volcanic explosions are known to trigger acoustic waves that propagate in the atmosphere at infrasonic speeds. At ionospheric heights, coupling between neutral particles and free electrons induces variations of electron density detectable by dual-frequency Global Positioning System (GPS) measurements. In November 21 2012, the explosion of the Mount Tongariro volcano in New Zealand occurred at UT 0:20, when there were active synoptic waves passing over north New Zealand. The New Zealand dense array of Global Positioning System recorded ionospheric disturbances reflected in total electron content (TEC) ~10 minutes after the eruption, and the concentric spread of disturbances also can be observed this day. The velocity of disturbances varies from 130m/s to 700m/s. A spectral analysis of the rTEC time series shows two peaks. The larger amplitudes are centered at 800 and 1500 seconds, in the frequency range of acoustic waves and gravity waves. On the other hand, to model the rTEC perturbation created by the acoustic wave caused by the explosive eruption of the Mount Tongariro, we perform acoustic ray tracing and obtain sound speed at subionospheric height in a horizontally stratified atmosphere model (MSIS-E-90). The result show that the velocity of the disturbances is slower than sound speed range. Through using the MSIS-E-90 Atmosphere Model and Horizontal Wind Model(HWM), we obtain the vertical wave number and indicate that the gravity waves could propagate at subionospheric height for this event, suggesting that the ionospheric disturbances caused by the explosive eruption is gravity-wave type. This work demonstrates that GPS are useful for near real-time ionospheric disturbances monitoring, and help to understand the mechanism of the gravity wave caused by volcano eruption in the future.

Anamolous ionospheric TEC variations prior to the Indonesian earthquake (M 7.1) of November 15, 2014

NASA Astrophysics Data System (ADS)

Alcay, Salih

2017-05-01

This paper investigates preearthquake ionospheric variations with the use of TEC of Global Ionospheric Maps (GIMs) and regional maps based on Precise Point Positioning (PPP) during the 7.1-M Indonesian earthquake that occurred on November 15, 2014. TEC maps corresponding to 10 days before to 4 days after the event were examined. In addition, a time series of TEC values according to the PPP maps were also evaluated. In addition to GIMs, it was possible to detect TEC variations with PPP maps. The results showed that ionospheric TEC decreased strikingly 4 days prior to the earthquake. This TEC variation was highly likely related to seismic activity.

Effects of ionizing energetic electrons and plasma transport in the ionosphere during the initial phase of the December 2006 magnetic storm

NASA Astrophysics Data System (ADS)

Suvorova, A. V.; Huang, C.-M.; Dmitriev, A. V.; Kunitsyn, V. E.; Andreeva, E. S.; Nesterov, I. A.; Klimenko, M. V.; Klimenko, V. V.; Tumanova, Yu. S.

2016-06-01

The initial phase of a major geomagnetic storm on 14 December 2006 was selected in order to investigate the ionizing effect of energetic electrons in the ionosphere. The global network of GPS receivers was used to analyze the total electron content (TEC). A strong positive ionospheric storm of ~20 TEC units (TECU) with ~6 h duration was observed on the dayside during the interval of northward interplanetary magnetic field. At the same time, the NOAA/POES satellites observed long-lasting intense fluxes of >30 keV electrons in the topside ionosphere at middle and low latitudes, including a near-equatorial forbidden zone outside of the South Atlantic Anomaly (SAA). We found that the TEC increases overlapped well with the enhancements of energetic electrons. Modeling of the ionospheric response by using a Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere, based on the standard mechanisms of plasma transport, could only partially explain the ionospheric response and was unable to predict the long-duration increase of TEC. For the energetic electrons, we estimated the ionizing effect of ~45 TECU and ~23 TECU in the topside ionosphere, respectively, inside and outside of SAA. The ionizing effect contributed from 50% to 100% of TEC increases and provided the long duration and wide latitudinal extension of the positive ionospheric storm. This finding is a very important argument in supporting significant ionizing effect of energetic electrons in the storm time ionosphere both at middle and low latitudes.

Ionospheric detection of tsunami earthquakes: observation, modeling and ideas for future early warning

NASA Astrophysics Data System (ADS)

Occhipinti, G.; Manta, F.; Rolland, L.; Watada, S.; Makela, J. J.; Hill, E.; Astafieva, E.; Lognonne, P. H.

2017-12-01

Detection of ionospheric anomalies following the Sumatra and Tohoku earthquakes (e.g., Occhipinti 2015) demonstrated that ionosphere is sensitive to earthquake and tsunami propagation: ground and oceanic vertical displacement induces acoustic-gravity waves propagating within the neutral atmosphere and detectable in the ionosphere. Observations supported by modelling proved that ionospheric anomalies related to tsunamis are deterministic and reproducible by numerical modeling via the ocean/neutral-atmosphere/ionosphere coupling mechanism (Occhipinti et al., 2008). To prove that the tsunami signature in the ionosphere is routinely detected we show here perturbations of total electron content (TEC) measured by GPS and following tsunamigenic earthquakes from 2004 to 2011 (Rolland et al. 2010, Occhipinti et al., 2013), nominally, Sumatra (26 December, 2004 and 12 September, 2007), Chile (14 November, 2007), Samoa (29 September, 2009) and the recent Tohoku-Oki (11 Mars, 2011). Based on the observations close to the epicenter, mainly performed by GPS networks located in Sumatra, Chile and Japan, we highlight the TEC perturbation observed within the first 8 min after the seismic rupture. This perturbation contains information about the ground displacement, as well as the consequent sea surface displacement resulting in the tsunami. In addition to GNSS-TEC observations close to the epicenter, new exciting measurements in the far-field were performed by airglow measurement in Hawaii show the propagation of the internal gravity waves induced by the Tohoku tsunami (Occhipinti et al., 2011). This revolutionary imaging technique is today supported by two new observations of moderate tsunamis: Queen Charlotte (M: 7.7, 27 October, 2013) and Chile (M: 8.2, 16 September 2015). We finally detail here our recent work (Manta et al., 2017) on the case of tsunami alert failure following the Mw7.8 Mentawai event (25 October, 2010), and its twin tsunami alert response following the Mw7.8 Benyak event (2010). In this talk we present all this new tsunami observations in the ionosphere and we discuss, under the light of modelling, the potential role of ionospheric sounding by GNSS-TEC and airglow cameras in oceanic monitoring and future tsunami warning system. All ref. here @ www.ipgp.fr/ ninto

Mahali: Space Weather Monitoring Using Multicore Mobile Devices

NASA Astrophysics Data System (ADS)

Pankratius, V.; Lind, F. D.; Coster, A. J.; Erickson, P. J.; Semeter, J. L.

2013-12-01

Analysis of Total Electron Content (TEC) measurements derived from Global Positioning System (GPS) signals has led to revolutionary new data products for space weather monitoring and ionospheric research. However, the current sensor network is sparse, especially over the oceans and in regions like Africa and Siberia, and the full potential of dense, global, real-time TEC monitoring remains to be realized. The Mahali project will prototype a revolutionary architecture that uses mobile devices, such as phones and tablets, to form a global space weather monitoring network. Mahali exploits the existing GPS infrastructure - more specifically, delays in multi-frequency GPS signals observed at the ground - to acquire a vast set of global TEC projections, with the goal of imaging multi-scale variability in the global ionosphere at unprecedented spatial and temporal resolution. With connectivity available worldwide, mobile devices are excellent candidates to establish crowd sourced global relays that feed multi-frequency GPS sensor data into a cloud processing environment. Once the data is within the cloud, it is relatively straightforward to reconstruct the structure of the space environment, and its dynamic changes. This vision is made possible owing to advances in multicore technology that have transformed mobile devices into parallel computers with several processors on a chip. For example, local data can be pre-processed, validated with other sensors nearby, and aggregated when transmission is temporarily unavailable. Intelligent devices can also autonomously decide the most practical way of transmitting data with in any given context, e.g., over cell networks or Wifi, depending on availability, bandwidth, cost, energy usage, and other constraints. In the long run, Mahali facilitates data collection from remote locations such as deserts or on oceans. For example, mobile devices on ships could collect time-tagged measurements that are transmitted at a later point in time when some connectivity is available. Our concept of the overall Mahali system will employ both auto-tuning and machine learning techniques to cope with the opportunistic nature of data collection, computational load distribution on mobile devices and in the cloud, and fault-tolerance in a dynamically changing network. "Kila Mahali" means "everywhere" in the Swahili language. This project will follow that spirit by enabling space weather data collection even in the most remote places, resulting in dramatic improvements in observational gaps that exist in space weather research today. The dense network may enable the use of the entire ionosphere as a sensor to monitor geophysical events from earthquakes to tsunamis, and other natural disasters.

JPL/USC GAIM: Validating COSMIC and Ground-Based GPS Assimilation Results to Estimate Ionospheric Electron Densities

NASA Astrophysics Data System (ADS)

Komjathy, A.; Wilson, B.; Akopian, V.; Pi, X.; Mannucci, A.; Wang, C.

2008-12-01

We seem to be in the midst of a revolution in ionospheric remote sensing driven by the abundance of ground and space-based GPS receivers, new UV remote sensing satellites, and the advent of data assimilation techniques for space weather. In particular, the COSMIC 6-satellite constellation was launched in April 2006. COSMIC now provides unprecedented global coverage of GPS occultations measurements, each of which yields electron density information with unprecedented ~1 km vertical resolution. Calibrated measurements of ionospheric delay (total electron content or TEC) suitable for input into assimilation models is currently made available in near real-time (NRT) from the COSMIC with a latency of 30 to 120 minutes. The University of Southern California (USC) and the Jet Propulsion Laboratory (JPL) have jointly developed a real-time Global Assimilative Ionospheric Model (GAIM) to monitor space weather, study storm effects, and provide ionospheric calibration for DoD customers and NASA flight projects. JPL/USC GAIM is a physics- based 3D data assimilation model that uses both 4DVAR and Kalman filter techniques to solve for the ion and electron density state and key drivers such as equatorial electrodynamics, neutral winds, and production terms. Daily (delayed) GAIM runs can accept as input ground GPS TEC data from 1200+ sites, occultation links from CHAMP, SAC-C, and the COSMIC constellation, UV limb and nadir scans from the TIMED and DMSP satellites, and in situ data from a variety of satellites (DMSP and C/NOFS). Real-Time GAIM (RTGAIM) ingests multiple data sources in real time, updates the 3D electron density grid every 5 minutes, and solves for improved drivers every 1-2 hours. Since our forward physics model and the adjoint model were expressly designed for data assimilation and computational efficiency, all of this can be accomplished on a single dual- processor Unix workstation. Customers are currently evaluating the accuracy of JPL/USC GAIM 'nowcasts' for ray tracing applications and trans-ionospheric path delay calibration. In the presentation, we will discuss the expected impact of NRT COSMIC occultation and NRT ground-based measurements and present validation results for ingest of COSMIC data into GAIM using measurements from World Days. We will quality check our COSMIC-derived products by comparing Abel profiles and JPL- processed results. Furthermore, we will validate GAIM assimilation results using Incoherent Scatter Radar measurements from Arecibo, Jicamarca and Millstone Hill datasets. We will conclude by characterizing the improved electron density states using dual-frequency altimeter-derived Jason vertical TEC measurements.

GNSS-Based Space Weather Systems Including COSMIC Ionospheric Measurements

NASA Technical Reports Server (NTRS)

Komjathy, Attila; Mandrake, Lukas; Wilson, Brian; Iijima, Byron; Pi, Xiaoqing; Hajj, George; Mannucci, Anthony J.

2006-01-01

The presentation outline includes University Corporation for Atmospheric Research (UCAR) and Jet Propulsion Laboratory (JPL) product comparisons, assimilating ground-based global positioning satellites (GPS) and COSMIC into JPL/University of Southern California (USC) Global Assimilative Ionospheric Model (GAIM), and JPL/USC GAIM validation. The discussion of comparisons examines Abel profiles and calibrated TEC. The JPL/USC GAIM validation uses Arecibo ISR, Jason-2 VTEC, and Abel profiles.

How and in Which way Space Weather Changed the Ionospheric Irregularities Occurrence During the St. Patricḱs Storm

NASA Astrophysics Data System (ADS)

Fagundes, P. R.; Barbosa, F. R. E., Sr.; Kavutarapu, V.; Fejer, B. G.; Pillat, V. G.; De Nardin, C. M.; Muella, M.

2017-12-01

During the solar cycle 24 there was a very intense geomagnetic storm, called St. Patricḱs Day storm and the effects of this storm on ionosphere has become a topic of extensive space weather investigation. The Dst during this storm reached -223 nT on March 17, 2015 at 23:00 UT. Special efforts have been devoted so far to investigate many aspects of the St. Patricḱs Day ionospheric storm such as the prompt penetration electric fields (PPEFs), GPS-TEC changes, electron density disturbances, plasma drift, O+ concentration modification, hemispherical asymmetry developments, equatorial ionization anomaly (EIA) modification, and ionospheric irregularities. Besides all these important studies, there are some essential aspects, which have not been addressed yet, related to the occurrence of ionospheric irregularities with different scale sizes. In this paper, we present and discuss the generation and suppression of ionospheric irregularities during March 2015, using the observations conducted in the Latin American Sector from 4 ionosondes (ESF) and 20 GPS-TEC stations (ROT phase fluctuation), which includes the St. Patricḱs Day geomagnetic storm period. Suppression of large-small scales ionospheric irregularities has occurred during the main and second night of the recovery phases. However, during the first night of recovery phase there was post-midnight ionospheric irregularities.

The origin of infrasonic ionosphere oscillations over tropospheric thunderstorms

DOE PAGES

Shao, Xuan -Min; Lay, Erin Hoffmann

2016-07-01

Thunderstorms have been observed to introduce infrasonic oscillations in the ionosphere, but it is not clear what processes or which parts of the thunderstorm generate the oscillations. In this paper, we present a new technique that uses an array of ground-based GPS total electron content (TEC) measurements to locate the source of the infrasonic oscillations and compare the source locations with thunderstorm features to understand the possible source mechanisms. The location technique utilizes instantaneous phase differences between pairs of GPS-TEC measurements and an algorithm to best fit the measured and the expected phase differences for assumed source positions and othermore » related parameters. In this preliminary study, the infrasound waves are assumed to propagate along simple geometric raypaths from the source to the measurement locations to avoid extensive computations. The located sources are compared in time and space with thunderstorm development and lightning activity. Sources are often found near the main storm cells, but they are more likely related to the downdraft process than to the updraft process. As a result, the sources are also commonly found in the convectively quiet stratiform regions behind active cells and are in good coincidence with extensive lightning discharges and inferred high-altitude sprites discharges.« less

Ionospheric disturbances induced by a missile launched from North Korea on 12 December 2012

NASA Astrophysics Data System (ADS)

Kakinami, Yoshihiro; Yamamoto, Masayuki; Chen, Chia-Hung; Watanabe, Shigeto; Lin, Charles; Liu, Jenn-Yanq; Habu, Hiroto

2013-08-01

disturbances caused by a missile launched from North Korea on 12 December 2012 were investigated by using the GPS total electron content (TEC). The spatial characteristic of the front edge of V-shaped disturbances produced by missiles and rockets was first determined. Considering the launch direction and the height of estimated ionospheric points at which GPS radio signal pierces the ionosphere, the missile passed through the ionosphere at heights of 391, 425, and 435 km at 0056:30, 0057:00, and 0057:30 UT, respectively. The observed velocities of the missile were 2.8 and 3.2 km/s at that time, which was estimated from the traveling speed of the front edge of V-shaped disturbances. Westward and eastward V-shaped disturbances propagated at 1.8-2.6 km/s. The phase velocities of the westward and eastward V-shaped disturbances were much faster than the speed of acoustic waves reported in previous studies, suggesting that sources other than acoustic waves may have played an important role. Furthermore, the plasma density depletion that is often observed following missile and rocket launches was not found. This suggests that the depletion resulting from the missile's exhaust was not strong enough to be observed in the TEC distribution in the topside ionosphere.

The origin of infrasonic ionosphere oscillations over tropospheric thunderstorms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Xuan -Min; Lay, Erin Hoffmann

Thunderstorms have been observed to introduce infrasonic oscillations in the ionosphere, but it is not clear what processes or which parts of the thunderstorm generate the oscillations. In this paper, we present a new technique that uses an array of ground-based GPS total electron content (TEC) measurements to locate the source of the infrasonic oscillations and compare the source locations with thunderstorm features to understand the possible source mechanisms. The location technique utilizes instantaneous phase differences between pairs of GPS-TEC measurements and an algorithm to best fit the measured and the expected phase differences for assumed source positions and othermore » related parameters. In this preliminary study, the infrasound waves are assumed to propagate along simple geometric raypaths from the source to the measurement locations to avoid extensive computations. The located sources are compared in time and space with thunderstorm development and lightning activity. Sources are often found near the main storm cells, but they are more likely related to the downdraft process than to the updraft process. As a result, the sources are also commonly found in the convectively quiet stratiform regions behind active cells and are in good coincidence with extensive lightning discharges and inferred high-altitude sprites discharges.« less

A study of the Ionospheric electron density profile with FORMOSAT-3/COSMIC observation data

NASA Astrophysics Data System (ADS)

Chou, Min-Yang; Tsai, Ho-Fang; Lin, Chi-Yen; Lee, I.-Te; Lin, Charles; Liu, Jann-Yenq

2015-04-01

The GPS Occultation Experiment payload onboard FORMOSAT-3/COSMIC microsatellite constellation is capable of scanning the ionospheric structure by the radio occultation (RO) technique to retrieve precise electron density profiles since 2006. Due to the success of FORMOSAT-3/COSMIC, the follow-on mission, FORMOSAT-7/COSMIC-2, is to launch 12 microsatellites in 2016 and 2018, respectively, with　the Global Navigation Satellite Systems (GNSS) RO instrument onboard for tracking GPS, Galileo and/or GLONASS satellite signals and to provide more than 8,000 RO soundings per day globally. An overview of the validation of the FORMOSAT-3/COSMIC ionospheric profiling is given by means of the traditional Abel transform through bending angle and total electron content (TEC), while the ionospheric data assimilation is also applied, based on the Gauss-Markov Kalman filter with the International Reference Ionosphere model (IRI-2007) and global ionosphere map (GIM) as background model, to assimilate TEC observations from FORMOSAT-3/COSMIC. The results shows comparison of electron density profiles from Abel inversion and data assimilation. Furthermore, an observing system simulation experiment is also applied to determine the impact of FORMOSAT-7/COSMIC-2 on ionospheric weather monitoring, which reveals an opportunity on advanced study of small spatial and temporal variations in the ionosphere.

Modeling of the Ionospheric Scintillation and Total Electron Content Observations during the 21 August 2017 Total Solar Eclipse

NASA Astrophysics Data System (ADS)

Datta-Barua, S.; Gachancipa, J. N.; Deshpande, K.; Herrera, J. A.; Lehmacher, G. A.; Su, Y.; Gyuk, G.; Bust, G. S.; Hampton, D. L.

2017-12-01

High concentration of free electrons in the ionosphere can cause fluctuations in incoming electromagnetic waves, such as those from the different Global Navigation Satellite Systems (GNSS). The behavior of the ionosphere depends on time and location, and it is highly influenced by solar activity. The purpose of this study is to determine the impact of a total solar eclipse on the local ionosphere in terms of ionospheric scintillations, and on the global ionosphere in terms of TEC (Total Electron Content). The studied eclipse occurred on 21 August 2017 across the continental United States. During the eclipse, we expected to see a decrease in the scintillation strength, as well as in the TEC values. As a broader impact part of our recently funded NSF proposal, we temporarily deployed two GNSS receivers on the eclipse's totality path. One GNSS receiver was placed in Clemson, SC. This is a multi-frequency GNSS receiver (NovAtel GPStation-6) capable of measuring high and low rate scintillation data as well as TEC values from four different GNSS systems. We had the receiver operating before, during, and after the solar eclipse to enable the comparison between eclipse and non-eclipse periods. A twin receiver collected data at Daytona Beach, FL during the same time, where an 85% partial solar eclipse was observed. Additionally, we set up a ground receiver onsite in the path of totality in Perryville, Missouri, from which the Adler Planetarium of Chicago launched a high-altitude balloon to capture a 360-degree video of the eclipse from the stratosphere. By analyzing the collected data, this study looks at the effects of partial and total solar eclipse periods on high rate GNSS scintillation data at mid-latitudes, which had not been explored in detail. This study also explores the impact of solar eclipses on signals from different satellite constellations (GPS, GLONASS, and Galileo). Throughout the eclipse, the scintillation values did not appear to have dramatic changes. However, we observed lower scintillation activity on several satellites from different constellations. For example, between 16 UTC and 22 UTC, there was a slight drop in the S4 scintillation Index (amplitude) values, reaching a local minimum during the time of eclipse totality ( 18:30 UTC). Regarding the Total Electron Content (TEC), which measures the quantity of electrons in the ionosphere, there was a more drastic decrease in the values throughout the partial and total solar eclipse. Additionally, σφ (sigma-phi) values for phase scintillation showed the similar behavior compared to previous few days. This reveals that the solar eclipse did not have a major effect on the phase scintillation. In any case, the totality path was entirely in mid-latitude regions, where phase scintillations are expected to be lower compared to high latitudes.

