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.

Total electron content anomalies associated with global VEI4 + volcanic eruptions during 2002-2015

NASA Astrophysics Data System (ADS)

Li, Wang; Guo, Jinyun; Yue, Jianping; Shen, Yi; Yang, Yang

2016-10-01

In previous studies, little attention has been paid to the total electron content (TEC) anomalies preceding the volcanic eruption. We analyze the coupling relationship between volcanic eruption and TEC anomalies, and discuss the spatial distribution of TEC anomalies associated with volcanic geographical location. We utilize the global ionosphere map (GIM) data from the Center for Orbit Determination in Europe (CODE) to analyze TEC variations before the global volcanic eruptions indicated by VEI (Volcanic Explosivity Index) 4 + from 2002 to 2015 with the sliding interquartile range method. The results indicate the occurrence rate of TEC anomalies before great volcanic eruptions is related with the volcanic type and geographical position. The occurrence rate of TEC anomalies before stratovolcano and caldera eruptions is higher than that before shield and pyroclastic shield eruptions, and the occurrence rate of TEC anomalies has a descending trend from low latitudes to high latitudes. The TEC anomalies before the volcanic eruptions in low-mid latitudes are within the volcanic affected areas, but do not coincide with the volcanic foci. The corresponding TEC anomalies could be observed in the conjugated region, and all the TEC anomalies in the volcanic affected areas are usually close to bounds of equatorial anomaly zones. However, the TEC anomalies preceding these eruptions in high latitudes usually surround the volcano, and no TEC anomalies appear in the conjugated region. These conclusions have potential applications to the prediction of great volcanic eruptions in the future.

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.

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.

US-TEC: A new data assimilation product from the Space Environment Center characterizing the ionospheric total electron content using real-time GPS data

NASA Astrophysics Data System (ADS)

Fuller-Rowell, Tim; Araujo-Pradere, Eduardo; Minter, Cliff; Codrescu, Mihail; Spencer, Paul; Robertson, Doug; Jacobson, Abram R.

2006-12-01

The potential of data assimilation for operational numerical weather forecasting has been appreciated for many years. For space weather it is a new path that we are just beginning to explore. With the emergence of satellite constellations and the networks of ground-based observations, sufficient data sources are now available to make the application of data assimilation techniques a viable option. The first space weather product at Space Environment Center (SEC) utilizing data assimilation techniques, US-TEC, was launched as a test operational product in November 2004. US-TEC characterizes the ionospheric total electron content (TEC) over the continental United States (CONUS) every 15 min with about a 15-min latency. US-TEC is based on a Kalman filter data assimilation scheme driven by a ground-based network of real-time GPS stations. The product includes a map of the vertical TEC, an estimate of the uncertainty in the map, and the departure of the TEC from a 10-day average at that particular universal time. In addition, data files are provided for vertical TEC and the line-of-sight electron content to all GPS satellites in view over the CONUS at that time. The information can be used to improve single-frequency GPS positioning by providing more accurate corrections for the ionospheric signal delay, or it can be used to initialize rapid integer ambiguity resolution schemes for dual-frequency GPS systems. Validation of US-TEC indicates an accuracy of the line-of-sight electron content of between 2 and 3 TEC units (1 TECU = 1016 el m-2), equivalent to less than 50 cm signal delay at L1 frequencies, which promises value for GPS users. This is the first step along a path that will likely lead to major improvement in space weather forecasting, paralleling the advances achieved in meteorological weather forecasting.

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.