Investigation of Ionospheric Spatial Gradients for Gagan Error Correction

NASA Astrophysics Data System (ADS)

Chandra, K. Ravi

In India, Indian Space Research Organization (ISRO) has established with an objective to develop space technology and its application to various national tasks. The national tasks include, establishment of major space systems such as Indian National Satellites (INSAT) for communication, television broadcasting and meteorological services, Indian Remote Sensing Satellites (IRS), etc. Apart from these, to cater to the needs of civil aviation applications, GPS Aided Geo Augmented Navigation (GAGAN) system is being jointly implemented along with Airports Authority of India (AAI) over the Indian region. The most predominant parameter affecting the navigation accuracy of GAGAN is ionospheric delay which is a function of total number of electrons present in one square meter cylindrical cross-sectional area in the line of site direction between the satellite and the user on the earth, i.e. Total Electron Content (TEC). In the equatorial and low latitude regions such as India, TEC is often quite high with large spatial gradients. Carrier phase data from the GAGAN network of Indian TEC Stations is used for estimating and identifying ionospheric spatial gradients inmultiple viewing directions. In this paper amongst the satellite signals arriving in multipledirections,Vertical ionospheric gradients (σVIG) are calculated, inturn spatial ionospheric gradients are identified. In addition, estimated temporal gradients, i.e. rate of TEC Index is also compared. These aspects which contribute to errors can be treated for improved GAGAN system performance.

77 FR 1464 - Hand Trucks and Certain Parts Thereof From the People's Republic of China: Preliminary Results of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-10

... Surrogate Values Memorandum at Exhibit 8. Other inputs consisted of water, electricity, carbon dioxide, and.... See New-Tec Surrogate Values Memorandum at Exhibit 4. We valued carbon dioxide and liquid petroleum... Integration (Xiamen) Co., Ltd. (New-Tec), were below normal value (NV) at a de minimis level. We invite...

Tsunami Ionospheric warning and Ionospheric seismology

NASA Astrophysics Data System (ADS)

Lognonne, Philippe; Rolland, Lucie; Rakoto, Virgile; Coisson, Pierdavide; Occhipinti, Giovanni; Larmat, Carene; Walwer, Damien; Astafyeva, Elvira; Hebert, Helene; Okal, Emile; Makela, Jonathan

2014-05-01

The last decade demonstrated that seismic waves and tsunamis are coupled to the ionosphere. Observations of Total Electron Content (TEC) and airglow perturbations of unique quality and amplitude were made during the Tohoku, 2011 giant Japan quake, and observations of much lower tsunamis down to a few cm in sea uplift are now routinely done, including for the Kuril 2006, Samoa 2009, Chili 2010, Haida Gwai 2012 tsunamis. This new branch of seismology is now mature enough to tackle the new challenge associated to the inversion of these data, with either the goal to provide from these data maps or profile of the earth surface vertical displacement (and therefore crucial information for tsunami warning system) or inversion, with ground and ionospheric data set, of the various parameters (atmospheric sound speed, viscosity, collision frequencies) controlling the coupling between the surface, lower atmosphere and the ionosphere. We first present the state of the art in the modeling of the tsunami-atmospheric coupling, including in terms of slight perturbation in the tsunami phase and group velocity and dependance of the coupling strength with local time, ocean depth and season. We then show the confrontation of modelled signals with observations. For tsunami, this is made with the different type of measurement having proven ionospheric tsunami detection over the last 5 years (ground and space GPS, Airglow), while we focus on GPS and GOCE observation for seismic waves. These observation systems allowed to track the propagation of the signal from the ground (with GPS and seismometers) to the neutral atmosphere (with infrasound sensors and GOCE drag measurement) to the ionosphere (with GPS TEC and airglow among other ionospheric sounding techniques). Modelling with different techniques (normal modes, spectral element methods, finite differences) are used and shown. While the fits of the waveform are generally very good, we analyse the differences and draw direction of future studies and improvements, enabling the integration of lateral variations of the solid earth, bathymetry or atmosphere, finite model sources, non-linearity of the waves and better attenuation and coupling processes. All these effects are revealed by phase or amplitude discrepancies in selected observations. We then present goals and first results of source inversions, with a focus on estimations of the sea level uplift location and amplitude, either by using GPS networks close from the epicentre or, for tsunamis, GPS of the Hawaii Islands.

Three Dimensional High-Resolution Reconstruction of the Ionosphere Over the Very Large Array

DTIC Science & Technology

2010-12-15

Watts Progress Report, Dec 10; 1 Final Report: Three Dimensional High-Resolution Reconstruction of the Ionosphere over the Very Large Array...proposed research is reconstruct the three-dimensional regional electron density profile of Earth’s ionosphere with spatial resolution of better than 10 km...10x better sensitivity to total electron content (TEC, or chord integrated density) in the ionosphere that does GPS. The proposal funds the

Ionospheric reaction on sudden stratospheric warming events in Russiás Asia region

NASA Astrophysics Data System (ADS)

Polyakova, Anna; Perevalova, Natalya; Chernigovskaya, Marina

2015-12-01

The response of the ionosphere to sudden stratospheric warmings (SSWs) in the Asian region of Russia is studied. Two SSW events observed in 2008-2009 and 2012-2013 winter periods of extreme solar minimum and moderate solar maximum are considered. To detect the ionospheric effects caused by SSWs, we carried out a joint analysis of global ionospheric maps (GIM) of the total electron content (TEC), MLS (Microwave Limb Sounder, EOS Aura) measurements of temperature vertical profiles, as well as NCEP/NCAR and UKMO Reanalysis data. For the first time, it was found that during strong SSWs, in the mid-latitude ionosphere the amplitude of diurnal TEC variation decreases nearly half compared to quiet days. At the same time, the intensity of TEC deviations from the background level increases. It was also found that at SSW peak the midday TEC maximum decreases, and night/morning TEC values increase compared to quiet days. It was shown that during SSWs, TEC dynamics was identical for different geophysical conditions.The response of the ionosphere to sudden stratospheric warmings (SSWs) in the Asian region of Russia is studied. Two SSW events observed in 2008-2009 and 2012-2013 winter periods of extreme solar minimum and moderate solar maximum are considered. To detect the ionospheric effects caused by SSWs, we carried out a joint analysis of global ionospheric maps (GIM) of the total electron content (TEC), MLS (Microwave Limb Sounder, EOS Aura) measurements of temperature vertical profiles, as well as NCEP/NCAR and UKMO Reanalysis data. For the first time, it was found that during strong SSWs, in the mid-latitude ionosphere the amplitude of diurnal TEC variation decreases nearly half compared to quiet days. At the same time, the intensity of TEC deviations from the background level increases. It was also found that at SSW peak the midday TEC maximum decreases, and night/morning TEC values increase compared to quiet days. It was shown that during SSWs, TEC dynamics was identical for different geophysical conditions.

JPL/USC GAIM: Using COSMIC Occultations in a Real-Time Global Ionospheric Data Assimilation Model

NASA Astrophysics Data System (ADS)

Mandrake, L.; Komjathy, A.; Wilson, B. D.; Pi, X.; Hajj, G.; Iijima, B.; Wang, C.

2006-12-01

We are in the midst of a revolution in ionospheric remote sensing driven by the illuminating powers of ground and space-based GPS receivers, new UV remote sensing satellites, and the advent of data assimilation techniques for space weather. In particular, the COSMIC 6-satellite constellation launched in April 2006. COSMIC will provide unprecedented global coverage of GPS occultations (~5000 per day), each of which yields electron density information with unprecedented ~1 km vertical resolution. Calibrated measurements of ionospheric delay (total electron content or TEC) suitable for input into assimilation models will be available in near real-time (NRT) from the COSMIC project with a latency of 30 to 120 minutes. Similarly, NRT TEC data are available from two worldwide NRT networks of ground GPS receivers (~75 5-minute sites and ~125 more hourly sites, operated by JPL and others). The combined NRT ground and space-based GPS datasets provide a new opportunity to more accurately specify the 3-dimensional ionospheric density with a time lag of only 15 to 120 minutes. With the addition of the vertically-resolved NRT occultation data, the retrieved profile shapes will model the hour-to-hour ionospheric "weather" much more accurately. The University of Southern California (USC) and the Jet Propulsion Laboratory (JPL) have jointly developed a real-time Global Assimilative Ionospheric Model (GAIM) to monitor space weather, study storm effects, and provide ionospheric calibration for DoD customers and NASA flight projects. JPL/USC GAIM is a physics- based 3D data assimilation model that uses both 4DVAR and Kalman filter techniques to solve for the ion & electron density state and key drivers such as equatorial electrodynamics, neutral winds, and production terms. Daily (delayed) GAIM runs can accept as input ground GPS TEC data from 1000+ sites, occultation links from CHAMP, SAC-C, and the COSMIC constellation, UV limb and nadir scans from the TIMED and DMSP satellites, and in situ data from a variety of satellites (DMSP and C/NOFS). RTGAIM ingests multiple data sources in real time, updates the 3D electron density grid every 5 minutes, and solves for improved drivers every 1-2 hours. Since our forward physics model and the adjoint model were expressly designed for data assimilation and computational efficiency, all of this can be accomplished on a single dual-processor Unix workstation. Customers are currently evaluating the accuracy of JPL/USC GAIM "nowcasts" for ray tracing applications and trans-ionospheric path delay calibration. In the talk, we will discuss the expected impact of COSMIC occultation data; show first results for ingest of COSMIC data using the GAIM Kalman filter; present validation of the GAIM electron density grid by comparisons to Abel profiles and independent datasets; describe recent improvements to the JPL/USC GAIM model; and describe our plans for NRT ingest of COSMIC data into RTGAIM.

Ionospheric response to the total solar eclipse in India on 22 July, 2009

NASA Astrophysics Data System (ADS)

Chauhan, Vishal; Agrawal, Shikha; Singh, O. P.; Singh, Birbal

2010-10-01

Since The variations of Total Electron Content (TEC) and amplitude of the fixed frequency VLF transmitter signal (f = 19.8 kHz, NWC, Australia) are studied at Agra (Geographic Lat. 27.2°N, Long. 78°E), India during the total solar eclipse of 22 July, 2009 which was longest seen in India ever since 18 August, 1968. The equipment used for the study are a dual frequency GPS receiver (GSV 4004V) and a Soft PAL (Software based phase and amplitude logger) receiver. The data for a period of fifteen days (+/-7 days from the date of the event) are analysed and it is found that the TEC decreased by about 30% from normal days during the total solar eclipse, and the amplitude of the VLF signal also decreased likewise. The period of the data analysis is characterised by a low level of geomagnetic activity, hence the decrease in TEC and amplitude of the VLF signal is unlikely to be influenced by geomagnetic disturbances. The results are interpreted in terms of depression in electron densities at all ionospheric heights and are consistent with those obtained by earlier workers during similar eclipse events.

A new physics-based modeling approach for tsunami-ionosphere coupling

NASA Astrophysics Data System (ADS)

Meng, X.; Komjathy, A.; Verkhoglyadova, O. P.; Yang, Y.-M.; Deng, Y.; Mannucci, A. J.

2015-06-01

Tsunamis can generate gravity waves propagating upward through the atmosphere, inducing total electron content (TEC) disturbances in the ionosphere. To capture this process, we have implemented tsunami-generated gravity waves into the Global Ionosphere-Thermosphere Model (GITM) to construct a three-dimensional physics-based model WP (Wave Perturbation)-GITM. WP-GITM takes tsunami wave properties, including the wave height, wave period, wavelength, and propagation direction, as inputs and time-dependently characterizes the responses of the upper atmosphere between 100 km and 600 km altitudes. We apply WP-GITM to simulate the ionosphere above the West Coast of the United States around the time when the tsunami associated with the March 2011 Tohuku-Oki earthquke arrived. The simulated TEC perturbations agree with Global Positioning System observations reasonably well. For the first time, a fully self-consistent and physics-based model has reproduced the GPS-observed traveling ionospheric signatures of an actual tsunami event.

The Mesoscale Ionospheric Simulation Testbed (MIST) Regional Data Assimilation Model (Invited)

NASA Astrophysics Data System (ADS)

Comberiate, J.; Kelly, M. A.; Miller, E.; Paxton, L.

2013-12-01

The Mesoscale Ionospheric Simulation Testbed (MIST) provides a regional nowcast and forecast of electron density values and has sufficient resolution to include equatorial plasma bubbles. The SSUSI instrument on the DMSP F18 satellite has high-resolution nightly observations of plasma bubbles at 8 PM local time throughout the current solar maximum. MIST can assimilate SSUSI UV observations, GPS TEC measurements, and SCINDA S4 readings simultaneously into a single scintillation map over a region of interest. MIST also models ionospheric physics to provide a short-term UHF scintillation forecast based on assimilated data. We will present examples of electron density and scintillation maps from MIST. We will also discuss the potential to predict scintillation occurrence up to 6 hours in advance using observations of the equatorial arcs from SSUSI observations at 5:30 PM local time on the DMSP F17 satellite.

Evaluation of Inversion Methods Applied to Ionospheric ro Observations

NASA Astrophysics Data System (ADS)

Rios Caceres, Arq. Estela Alejandra; Rios, Victor Hugo; Guyot, Elia

The new technique of radio-occultation can be used to study the Earth's ionosphere. The retrieval processes of ionospheric profiling from radio occultation observations usually assume spherical symmetry of electron density distribution at the locality of occultation and use the Abel integral transform to invert the measured total electron content (TEC) values. This pa-per presents a set of ionospheric profiles obtained from SAC-C satellite with the Abel inversion technique. The effects of the ionosphere on the GPS signal during occultation, such as bending and scintillation, are examined. Electron density profiles are obtained using the Abel inversion technique. Ionospheric radio occultations are validated using vertical profiles of electron con-centration from inverted ionograms , obtained from ionosonde sounding in the vicinity of the occultation. Results indicate that the Abel transform works well in the mid-latitudes during the daytime, but is less accurate during the night-time.

Harmonic analysis of the ionospheric electron densities retrieved from FORMOSAT-3/COSMIC radio occultation measurements

NASA Astrophysics Data System (ADS)

Masoumi, S.; Safari, A.; Sharifi, M.; Sam Khaniani, A.

2011-12-01

In order to investigate regular variations of the ionosphere, the least-squares harmonic estimation is applied to the time series of ionospheric electron densities in the region of Iran derived from about five years of Global Positioning System Radio Occultation (GPS RO) observations by FORMOSAT-3/COSMIC satellites. Although the obtained results are slightly different from the expected ones due to the low horizontal resolution of RO measurements, high vertical resolution of the observations enables us to detect not only the Total Electron Content (TEC) variations, but also periodic patterns of electron densities in different altitudes of the ionosphere. Dominant diurnal and annual signals, together with their Fourier series decompositions, and also periods close to 27 days are obtained, which is consistent with the previous analyses on TEC. In the equatorial anomaly band, the annual component is weaker than its Fourier decomposition periods. In particular, the semiannual period dominates the annual component, which is probably due to the effect of geomagnetic field. By the investigation of the frequencies at different local times, the semiannual signal is more significant than the annual one in the daytime, while the annual frequency is dominant at night. By the detection of the phases of the components, it is revealed that the annual signal has its maximum in summer at high altitudes, and in winter at lower altitudes. This suggests the effect of neutral compositions in the lower atmosphere. Further, the semiannual component peaks around equinox during the day, while its maximum mostly occurs in solstice at night. Since RO measurements can be used to derive TEC along the signal path between a GPS satellite and a receiver, study on the potentiality of using these observations for the prediction of electron densities and its application to the ionospheric correction of the single frequency receivers is suggested.

Ionospheric "Volcanology": Ionospheric Detection of Volcano Eruptions

NASA Astrophysics Data System (ADS)

Astafyeva, E.; Shults, K.; Lognonne, P. H.; Rakoto, V.

2016-12-01

It is known that volcano eruptions and explosions can generate acoustic and gravity waves. These neutral waves further propagate into the atmosphere and ionosphere, where they are detectable by atmospheric and ionospheric sounding tools. So far, the features of co-volcanic ionospheric perturbations are not well understood yet. The development of the global and regional networks of ground-based GPS/GNSS receivers has opened a new era in the ionospheric detection of natural hazard events, including volcano eruptions. It is now known that eruptions with the volcanic explosivity index (VEI) of more than 2 can be detected in the ionosphere, especially in regions with dense GPS/GNSS-receiver coverage. The co-volcanic ionospheric disturbances are usually characterized as quasi-periodic oscillations. The Calbuco volcano, located in southern Chile, awoke in April 2015 after 43 years of inactivity. The first eruption began at 21:04UT on 22 April 2015, preceded by only an hour-long period of volcano-tectonic activity. This first eruption lasted 90 minutes and generated a sub-Plinian (i.e. medium to large explosive event), gray ash plume that rose 15 km above the main crater. A larger second event on 23 April began at 04:00UT (01:00LT), it lasted six hours, and also generated a sub-Plinian ash plume that rose higher than 15 km. The VEI was estimated to be 4 to 5 for these two events. In this work, we first study ionospheric TEC response to the Calbuco volcano eruptions of April 2015 by using ground-based GNSS-receivers located around the volcano. We analyze the spectral characteristics of the observed TEC variations and we estimate the propagation speed of the co-volcanic ionospheric perturbations. We further proceed with the normal mode summation technique based modeling of the ionospheric TEC variations due to the Calbuco volcano eruptions. Finally, we attempt to localize the position of the volcano from the ionospheric measurements, and we also estimate the time of the beginning of the eruption.

Equatorial and Low-Latitude Ionospheric Response to the Extreme Space Weather Event of March 2015, in the Brazilian Sector.

NASA Astrophysics Data System (ADS)

Fagundes, P. R.; Cardoso, F. A.; Fejer, B. G.; Kavutarapu, V.; Ribeiro, B. A.; Pillat, V. G.

2015-12-01

Fagundes PR, Cardoso FA and Venkatesh KPhysics and Astronomy Laboratory, Universidade do Vale do Paraiba (UNIVAP), Sao Jose dos Campos, Sao Paulo, Brazil In the present investigation we discuss the results on the response of the ionosphere (F-region) in the Brazilian sector, during extreme space weather event of March 2015. This geomagnetic storm has been considered as one of strongest storms in the solar cycle 24 where, the Dst index reached a minimum of -227 nT at 23:00 UT (17/03/2015) with KP reaching to 8-, and the monthly mean F10.7 solar flux was 125 sfu. This space weather event was studied using a large network of 110 GPS stations. It has been noticed that the Total Electron Content (TEC) was severely disturbed during the geomagnetic storm main and recovery phases. A wavelike oscillation with three peaks is observed from equator to low latitudes during the storm main phase on 17th and 18th March, 2015. Using a latitudinal chain of 8 GPS stations from equatorial region to low latitudes the storm time behavior of the Equatorial Ionization Anomaly (EIA) is investigated. It was noticed that the wavelike oscillation peak latitudinal extent decreases from the beginning of main phase to the recovery phase. The first maximum extends beyond from 2oS to 20oS, the second one from 8oS to 18oS and the third one from 13oS to 17oS. In addition, a strong negative phase in TEC variations is observed during the recovery phase on March 18, 2015. This negative phase is found to be stronger at low-latitude compared to the equatorial region. An anomalous behavior of EIA caused by the wavelike oscillations is observed during the main phase on March 17, 2015. Also, due to the strong negative phase in TEC resulted in strong EIA suppression on March 18, 2015.

The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

NASA Astrophysics Data System (ADS)

Yuan, Y.; Tscherning, C. C.; Knudsen, P.; Xu, G.; Ou, J.

2008-01-01

A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) λ of the ionospheric pierce point (IPP) and the IEF’s influence factor (IFF) bar{λ}. The IEF can be used to make a relatively precise distinction between ionospheric daytime and nighttime, whereas the IFF is advantageous for describing the IEF’s variations with day, month, season and year, associated with seasonal variations of total electron content (TEC) of the ionosphere. By combining λ and bar{λ} with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM may further improve ionospheric delay modeling using GPS data.

Multi-Scale Ionospheric Responses to the St. Patrick's Day Storm (2015) Studied Using a Multimodel Ensemble Prediction System and GPS Data

NASA Astrophysics Data System (ADS)

Pi, X.; Butala, M.; Vergados, P.; Mannucci, A. J.; Komjathy, A.; Wang, C.; Rosen, G.; Schunk, R. W.; Scherliess, L.; Eccles, V.; Gardner, L. C.; Sojka, J. J.; Zhu, L.

2015-12-01

Under the U.S. NASA and NSF collaborative space weather modeling initiative, a Multimodel Ensemble Prediction System (MEPS) for ionosphere-thermosphere-electrodynamics is being developed. The system includes several Global Assimilative Ionospheric Models (GAIMs) developed by the investigators from Utah State University, Jet Propulsion Laboratory, and University of Southern California. In this study, four GAIMs are applied to a study of ionospheric response to the 17 March 2015 St. Patrick's Day storm. It is the most severe geomagnetic storm in the current solar cycle so far. The daily planetary magnetic Ap index and magnetic Kp, Dst, as well as AE indices reached their very high values, i.e., 108, 8, -202 nT, and 2269 nT, respectively. In the assimilative modeling, GPS data from hundreds of globally-distributed ground stations and a number of COSMIC satellites are assimilated into GAIMs to reproduce ionospheric 3-D volume densities and 2-D total electron content (TEC) during the severe storm. Evolution of strong, latitudinally-dependent, and hemispherically asymmetric ionospheric disturbances is revealed through the assimilative modeling. Using the same GPS data, Global Maps of Ionospheric Irregularities and Scintillation (GMIIS) have also been produced. Comparisons of the modeled large-scale ionospheric disturbances and measured small-scale ionospheric irregularities offer additional insight into the M-I-T coupling processes in different regions during varying storm phases. This presentation will provide a picture of distinguished multi-scale ionospheric response to the coronal mass ejection (CME) event during the major geomagnetic storm.

Variability of ionospheric TEC during solar and geomagnetic minima (2008 and 2009): external high speed stream drivers

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Tsurutani, B. T.; Mannucci, A. J.; Mlynczak, M. G.; Hunt, L. A.; Runge, T.

2013-02-01

We study solar wind-ionosphere coupling through the late declining phase/solar minimum and geomagnetic minimum phases during the last solar cycle (SC23) - 2008 and 2009. This interval was characterized by sequences of high-speed solar wind streams (HSSs). The concomitant geomagnetic response was moderate geomagnetic storms and high-intensity, long-duration continuous auroral activity (HILDCAA) events. The JPL Global Ionospheric Map (GIM) software and the GPS total electron content (TEC) database were used to calculate the vertical TEC (VTEC) and estimate daily averaged values in separate latitude and local time ranges. Our results show distinct low- and mid-latitude VTEC responses to HSSs during this interval, with the low-latitude daytime daily averaged values increasing by up to 33 TECU (annual average of ~20 TECU) near local noon (12:00 to 14:00 LT) in 2008. In 2009 during the minimum geomagnetic activity (MGA) interval, the response to HSSs was a maximum of ~30 TECU increases with a slightly lower average value than in 2008. There was a weak nighttime ionospheric response to the HSSs. A well-studied solar cycle declining phase interval, 10-22 October 2003, was analyzed for comparative purposes, with daytime low-latitude VTEC peak values of up to ~58 TECU (event average of ~55 TECU). The ionospheric VTEC changes during 2008-2009 were similar but ~60% less intense on average. There is an evidence of correlations of filtered daily averaged VTEC data with Ap index and solar wind speed. We use the infrared NO and CO2 emission data obtained with SABER on TIMED as a proxy for the radiation balance of the thermosphere. It is shown that infrared emissions increase during HSS events possibly due to increased energy input into the auroral region associated with HILDCAAs. The 2008-2009 HSS intervals were ~85% less intense than the 2003 early declining phase event, with annual averages of daily infrared NO emission power of ~ 3.3 × 1010 W and 2.7 × 1010 W in 2008 and 2009, respectively. The roles of disturbance dynamos caused by high-latitude winds (due to particle precipitation and Joule heating in the auroral zones) and of prompt penetrating electric fields (PPEFs) in the solar wind-ionosphere coupling during these intervals are discussed. A correlation between geoeffective interplanetary electric field components and HSS intervals is shown. Both PPEF and disturbance dynamo mechanisms could play important roles in solar wind-ionosphere coupling during prolonged (up to days) external driving within HILDCAA intervals.

Variabilities of Low-Latitude Migrating and Nonmigrating Tides in GPS-TEC and TIMED-SABER Temperature During the Sudden Stratospheric Warming Event of 2013

NASA Astrophysics Data System (ADS)

Sridharan, S.

2017-10-01

The Global Positioning System deduced total electron content (TEC) data at 15°N (geomagnetic), which is the crest region of equatorial ionization anomaly, are used to study tidal variabilities during the 2013 sudden stratospheric warming (SSW) event. The results from space-time spectral analysis reveal that the amplitudes of migrating diurnal (DW1) and semidiurnal (SW2) tides are larger than those of nonmigrating tides. After the SSW onset, the amplitudes of DW1, SW2, SW1, and DS0 increase. Moreover, they show 16 day variations similar to the periodicity of the high-latitude stratospheric planetary wave (PW), suggesting that the nonmigrating tides (SW1 and DS0) are possibly generated due to nonlinear interaction of migrating tides with PW. Similar spectral analysis on temperature at 10°N obtained from the Sounding of Atmosphere by Broadband Emission Radiometry (SABER) shows that the SW2 enhances at stratospheric heights and the SW2 is more dominant at 80-90 km, but its amplitude decreases around 100 km. The amplitudes of nonmigrating tides become comparable to those of SW2 around 100 km, and their contribution becomes increasingly important at higher heights. This suggests that the nonlinear interaction between migrating tides and PW occurs at low-latitude upper mesospheric heights, as SW2 exhibits 16 day periodicity in SABER temperature at 100 km as observed in TEC. Besides, it is observed that the eastward propagating tides are less dominant than westward propagating tides in both TEC and SABER temperatures.

Modeling magnetic field and TEC signatures of large-amplitude acoustic and gravity waves generated by natural hazard events

NASA Astrophysics Data System (ADS)

Zettergren, M. D.; Snively, J. B.; Inchin, P.; Komjathy, A.; Verkhoglyadova, O. P.

2017-12-01

Ocean and solid earth responses during earthquakes are a significant source of large amplitude acoustic and gravity waves (AGWs) that perturb the overlying ionosphere-thermosphere (IT) system. IT disturbances are routinely detected following large earthquakes (M > 7.0) via GPS total electron content (TEC) observations, which often show acoustic wave ( 3-4 min periods) and gravity wave ( 10-15 min) signatures with amplitudes of 0.05-2 TECU. In cases of very large earthquakes (M > 8.0) the persisting acoustic waves are estimated to have 100-200 m/s compressional velocities in the conducting ionospheric E and F-regions and should generate significant dynamo currents and magnetic field signatures. Indeed, some recent reports (e.g. Hao et al, 2013, JGR, 118, 6) show evidence for magnetic fluctuations, which appear to be related to AGWs, following recent large earthquakes. However, very little quantitative information is available on: (1) the detailed spatial and temporal dependence of these magnetic fluctuations, which are usually observed at a small number of irregularly arranged stations, and (2) the relation of these signatures to TEC perturbations in terms of relative amplitudes, frequency, and timing for different events. This work investigates space- and time-dependent behavior of both TEC and magnetic fluctuations following recent large earthquakes, with the aim to improve physical understanding of these perturbations via detailed, high-resolution, two- and three-dimensional modeling case studies with a coupled neutral atmospheric and ionospheric model, MAGIC-GEMINI (Zettergren and Snively, 2015, JGR, 120, 9). We focus on cases inspired by the large Chilean earthquakes from the past decade (viz., the M > 8.0 earthquakes from 2010 and 2015) to constrain the sources for the model, i.e. size, frequency, amplitude, and timing, based on available information from ocean buoy and seismometer data. TEC data are used to validate source amplitudes and to constrain background ionospheric conditions. Preliminary comparisons against available magnetic field and TEC data from these events provide evidence, albeit limited and localized, that support the validity of the spatially-resolved simulation results.

Comparison of Ionospheric and Thermospheric Effects During Two High Speed Stream Events

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Tsurutani, B.; Mannucci, A. J.; Paxton, L.; Mlynczak, M. G.; Hunt, L. A.; Echer, E.

2013-12-01

We analyze two CIR-HSS events during ascending phase of the current solar cycle. The first event occurred on 8-12 May 2012 and was characterized by a large CIR and intense High Intensity Long Duration Continuous Auroral Activity (HILDCAA). Long-duration moderate geomagnetic storm (Dst ~ -50 nT) occurred during this event. The second event on 29 April - 4 May 2011 had a large CIR and extended HSS, but weaker geomagnetic activity. We focus on understanding differences and similarities of the magnetosphere-ionosphere-thermosphere coupling during these two events. We will use a suite of ground-based and satellite measurements to create a comprehensive picture of the events. Evolution of the polar cap convection pattern is analyzed based on SuperDARN data. DMSP/SSUSI far ultraviolet measurements provide information on airglow intensity and characteristics of the F-region of the dusktime ionosphere. The GPS total electron content (TEC) database and JPL's Global Ionospheric Maps (GIM) are used to study vertical TEC (VTEC) for different local times and latitude ranges. We discuss dynamics of VTEC above individual ground GPS sites with respect to local time and latitude ranges. We analyze the TIMED/SABER zonal flux of nitric oxide (NO) infrared cooling radiation and auroral heating throughout the events. Global dynamics of the column density ratio ΣO/N2 is studied based on TIMED/GUVI measurements. Our results will advance understanding of the ionosphere-thermosphere response to external forcing and help future forecasting efforts.

Inverting Coseismic TEC Disturbances for Neutral Atmosphere Pressure Wave

NASA Astrophysics Data System (ADS)

Lee, R. F.; Mikesell, D.; Rolland, L.

2017-12-01

Research from the past 20 years has shown that we can detect coseismic disturbances in the total electron content (TEC) using global navigation space systems (GNSS). In the near field, TEC disturbances are created by the direct wave from rupture on the surface. This pressure wave travels through the neutral atmosphere to the ionosphere within about 10 minutes. This provides the opportunity to almost immediately characterize the source of the acoustic disturbance on the surface using methods from seismology. In populated areas, this could provide valuable information to first responders. To retrieve the surface motion amplitude information we must account for changes in the waveform caused by the geomagnetic field, motion of the satellites and the geometry of the satellites and receivers. One method is to use a transfer function to invert for the neutral atmosphere pressure wave. Gómez et al (2015) first employed an analytical model to invert for acoustic waves produced by Rayleigh waves propagating along the Earth's surface. Here, we examine the same model in the near field using the TEC disturbances from the direct wave produced by rupture at the surface. We compare results from the forward model against a numerical model that has been shown to be in good agreement with observations from the 2011 Van (Turkey) earthquake. We show the forward model predictions using both methods for the Van earthquake. We then analyze results for hypothetical events at different latitudes and discuss the reliability of the analytical model in each scenario. Gómez, D., R. Jr. Smalley, C. A. Langston, T. J. Wilson, M. Bevis, I. W. D. Dalziel, E. C. Kendrick, S. A. Konfal, M. J. Willis, D. A. Piñón, et al. (2015), Virtual array beamforming of GPS TEC observations of coseismic ionospheric disturbances near the Geomagnetic South Pole triggered by teleseismic megathrusts, J. Geophys. Res. Space Physics, 120, 9087-9101, doi:10.1002/2015JA021725.

Satellite-motion Compensation for Monitoring Travelling Ionospheric Disturbances (TIDs) Using GPS

NASA Astrophysics Data System (ADS)

Jackson-Booth, N.; Penney, R.

2016-12-01

The ionosphere exerts a strong influence over a wide range of modern communications and navigtion systems, but is subject to complex influences from both terrestrial and solar sources. Ionospheric disturbances can be triggered by lower-atmosphere phenomena such as hurricanes as well as geophysical events such as earthquakes, as well as being strongly influenced by cyclical and unpredictable solar behaviour. Dual-band GPS receivers provide a popular and convenient means of obtaining information about the ionosphere, and ionospheric disturbances. While GPS measurements can provide clues about the state of the ionosphere, there are many challenges in obtaining reliable information from them. For example, drop-outs and carrier-phase cycle slips may have little influence on using GPS for (medium-precision) navigation, but can lead to signal-processing artefacts that would cause false alarms in detecting ionospheric disturbances. If one is interested in measuring the motion of travelling ionospheric disturbances (TIDs) one must also be able to disentangle the effects of satellite motion from the TID motion. We discuss a novel approach to robustly separating TID waveforms from background trends within GPS time-series of total electron content (TEC), as well as innovative techniques for estimating TID velocities using ideas from Synthetic Aperture Radar (SAR). Underpinning these, we consider how to robustly pre-process GPS time-series to reduce the influence of drop-outs while also reducing data volumes. We present comparisons of our TID velocity estimates with more standard "cross-correlation" techniques, including cases where these standard techniques produce pathological results. We also show results from simulated GPS time-series derived from modelled ionospheric disturbances.

Reconstruction of missed critical frequency of F2-layer over Mexico using TEC

NASA Astrophysics Data System (ADS)

Sergeeva, M. A.; Maltseva, O. A.; Gonzalez-Esparza, A.; Romero Hernandez, E.; De la Luz, V.; Rodriguez-Martinez, M. R.

2016-12-01

The study of the Earth's ionosphere's state is one of the key issues within the Space Weather monitoring task. It is hard to overestimate the importance of diagnostics of its current state and forecasts of Space Weather conditions. There are different methods of short-time predictions for the ionosphere state change. The real-time monitoring of the ionospheric Total Electron Content (TEC) provides the opportunity to choose an appropriate technique for the particular observation point on the Earth. From September 2015 the continuous monitoring of TEC variations over the territory of Mexico is performed by the Mexican Space Weather Service (SCiESMEX). Regular patterns of the diurnal and seasonal TEC variations were revealed in base of past statistics and real-time observations which can be used to test the prediction method. Some specific features of the ionosphere behaviour are discussed. However, with all the merits of TEC as an ionospheric parameter, for the full picture of the processes in the ionosphere and for practical applications it is needed to identify the behaviour of other principal ionospheric parameters provided by ionosondes. Currently, SCiESMEX works on the project of the ionosonde installation in Mexico. This study was focused on the reconstruction of the critical frequency of F2-layer of the ionosphere (foF2) when this data is missing. For this purpose measurements of TEC and the median value of the equivalent slab thickness of the ionosphere were used. First, the foF2 values reconstruction was made for the case of the ionosonde data being absent during some hours or days. Second, the possibility of foF2 reconstruction was estimated for the Mexican region having no ionosonde using local TEC data and foF2 data obtained in the regions close to Mexico. Calculations were performed for quiet and disturbed periods. The results of reconstruction were compared to the foF2 obtained from the International Reference Model and to median foF2 values. Comparison with other low-and mid-latitude regions was made. It was shown that foF2 reconstructed using TEC have better agreement with the experimental data. Considering the said above, the use of the reconstructed foF2 values is a great aid for the ionosphere state estimation over Mexico when foF2 information is missed.

Response of the EIA ionosphere to the 7-8 May 2005 geomagnetic storm

NASA Astrophysics Data System (ADS)

Aggarwal, Malini; Joshi, H. P.; Iyer, K. N.; Kwak, Y. S.

2013-08-01

In this paper, response of low latitude ionosphere to a moderate geomagnetic storm of 7-8 May 2005 (SSC: 1920 UT on 7 May with Sym-H minimum, ∼-112 nT around 1600 UT on 8 May) has been investigated using the GPS measurements from a near EIA crest region, Rajkot (Geog. 22.29°N, 70.74°E, Geomag.14°), India. We found a decrease in total electron content (TEC) in 12 h after the onset of the storm, an increase during and after 6 h of Sym-H deep minimum with a decrease below its usual-day level on the second day during the recovery phase of the storm. On 8 May, an increase of TEC is observed after sunset and during post-midnight hours (maximum up to 170%) with the formation of ionospheric plasma bubbles followed by a nearly simultaneous onset of scintillations at L-band frequencies following the time of rapid decrease in Sym-H index (-30 nT/h around 1300 UT).

Pre-earthquake Anomalies of the Ion Velocity in the Ionosphere

NASA Astrophysics Data System (ADS)

Liu, J. Y. G.; Chao, C. K.

2016-12-01

In the paper, pre-earthquake ionospheric anomalies (PEIAs) of the ion velocity, which are further employed to estimate the seismo-ionospheric electric fields, are for the first time reported. To see whether ionospheric ion velocity can be used to detect PEIAs or not, we examine concurrent measurements of the ion density, ion temperature, and the ion velocity probed by ROCSAT/IPEI (ionospheric Plasma and Electrodynamics Instrument), as well as the global ionospheric map (GIM) of the total electron content (TEC) derived by ground-based GPS receivers during the 31 March 2002 M6.8 Earthquake in Taiwan. It is found around the epicenter area 1-5 days before the earthquake that the GIM TEC significantly decreases, while the ROCSAT/IPEI ion density significantly decreases and ion velocity in the downward direction anomalously increases. The increase in the downward velocity implies that a westward electric field of about 0.91mV/m generated during the earthquake period is essential.

Probability Distribution Extraction from TEC Estimates based on Kernel Density Estimation

NASA Astrophysics Data System (ADS)

Demir, Uygar; Toker, Cenk; Çenet, Duygu

2016-07-01

Statistical analysis of the ionosphere, specifically the Total Electron Content (TEC), may reveal important information about its temporal and spatial characteristics. One of the core metrics that express the statistical properties of a stochastic process is its Probability Density Function (pdf). Furthermore, statistical parameters such as mean, variance and kurtosis, which can be derived from the pdf, may provide information about the spatial uniformity or clustering of the electron content. For example, the variance differentiates between a quiet ionosphere and a disturbed one, whereas kurtosis differentiates between a geomagnetic storm and an earthquake. Therefore, valuable information about the state of the ionosphere (and the natural phenomena that cause the disturbance) can be obtained by looking at the statistical parameters. In the literature, there are publications which try to fit the histogram of TEC estimates to some well-known pdf.s such as Gaussian, Exponential, etc. However, constraining a histogram to fit to a function with a fixed shape will increase estimation error, and all the information extracted from such pdf will continue to contain this error. In such techniques, it is highly likely to observe some artificial characteristics in the estimated pdf which is not present in the original data. In the present study, we use the Kernel Density Estimation (KDE) technique to estimate the pdf of the TEC. KDE is a non-parametric approach which does not impose a specific form on the TEC. As a result, better pdf estimates that almost perfectly fit to the observed TEC values can be obtained as compared to the techniques mentioned above. KDE is particularly good at representing the tail probabilities, and outliers. We also calculate the mean, variance and kurtosis of the measured TEC values. The technique is applied to the ionosphere over Turkey where the TEC values are estimated from the GNSS measurement from the TNPGN-Active (Turkish National Permanent GNSS Network) network. This study is supported by by TUBITAK 115E915 and Joint TUBITAK 114E092 and AS CR14/001 projects.

Using GPS TEC measurements to probe ionospheric spatial spectra at mid-latitudes

NASA Astrophysics Data System (ADS)

Lay, E. H.; Parker, P. A.; Light, M. E.; Carrano, C. S.; Debchoudhury, S.; Haaser, R. A.

2017-12-01

The physics of how random ionospheric structure causes signal degradation is well understood as weak forward scattering through an effective diffraction grating created by plasma irregularities in the ionosphere. However, the spatial scale spectrum of those irregularities required for input into scintillation models and models of traveling ionospheric disturbances is poorly characterized, particularly at the kilometer to tens of kilometer scale lengths important for very-high-frequency (VHF) scintillation prediction. Furthermore, the majority of characterization studies have been performed in low-latitude or high-latitude regions where geomagnetic activity dominates the physical processes. At mid-latitudes, tropospheric and geomagnetic phenomena compete in disturbing the ionosphere, and it is not well understood how these multiple sources affect the drivers that influence the spatial spectrum. In this study, we are interested in mid-latitude electron density irregularities on the order of 10s of kilometers that would affect VHF signals. Data from the GPS networks Japan GEONET and the Plate Boundary Observatory (PBO, UNAVCO) in the western United States were analyzed for this study. Japan GEONET is a dense network of GPS receivers (station spacing of tens of km), with fairly evenly spaced positions over all of Japan. The PBO, on the other hand, has several pockets of extremely dense coverage (station spacing within a few km), but is less dense on average. We analyze a day with a large solar storm (2015/03/17, St. Patrick's Day Storm) to allow high scintillation potential at mid-latitudes, a day with low geomagnetic activity and low thunderstorm activity (2016/01/31), and a day with low geomagnetic activity and high thunderstorm activity (2015/08/02). We then perform two-dimensional spatial analyses on the TEC data from these two networks on scale lengths of 20 to 200 km to infer the spatial scale spectra.

Application of GPS Technologies to study Pre-earthquake processes. A review and future prospects

NASA Astrophysics Data System (ADS)

Pulinets, S. A.; Liu, J. Y. G.; Ouzounov, D.; Hernandez-Pajares, M.; Hattori, K.; Krankowski, A.; Zakharenkova, I.; Cherniak, I.