GNSS Observations of Ionospheric Variations During the 21 August 2017 Solar Eclipse

NASA Astrophysics Data System (ADS)

Coster, Anthea J.; Goncharenko, Larisa; Zhang, Shun-Rong; Erickson, Philip J.; Rideout, William; Vierinen, Juha

2017-12-01

On 21 August 2017, during daytime hours, a total solar eclipse with a narrow ˜160 km wide umbral shadow occurred across the continental United States. Totality was observed from the Oregon coast at ˜9:15 local standard time (LST) (17:20 UT) to the South Carolina coast at ˜13:27 LST (18:47 UT). A dense network of Global Navigation Satellite Systems (GNSS) receivers was utilized to produce total electron content (TEC) and differential TEC. These data were analyzed for the latitudinal and longitudinal response of the TEC and for the presence of traveling ionospheric disturbances (TIDs) during eclipse passage. A significant TEC depletion, in some cases greater than 60%, was observed associated with the eclipse shadow, exceeding initial model predictions of 35%. Evidence of enhanced large-scale TID activity was detected over the United States prior to and following the large TEC depletion observed near the time of totality. Signatures of enhanced TEC structures were observed over the Rocky Mountain chain during the main period of TEC depletion.

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

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.

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

NASA Astrophysics Data System (ADS)

Lin, Jyh-Woei

2012-10-01

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

Earthquake Related Variation of Total Electron Content in Ionosphere over Chinese Mainland Derived from Observations of a Nationwide GNSS Network

NASA Astrophysics Data System (ADS)

Gan, Weijun

2016-07-01

Crustal Movement Observation Network of China (CMONOC) is a key national scientific infrastructure project carried out during 1997-2012 with 2 phases. The network is composed of 260 continuously observed GNSS stations (CORS) and 2081 campaign mode GNSS stations, with the main purpose to monitor the crustal movement, perceptible water vapor (PWV), total electron content (TEC), and many other tectonic and environmental elements around mainland China, by mainly using the Global Navigation Satellite System (GNSS) technology. Here, based on the GNSS data of 260 CORS of COMNOC for about 5 years, we investigated the characteristics of TEC in ionosphere over Chinese Mainland and discussed if there was any abnormal change of TEC before and after a big earthquake. our preliminary results show that it is hard to see any convincing precursor of TEC before a big earthquake. However, the huge energy released by a big earthquake can obviously disturb the TEC over meizoseismal area.

Morphology of the winter anomaly in NmF2 and Total Electron Content

NASA Astrophysics Data System (ADS)

Yasyukevich, Yury; Ratovsky, Konstantin; Yasyukevich, Anna; Klimenko, Maksim; Klimenko, Vladimir; Chirik, Nikolay

2017-04-01

We analyzed the winter anomaly manifestation in the F2 peak electron density (NmF2) and Total Electron Content (TEC) based on the observation data and model calculation results. For the analysis we used 1998-2015 TEC Global Ionospheric Maps (GIM) and NmF2 ground-based ionosonde observation data from and COSMIC, CHAMP and GRACE radio occultation data. We used Global Self-consistent Model of the Thermosphere, Ionosphere, and Protonosphere (GSM TIP) and International Reference Ionosphere model (IRI-2012). Based on the observation data and model calculation results we constructed the maps of the winter anomaly intensity in TEC and NmF2 for the different solar and geomagnetic activity levels. The winter anomaly intensity was found to be higher in NmF2 than in TEC according to both observation and modeling. In this report we show the similarity and difference in winter anomaly as revealed in experimental data and model results.

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.

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.

Ionospheric total electron content measurements from Turkey during the solar eclipse of 29 April 1976

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

Artac, E.; Tulunay, Y.K.

1977-12-31

Total ionospheric electron content (TEC) has been determined from the measurements of the Faraday rotation of a plane polarized wave that have been returned from the geostationary satellite ATS 6 transmitting at a frequency of 140 MHz. The results of the computations have been presented in the form of diurnal curves in order to investigate the effect of the solar eclipse of 29 April 1976 on the TEC over Ankara longitudes.

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.

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.