2016-12-01

We present the progress reached by the GPS TEC technologies in study of pre-seismic anomalies in the ionosphere appearing few days before the strong earthquakes. Starting from the first case studies such as 17 August 1999 M7.6 Izmit earthquake in Turkey the technology has been developed and converted into the global near real-time monitoring of seismo-ionospheric effects which is used now in the multiparameter nowcast and forecast of the strong earthquakes. Development of the techniques of the seismo-ionospheric anomalies identification was carried out in parallel with the development of the physical mechanism explaining these anomalies generation. It was established that the seismo-ionospheric anomalies have a self-similarity property, are dependent on the local time and are persistent at least for 4 hours, deviation from undisturbed level could be both positive and negative depending on the leading time (in days) to the moment of impending earthquake and from longitude of anomaly in relation to the epicenter longitude. Low latitude and near equatorial earthquakes demonstrate the magnetically conjugated effect, while the middle and high latitude earthquakes demonstrate the single anomaly over the earthquake preparation zone. From the anomalies morphology the physical mechanism was derived within the framework of the more complex Lithosphere-Atmosphere-Ionosphere-Magnetosphere Coupling concept. In addition to the multifactor analysis of the GPS TEC time series the GIM MAP technology was applied also clearly showing the seismo-ionospheric anomalies locality and their spatial size correspondence to the Dobrovolsky determination of the earthquake preparation zone radius. Application of ionospheric tomography techniques permitted to study not only the total electron content variations but also the modification of the vertical distribution of electron concentration in the ionosphere before earthquakes. The statistical check of the ionospheric precursors passed the Molchan diagram criteria, the most severe criteria used in seismology for precursor's verification.

78 FR 1835 - Hand Trucks and Certain Parts Thereof From the People's Republic of China: Preliminary Results of...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-09

... Integration (Xiamen) Co., Ltd. (New-Tec) were below normal value (NV). In addition, we are not rescinding this... November 30, 2011: Weighted- Manufacturer/exporter average margin (percent) New-Tec Integration (Xiamen) Co...

Observational evidence of predawn plasma bubble and its irregularity scales in Southeast Asia

NASA Astrophysics Data System (ADS)

Watthanasangmechai, K.; Tsunoda, R. T.; Yokoyama, T.; Ishii, M.; Tsugawa, T.

2016-12-01

This paper describes an event of deep plasma depletion simultaneously detected with GPS, GNU Radio Beacon Receiver (GRBR) and in situ satellite measurement from DMFPF15. The event is on March 7, 2012 at 4:30 LT with geomagnetic quiet condition. Such a sharp depletion at plasma bubble wall detected at predawn is interesting but apparently rare event. Only one event is found from all dataset in March 2012. The inside structure of the predawn plasma bubble was clearly captured by DMSPF15 and the ground-based GRBR. The envelop structure seen from the precessed GPS-TEC appeares as a cluster. The observed cluster is concluded as the structure at the westwall of an upwelling of the large-scale wave structure, that accompanies the fifty- and thousand-km scales. This event is consistent with the plasma bubble structure simulated from the high-resolution bubble (HIRB) model.

Multi-instrument observations of midlatitude summer nighttime anomaly from satellite and ground

NASA Astrophysics Data System (ADS)

Yamamoto, Mamoru; Thampi, Smitha V.; Liu, Huixin; Lin, Charles

"Midlatitude Summer Nighttime Anomaly (MSNA)" is a phenomenon that the nighttime elec-tron densities exceed the daytime values on almost all days in summer over latitudes of 33-34N of more. We recently found the MSNA over the northeast Asian region from multi-instrument observations. The observations include the tomography analysis based on the chain of digital beacon receivers at Shionomisaki (33.45N, 135.8E), Shigaraki (34.85N, 136.1E), and Fukui (36.06N,136E), the ionosonde network over Japan (especially data from Wakkanai (45.4N, 141.7E)), ground-based GPS TEC observations using the GEONET. Also from satellites, CHAMP in situ electron density measurements, and Formosat3/COSMIC (F3/C) occultation measurements are useful to confirm the presence of MSNA over this region. In the presen-tation we show detailed features of the MSNA based on these multi-instrument, and discuss importance of the neutral atmosphere as a driver of the phenomenon.

Meteorology and GNSS? What is the benefit?

NASA Astrophysics Data System (ADS)

Drummond, P.; Grünig, S.

2010-12-01

Due to the strong correlation between water vapor in the atmosphere and GNSS tropospheric propagation delays, we can estimate the Integrated Precipitable Water Vapor (IPWV) in the atmosphere through GNSS measurements. This parameter is crucial for meteorologists as the water content in the atmosphere is a key parameter in the weather models. The Total Electron Content (TEC) in the ionosphere has a huge impact on the ionospheric propagation delay in GNSS signals. By computing the ionospheric delay from GNSS measurements it is possible to predict the TEC which is an excellent indicator for ionospheric activity. The benefit is that we can estimate the influence on the RTK performance from TEC values. The atmospheric feature in the Trimble Atmosphere App (as well as in VRSNet software) allows computing both IPWV and TEC values from a CORS network. IPWV is computed using surface meteorological data such as temperature and pressure as well as radiosonde data. The results are shown in a table like form as well as in numerous graphical forms such as contour and surface plots, station and condition charts. The computed values can be animated in a movie over the last 24 hours.

Ionospheric response to the 17-18 March 2015 geomagnetic storm as seen from multiple TEC and NmF2 measurements along 100°E

NASA Astrophysics Data System (ADS)

Bhuyan, Pradip; Yokoyama, Tatsuhiro; Kalita, Bitap Raj; Seemala, G. K.; Hazarika, Rumajyoti; Komolmis, Tharadol; Yatini, Clara; Chakrabarty, Dibyendu; Supnithi, Pornchai

2016-07-01

The response of the ionosphere along 100°E to the strong geomagnetic storm of 17-18 March 2015 has been investigated combining TEC and NmF2 data from multiple stations spanning low latitudes in the northern and southern hemispheres to the equator. The GPS TEC data measured over Dibrugarh (27.4°N, 95°E), Kohima (25.6°N, 94.1°E) and Ahmedabad (23.0°N, 72.5°E) and NmF2 measured along a chain of ionosonde stations Dibrugarh (27.5°N, 95°E), Chiang Mai (18.76ºN, 98.93ºE), Chumphon (10.72ºN,99.37ºE), Kototabang (0.2ºS,100.32ºE) and Cocos Island (12.2ºS,96.8ºE ) were used to examine the signature of the storm around the low-mid latitude ionosphere in this sector. Nearly similar TEC variation has been observed over Dibrugarh and Kohima located at the northern edge of the EIA. The maximum TEC on 18 March over Dibrugarh and Kohima was reduced by more than ~80 TECU compared to that on the geomagnetically quiet day of 16 March 2015. In contrast to the substantial reduction in TEC over ~100°E TEC from the ~75°E longitude station Ahmedabad showed insignificant variations on the same day. Strong reduction in NmF2 at the crest of the anomaly in both northern and southern hemisphere (Dibrugarh, Ching Mai and Cocos Island) and enhancement near the equator (Cumphon and Kototbang) has been observed. The O/N2 ratio as obtained from the TIMED/GUVI reduced substantially along 100°E on 18 March compared to other longitude sectors. Equatorward meridional winds depleted the ionization at the crest region and enhanced the same near the equator. No L band scintillation was observed in the evening of 17 March at Dibrugarh and Kohima indicating absence of F region irregularity along this longitude while strong scintillations were observed at 75°E. The reversal of the IMF Bz from southward to northward direction in the dusk to evening sector inhibited the growth of the irregularity due to reversal of the PPEF at 100°E while the PPEF favoured generation and growth of Spread F at 75°E.

Multi-instrumental Analysis of the Ionospheric Density Response to Geomagnetic Disturbances

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Astafyeva, E.

2014-12-01

Measurements provided by Low Earth Orbit (LEO) satellite missions have already proved to be very efficient in investigations of global redistribution of ionospheric plasma and thermosphere mass density during such phenomena as geomagnetic storms. LEO satellites have various instruments for research of the ionosphere response to the space weather events like GPS receiver for precise orbit determination (POD), total electron content estimation and radio occultation, altimeter, planar Langmuir probe, topside sounder, special detectors for particle fluxes, magnetometer etc. In this paper, we present results of joint analysis of LEO satellite data, in particular CHAMP, DMSP, JASON, as well as data provided by ground-based networks of GPS receivers and ionosonde stations for global ionospheric response to the geomagnetic disturbances. We use in-situ plasma density data from CHAMP and DMSP satellites, along with data of GPS receiver onboard CHAMP-satellite and ground-based GPS-receivers to study occurrence and global distribution of ionospheric irregularities during the main phase of the storm. Using CHAMP GPS measurements, we created maps of GPS phase fluctuation activity and found two specific zones of the most intense irregularities - first is the region of the auroral oval at high latitudes of both hemispheres, the second one is the low-latitudes/equatorial region between Africa and South America. The interhemispheric asymmetry of the ionospheric irregularities intensity and occurrence in polar region is discussed. Analysis of the topside TEC, derived from CHAMP onboard GPS POD antenna, indicate the significant redistribution of the topside ionospheric plasma density in the equatorial, middle and high-latitude ionosphere during main and recovery phases of geomagnetic storm. Multi-instrumental data allow to analyze in detail the complex modification and dynamics of the upper atmosphere in different altitudinal, spatial and temporal scales.

TEC Variations Over Korean Peninsula During Magnetic Storm

NASA Astrophysics Data System (ADS)

Ji, E.-Y.; Choi, B.-K.; Kim, K.-H.; Lee, D.-H.; Cho, J.-H.; Chung, J.-K.; Park, J.-U.

2008-03-01

By analyzing the observations from a number of ground- and space-based instruments, including ionosonde, magnetometers, and ACE interplanetary data, we examine the response of the ionospheric TEC over Korea during 2003 magnetic storms. We found that the variation of vertical TEC is correlated with the southward turning of the interplanetary magnetic field B_z. It is suggested that the electric fields produced by the dynamo process in the high-latitude region and the prompt penetration in the low-latitude region are responsible for TEC increases. During the June 16 event, dayside TEC values increase more than 15%. And the ionospheric F2-layer peak height (hmF2) was ˜300km higher and the vertical E×B drift (estimated from ground-based magnetometer equatorial electrojet delta H) showed downward drift, which may be due to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high-latitude regions. In contr! ast, during November 20 event, the nightside TEC increases may be due to the prompt penetration westward electric field. The ionospheric F2-layer peak height was below 200km and the vertical E×B drift showed downward drift. Also, a strong correlation is observed between enhanced vertical TEC and enhanced interplanetary electric field. It is shown that, even though TEC increases are caused by the different processes, the electric field disturbances in the ionosphere play an important role in the variation of TEC over Korea.

Real-Time Three-Dimensional Echocardiography of the Left Ventricle-Pediatric Percentiles and Head-to-Head Comparison of Different Contour-Finding Algorithms: A Multicenter Study.

PubMed

Krell, Kristina; Laser, Kai Thorsten; Dalla-Pozza, Robert; Winkler, Christian; Hildebrandt, Ursula; Kececioglu, Deniz; Breuer, Johannes; Herberg, Ulrike

2018-03-28

Real-time three-dimensional echocardiography (RT3DE) is a promising method for accurate assessment of left ventricular (LV) volumes and function, however, pediatric reference values are scarce. The aim of the study was to establish pediatric percentiles in a large population and to compare the inherent influence of different evaluation software on the resulting measurements. In a multicenter prospective-design study, 497 healthy children (ages 1 day to 219 months) underwent RT3DE imaging of the LV (ie33, Philips, Andover, MA). Volume analysis was performed using QLab 9.0 (Philips) and TomTec 4DLV2.7 (vendor-independent; testing high (TomTec 75 ) and low (TomTec 30 ) contour-finding activity). Reference percentiles were computed using Cole's LMS method. In 22 subjects, cardiovascular magnetic resonance imaging (CMR) was used as the reference. A total of 370/497 (74.4%) of the subjects provided adequate data sets. LV volumes had a significant association with age, body size, and gender; therefore, sex-specific percentiles were indexed to body surface area. Intra- and interobserver variability for both workstations was good (relative bias ± SD for end-diastolic volume [EDV] in %: intraobserver: QLab = -0.8 ± 2.4; TomTec 30  = -0.7 ± 7.2; TomTec 75  = -1.9 ± 6.7; interobserver: QLab = 2.4 ± 7.5; TomTec 30  = 1.2 ± 5.1; TomTec 75  = 1.3 ± 4.5). Intervendor agreement between QLab and TomTec 30 showed larger bias and wider limits of agreement (bias: QLab vs TomTec 30 : end-systolic volume [ESV] = 0.8% ± 23.6%; EDV = -2.2% ± 17.0%) with notable individual differences in small children. QLab and TomTec underestimated CMR values, with the highest agreement between CMR and QLab. RT3DE allows reproducible noninvasive assessment of LV volumes and function. However, intertechnique variability is relevant. Therefore, our software-specific percentiles, based on a large pediatric population, serve as a reference for both commonly used quantification programs. Copyright © 2018 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

A pilot study comparing the use of Thiel- and formalin-embalmed cadavers in the teaching of human anatomy.

PubMed

Balta, Joy Y; Lamb, Clare; Soames, Roger W

2015-01-01

Formalin had traditionally been used to preserve human material to teach gross anatomy. In 2008 the Centre for Anatomy and Human Identification (CAHID) at the University of Dundee embarked on the use of the Thiel method of embalming. The aim of this pilot study was to assess the difference between formalin-embalmed cadavers (FEC) and Thiel-embalmed cadavers (TEC) used for teaching and surgical training. Three different questionnaires were prepared for data collection from undergraduate and postgraduate students and clinical staff. All undergraduate and postgraduate students as well as clinical staff commented on the appearance of the TEC. There was no overall consensus concerning the use of TEC, some respondents preferred TEC for the entire dissection, some only for certain areas such as the musculoskeletal system. On a technical level TEC were considered less hazardous then FEC by one-third of participants with fewer than 10% regarding TEC as more irritating than FEC. Psychologically, 32.7% of undergraduate students expressed the view that TEC made them feel more uncomfortable compared with FEC because of their life-like appearance. However, 57.1% of undergraduate students encountered the same uncomfortable feelings when viewing both TEC and FEC. The use of Thiel-embalmed cadavers to teach anatomy has an added value, though further research is required over longer periods of time to identify its best usage. © 2014 American Association of Anatomists.

An Adaptive Network-based Fuzzy Inference System for the detection of thermal and TEC anomalies around the time of the Varzeghan, Iran, (Mw = 6.4) earthquake of 11 August 2012

NASA Astrophysics Data System (ADS)

Akhoondzadeh, M.

2013-09-01

Anomaly detection is extremely important for forecasting the date, location and magnitude of an impending earthquake. In this paper, an Adaptive Network-based Fuzzy Inference System (ANFIS) has been proposed to detect the thermal and Total Electron Content (TEC) anomalies around the time of the Varzeghan, Iran, (Mw = 6.4) earthquake jolted in 11 August 2012 NW Iran. ANFIS is the famous hybrid neuro-fuzzy network for modeling the non-linear complex systems. In this study, also the detected thermal and TEC anomalies using the proposed method are compared to the results dealing with the observed anomalies by applying the classical and intelligent methods including Interquartile, Auto-Regressive Integrated Moving Average (ARIMA), Artificial Neural Network (ANN) and Support Vector Machine (SVM) methods. The duration of the dataset which is comprised from Aqua-MODIS Land Surface Temperature (LST) night-time snapshot images and also Global Ionospheric Maps (GIM), is 62 days. It can be shown that, if the difference between the predicted value using the ANFIS method and the observed value, exceeds the pre-defined threshold value, then the observed precursor value in the absence of non seismic effective parameters could be regarded as precursory anomaly. For two precursors of LST and TEC, the ANFIS method shows very good agreement with the other implemented classical and intelligent methods and this indicates that ANFIS is capable of detecting earthquake anomalies. The applied methods detected anomalous occurrences 1 and 2 days before the earthquake. This paper indicates that the detection of the thermal and TEC anomalies derive their credibility from the overall efficiencies and potentialities of the five integrated methods.

Incredibly distant ionospheric responses to earthquake

NASA Astrophysics Data System (ADS)

Yusupov, Kamil; Akchurin, Adel

2015-04-01

Attempts to observe ionospheric responses to the earthquake has been going on for decades. In recent years, the greatest progress in the study of this question have GPS-measurements with simultaneous HF-measurements. The use of a dense network of GPS-receivers and getting with it sufficiently detailed two-dimensional maps of the total electron content (TEC) greatly clarified the nature of the ionospheric response to strong earthquakes. For ionospheric responses observation, that are remote more than 1000 km from the strong earthquakes epicentres, it is necessary to applying more sensitive methods than GPS. The most experience in the observation of the ionospheric responses to earthquakes accumulated with Doppler sounding. Using these measurements, ionospheric disturbances characteristic features (signature) have been allocated, which associated with the passage of Rayleigh waves on the surface. Particular, this Rayleigh wave signatures allocation is implemented in the Nostradamus coherent backscatter radar. The authors of this method suggest using radar techniques like a sensitive "ionospheric seismometer." The most productive allocation and studying of the vertical structure ionospheric responses could be ionosonde observations. However, their typical 15 minute sounding rate is quite sufficient for observing the regular ionosphere, but it is not enough for studying the ionospheric responses to earthquakes, because ionospheric responses is often seen only in one ionogram and it is absent in adjacent. The decisive factor in establishing the striking ionospheric response to the earthquake was the Tohoku earthquake in 2011, when there was three ionosondes distant at 870-2000 km from the epicentre. These ionosondes simultaneously showed distortion of the F1-layer traces as its multiple stratification (multiple-cusp signature - MCS), which generated by Rayleigh wave. Note that there was another fourth Japanese ionosonde. It is located a little further near boundaries area of medium-scale wave (387 km), which ionograms showed F-spread rather than MCS. Obviously, this is due to the vertical structure of the disturbance in the near zone. Another interesting feature associated with the vertical structure is a 1-2 minute advance of the appearance MCS in ionograms in relation to the advent of large-scale TEC disturbance. Naturally, such appearance time comparison can only be in such distances, when there are large-scale TEC disturbances (<1000-1200 km). Only MCS and Doppler shifts are observing at large distances. Look-back analysis of Japanese ionograms showed only eight cases of ionogram MCS observation from 43 strongest earthquakes (magnitude> 8) during the period from 1957-2011. This indirectly explains why it had to wait 50 years to recognize the MCS as a response to the earthquake. Previously performed statistical analyses showed that the MCS appear mainly from 9 to 15 LT and the epicentre distances range is the 800-6000 km. The MCS signatures at distances removing from earthquake epicentre more than 6000 km seen in ionosondes in Kazan, Kaliningrad and Sodankyla. These MCS in Kazan (as well in Kaliningrad, in Sodankyla) observed during the daytime from 9 to 15 LT. At this time, the height electron concentration gradient is significantly reducing in the F1-layer. This leads to the fact that a small disturbance of this gradient distorts some area of electron density profile and it reduces the value of the local gradient to zero (or even negative) values. Observations in our ionosonde first showed that the ionospheric response to the strong earthquakes (magnitude more than 8) could be observing at distances more than 15,000 km. In the daytime such responses appearance distort the form of the electron density profile of the F-layer, which is appearing in the ionograms as a multiple trace stratification of F1-layer.

Ionospheric Irregularities Characterization by Ground and Space-based GPS Observations

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Cherniak, I.; Krankowski, A.

2017-12-01

We present new results on detection and investigation of the topside ionospheric irregularities using GPS measurements from Precise Orbit Determination (POD) GPS antenna onboard Low Earth Orbit satellites. Our investigation is based on the recent ESA's Swarm mission launched on 22 November 2013 and consisted of three identical satellites, two of them fly in a tandem at an orbit altitude of 460 km while the third satellite - at an orbit altitude of 510 km. Each satellite is equipped with a zenith-looking antenna and 8-channel dual-frequency GPS receiver that delivered 1 Hz data for POD purposes, as well as Langmuir Probe instrument for in situ electron density. Additionally, we have analyzed GPS measurements onboard GRACE and TerraSAR-X satellite, which have rather similar to Swarm orbit altitude of 500 km. GPS measurements onboard MetOP-A and MetOP-B satellites (altitude of 840 km) can complement these observations in order to estimate an altitudinal extent of the ionospheric irregularities penetrating to higher altitudes. We demonstrate that space-based GPS observations can be effectively used for monitoring of the topside ionospheric irregularities occurrence in both high-latitude and equatorial regions and may essentially contribute to the multi-instrumental analysis of the ground-based and in situ data. Climatological characteristics of the equatorial ionospheric irregularities occurrence probability are derived from POD GPS measurements for all longitudinal sectors for the years 2013-2016. Several examples of strong geomagnetic storms, including the 2015 St. Patrick's Day storm, were analyzed to demonstrate differences between the climatlogical characteristics in space-based GPS data and storm-induced equatorial irregularities observations (postsunset suppression, night/morning-time occurrence). To support our observations and conclusions, we involve into our analysis in situ plasma density provided by Swarm constellation, GRACE KBR, DMSP satellites, as well as ground-based GNSS and digisonde networks. New International GNSS Service (IGS) product - the Northern Hemisphere GPS-based ROTI (rate of the TEC index) maps - was analyzed to determine similarities and differences in ionospheric irregularities signatures in the ground and space-based GPS observations.

Remote Sensing of Ionosphere by IONOLAB Group

NASA Astrophysics Data System (ADS)

Arikan, Feza

2016-07-01

Ionosphere is a temporally and spatially varying, dispersive, anisotropic and inhomogeneous medium that is characterized primarily by its electron density distribution. Electron density is a complex function of spatial and temporal variations of solar, geomagnetic, and seismic activities. Ionosphere is the main source of error for navigation and positioning systems and satellite communication. Therefore, characterization and constant monitoring of variability of the ionosphere is of utmost importance for the performance improvement of these systems. Since ionospheric electron density is not a directly measurable quantity, an important derivable parameter is the Total Electron Content (TEC), which is used widely to characterize the ionosphere. TEC is proportional to the total number of electrons on a line crossing the atmosphere. IONOLAB is a research group is formed by Hacettepe University, Bilkent University and Kastamonu University, Turkey gathered to handle the challenges of the ionosphere using state-of-the-art remote sensing and signal processing techniques. IONOLAB group provides unique space weather services of IONOLAB-TEC, International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model based IRI-Plas-MAP, IRI-Plas-STEC and Online IRI-Plas-2015 model at www.ionolab.org. IONOLAB group has been working for imaging and monitoring of ionospheric structure for the last 15 years. TEC is estimated from dual frequency GPS receivers as IONOLAB-TEC using IONOLAB-BIAS. For high spatio-temporal resolution 2-D imaging or mapping, IONOLAB-MAP algorithm is developed that uses automated Universal Kriging or Ordinary Kriging in which the experimental semivariogram is fitted to Matern Function with Particle Swarm Optimization (PSO). For 3-D imaging of ionosphere and 1-D vertical profiles of electron density, state-of-the-art IRI-Plas model based IONOLAB-CIT algorithm is developed for regional reconstruction that employs Kalman Filters for state/temporal transition. IONOLAB group contributes to remote sensing of upper atmosphere, ionosphere and plasmasphere with continuing TUBITAK projects. IONOLAB group is open to joint research and collaboration with researchers from all disciplines that investigate the challenges of ionosphere and space weather. This study is supported by TUBITAK 114E541, 115E915 and Joint TUBITAK 114E092 and AS CR 14/001 projects.

Use of IRI to Model the Effect of Ionosphere Emission on Earth Remote Sensing at L-Band

NASA Technical Reports Server (NTRS)

Abraham, Saji; LeVine, David M.

2004-01-01

Microwave remote sensing in the window at 1.413 GHz (L-band) set aside for passive use only is important for monitoring sea surface salinity and soil moisture. These parameters are important for understanding ocean dynamics and energy exchange between the surface and atmosphere, and both NASA and ESA plan to launch satellite sensors to monitor these parameters at L-band (Aquarius, Hydros and SMOS). The ionosphere is an important source of error for passive remote sensing at this frequency. In addition to Faraday rotation, emission from the ionosphere is also a potential source of error at L-band. As an aid for correcting for emission, a regression model is presented that relates ionosphere emission to the integrated electron density (TEC). The goal is to use TEC from sources such as TOPEX, JASON or GPS to obtain estimates of emission over the oceans where the electron density profiles needed to compute emission are not available. In addition, data will also be presented to evaluate the use of the IRI for computing emission over the ocean.

Vodcasting Space Weather

NASA Astrophysics Data System (ADS)

Collins Petersen, Carolyn; Erickson, P. J.; Needles, M.

2009-01-01

The topic of space weather is the subject of a series of vodcasts (video podcasts) produced by MIT Haystack Observatory (Westford, MA) and Loch Ness Productions (Groton, MA). This paper discusses the production and distribution of the series via Webcast, Youtube, and other avenues. It also presents preliminary evaluation of the effectiveness and outreach of the project through feedback from both formal and information education venues. The vodcast series is linked to the NASA Living With a Star Targeted Research and Technology project award "Multi-Instrument Investigation of Inner-Magnetospheric/Ionosphere Disturbances.” It is being carried out by Principal Investigator Dr. John Foster, under the auspices of NASA Grant # NNX06AB86G. The research involves using ionospheric total electron content (TEC) observations to study the location, extent, and duration of perturbations within stormtime ionospheric electric fields at mid- to low latitudes. It combines ground-based global positioning system (GPS) TEC data, incoherent scatter radar measurements of the mid-latitude ionospheric state, and DMSP satellite observations to characterize conditions which lead to severe low-latitude ionospheric perturbations. Each vodcast episode covers a certain aspect of space weather and the research program.

Large-scale traveling ionospheric disturbances using ionospheric imaging at storm time: A case study on 17 march 2013

NASA Astrophysics Data System (ADS)

Tang, Jun; Yao, Yibin; Kong, Jian; Zhang, Liang

2016-07-01

A moderate geomagnetic storm occurred on March 17, 2013, during which large-scale traveling ionospheric disturbances (LSTIDs) are observed over China by ionosondes and GPS from Crustal Movement Observation Network of China (CMONOC) and the International GNSS Service (IGS). Ionosonde data and computerized ionospheric tomography (CIT) technique are employed to analyze the disturbances in our study. The maximum entropy cross spectral analysis (MECSA) method is used to obtain the propagation parameters of the LSTIDs. Spatio-temporal variations of ionospheric electron density (IED) and total electron content (TEC) during this geomagnetic storm over China are investigated. Disturbance images of IED and TEC are also presented in the paper. The results show two LSTID events at about 12:00 UT and 15:00 UT during the main phase of the storm. Besides, the LSTIDs with a duration of 40 min are detected over China. It is confirmed that the LSTIDs travel from north to south with a horizontal velocity of 400-500 m/s, and moved southwestwards with a horizontal velocity of 250-300 m/s, respectively.

Assessment of Ionospheric Anomaly Prior to the Large Earthquake: 2D and 3D Analysis in Space and Time for the 2011 Tohoku Earthquake (Mw9.0)

NASA Astrophysics Data System (ADS)

Hattori, Katsumi; Hirooka, Shinji; Han, Peng

2016-04-01

The ionospheric anomalies possibly associated with large earthquakes have been reported by many researchers. In this paper, Total Electron Content (TEC) and tomography analyses have been applied to investigate the spatial and temporal distributions of ionospheric electron density prior to the 2011 Off the Pacific Coast of Tohoku earthquake (Mw9.0). Results show significant TEC enhancements and an interesting three dimensional structure prior to the main shock. As for temporal TEC changes, the TEC value increases 3－4 days before the earthquake remarkably, when the geomagnetic condition was relatively quiet. In addition, the abnormal TEC enhancement area in space was stalled above Japan during the period. Tomographic results show that three dimensional distribution of electron density decreases around 250 km altitude above the epicenter (peak is located just the east-region of the epicenter) and increases the mostly entire region between 300 and 400 km.

Evaluating the performance of the Electron Density Assimilative Model (EDAM) in the Western European sector using modified Taylor diagrams

NASA Astrophysics Data System (ADS)

Jackson-Booth, N.; Parker, J.; Pryse, S. E.; Buckland, R.

2017-12-01

The Electron Density Assimilative Model (EDAM) is an ionospheric model that assimilates data sources into a background model, currently provided by IRI2007, to generate a global, or regional, 3D representation of the ionospheric electron density. In this study, slant total electron content (sTEC) between GPS satellites and 43 ground receivers in Europe were assimilated into EDAM to model the ionospheric electron density over western Europe. For the evaluation of the model an additional ground receiver (the truth station) was considered, which was not used in the assimilation process. Slant total electron contents for this station were calculated through the EDAM model along satellite-to-receiver paths corresponding to those of the observations made by the receiver. The modelled and observed sTEC were compared for each satellite and every day, between September 2002 and August 2003. For the comparison standard deviations of the modelled and observed sTEC were determined. These were used in modified Taylor Diagrams to display the mean-removed rms difference between the model and observations, the correlation between the two data sets and the bias of the modelled data. Taylor diagrams were obtained for the entire year, and each season and month. Results of the comparisons are presented and discussed, with a specific interest in times that show increased rms differences and decreased correlations between the data sets. The effect of the satellite calibration biases on the results are also considered.

Near Space Tracking of the EM Phenomena Associated with the Main Earthquakes

NASA Technical Reports Server (NTRS)

Ouzounov, Dimitar; Taylor, Patrick; Bryant, Nevin; Pulinets, Sergey; Liu, Jann-Yenq; Yang, Kwang-Su

2004-01-01

Searching for electromagnetic (EM) phenomena originating in the Earth's crust prior to major earthquakes (M>5) are the object of this exploratory study. We present the idea of a possible relationship between: (1) electro-chemical and thermodynamic processes in the Earth's crust and (2) ionic enhancement of the atmosphere/ionosphere with tectonic stress and earthquake activity. The major source of these signals are proposed to originate from electromagnetic phenomenon which are responsible for these observed pre-seismic processes, such as, enhanced IR emission, also born as thermal anomalies, generation of long wave radiation, light emission caused by ground-to-air electric discharges, Total Electron Content (TEC) ionospheric anomalies and ionospheric plasma variations. The source of these data will include: (i) ionospheric plasma perturbations data from the recently launched DEMETER mission and currently available TEC/GPS network data; (ii) geomagnetic data from ORSTED and CHAMP; (iii) Thermal infra-red (TIR) transients mapped by the polar orbiting (NOAA/AVHRR, MODIS) and (iv) geosynchronous weather satellites measurements of GOES, METEOSAT. This approach requires continues observations and data collecting, in addition to both ground and space based monitoring over selected regions in order to investigate the various techniques for recording possible anomalies. During the space campaign emphasis will be on IR emission, obtained from TIR (thermal infrared) satellites, that records land/sea surface temperature anomalies and changes in the plasma and total electron content (TEC) of the ionosphere that occur over areas of potential earthquake activity.

The Seismo-Generated Electric Field Probed by the Ionospheric Ion Velocity

NASA Astrophysics Data System (ADS)

(Tiger) Liu, Jann-Yenq

2017-04-01

The ion density, ion temperature, and the ion velocity probed by IPEI (ionospheric Plasma and Electrodynamics Instrument) onboard ROCSAT (i.e. FORMOSAT-1), and the global ionospheric map (GIM) of the total electron content (TEC) derived from measurements of ground-based GPS receivers are employed to study seismo-ionospheric precursors (SIPs) of the 31 March 2002 M6.8 Earthquake in Taiwan. The GIM TEC and ROCSAT/IPEI ion density significantly decrease specifically over the epicenter area 1-5 days before the earthquake, which suggests that the associated SIPs have observed. The ROCSAT/IPEI ion temperature reveals no significant changes before and after the earthquake, while the latitude-time-TEC plots extracted from the GIMs along the Taiwan longitude illustrate that the equatorial ionization anomaly significantly weakens and moves equatorward, which indicates that the daily dynamo electric field has been disturbed and cancelled by possible seismo-generated electric field on 2 days before (29 March) the earthquake. Here, for the first time a vector parameter of ion velocity is employed to study SIPs. It is found that ROCSAT/IPEI ion velocity becomes significantly downward, which confirms that a westward electric field of about 0.91mV/m generated during the earthquake preparation period being essential 1-5 days before the earthquake. Liu, J. Y., and C. K. Chao (2016), An observing system simulation experiment for FORMOSAT-5/AIP detecting seismo-ionospheric precursors, Terrestrial Atmospheric and Oceanic Sciences, DOI: 10.3319/TAO.2016.07.18.01(EOF5).

An alternative ionospheric correction model for global navigation satellite systems

NASA Astrophysics Data System (ADS)

Hoque, M. M.; Jakowski, N.

2015-04-01

The ionosphere is recognized as a major error source for single-frequency operations of global navigation satellite systems (GNSS). To enhance single-frequency operations the global positioning system (GPS) uses an ionospheric correction algorithm (ICA) driven by 8 coefficients broadcasted in the navigation message every 24 h. Similarly, the global navigation satellite system Galileo uses the electron density NeQuick model for ionospheric correction. The Galileo satellite vehicles (SVs) transmit 3 ionospheric correction coefficients as driver parameters of the NeQuick model. In the present work, we propose an alternative ionospheric correction algorithm called Neustrelitz TEC broadcast model NTCM-BC that is also applicable for global satellite navigation systems. Like the GPS ICA or Galileo NeQuick, the NTCM-BC can be optimized on a daily basis by utilizing GNSS data obtained at the previous day at monitor stations. To drive the NTCM-BC, 9 ionospheric correction coefficients need to be uploaded to the SVs for broadcasting in the navigation message. Our investigation using GPS data of about 200 worldwide ground stations shows that the 24-h-ahead prediction performance of the NTCM-BC is better than the GPS ICA and comparable to the Galileo NeQuick model. We have found that the 95 percentiles of the prediction error are about 16.1, 16.1 and 13.4 TECU for the GPS ICA, Galileo NeQuick and NTCM-BC, respectively, during a selected quiet ionospheric period, whereas the corresponding numbers are found about 40.5, 28.2 and 26.5 TECU during a selected geomagnetic perturbed period. However, in terms of complexity the NTCM-BC is easier to handle than the Galileo NeQuick and in this respect comparable to the GPS ICA.

New comparisons of ISR and RO data with the model IRI-Plas

NASA Astrophysics Data System (ADS)

Maltseva, Olga; Mozhaeva, Natalya; Zhbankov, Gennadii

2012-07-01

Space Weather events lead to strong changes in peak parameters of the ionosphere. These parameters, foF2 and hmF2, define the N(h)-profile, which is known to include bottom side and topside parts. Numerous studies have shown that adaptation of the IRI model to the experimental values of foF2 and hmF2 gave a good agreement between experimental and model N(h)-profiles of the bottom side ionosphere. This is not about the topside N(h)-profile. To improve the situation measurements of the total electron content TEC are involved. This work is devoted to the use of peak parameters with the TEC during Space Weather events for the evaluation of propagation conditions in both the bottom side and the topside ionosphere, based on the model IRI-Plas. To assess how well the model N(h)-profile matches the experimental one, the model IRI-Plas is tested according to the Incoherent Scatter Radars and the Radio Occultation measurements in various parts of the globe and at different levels of solar activity. The experimental N(h)-profiles are compared with profiles for the original model, the model adapted to the foF2 and hmF2, and for a model with full adaptation (including the TEC). The best fit is obtained in the European region, so the SW variations of peak parameters and N(h)-profiles are studied on the example of the European area. The IRI-Plas model allows to estimate the relative contributions of each region (bottom side BOT, topside TOP and plasmaspheric PL parts) in the value of the TEC. As the analysis of two W- and Wp-indexes (Gulyaeva, 2008; Gulyaeva and Stanislawska, 2008) is shown, TEC-storms occur in 2 times more likely than foF2-storms. This testifies that the variations of parts BOT, TOP and PL in the TEC are different. It determines different variations of N(h)-profiles. Results are given for several types of SW-events, in particular, for the strong positive and negative disturbances, when the variations of TEC and foF2 are of the same sign and the corresponding perturbation covers all regions of the ionosphere. Particular attention is paid to variations of peak parameters and N(h)-profiles during weak and moderate disturbances and bursts of TEC in long period of low activity, when the TEC and foF2 variations and variations of different parts of TEC are in the opposite phase.

Empirical model of TEC response to geomagnetic and solar forcing over Balkan Peninsula

NASA Astrophysics Data System (ADS)

Mukhtarov, P.; Andonov, B.; Pancheva, D.

2018-01-01

An empirical total electron content (TEC) model response to external forcing over Balkan Peninsula (35°N-50°N; 15°E-30°E) is built by using the Center for Orbit Determination of Europe (CODE) TEC data for full 17 years, January 1999 - December 2015. The external forcing includes geomagnetic activity described by the Kp-index and solar activity described by the solar radio flux F10.7. The model describes the most probable spatial distribution and temporal variability of the externally forced TEC anomalies assuming that they depend mainly on latitude, Kp-index, F10.7 and LT. The anomalies are expressed by the relative deviation of the TEC from its 15-day mean, rTEC, as the mean value is calculated from the 15 preceding days. The approach for building this regional model is similar to that of the global TEC model reported by Mukhtarov et al. (2013a) however it includes two important improvements related to short-term variability of the solar activity and amended geomagnetic forcing by using a "modified" Kp index. The quality assessment of the new constructing model procedure in terms of modeling error calculated for the period of 1999-2015 indicates significant improvement in accordance with the global TEC model (Mukhtarov et al., 2013a). The short-term prediction capabilities of the model based on the error calculations for 2016 are improved as well. In order to demonstrate how the model is able to reproduce the rTEC response to external forcing three geomagnetic storms, accompanied also with short-term solar activity variations, which occur at different seasons and solar activity conditions are presented.

Short-term estimation of GNSS TEC using a neural network model in Brazil

NASA Astrophysics Data System (ADS)

Ferreira, Arthur Amaral; Borges, Renato Alves; Paparini, Claudia; Ciraolo, Luigi; Radicella, Sandro M.

2017-10-01

This work presents a novel Neural Network (NN) model to estimate Total Electron Content (TEC) from Global Navigation Satellite Systems (GNSS) measurements in three distinct sectors in Brazil. The purpose of this work is to start the investigations on the development of a regional model that can be used to determine the vertical TEC over Brazil, aiming future applications on a near real-time frame estimations and short-term forecasting. The NN is used to estimate the GNSS TEC values at void locations, where no dual-frequency GNSS receiver that may be used as a source of data to GNSS TEC estimation is available. This approach is particularly useful for GNSS single-frequency users that rely on corrections of ionospheric range errors by TEC models. GNSS data from the first GLONASS network for research and development (GLONASS R&D network) installed in Latin America, and from the Brazilian Network for Continuous Monitoring of the GNSS (RMBC) were used on TEC calibration. The input parameters of the NN model are based on features known to influence TEC values, such as geographic location of the GNSS receiver, magnetic activity, seasonal and diurnal variations, and solar activity. Data from two ten-days periods (from DoY 154 to 163 and from 282 to 291) are used to train the network. Three distinct analyses have been carried out in order to assess time-varying and spatial performance of the model. At the spatial performance analysis, for each region, a set of stations is chosen to provide training data to the NN, and after the training procedure, the NN is used to estimate vTEC behavior for the test station which data were not presented to the NN in training process. An analysis is done by comparing, for each testing station, the estimated NN vTEC delivered by the NN and reference calibrated vTEC. Also, as a second analysis, the network ability to forecast one day after the time interval (DoY 292) based on information of the second period of investigation is also assessed in order to verify the feasibility on using low amount of data for short-term forecasting. In a third analysis, the spatial performance of the NN model is assessed and compared against CODE Global Ionospheric Maps during the geomagnetic storm registered on 13th and 14th October 2016. The results obtained from the three described analyses indicate that even using a ten-days period of data to train the network, the proposed NN model provides good spatial performance and presents to be a promising tool for short-term forecasting. The results obtained in the analysis presented a root mean squared error less than 7.9 TECU in all scenarios under investigation.

Ionospheric Response during the Equinox and the Solstice Periods over Turkey

NASA Astrophysics Data System (ADS)

Cinar, Ali; Arikan, Feza; Karatay, Secil

2016-07-01

Ionosphere is a layer of the atmosphere which is an integral part of whole geomagnetic and geological framework. Ionosphere responds to solar EUV radiation by varying within the diurnal 24-hour period, seasonal periods and annually and over the 11-year cycle of solar activity. Therefore, relying on the evidence that there have been variations observed in the VLF, LF and HF signals, magnetic field of the earth and in the local electric field, a unified theory, that would explain the mechanism and cause of the disturbance in the layers of atmosphere, is a widely investigated research topic. In this study, the behavior of the IONOLAB- Total Electron Content (TEC) estimates obtained from dual frequency ground-based GPS receivers are examined using Symmetric Kullback Leibler Distance (SKLD) and L2 Norm (L2N) methods both for the periods that include the equinox and solstice between 2010 and 2012 for Turkey. The solstice and equinox periods within the same year and the solstice periods and the equinox periods from 2010 to 2012 are compared with each other for 18 Turkish National Permanent GPS Network (TNPGN-Active) stations. It is observed that the difference between solstice and equinox periods increases related to the upgrading geomagnetic activity. SKLD and L2N values in the solstice are larger than those in the equinox. This study is supported by TUBITAK EEEAG 114E541 a part of the Scientific and Technological Research Projects Funding Program.

Support vector machines for TEC seismo-ionospheric anomalies detection

NASA Astrophysics Data System (ADS)

Akhoondzadeh, M.

2013-02-01

Using time series prediction methods, it is possible to pursue the behaviors of earthquake precursors in the future and to announce early warnings when the differences between the predicted value and the observed value exceed the predefined threshold value. Support Vector Machines (SVMs) are widely used due to their many advantages for classification and regression tasks. This study is concerned with investigating the Total Electron Content (TEC) time series by using a SVM to detect seismo-ionospheric anomalous variations induced by the three powerful earthquakes of Tohoku (11 March 2011), Haiti (12 January 2010) and Samoa (29 September 2009). The duration of TEC time series dataset is 49, 46 and 71 days, for Tohoku, Haiti and Samoa earthquakes, respectively, with each at time resolution of 2 h. In the case of Tohoku earthquake, the results show that the difference between the predicted value obtained from the SVM method and the observed value reaches the maximum value (i.e., 129.31 TECU) at earthquake time in a period of high geomagnetic activities. The SVM method detected a considerable number of anomalous occurrences 1 and 2 days prior to the Haiti earthquake and also 1 and 5 days before the Samoa earthquake in a period of low geomagnetic activities. In order to show that the method is acting sensibly with regard to the results extracted during nonevent and event TEC data, i.e., to perform some null-hypothesis tests in which the methods would also be calibrated, the same period of data from the previous year of the Samoa earthquake date has been taken into the account. Further to this, in this study, the detected TEC anomalies using the SVM method were compared to the previous results (Akhoondzadeh and Saradjian, 2011; Akhoondzadeh, 2012) obtained from the mean, median, wavelet and Kalman filter methods. The SVM detected anomalies are similar to those detected using the previous methods. It can be concluded that SVM can be a suitable learning method to detect the novelty changes of a nonlinear time series such as variations of earthquake precursors.