A comparison of mapped and measured total ionospheric electron content using global positioning system and beacon satellite observations

NASA Technical Reports Server (NTRS)

Lanyi, Gabor E.; Roth, Titus

1988-01-01

Total ionospheric electron contents (TEC) were measured by global positioning system (GPS) dual-frequency receivers developed by the Jet Propulsion Laboratory. The measurements included P-code (precise ranging code) and carrier phase data for six GPS satellites during multiple five-hour observing sessions. A set of these GPS TEC measurements were mapped from the GPS lines of sight to the line of sight of a Faraday beacon satellite by statistically fitting the TEC data to a simple model of the ionosphere. The mapped GPS TEC values were compared with the Faraday rotation measurements. Because GPS transmitter offsets are different for each satellite and because some GPS receiver offsets were uncalibrated, the sums of the satellite and receiver offsets were estimated simultaneously with the TEC in a least squares procedure. The accuracy of this estimation procedure is evaluated indicating that the error of the GPS-determined line of sight TEC can be at or below 1 x 10 to the 16th el/sq cm. Consequently, the current level of accuracy is comparable to the Faraday rotation technique; however, GPS provides superior sky coverage.

Determinations of ionosphere and plasmasphere electron content for an African chain of GPS stations

NASA Astrophysics Data System (ADS)

Mazzella, Andrew J., Jr.; Bosco Habarulema, John; Yizengaw, Endawoke

2017-05-01

The confluence of recent instrumentation deployments in Africa with developments for the determination of plasmasphere electron content using Global Positioning System (GPS) receivers has provided new opportunities for investigations in that region. This investigation, using a selected chain of GPS stations, extends the method (SCORPION) previously applied to a chain of GPS stations in North America in order to separate the ionosphere and plasmasphere contributions to the total electron content (TEC) during a day (24 July) in 2011. The results span latitudes from the southern tip of Africa, across the Equator, to the southern Arabian Peninsula, providing a continuous latitudinal profile for both the ionosphere and plasmasphere during this day.The peak diurnal vertical ionosphere electron content (IEC) increases from about 14 TEC units (1 TEC unit = 1016 electrons m-2) at the southernmost station to about 32 TEC units near the geographic equator, then decreases to about 28 TEC units at the Arabian Peninsula. The peak diurnal slant plasmasphere electron content (PEC) varies between about 4 and 7 TEC units among the stations, with a local latitudinal profile that is significantly influenced by the viewing geometry at the station location, relative to the magnetic field configuration. In contrast, the peak vertical PEC varies between about 1 and 6 TEC units among the stations, with a more uniform latitudinal variation.Comparisons to other GPS data analyses are also presented for TEC, indicating the influence of the PEC on the determination of latitudinal TEC variations and also on the absolute TEC levels, by inducing an overestimate of the receiver bias. The derived TEC latitudinal profiles, in comparison to global map profiles, tend to differ from the map results only about as much as the map results differ among themselves. A combination of ionosonde IEC and alternative GPS TEC measurements, which in principle permits a PEC determination through their difference, was compared to the composite and separate ionosphere and plasmasphere contributions derived solely by the SCORPION method for one station. Although there is considerably more scatter in the PEC values derived from the difference of the GPS TEC and ionosonde IEC measurements compared to the PEC values derived by the SCORPION method, the average overhead values for this day are comparable for the two methods, near 2 TEC units, at the South African site examined.This initial investigation provides a basis for day-to-day TEC monitoring for Africa, with separate ionosphere and plasmasphere electron content determinations.

Behaviour of Electron Content in the Ionospheric D-Region During Solar X-Ray Flares

NASA Astrophysics Data System (ADS)

Todorović Drakul, M.; Čadež, V. M.; Bajčetić, J.; Popović, L. Č.; Blagojević, D.; Nina, A.

2016-12-01

One of the most important parameters in ionospheric plasma research, also having a wide practical application in wireless satellite telecommunications, is the total electron content (TEC) representing the columnal electron number density. The F-region with high electron density provides the biggest contribution to TEC while the relatively weakly ionized plasma of the D-region (60 km - 90 km above Earth's surface) is often considered as a negligible cause of satellite signal disturbances. However, sudden intensive ionization processes, like those induced by solar X-ray flares, can cause relative increases of electron density that are significantly larger in the D-region than in regions at higher altitudes. Therefore, one cannot exclude a priori the D-region from investigations of ionospheric influences on propagation of electromagnetic signals emitted by satellites. We discuss here this problem which has not been sufficiently treated in literature so far. The obtained results are based on data collected from the D-region monitoring by very low frequency radio waves and on vertical TEC calculations from the Global Navigation Satellite System (GNSS) signal analyses, and they show noticeable variations in the D-region's electron content (TEC_{D) during activity of a solar X-ray flare (it rises by a factor of 136 in the considered case) when TEC_{D} contribution to TEC can reach several percent and which cannot be neglected in practical applications like global positioning procedures by satellites.

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.

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.

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.

Estimation of the Total Electron Content of the Martian Ionosphere using Radar Sounder Surface Echoes

NASA Technical Reports Server (NTRS)

Safaeinili, Ali; Kofman, Wlodek; Mouginot, Jeremie; Gim, Yonggyu; Herique, Alain; Ivanov, Anton B.; Plaut, Jeffrey J.; Picardi, Giovanni

2007-01-01

The Martian ionosphere's local total electron content (TEC) and the neutral atmosphere scale height can be derived from radar echoes reflected from the surface of the planet. We report the global distribution of the TEC by analyzing more than 750,000 echoes of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This is the first direct measurement of the TEC of the Martian ionosphere. The technique used in this paper is a novel 'transmission-mode' sounding of the ionosphere of Mars in contrast to the Active Ionospheric Sounding experiment (AIS) on MARSIS, which generally operates in the reflection mode. This technique yields a global map of the TEC for the Martian ionosphere. The radar transmits a wideband chirp signal that travels through the ionosphere before and after being reflected from the surface. The received waves are attenuated, delayed and dispersed, depending on the electron density in the column directly below the spacecraft. In the process of correcting the radar signal, we are able to estimate the TEC and its global distribution with an unprecedented resolution of about 0.1 deg in latitude (5 km footprint). The mapping of the relative geographical variations in the estimated nightside TEC data reveals an intricate web of high electron density regions that correspond to regions where crustal magnetic field lines are connected to the solar wind. Our data demonstrates that these regions are generally but not exclusively associated with areas that have magnetic field lines perpendicular to the surface of Mars. As a result, the global TEC map provides a high-resolution view of where the Martian crustal magnetic field is connected to the solar wind. We also provide an estimate of the neutral atmospheric scale height near the ionospheric peak and observe temporal fluctuations in peak electron density related to solar activity.

A Statistical Study of Total Electron Content Changes in the Ionosphere Prior to Earthquake Occurrences

NASA Astrophysics Data System (ADS)

Thomas, J. N.; Huard, J.; Masci, F.

2015-12-01

There are many published reports of anomalous changes in the ionosphere prior to large earthquakes. However, whether or not these ionospheric changes are reliable precursors that could be useful for earthquake prediction is controversial within the scientific community. To test a possible statistical relationship between the ionosphere and earthquakes, we compare changes in the total electron content (TEC) of the ionosphere with occurrences of M≥6.0 earthquakes globally for a multiyear period. We use TEC data from a global ionosphere map (GIM) and an earthquake list declustered for aftershocks. For each earthquake, we look for anomalous changes in TEC within ±30 days of the earthquake time and within 2.5° latitude and 5.0° longitude of the earthquake location (the spatial resolution of GIM). Our preliminary analysis, using global TEC and earthquake data for 2002-2010, has not found any statistically significant changes in TEC prior to earthquakes. Thus, we have found no evidence that would suggest that TEC changes are useful for earthquake prediction. Our results are discussed in the context of prior statistical and case studies. Namely, our results agree with Dautermann et al. (2007) who found no relationship between TEC changes and earthquakes in the San Andreas fault region. Whereas, our results disagree with Le et al. (2011) who found an increased rate in TEC anomalies within a few days before global earthquakes M≥6.0.