Atmosphere-ionosphere coupling from convectively generated gravity waves

NASA Astrophysics Data System (ADS)

Azeem, Irfan; Barlage, Michael

2018-04-01

Ionospheric variability impacts operational performances of a variety of technological systems, such as HF communication, Global Positioning System (GPS) navigation, and radar surveillance. The ionosphere is not only perturbed by geomagnetic inputs but is also influenced by atmospheric tides and other wave disturbances propagating from the troposphere to high altitudes. Atmospheric Gravity Waves (AGWs) excited by meteorological sources are one of the largest sources of mesoscale variability in the ionosphere. In this paper, Total Electron Content (TEC) data from networks of GPS receivers in the United States are analyzed to investigate AGWs in the ionosphere generated by convective thunderstorms. Two case studies of convectively generated gravity waves are presented. On April 4, 2014 two distinct large convective systems in Texas and Arkansas generated two sets of concentric AGWs that were observed in the ionosphere as Traveling Ionospheric Disturbances (TIDs). The period of the observed TIDs was 20.8 min, the horizontal wavelength was 182.4 km, and the horizontal phase speed was 146.4 m/s. The second case study shows TIDs generated from an extended squall line on December 23, 2015 stretching from the Gulf of Mexico to the Great Lakes in North America. Unlike the concentric wave features seen in the first case study, the extended squall line generated TIDs, which exhibited almost plane-parallel phase fronts. The TID period was 20.1 min, its horizontal wavelength was 209.6 km, and the horizontal phase speed was 180.1 m/s. The AGWs generated by both of these meteorological events have large vertical wavelength (>100 km), which are larger than the F2 layer thickness, thus allowing them to be discernible in the TEC dataset.

Radon observations as an integrated part of the multi parameter approach to study pre-earthquake processes

NASA Astrophysics Data System (ADS)

Ouzounov, Dimitar; Pulinets, Sergey; Lee, Lou; Giuliani, Guachino; Fu, Ching-Chou; Liu, Tiger; Hattori, Katsumi

2017-04-01

This work is part of international project to study the complex chain of interactions Lithosphere - Atmosphere -Ionosphere (LAI) in presence of ionization in atmosphere loaded by radon and other gases and is supported by International Space Science Institute (ISSI) in Bern and Beijing. We are presenting experimental measurements and theoretical estimates showing that radon measurements recorded before large earthquake are correlated with release of the heat flux in atmosphere during ionization of the atmospheric boundary layer .The recorded anomalous heat (observed by the remote sounding -infrared radiometers installed on satellites) are followed also by ionospheric anomalies (observed by GPS/TEC, ionosonde or satellite instruments). As ground proof we are using radon measurements installed and coordinated in four different seismic active regions California, Taiwan, Italy and Japan. Radon measurements are performed indirectly by means of gamma ray spectrometry of its radioactive progenies 214Pb and 214Bi (emitted at 351 keV and 609 keV, respectively) and also by Alfa detectors. We present data of five physical parameters- radon, seismicity, temperature of the atmosphere boundary layer, outgoing earth infrared radiation and GPS/TEC and their temporal and spatial variations several days before the onset of the following recent earthquakes: (1) 2016 M6.6 in California; (2) 2016 Amatrice-Norcia (Central Italy), (3) 2016 M6.4 of Feb 06 in Taiwan and (4) 2016 M7.0 of Nov 21 in Japan. Our preliminary results of simultaneous analysis of radon and space measurements in California, Italy, Taiwan and Japan suggests that pre-earthquake phase follows a general temporal-spatial evolution pattern in which radon plays a critical role in understanding the LAI coupling. This pattern could be reviled only with multi instruments observations and been seen and in other large earthquakes worldwide.

Analysis of Total Electron Content and Electron Density Profile during Different Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Chapagain, N. P.; Rana, B.; Adhikari, B.

2017-12-01

Total Electron content (TEC) and electron density are the key parameters in the mitigation of ionospheric effects on radio communication system. Detail study of the TEC and electron density variations has been carried out during geomagnetic storms, with longitude and latitude, for four different locations: (13˚N -17˚N, 88˚E -98˚E), (30˚N-50˚N, 120˚W -95˚W), (29˚S-26˚S, 167˚W-163˚W,) and (60˚S-45˚S, 120˚W-105˚W) using the Gravity Recovery and Climate Experiment (GRACE) satellite observations. In order to find the geomagnetic activity, the solar wind parameters such as north-south component of inter planetary magnetic field (Bz), plasma drift velocity (Vsw), flow pressure (nPa), AE, Dst and Kp indices were obtained from Operating Mission as Nodes on the Internet (OMNI) web system. The data for geomagnetic indices have been correlated with the TEC and electron density for four different events of geomagnetic storms on 6 April 2008, 27 March 2008, 4 September 2008, and 11 October 2008. The result illustrates that the observed TEC and electron density profile significantly vary with longitudes and latitudes. This study illustrates that the values of TEC and the vertical electron density profile are influenced by the solar wind parameters associated with solar activities. The peak values of electron density and TEC increase as the geomagnetic storms become stronger. Similarly, the electron density profile varies with altitudes, which peaks around the altitude range of about 250- 350 km, depending on the strength of geomagnetic storms. The results clearly show that the peak electron density shifted to higher altitude (from about 250 km to 350 km) as the geomagnetic disturbances becomes stronger.

Performance evaluation of GIM-TEC assimilation of the IRI-Plas model at two equatorial stations in the American sector

NASA Astrophysics Data System (ADS)

Adebiyi, S. J.; Adebesin, B. O.; Ikubanni, S. O.; Joshua, B. W.

2017-05-01

Empirical models of the ionosphere, such as the International Reference Ionosphere (IRI) model, play a vital role in evaluating the environmental effect on the operation of space-based communication and navigation technologies. The IRI extended to Plasmasphere (IRI-Plas) model can be adjusted with external data to update its electron density profile while still maintaining the overall integrity of the model representations. In this paper, the performance of the total electron content (TEC) assimilation option of the IRI-Plas at two equatorial stations, Jicamarca, Peru (geographic: 12°S, 77°W, dip angle 0.8°) and Cachoeira Paulista, Brazil (Geographic: 22.7°S, 45°W, dip angle -26°), is examined during quiet and disturbed conditions. TEC, F2 layer critical frequency (foF2), and peak height (hmF2) predicted when the model is operated without external input were used as a baseline in our model evaluation. Results indicate that TEC predicted by the assimilation option generally produced smaller estimation errors compared to the "no extra input" option during quiet and disturbed conditions. Generally, the error is smaller at the equatorial trough than near the crest for both quiet and disturbed days. With assimilation option, there is a substantial improvement of storm time estimations when compared with quiet time predictions. The improvement is, however, independent on storm's severity. Furthermore, the modeled foF2 and hmF2 are generally poor with TEC assimilation, particularly the hmF2 prediction, at the two locations during both quiet and disturbed conditions. Consequently, IRI-Plas model assimilated with TEC value only may not be sufficient where more realistic instantaneous values of peak parameters are required.

Regional application of multi-layer artificial neural networks in 3-D ionosphere tomography

NASA Astrophysics Data System (ADS)

Ghaffari Razin, Mir Reza; Voosoghi, Behzad

2016-08-01

Tomography is a very cost-effective method to study physical properties of the ionosphere. In this paper, residual minimization training neural network (RMTNN) is used in voxel-based tomography to reconstruct of 3-D ionosphere electron density with high spatial resolution. For numerical experiments, observations collected at 37 GPS stations from Iranian permanent GPS network (IPGN) are used. A smoothed TEC approach was used for absolute STEC recovery. To improve the vertical resolution, empirical orthogonal functions (EOFs) obtained from international reference ionosphere 2012 (IRI-2012) used as object function in training neural network. Ionosonde observations is used for validate reliability of the proposed method. Minimum relative error for RMTNN is 1.64% and maximum relative error is 15.61%. Also root mean square error (RMSE) of 0.17 × 1011 (electrons/m3) is computed for RMTNN which is less than RMSE of IRI2012. The results show that RMTNN has higher accuracy and compiles speed than other ionosphere reconstruction methods.

The Relationship between Ionospheric Slab Thickness and the Peak Density Height, hmF2

NASA Astrophysics Data System (ADS)

Meehan, J.; Sojka, J. J.

2017-12-01

The electron density profile is one of the most critical elements in the ionospheric modeling-related applications today. Ionosphere parameters, hmF2, the height of the peak density layer, and slab thickness, the ratio of the total electron content, TEC, to the peak density value, NmF2, are generally obtained from any global sounding observation network and are easily incorporated into models, theoretical or empirical, as numerical representations. Slab thickness is a convenient one-parameter summary of the electron density profile and can relate a variety of elements of interest that effect the overall electron profile shape, such as the neutral and ionospheric temperatures and gradients, the ionospheric composition, and dynamics. Using ISR data from the 2002 Millstone Hill ISR data campaign, we found, for the first time, slab thickness to be correlated to hmF2. For this, we introduce a new ionospheric index, k, which ultimately relates electron density parameters and can be a very useful tool for describing the topside ionosphere shape. Our study is an initial one location, one season, 30-day study, and future work is needed to verify the robustness of our claim. Generally, the ionospheric profile shape, requires knowledge of several ionospheric parameters: electron, ion and neutral temperatures, ion composition, electric fields, and neutral winds, and is dependent upon seasons, local time, location, and the level of solar and geomagnetic activity; however, with this new index, only readily-available, ionospheric density information is needed. Such information, as used in this study, is obtained from a bottomside electron density profile provided by an ionosonde, and TEC data provided by a local, collocated GPS receiver.

Behavior of ionospheric total electron content over Ankara. Final report, 1 January 1975--31 December 1977

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tulunay, Y.K.

1977-12-31

Total Electron Content (TEC) was determined between October, 1975 and August, 1976 from measurements of the Faraday rotation of a plane polarized wave transmitted at 140 MHz from the geostationary satellite ATS 6, located at approximately 35 deg E over the equator. The computed results are presented as diurnal variations for single days and monthly means. Maximum daytime TEC values were observed in April (about 20 x 10/sup 16/ el/sq m) and minimum in January (about 9 x 10/sup 16/ el/sq m); maximum night-time values were observed in January and February (about 3 x 10/sup 16/ el/sq m). The responsemore » of TEC to the high magnetic activity associated with substorms was found to depend greatly on the time of day when the storm occurred.« less

Time series of GNSS-derived ionospheric maps to detect anomalies as possible precursors of high magnitude earthquakes

NASA Astrophysics Data System (ADS)

Barbarella, M.; De Giglio, M.; Galeandro, A.; Mancini, F.

2012-04-01

The modification of some atmospheric physical properties prior to a high magnitude earthquake has been recently debated within the Lithosphere-Atmosphere-Ionosphere (LAI) Coupling model. Among this variety of phenomena the ionization of air at the higher level of the atmosphere, called ionosphere, is investigated in this work. Such a ionization occurrences could be caused by possible leaking of gases from earth crust and their presence was detected around the time of high magnitude earthquakes by several authors. However, the spatial scale and temporal domain over which such a disturbances come into evidence is still a controversial item. Even thought the ionospheric activity could be investigated by different methodologies (satellite or terrestrial measurements), we selected the production of ionospheric maps by the analysis of GNSS (Global Navigation Satellite Data) data as possible way to detect anomalies prior of a seismic event over a wide area around the epicentre. It is well known that, in the GNSS sciences, the ionospheric activity could be probed by the analysis of refraction phenomena occurred on the dual frequency signals along the satellite to receiver path. The analysis of refraction phenomena affecting data acquired by the GNSS permanent trackers is able to produce daily to hourly maps representing the spatial distribution of the ionospheric Total Electron Content (TEC) as an index of the ionization degree in the upper atmosphere. The presence of large ionospheric anomalies could be therefore interpreted in the LAI Coupling model like a precursor signal of a strong earthquake, especially when the appearance of other different precursors (thermal anomalies and/or gas fluxes) could be detected. In this work, a six-month long series of ionospheric maps produced from GNSS data collected by a network of 49 GPS permanent stations distributed within an area around the city of L'Aquila (Abruzzi, Italy), where an earthquake (M = 6.3) occurred on April 6, 2009, were investigated. Basically, the proposed methodology is able to perform a time series analysis of the TEC maps and, eventually, define the spatial and temporal domains of ionospheric disturbances. This goal was achieved by a time series analysis of the spatial dataset able to compare a local pattern of ionospheric activity with its historical mean value and detect areas where the TEC content exhibits anomalous values. This data processing shows some 1 to 2 days long anomalies about 20 days before of the seismic event (confirming also results provided in recent studies by means of ionospheric soundings).

Long-term trends in the total electron content (TEC)

NASA Astrophysics Data System (ADS)

Laštovička, Jan

2017-04-01

The long-term trends in the total electron content (TEC) have very little been studied. Lean et al. (2011; J. Geophys. Res., 116, A00H04, doi:10.1029/2010JA016378) studied trends in TEC globally based on JPL maps for 1995-2010. However, their trends appear to be too positive, which is not plausible taking into account the trends in other ionospheric parameters. Therefore they prefer the less positive trends calculated under the assumption of the same level of solar activity in solar cycle minima 22/23 and 23/24. However, as it is now clear, this is not a correct assumption. Lastovicka (2013; J. Geophys. Res. Space Phys., 118, 3831-3835, doi:10.1002/jgra.50261) selected a region around Florence, Italy, as a region with available historical TEC data based on Faraday rotation measurements and remarkably larger than average trends in TEC by Lean et al. (2011). Historical data from Florence provide no trend in TEC. However, foF2 from Juliusruh provide slight negative trends for 1976-1996 but no trends for 1995-2010. Thus the question of reality of trends by Lean et al. (2011) remained open. Here we use TEC from GIM and JPL data for two European regions with high Lean's trends, regions around Florence and around Prague, using 10-14 LT medians, 1998-2015, yearly average values. A classical approach is applied. First a model of solar activity dependence of TEC is constructed separately for each region from all data. Then model data are subtracted from experimental data and analysis is made with residuals. This analysis shows that early data (1998-2001) are by several TECU lower than they should be according to solar activity, the year 2002 is intermediate and in 2003-2015 the data fit well a weak or rather no trend of TEC. The change in TEC data does not seem to be jump-like, it lasted at least a year, if not longer. Thus the positive TEC trends reported by Lean et al. (2011) appear to be affected by data problem; real trends are evidently less positive if any.

Multi-sensor Integration of Space and Ground Observations of Pre-earthquake Anomalies Associated with M6.0, August 24, 2014 Napa, California

NASA Astrophysics Data System (ADS)

Ouzounov, Dimitar; Tramutoli, Valerio; Pulinets, Sergey; Liu, Tiger; Filizzola, Carolina; Genzano, Nicola; Lisi, Mariano; Petrov, Leonid; Kafatos, Menas

2015-04-01

We integrate multiple space-born and ground sensors for monitoring pre-earthquake geophysical anomalies that can provide significant early notification for earthquakes higher than M5.5 worldwide. The latest M6.0 event of August 24, 2014 in South Napa, California generated pre-earthquake signatures during our outgoing tests for California, and an experimental warning was documented about 17 days in advance. We process in controlled environment different satellite and ground data for California (and several other test areas) by using: a) data from the NPOES sensors recording OLR (Outgoing Longwave Radiation) in the infrared; b) 2/GNSS, FORMOSAT (GPS/TEC); c) Earth Observing System assimilation models from NASA; d) ground-based gas observations and meteorological data; e) TIR (Thermal Infrared) data from geostationary satellite (GOES). On Aug 4th, we detected (prospectively) a large anomaly of OLR transient field at the TOA over Northern California. The location was shifted in the northeast direction about 150 km from the Aug 23rd epicentral area. Compared to the reference field of August 2004 to 2014 the hotspot anomaly was the largest energy flux anomaly over the entire continental United States at this time. Based on the temporal and spatial estimates of the anomaly, on August 4th we issued an internal warning for a M5.5+ earthquake in Northern California within the next 1-4 weeks. TIR retrospective analysis showed significant (spatially extended and temporally persistent) sequences of TIR anomalies starting August 1st just in the future epicenter area and approximately in the same area affected by OLR anomalies in the following days. GPS/TEC retrospective analysis based on GIM and TGIM products show anomalies TEC variations 1-3 days, over region north form the Napa earthquake epicenter. The calculated index of atmospheric chemical potential based on the NASA numerical Assimilation weather model GEOS5 indicates for abnormal variations near the epicentral area days before the quake; Our real-time and post-event integration of several atmospheric parameters from satellite and ground observations during the M6.0 on 08.24.2014 in Napa California demonstrated the synergy of related variations of these parameters implying their connection with the earthquake preparation process.

Empirical forecast of quiet time ionospheric Total Electron Content maps over Europe

NASA Astrophysics Data System (ADS)

Badeke, Ronny; Borries, Claudia; Hoque, Mainul M.; Minkwitz, David

2018-06-01

An accurate forecast of the atmospheric Total Electron Content (TEC) is helpful to investigate space weather influences on the ionosphere and technical applications like satellite-receiver radio links. The purpose of this work is to compare four empirical methods for a 24-h forecast of vertical TEC maps over Europe under geomagnetically quiet conditions. TEC map data are obtained from the Space Weather Application Center Ionosphere (SWACI) and the Universitat Politècnica de Catalunya (UPC). The time-series methods Standard Persistence Model (SPM), a 27 day median model (MediMod) and a Fourier Series Expansion are compared to maps for the entire year of 2015. As a representative of the climatological coefficient models the forecast performance of the Global Neustrelitz TEC model (NTCM-GL) is also investigated. Time periods of magnetic storms, which are identified with the Dst index, are excluded from the validation. By calculating the TEC values with the most recent maps, the time-series methods perform slightly better than the coefficient model NTCM-GL. The benefit of NTCM-GL is its independence on observational TEC data. Amongst the time-series methods mentioned, MediMod delivers the best overall performance regarding accuracy and data gap handling. Quiet-time SWACI maps can be forecasted accurately and in real-time by the MediMod time-series approach.

Stormtime Simulations of Sub-Auroral Polarization Streams (SAPS)

NASA Astrophysics Data System (ADS)

Huba, J.; Sazykin, S. Y.; Coster, A. J.

2017-12-01

We present simulation results from the self-consistently coupled SAMI3/RCM code on the impact of geomagnetic storms on the ionosphere/plasmasphere system with an emphasis on the development of sub-auroral plasma streams (SAPS). We consider the following storm events: March 31, 2001, March 17, 2013, March 17, 2015, September 3, 2012, and June 23, 2015. We compare and contrast the development of SAPS for these storms. The main results are the development of sub-auroral (< 60 degrees) low-density, high-speed flows (1 - 2 km/s). Additionally, we discuss the impact on plasmaspheric dynamics. We compare our model results to data (e.g., Millstone Hill radar, GPS TEC).

Ionospheric Anomalies of the 2011 Tohoku Earthquake with Multiple Observations during Magnetic Storm Phase

NASA Astrophysics Data System (ADS)

Liu, Yang

2017-04-01

Ionospheric anomalies linked with devastating earthquakes have been widely investigated by scientists. It was confirmed that GNSS TECs suffered from drastically increase or decrease in some diurnal periods prior to the earthquakes. Liu et al (2008) applied a TECs anomaly calculation method to analyze M>=5.9 earthquakes in Indonesia and found TECs decadence within 2-7 days prior to the earthquakes. Nevertheless, strong TECs enhancement was observed before M8.0 Wenchuan earthquake (Zhao et al 2008). Moreover, the ionospheric plasma critical frequency (foF2) has been found diminished before big earthquakes (Pulinets et al 1998; Liu et al 2006). But little has been done regarding ionospheric irregularities and its association with earthquake. Still it is difficult to understand real mechanism between ionospheric anomalies activities and its precursor for the huge earthquakes. The M9.0 Tohoku earthquake, happened on 11 March 2011, at 05:46 UT time, was recognized as one of the most dominant events in related research field (Liu et al 2011). A median geomagnetic disturbance also occurred accompanied with the earthquake, which makes the ionospheric anomalies activities more sophisticated to study. Seismic-ionospheric disturbance was observed due to the drastic activities of earth. To further address the phenomenon, this paper investigates different categories of ionospheric anomalies induced by seismology activity, with multiple data sources. Several GNSS ground data were chosen along epicenter from IGS stations, to discuss the spatial-temporal correlations of ionospheric TECs in regard to the distance of epicenter. We also apply GIM TEC maps due to its global coverage to find diurnal differences of ionospheric anomalies compared with geomagnetic quiet day in the same month. The results in accordance with Liu's conclusions that TECs depletion occurred at days quite near the earthquake day, however the variation of TECs has special regulation contrast to the normal quiet days. Associated with geomagnetic storm at similar time, radio occultation data provided by COSMIC were deeply investigated within the whole month. It's quite different that the storm or earthquake didn't trigger scintillation burst. This is probably due to the storm occurrence local time was in noon sector, which has little impact on ionospheric irregularities increase, but help to enhance the effect of westward electricity, which on the other hand diminishes scintillation bubbles (Li et al 2008). A small geomagnetic disturbance was also found almost a week prior to the earthquake, the relationship of this event to the major earthquake is worth further discussion. Similar analysis of GNSS TECs have been done, the results indicated that it can be also referred as precursor to the major earthquake. Li G, Ning B, Zhao B, et al. Effects of geomagnetic storm on GPS ionospheric scintillations at Sanya[J]. Journal of Atmospheric and Solar-Terrestrial Physics, 2008, 70(7):1034-1045. Liu J Y, Chen Y I, Chuo Y J, et al. A statistical investigation of pre-earthquake ionospheric anomaly[J]. Journal of Geophysical Research Atmospheres, 2006, 111(A5). Liu J Y, Sun Y Y. Seismo-traveling ionospheric disturbances of ionograms observed during the 2011 Mw 9.0 Tohoku Earthquake[J]. Earth, Planets and Space, 2011, 63(7):897-902. Zhao B, Wang M, Yu T, et al. Is an unusual large enhancement of ionospheric electron density linked with the 2008 great Wenchuan earthquake?[J]. Journal of Geophysical Research Atmospheres, 2008, 113(A11):A11304. Pulinets S A. Seismic activity as a source of the ionospheric variability [J]. Advances in Space Research, 1998, 22(6):903-906.

Peculiarities of the ionospheric disturbances in the East-Asian region during geoactive periods on November 2004

NASA Astrophysics Data System (ADS)

Voeikov, S. V.; Zherebtsov, G. A.; Polekh, N. M.; Pirog, O. M.; Tatarinov, P. V.

In this study we present the results of investigations of variations of ionospheric parameters in the sector 20--80 r N 60--180 r E during intensive geomagnetic storm on November 7-11 2004 The data obtained at ionosonds and receivers of the global GPS network and receiver located on board of low-orbital satellite CHAMP are used for the analysis During this storm with two main phases the periods of total absorption and the blanketing Es layers typical for high- intensity geomagnetic storms are observed at high latitudes The prolonged negative disturbances are observed at the mid latitudes The large-scale traveling ionospheric disturbance of the frontal type is registered after during postmeridian LT hours on November 8 An analysis of disturbance front form shows that it presents the fragment of circular disturbance propagated from the region of Chukotka This disturbance exists during several hours and reaches Ural in the west direction and the south region of China in the south direction The velocity of its moving decreases with propagation sim from 300 m c to 200m s The characteristic spatial size is about 2000 km A comparison of relative amplitudes of this large-scale disturbance according to the TEC Delta TEC TEC approx 70 and foF2 Delta N N approx 80 data suggests it to be extensive in altitude The similar disturbance of smaller intensity was observed on November 10 This work was supported by the Russian Foundation for Basic Research grant N grant 04-05-39008

Radiotomographic imaging and GNSS remote sensing of the midlatitude ionosphere modified by powerful HF radiowaves.

NASA Astrophysics Data System (ADS)

Kunitsyn, V.; Andreeva, E. S.; Padokhin, A. M.; Vorontsov, A.; Frolov, V. L.; Komrakov, G.; Bernhardt, P. A.; Siefring, C. L.

2014-12-01

We present the results of the radiotomographic imaging and GNSS remote sensing of the artificial ionospheric disturbances obtained in the recent experiments on the modification of the midlatitude ionosphere by powerful HF radiowaves carried out at the Sura heating facility. The experiments were conducted using both O- and X- mode radiowaves, in daytime and nighttime conditions with various schemes of the radiation of the heating wave. Radio transmissions from the low- (Parus, e-POP on CASSIOPE) and high-orbital (GPS/GLONASS) navigational satellites received at the mobile network of receiving sites were used for the remote sensing of the heated area of the ionosphere. We study the variations in TEC caused by HF heating showing that the GNSS TEC spectra often contain frequency components corresponding to the modulation periods of the ERP of the heating wave. The manifestations of the heating-induced variations in TEC are most prominent in the area of magnetic zenith of the pumping wave. In this work we also present the radiotomographic reconstructions (including first time e-POP-SURA reconstructions) of the spatial structure of the disturbed area of the ionosphere corresponding to the directivity pattern of the heater as well as the spatial structure of the wave- like disturbances, which are possibly heating-induced AGWs, diverging from the heated area of the ionosphere. The spatial period of observed disturbances is 200-250 km and they are easily traced up to a distance of 700-800 km from the heated region, which is in good agreement with the modeling results.

Superstorms of November 2003 and 2004: the role of solar wind driving in the ionosphere-thermosphere dynamics

NASA Astrophysics Data System (ADS)

Verkhoglyadova, O. P.; Komjathy, A.; Mannucci, A. J.; Mlynczak, M. G.; Hunt, L. A.; Paxton, L. J.

2017-12-01

We revisit three complex superstorms of 19-20 November 2003, 7-8 November 2004 and 9-11 November 2004 to analyze ionosphere-thermosphere (IT) effects driven by different solar wind structures. We distinguish structures associated with ICMEs and their upstream sheaths. The efficiencies of the solar wind-magnetosphere connection throughout the storms are estimated by coupling functions. The daytime IT responses to the complex driving are characterized by combining measurements of characteristic IT parameters. We focus on low- and middle-latitude TEC, global thermospheric infrared nitric oxide emission, composition ratio and locations of the auroral boundary obtained from multiple satellite platforms and ground-based measurements (GPS, TIMED/SABER, TIMED/GUVI, DMSP/SSUSI). A variety of metrics are utilized to examine IT phenomena at 1 hour time scales. It is well-known that the November storm periods featured TEC responses that did not fit a typical pattern. The role of direct driving of IT dynamics by solar wind structures and the role of IT pre-conditioning in these storms are examined to explain the complex unusual ionospheric responses. We identify IT feedback effects that can be important for long-lasting strong storms.

Assessment of Radiometer Calibration with GPS Radio Occultation for the MiRaTA CubeSat Mission.

PubMed

Marinan, Anne D; Cahoy, Kerri L; Bishop, Rebecca L; Lui, Susan S; Bardeen, James R; Mulligan, Tamitha; Blackwell, William J; Leslie, R Vincent; Osaretin, Idahosa; Shields, Michael

2016-12-01

The Microwave Radiometer Technology Acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office (ESTO). The science payload on MiRaTA consists of a tri-band microwave radiometer and Global Positioning System (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporation's GPSRO experiment, called the Compact TEC (Total Electron Content) and Atmospheric GPS Sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (∼20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPS radio occultation: (1) new ultra-compact and low-power technology for multi-channel and multi-band passive microwave radiometers, (2) the application of a commercial off the shelf (COTS) GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and (3) a new approach to spaceborne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective (3), developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise. Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 K and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K.

Assessment of Radiometer Calibration with GPS Radio Occultation for the MiRaTA CubeSat Mission

PubMed Central

Marinan, Anne D.; Cahoy, Kerri L.; Bishop, Rebecca L.; Lui, Susan S.; Bardeen, James R.; Mulligan, Tamitha; Blackwell, William J.; Leslie, R. Vincent; Osaretin, Idahosa; Shields, Michael

2017-01-01

The Microwave Radiometer Technology Acceleration (MiRaTA) is a 3U CubeSat mission sponsored by the NASA Earth Science Technology Office (ESTO). The science payload on MiRaTA consists of a tri-band microwave radiometer and Global Positioning System (GPS) radio occultation (GPSRO) sensor. The microwave radiometer takes measurements of all-weather temperature (V-band, 50-57 GHz), water vapor (G-band, 175-191 GHz), and cloud ice (G-band, 205 GHz) to provide observations used to improve weather forecasting. The Aerospace Corporation's GPSRO experiment, called the Compact TEC (Total Electron Content) and Atmospheric GPS Sensor (CTAGS), measures profiles of temperature and pressure in the upper troposphere/lower stratosphere (∼20 km) and electron density in the ionosphere (over 100 km). The MiRaTA mission will validate new technologies in both passive microwave radiometry and GPS radio occultation: (1) new ultra-compact and low-power technology for multi-channel and multi-band passive microwave radiometers, (2) the application of a commercial off the shelf (COTS) GPS receiver and custom patch antenna array technology to obtain neutral atmospheric GPSRO retrieval from a nanosatellite, and (3) a new approach to spaceborne microwave radiometer calibration using adjacent GPSRO measurements. In this paper, we focus on objective (3), developing operational models to meet a mission goal of 100 concurrent radiometer and GPSRO measurements, and estimating the temperature measurement precision for the CTAGS instrument based on thermal noise. Based on an analysis of thermal noise of the CTAGS instrument, the expected temperature retrieval precision is between 0.17 K and 1.4 K, which supports the improvement of radiometric calibration to 0.25 K. PMID:28828144

Combining various space geodetic techniques for regional modeling of ionospheric electron density over Iran

NASA Astrophysics Data System (ADS)

Zare, Saeed; Alizadeh, M. Mahdi; Schuh, Harald

2017-04-01

Ionosphere is a layer of the upper atmosphere, between the thermosphere and the exosphere, distinguished because it is ionized by solar radiation. As an important part of human living environment, ionosphere affects our modern society in many ways. International broadcasters use this medium to reflect radio signals back toward the Earth. Ionosphere provides long range capabilities for commercial ship-to-shore communications, for trans-oceanic aircraft links, and for military communication and surveillance systems. Space geodetic techniques have turned into a capable tool for studying the ionosphere in the last decades. Up to now, two dimensional (2-D) models of vertical TEC (VTEC) have been widely developed and used by different communities; however, due to the fact that these models provide information about the integral of the whole electron content along the vertical or slant ray path, these maps are not useful when information about the ionosphere at different altitude is required. The aim of this study is to develop three dimensional (3-D) regional model of electron density by using combination of various space geodetic techniques. B-Spline basis functions are used for longitude and latitude variations of the electron density and Chapman profile function for altitude variations. The National Cartographic Center of Iran (NCC) has established a network of one hundred GPS stations: The Iranian Permanent GPS Network for Geodynamics (IPGN). The main task of the GPS stations is to collect and store raw GPS data and send it to Tehran processing center on a daily basis for final processing. The required data for our investigation are ground based measurements of permanent GPS stations over Iran and radio occultation data from Formosat-3/Cosmic for region of interest. We expect to increase accuracy and reliability of final model by integrating different observation techniques.

The Utility and Validity of Kinematic GPS Positioning for the Geosar Airborne Terrain Mapping Radar System

NASA Technical Reports Server (NTRS)

Freedman, Adam; Hensley, Scott; Chapin, Elaine; Kroger, Peter; Hussain, Mushtaq; Allred, Bruce

1999-01-01

GeoSAR is an airborne, interferometric Synthetic Aperture Radar (IFSAR) system for terrain mapping, currently under development by a consortium including NASA's Jet Propulsion Laboratory (JPL), Calgis, Inc., a California mapping sciences company, and the California Department of Conservation (CaIDOC), with funding provided by the U.S. Army Corps of Engineers Topographic Engineering Center (TEC) and the U.S. Defense Advanced Research Projects Agency (DARPA). IFSAR data processing requires high-accuracy platform position and attitude knowledge. On 9 GeoSAR, these are provided by one or two Honeywell Embedded GPS Inertial Navigation Units (EGI) and an Ashtech Z12 GPS receiver. The EGIs provide real-time high-accuracy attitude and moderate-accuracy position data, while the Ashtech data, post-processed differentially with data from a nearby ground station using Ashtech PNAV software, provide high-accuracy differential GPS positions. These data are optimally combined using a Kalman filter within the GeoSAR motion measurement software, and the resultant position and orientation information are used to process the dual frequency (X-band and P-band) radar data to generate high-accuracy, high -resolution terrain imagery and digital elevation models (DEMs). GeoSAR requirements specify sub-meter level planimetric and vertical accuracies for the resultant DEMS. To achieve this, platform positioning errors well below one meter are needed. The goal of GeoSAR is to obtain 25 cm or better 3-D positions from the GPS systems on board the aircraft. By imaging a set of known point target corner-cube reflectors, the GeoSAR system can be calibrated. This calibration process yields the true position of the aircraft with an uncertainty of 20- 50 cm. This process thus allows an independent assessment of the accuracy of our GPS-based positioning systems. We will present an overview of the GeoSAR motion measurement system, focusing on the use of GPS and the blending of position data from the various systems. We will present the results of our calibration studies that relate to the accuracy the GPS positioning. We will discuss the effects these positioning, errors have on the resultant DEM products and imagery.

Ionospheric turbulence from TEC variations and VLF/LF transmitter signal observations before and during the destructive seismic activity of August and October 2016 in Central Italy

NASA Astrophysics Data System (ADS)

Contadakis, Michael E.; Arabelos, Demetrios N.; Vergos, George; Spatala, Spyrous; Skeberis, Christos; Xenos, Tomas D.; Biagi, Pierfrancesco; Scordilis, Emmanuel M.

2017-04-01

In this paper we investigate the ionospheric turbulence from TEC variations and VLF/LF transmitter signal observations before and during the disastrous seismic activity of August and October 2016 in Central Italy . The Total Electron Content (TEC) data of 8 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations (Contadakis et al. 2009, Contadakis et al. 2012, Contadakis et al. 2015). The data acquired for VLF/LF signal observations are from the receiver of Thessaloniki(40.59N, 22,78E), Greece (Skeberis et al. 2015) which monitor the VLF/LF transmitters of the International Network for Frontier Research on Earthquake Precursors (INFREP). A method of normalization according to the distance between the receiver and the transmitter is applied on the above data and then they are processed by the Hilbert Huang Transform (HHT) to produce the corresponding spectra for visual analysis. The results of this investigation indicate that the High- Frequency limit fo, of the ionospheric turbulence content, increases as the site and the moment of the earthquake occurrence is approaching, pointing to the earthquake locus. In accordence ,the analyzed data from the receiver of INFREP network in Thessaloniki, Greece show that the signals from the two VLF European transmitters, Tavolara ( Italy) and Le Blanc (France), for wich the transmission path crosses the epicentral zones, indicate enhanced high frequency variations, the last ten days before the moment of the earthquake occurrence. We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology. Reference Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C. TEC variations over the Mediterranean during the seismic activity period of the last quarter of 2005 in the area of Greece, Nat. Hazards and Earth Syst. Sci., 8, 1267-1276, 2008. Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C. TEC variations over Southern Europe before and during the M6.3 Abruzzo earthquake of 6th April 2009, Annals of Geophysics, vol. 55, iss. 1, p. 83-93, 2012a. Contadakis, M. E., Arabelos, D.N., Vergos, G., Spatalas, S. D., Skordilis, M., 2015,TEC variations over the Mediterranean before and during the strong earthquake (M = 6.5) of 12th October 2013 in Crete, Greece, Physics and Chemistry of the Earth, Volume 85, p. 9-16. Skeberis, C., Zaharis, Z. D., Xenos, T. D., Spatalas, S., Arabelos, D. N., & Contadakis, M. E. (2015). Time-frequency analysis of VLF for seismic-ionospheric precursor detection: Evaluation of Zhao-Atlas-Marks and Hilbert-Huang Transforms. Physics and Chemistry of the Earth, Parts A/B/C, 85, 174-184

Medium Calcium Concentration Determines Keratin Intermediate Filament Density and Distribution in Immortalized Cultured Thymic Epithelial Cells (TECs)

NASA Astrophysics Data System (ADS)

Sands, Sandra S.; Meek, William D.; Hayashi, Jun; Ketchum, Robert J.

2005-08-01

Isolation and culture of thymic epithelial cells (TECs) using conventional primary tissue culture techniques under conditions employing supplemented low calcium medium yielded an immortalized cell line derived from the LDA rat (Lewis [Rt1l] cross DA [Rt1a]) that could be manipulated in vitro. Thymi were harvested from 4 5-day-old neonates, enzymically digested using collagenase (1 mg/ml, 37°C, 1 h) and cultured in low calcium WAJC404A medium containing cholera toxin (20 ng/ml), dexamethasone (10 nM), epidermal growth factor (10 ng/ml), insulin (10 [mu]g/ml), transferrin (10 [mu]g/ml), 2% calf serum, 2.5% Dulbecco's Modified Eagle's Medium (DMEM), and 1% antibiotic/antimycotic. TECs cultured in low calcium displayed round to spindle-shaped morphology, distinct intercellular spaces (even at confluence), and dense reticular-like keratin patterns. In high calcium (0.188 mM), TECs formed cobblestone-like confluent monolayers that were resistant to trypsinization (0.05%) and displayed keratin intermediate filaments concentrated at desmosomal junctions between contiguous cells. Changes in cultured TEC morphology were quantified by an analysis of desmosome/membrane relationships in high and low calcium media. Desmosomes were significantly increased in the high calcium medium. These studies may have value when considering the growth conditions of cultured primary cell lines like TECs.

Improving Science Teacher Preparation through the APS PhysTEC and NSF Noyce Programs

NASA Astrophysics Data System (ADS)

Williams, Tasha; Tyler, Micheal; van Duzor, Andrea; Sabella, Mel

2013-03-01

Central to the recruitment of students into science teaching at a school like CSU, is a focus on the professional nature of teaching. The purpose of this focus is twofold: it serves to change student perceptions about teaching and it prepares students to become teachers who value continued professional development and value the science education research literature. The Noyce and PhysTEC programs at CSU place the professional nature of teaching front and center by involving students in education research projects, paid internships, attendance at conferences, and participation in a new Teacher Immersion Institute and a Science Education Journal Reading Class. This poster will focus on specific components of our teacher preparation program that were developed through these two programs. In addition we will describe how these new components provide students with diverse experiences in the teaching of science to students in the urban school district. Supported by the NSF Noyce Program (0833251) and the APS PhysTEC Program.

Ionospheric signatures of Lightning

NASA Astrophysics Data System (ADS)

Hsu, M.; Liu, J.

2003-12-01

The geostationary metrology satellite (GMS) monitors motions of thunderstorm cloud, while the lightning detection network (LDN) in Taiwan and the very high Frequency (VHF) radar in Chung-Li (25.0›XN, 121.2›XE) observed occurrences of lightning during May and July, 1997. Measurements from the digisonde portable sounder (DPS) at National Central University shows that lightning results in occurrence of the sporadic E-layer (Es), as well as increase and decrease of plasma density at the F2-peak and E-peak in the ionosphere, respectively. A network of ground-based GPS receivers is further used to monitor the spatial distribution of the ionospheric TEC. To explain the plasma density variations, a model is proposed.

PCA and vTEC climatology at midnight over mid-latitude regions

NASA Astrophysics Data System (ADS)

Natali, M. P.; Meza, A.

2017-12-01

The effect of the thermospheric vertical neutral wind on vertical total electron content (vTEC) variations including longitudinal anomaly, remaining winter anomaly, mid-latitude summer night anomaly, and semiannual anomaly is studied at mid-latitude regions around zero magnetic declination at midnight during high solar activity. By using the principal component analysis (PCA) numerical technique, this work studies the spatial and temporal variations of the ionosphere at midnight over mid-latitude regions during 2000-2002. PCA is applied to a time series of global vTEC maps produced by the International Global Navigation Satellite System (GNSS) Service. Four regions were studied in particular, each located at mid-latitude and approximately centered at zero magnetic declination, with two in the northern hemisphere and two in southern hemisphere, and all are located near and far from geomagnetic poles in each case. This technique provides an effective method to analyze the main ionospheric variabilities at mid-latitudes. PCA is also applied to the vTEC computed using the International Reference Ionosphere (IRI) 2012 model, to analyze the capability of this model to represent ionospheric variabilities at mid-latitude. Also, the Horizontal Wind Model 2007 (HWM07) is used to improve our climatology interpretation, by analyzing the relationship between vTEC and thermospheric wind, both quantitatively and qualitatively. At midnight, the behavior of mean vTEC values strongly responds to vertical wind variation, experiencing a decrease of about 10-15% with the action of the positive vertical component of the field-aligned neutral wind lasting for 2 h in all regions except for Oceania. Notable results include: a significant increase toward higher latitudes during summer in the South America and Asia regions, associated with the mid-latitude summer night anomaly, and an increase toward higher latitudes in winter in the North America and Oceania regions, highlighting the remnant effect of the winter anomaly. Finally, the longitudinal variations of east-west differences, named longitudinal anomaly, show maximum values in March for North America, in December for South America and Oceania, and are not shown for Asia. Our results show that at mid-latitudes regions, the IRI model represents midnight ionospheric mean values with a similar spatial distribution, but the values are always lower than those obtained by GNSS. The differences between IRI and GNSS results include: the longitudinal anomaly is characterized by a stronger semiannual variation in both North America and South America, with a maximum in the equinoxes, while for the Asian region, the behavior is almost constant throughout the years, and finally, there is an absence of the winter anomaly remnant.

Long time series analysis of ionospheric TEC disturbance over seismically region in southwest China during low solar activity

NASA Astrophysics Data System (ADS)

Yan, Xiangxiang; Yu, Tao; Shan, Xinjian; Liu, Zhan; Wang, Zhenjie

2016-04-01

Recently, there are growing interests in studying the seismo-ionospheric disturbance prior to earthquakes, mainly including the anomalies in the electric field, magnetic field and plasma parameters. However, there are still some controversies over this topic, mainly because of strong day-to-day variability of the ionosphere itself. It is hard to determine whether the different forms of ionospheric disturbances are associated with earthquakes or not. Using data of Crustal Movement Observation Network of China (CMONC) and IGS (International GNSS Service), we attempt to give a statistical investigation about the total electron content (TEC) perturbation before 30 Mw6.0+ earthquakes during January 2000 to December 2010 in China. To determine the abnormal TEC signals, a quartile-based process is performed. At each time point we calculated the median M using the TEC values at the same local time for the preceding 15 days. In addition, we calculated the maps of differential TEC from global ionosphere maps (GIM) in the above period. It is shown that TEC anomalies were detected before 20 earthquakes, nearly 67%. The anomalies represent positive before most events and occurred mostly within 2-6 days before the shocks, significantly during the afternoon period, 1200-2000LT. Part of perturbations appeared more than one time. Moreover, the affected area of TEC is not coincide with the vertical projection of the epicenter but shifts equatorward and is controlled by equatorial ionization anomaly (EIA) crest. On the other hand, we analyzed variations of TEC over southwest China during a period of low solar and geomagnetic activity in April-October 2008, based on the data of CMONC. During that time, six large earthquakes with magnitude M≧6.0 occurred around the southwest region of China. The method to detect abnormal TEC signals is same with above statistical study. Known that the decisive role in the ionosphere state is performed by space weather effects, we compared the TEC variations with time series of EUV solar radiation, Bz component of the interplanetary magnetic field (IMF), index of geomagnetic activity Dst and planetary index Kp, respectively. It is found that the observed anomalies in the regional TEC were in good correlation with the variations of above solar and geomagnetic activities. We have not detected obvious TEC disturbance before five earthquakes expect for Wenchuan earthquake. In order to additionally check the spatial occurrence of the observed anomalies, we chose a 'check-region' with the same geomagnetic latitudes as the epicentral area of the six considered earthquakes, and analyzed the TEC changes. The result shows that the time series of anomalous TEC in 'check-region' is similar to the epicentral area, which was dominated by space weather. Therefore, we are suspicious of the results of statistical investigation showed here or other similar papers, which indicates the difficulties in identifying earthquake precursors in the ionosphere TEC. The seismo-ionospheric coupling process is complex, and it is necessary to strengthen the observation of multi-parameters on the ground, in the atmosphere and ionosphere synchronously.

A storm-time plasmasphere evolution study using data assimilation

NASA Astrophysics Data System (ADS)

Nikoukar, R.; Bust, G. S.; Bishop, R. L.; Coster, A. J.; Lemon, C.; Turner, D. L.; Roeder, J. L.

2017-12-01

In this work, we study the evolution of the Earth's plasmasphere during geomagnetic active periods using the Plasmasphere Data Assimilation (PDA) model. The total electron content (TEC) measurements from an extensive network of global ground-based GPS receivers as well as GPS receivers on-board Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites and Communications/Navigation Outage Forecasting System (C/NOFS) satellite are ingested into the model. Global Core Plasma model, which is an empirical plasmasphere model, is utilized as the background model. Based on the 3D-VAR optimization, the PDA assimilative model benefits from incorporation of regularization techniques to prevent non-physical altitudinal variation in density estimates due to the limited-angle observational geometry. This work focuses on the plasmapause location, plasmasphere erosion time scales and refilling rates during the main and recovery phases of geomagnetic storms as estimated from the PDA 3-dimensional global maps of electron density in the ionosphere/plasmasphere. The comparison between the PDA results with in-situ density measurements from THEMIS and Van Allen Probes, and the RCM-E first-principle model will be also presented.

Hierarchical Bayesian modeling of ionospheric TEC disturbances as non-stationary processes

NASA Astrophysics Data System (ADS)

Seid, Abdu Mohammed; Berhane, Tesfahun; Roininen, Lassi; Nigussie, Melessew

2018-03-01

We model regular and irregular variation of ionospheric total electron content as stationary and non-stationary processes, respectively. We apply the method developed to SCINDA GPS data set observed at Bahir Dar, Ethiopia (11.6 °N, 37.4 °E) . We use hierarchical Bayesian inversion with Gaussian Markov random process priors, and we model the prior parameters in the hyperprior. We use Matérn priors via stochastic partial differential equations, and use scaled Inv -χ2 hyperpriors for the hyperparameters. For drawing posterior estimates, we use Markov Chain Monte Carlo methods: Gibbs sampling and Metropolis-within-Gibbs for parameter and hyperparameter estimations, respectively. This allows us to quantify model parameter estimation uncertainties as well. We demonstrate the applicability of the method proposed using a synthetic test case. Finally, we apply the method to real GPS data set, which we decompose to regular and irregular variation components. The result shows that the approach can be used as an accurate ionospheric disturbance characterization technique that quantifies the total electron content variability with corresponding error uncertainties.

Real-time estimation of ionospheric delay using GPS measurements

NASA Astrophysics Data System (ADS)

Lin, Lao-Sheng

1997-12-01

When radio waves such as the GPS signals propagate through the ionosphere, they experience an extra time delay. The ionospheric delay can be eliminated (to the first order) through a linear combination of L1 and L2 observations from dual-frequency GPS receivers. Taking advantage of this dispersive principle, one or more dual- frequency GPS receivers can be used to determine a model of the ionospheric delay across a region of interest and, if implemented in real-time, can support single-frequency GPS positioning and navigation applications. The research objectives of this thesis were: (1) to develop algorithms to obtain accurate absolute Total Electron Content (TEC) estimates from dual-frequency GPS observables, and (2) to develop an algorithm to improve the accuracy of real-time ionosphere modelling. In order to fulfil these objectives, four algorithms have been proposed in this thesis. A 'multi-day multipath template technique' is proposed to mitigate the pseudo-range multipath effects at static GPS reference stations. This technique is based on the assumption that the multipath disturbance at a static station will be constant if the physical environment remains unchanged from day to day. The multipath template, either single-day or multi-day, can be generated from the previous days' GPS data. A 'real-time failure detection and repair algorithm' is proposed to detect and repair the GPS carrier phase 'failures', such as the occurrence of cycle slips. The proposed algorithm uses two procedures: (1) application of a statistical test on the state difference estimated from robust and conventional Kalman filters in order to detect and identify the carrier phase failure, and (2) application of a Kalman filter algorithm to repair the 'identified carrier phase failure'. A 'L1/L2 differential delay estimation algorithm' is proposed to estimate GPS satellite transmitter and receiver L1/L2 differential delays. This algorithm, based on the single-site modelling technique, is able to estimate the sum of the satellite and receiver L1/L2 differential delay for each tracked GPS satellite. A 'UNSW grid-based algorithm' is proposed to improve the accuracy of real-time ionosphere modelling. The proposed algorithm is similar to the conventional grid-based algorithm. However, two modifications were made to the algorithm: (1) an 'exponential function' is adopted as the weighting function, and (2) the 'grid-based ionosphere model' estimated from the previous day is used to predict the ionospheric delay ratios between the grid point and reference points. (Abstract shortened by UMI.)

Characteristics of Total Electron Content (TEC) observed from a chain of stations near the northern crest of the Equatorial Ionization Anomaly (EIA) along 88.5°E meridian in India

NASA Astrophysics Data System (ADS)

Paul, K. S.; Das, A.; Ray, S.; Paul, A.

2016-01-01

The equatorial ionosphere presents some of the highest TEC values in the world coupled with observations of periodic structures. Total Electron Content (TEC) and scintillation data were analyzed from a chain of stations Calcutta (22.58°N, 88.38°E geographic; 32°N magnetic dip), Baharampore (24.09°N, 88.25°E geographic; 35°N magnetic dip) and Farakka (24.79°N, 87.89°E geographic; 36.04°N magnetic dip) situated almost same meridian (88.5°E) during September 2011 and March-April 2012 for elevation greater than 20° so that the ionosphere can be tracked from the 15.50°N south of Calcutta to 31.80°N north of Farakka. Periodic variation of TEC was noticed before TEC bite out, predominantly within a particular latitudinal swath (19°N ‒26°N) along 88.5°E meridian. No periodic structures were observed over the magnetic equator during the observation period on ionosonde records from the magnetic equator station Trivandrum and COSMIC, GRACE and C/NOFS electron density measurements. The present paper reports, perhaps for the first time from the Indian longitude sector, confinement of such periodic structures in TEC primarily within a latitude swath of 19.00-26.00 °N almost along the same longitude of 88.5 °E.

Characteristics of nighttime E-region over Arecibo: Dependence on solar flux and geomagnetic variations

NASA Astrophysics Data System (ADS)

Raizada, Shikha; Brum, Christiano G. M.; Mathews, John D.; Gonzalez, Cristina; Franco, Efmi

2018-04-01

Electron concentration (Ne) inferred from Incoherent Scatter Radar (ISR) measurements has been used to determine the influence of solar flux and geomagnetic activity in the ionospheric E-region over Arecibo Observatory (AO). The approach is based on the determination of column integrated Ne, referred to as E-region total electron content (ErTEC) between 80 and 150 km altitude regions. The results discussed in this work are for the AO nighttime period. The study reveals higher ErTEC values during the low solar flux periods for all the seasons except for summer period. It is found that the E-region column abundance is higher in equinox periods than in the winter for low solar activity conditions. The column integrated Ne during the post-sunset/pre-sunrise periods always exceeds the midnight minima, independent of season or solar activity. This behavior has been attributed to the variations in the coupling processes from the F-region. The response of ErTEC to the geomagnetic variability is also examined for different solar flux conditions and seasons. During high solar flux periods, changes in Kp cause an ErTEC increase in summer and equinox, while producing a negative storm-like effect during the winter. Variations in ErTEC due to geomagnetic activity during low solar flux periods produce maximum variability in the E-region during equinox periods, while resulting in an increase/decrease in ErTEC before local midnight during the winter/summer periods, respectively.

Adjustments of the TaD electron density reconstruction model with GNSS-TEC parameters for operational application purposes

NASA Astrophysics Data System (ADS)

Kutiev, Ivan; Marinov, Pencho; Fidanova, Stefka; Belehaki, Anna; Tsagouri, Ioanna

2012-12-01

Validation results on the latest version of TaD model (TaDv2) show realistic reconstruction of the electron density profiles (EDPs) with an average error of 3 TECU, similar to the error obtained from GNSS-TEC calculated paremeters. The work presented here has the aim to further improve the accuracy of the TaD topside reconstruction, adjusting the TEC parameter calculated from TaD model with the TEC parameter calculated by GNSS transmitting RINEX files provided by receivers co-located with the Digisondes. The performance of the new version is tested during a storm period demonstrating further improvements in respect to the previous version. Statistical comparison of modeled and observed TEC confirms the validity of the proposed adjustment. A significant benefit of the proposed upgrade is that it facilitates the real-time implementation of TaD. The model needs a reliable measure of the scale height at the peak height, which is supposed to be provided by Digisondes. Oftenly, the automatic scaling software fails to correctly calculate the scale height at the peak, Hm, due to interferences in the receiving signal. Consequently the model estimated topside scale height is wrongly calculated leading to unrealistic results for the modeled EDP. The proposed TEC adjustment forces the model to correctly reproduce the topside scale height, despite the inaccurate values of Hm. This adjustment is very important for the application of TaD in an operational environment.

Development of a methodology for deriving Plasmaspheric Total Electron Content from In-Situ electron density measurements in highly eccentric equatorial orbits

NASA Astrophysics Data System (ADS)

Sadhique, Aliyuthuman; Buckley, Andrew; Gough, Paul; Sussex Space Science Centre Team

2017-10-01

The contribution of the Upper Plasmasphere (defined as the altitudes above semi-synchronous orbit height to the Plasmapause height) to the TEC has been and continues to be un-quantified. The PEACE instrument in the Chinese - ESA Double Star TC1 satellite, the mission's orbit's high eccentricity, low perigee, high apogee and the resulting smaller incident angle while in the above altitude range provide the ideal geometric opportunity to build a methodology and to utilize its empirical in-situ electron density measurements to determine the Upper Plasmaspheric TEC component. Furthermore, the variation of the Inclination Angle of TC1 makes it a suitable equatorial mission confined to the Near-Equatorial region, ie 200 - 250 on either sides of the magnetic equator. As the most pronounced absolute TEC values and variations are within this region, it offers an excellent opportunity to build a Upper Plasmaspheric TEC database. This research generates such, first-ever database along its orbital path, using a methodology of approximation equating arcs of the orbits to straight-line TEC Bars, utilizing complex mathematics, also enabling the determination of the whole Plasmaspheric TEC from any eccentric orbital probe. Presented the paper in 15th International Workshop on Technical and Scientific Aspects of MST radar (MST15/iMST2)'' and ``18th EISCAT Symposium (EISCAT18)'' in Tokyo, Japan and The Royal Astronomical Society National Astronomy Meeting 2017.

Joint estimation of vertical total electron content (VTEC) and satellite differential code biases (SDCBs) using low-cost receivers

NASA Astrophysics Data System (ADS)

Zhang, Baocheng; Teunissen, Peter J. G.; Yuan, Yunbin; Zhang, Hongxing; Li, Min

2018-04-01

Vertical total electron content (VTEC) parameters estimated using global navigation satellite system (GNSS) data are of great interest for ionosphere sensing. Satellite differential code biases (SDCBs) account for one source of error which, if left uncorrected, can deteriorate performance of positioning, timing and other applications. The customary approach to estimate VTEC along with SDCBs from dual-frequency GNSS data, hereinafter referred to as DF approach, consists of two sequential steps. The first step seeks to retrieve ionospheric observables through the carrier-to-code leveling technique. This observable, related to the slant total electron content (STEC) along the satellite-receiver line-of-sight, is biased also by the SDCBs and the receiver differential code biases (RDCBs). By means of thin-layer ionospheric model, in the second step one is able to isolate the VTEC, the SDCBs and the RDCBs from the ionospheric observables. In this work, we present a single-frequency (SF) approach, enabling the joint estimation of VTEC and SDCBs using low-cost receivers; this approach is also based on two steps and it differs from the DF approach only in the first step, where we turn to the precise point positioning technique to retrieve from the single-frequency GNSS data the ionospheric observables, interpreted as the combination of the STEC, the SDCBs and the biased receiver clocks at the pivot epoch. Our numerical analyses clarify how SF approach performs when being applied to GPS L1 data collected by a single receiver under both calm and disturbed ionospheric conditions. The daily time series of zenith VTEC estimates has an accuracy ranging from a few tenths of a TEC unit (TECU) to approximately 2 TECU. For 73-96% of GPS satellites in view, the daily estimates of SDCBs do not deviate, in absolute value, more than 1 ns from their ground truth values published by the Centre for Orbit Determination in Europe.

GPS detection of ionospheric Rayleigh wave and its source following the 2012 Haida Gwaii earthquake

NASA Astrophysics Data System (ADS)

Jin, Shuanggen; Jin, Rui; Li, D.

2017-01-01

The processes and sources of seismo-ionospheric disturbances are still not clear. In this paper, coseismic ionospheric disturbances (CIDs) are investigated by dual-frequency GPS observations following the Mw = 7.8 earthquake as results of the oblique-thrust fault in the Haida Gwaii region, Canada, on 28 October 2012. Results show that the CIDs with an amplitude of up to 0.15 total electron content units (TECU) are found with spreading out at 2.20 km/s, which agree well with the Rayleigh wave propagation speed at 2.22 km/s detected by the bottom pressure records at about 10 min after the onset. The CIDs are a result of the upward propagation acoustic waves trigged by the Rayleigh wave in sequence from near field to far field. The strong correlation is found between the CIDs and the vertical ground motion recorded by seismometers nearby the epicenter. The total electron content (TEC) series from lower-elevation angle GPS observations have higher perturbation amplitudes. Furthermore, the simulated ionospheric disturbance following a vertical Gauss pulse on the ground based on the finite difference time domain method confirms the ionospheric Rayleigh wave signature in the near field and the vertical ground motion dependence theoretically. The vertical ground motion is the dominant source of the ionospheric Rayleigh wave and affects the CID waveform directly.

Scintillation measurements at Bahir Dar during the high solar activity phase of solar cycle 24

NASA Astrophysics Data System (ADS)

Kriegel, Martin; Jakowski, Norbert; Berdermann, Jens; Sato, Hiroatsu; Wassaie Mersha, Mogese

2017-01-01

Small-scale ionospheric disturbances may cause severe radio scintillations of signals transmitted from global navigation satellite systems (GNSSs). Consequently, small-scale plasma irregularities may heavily degrade the performance of current GNSSs such as GPS, GLONASS or Galileo. This paper presents analysis results obtained primarily from two high-rate GNSS receiver stations designed and operated by the German Aerospace Center (DLR) in cooperation with Bahir Dar University (BDU) at 11.6° N, 37.4° E. Both receivers collect raw data sampled at up to 50 Hz, from which characteristic scintillation parameters such as the S4 index are deduced. This paper gives a first overview of the measurement set-up and the observed scintillation events over Bahir Dar in 2015. Both stations are located close to one another and aligned in an east-west, direction which allows us to estimate the zonal drift velocity and spatial dimension of equatorial ionospheric plasma irregularities. Therefore, the lag times of moving electron density irregularities and scintillation patterns are derived by applying cross-correlation analysis to high-rate measurements of the slant total electron content (sTEC) along radio links between a GPS satellite and both receivers and to the associated signal power, respectively. Finally, the drift velocity is derived from the estimated lag time, taking into account the geometric constellation of both receiving antennas and the observed GPS satellites.

Large-scale traveling ionospheric disturbances observed using GPS receivers over high-latitude and equatorial regions

NASA Astrophysics Data System (ADS)

Idrus, Intan Izafina; Abdullah, Mardina; Hasbi, Alina Marie; Husin, Asnawi; Yatim, Baharuddin

2013-09-01

This paper presents the first results of large-scale traveling ionospheric disturbances (LSTIDs) observation during two moderate magnetic storm events on 28 May 2011 (SYM-H∼ -94 nT and Dst∼-80 nT) and 6 August 2011 (SYM-H∼-126 nT and Dst∼-113 nT) over the high-latitude region in Russia, Sweden, Norway, Iceland and Greenland and equatorial region in the Peninsular Malaysia using vertical total electron content (VTEC) from the Global Positioning System (GPS) observations measurement. The propagation of the LSTID signatures in the GPS TEC measurements over Peninsular Malaysia was also investigated using VTEC map. The LSTIDs were found to propagate both equatorward and poleward directions during these two events. The results showed that the LSTIDs propagated faster at high-latitude region with an average phase velocity of 1074.91 m/s than Peninsular Malaysia with an average phase velocity of 604.84 m/s. The LSTIDs at the high-latitude region have average periods of 150 min whereas the ones observed over Peninsular Malaysia have average periods of 115 min. The occurrences of these LSTIDs were also found to be the subsequent effects of substorm activities in the auroral region. To our knowledge, this is the first result of observation of LSTIDs over Peninsular Malaysia during the 24th solar cycle.

Solar and lunar tidal variabilities in GPS-TEC and geomagnetic field variations: Seasonal as well as during the sudden stratospheric warming of 2010

NASA Astrophysics Data System (ADS)

Sridharan, S.

2017-04-01

The Global Positioning System (GPS) deduced total electron content (TEC) data at 15°N (geomagnetic), which is the northern crest region of equatorial ionization anomaly, are used to study solar and lunar tidal variabilities during the years 2008 and 2009 and also during the 2009-2010 winter, when a major sudden stratospheric warming (SSW) event has occurred. The diurnal and semidiurnal tidal amplitudes show semiannual variation with maximum amplitudes during February-March and September-November, whereas terdiurnal tide is larger during April-September. They show significant longitudinal variability with larger (smaller) amplitudes over 250°E-150°E (200°E-250°E). Lunar semidiurnal tidal amplitudes show sporadic enhancements during northern winter months and negligible amplitudes during northern summer months. They also show notable longitudinal variabilities. The solar migrating tides DW1 and SW2 show semiannual variation with larger amplitudes during spring equinox months, whereas TW3 maximizes during northern summer. DW2 shows larger amplitudes during summer months. During the SSW, except TW3, the migrating tides DW1 and SW2 show considerable enhancements. Among solar nonmigrating tides, SW1, TW2, and DS0 show larger enhancements. Solar tides in TEC and equatorial electrojet strength over Tirunelveli vary with the time scale of 60 days during October 2009-March 2010 similar to ozone mass mixing ratio at 10 hPa, and this confirms the vital role of ozone in tidal variabilities in ionospheric parameters. Lunar tidal amplitudes in changes in horizontal component of geomagnetic field (ΔH) are larger over Tirunelveli, a station near dip equator. Solar semidiurnal tides in ΔH have larger amplitudes than lunar tides over polar stations, Mawson and Godhavn.