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

Variations of total electron content in the equatorial anomaly region in Thailand

NASA Astrophysics Data System (ADS)

Chowdhary, V. Rajesh; Tripathi, N. K.; Arunpold, Sanit; Raju, Durairaju Kumaran

2015-01-01

This paper presents the first results of total electron content (TEC), derived by analyzing dual frequency Novatel GSV4004 GPS receiver's data which were installed by the SCINDA project, located at the Asian Institute of Technology, Bangkok (AITB, 14.079N, 100.612E) and Chiang Mai University, Chiang Mai (CHGM, 18.480N, 98.570E) with magnetic latitude of 4.13°N and 8.61°N respectively in Thailand, for the year 2011. These two stations are separated by 657 km in the equatorial anomaly region. The highest TEC values occurred from 1500 to 1900 LT throughout the study period. The diurnal, monthly and seasonal GPS-TEC have been plotted and analyzed. The diurnal peaks in GPS-TEC is observed to be maximum during equinoctial months (March, April, September and October) and minimum in solstice months (January, February, June, July and December). These high TEC values have been attributed to the solar extreme ultra-violet ionization coupled with the upward vertical E × B drift. A comparison of both station's TEC has been carried out and found that CHGM station experiences higher values of TEC than AITB station, due to formation of ionization crest over the CHGM station. Also, TEC values have shown increasing trend due to approaching solar maximum. These results from both stations were also compared with the TEC derived from the International Reference Ionosphere's (IRI) recently released, IRI-2012 model. Results have shown positive correlation with IRI-2012 model. Although, IRI-model does not show any response to geomagnetic activity, the IRI model normally remains smooth and underestimates TEC during a storm.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

Ionospheric storms—A challenge for empirical forecast of the total electron content

NASA Astrophysics Data System (ADS)

Borries, C.; Berdermann, J.; Jakowski, N.; Wilken, V.

2015-04-01

Since the last decades, the functioning of society depends more and more on well-functioning communication and navigation systems. As the availability and reliability of most of these satellite-based systems can be severely impacted by ionospheric storms, the accurate forecast of these events becomes a required task for mitigating social and economic risks. Here we aim to make initial steps toward an empirical model for ionospheric perturbations related to space weather events that are observable in the total electron content (TEC). The perturbation TEC forecast model will be a fast and robust approach, improving TEC forecasts based on climatological models during storm conditions. The derivation of such a model is a challenging task, because although a general dependence of the storm features (enhancement or depletion of electron density) on the storm onset time, local time, season and geomagnetic latitude is well known, there is a large deviation from the mean behavior. For a better understanding of storm conditions, this paper presents analyses of ionospheric storms observed in the TEC, broken down into diverse classes of storms. It provides a detailed characterization of the typical ionospheric storm behavior over Europe from high to midlatitudes, beyond case studies. Generally, the typical clear strong TEC enhancement starting in high latitudes and propagating equatorward is found to be strongest for storms starting in the morning hours independent of the season. In midlatitudes, it is strongest during noon. In addition, a clear difference between summer and winter storms is reported. While only winter storms develop high-latitude TEC enhancements, only summer storms typically exhibit TEC depletions during the storm recovery phase. During winter storms TEC enhancements can also occur the day following the storm onset, in contrast to summer storms. Strong correlation of TEC perturbation amplitudes to the Bz component of the interplanetary magnetic field and to a proxy of the polar cap potential are shown especially for summer midlatitude TEC enhancements during storms with and onset in the morning hours (6 to 12 UT over Europe) and for winter high-latitude TEC enhancements (around 60∘N). The results indicate the potential to derive improved predictions of maximum TEC deviations during space weather events, based on solar wind measurements.

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.

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.

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.

Statistical analysis of ionospheric TEC anomalies before global M w ≥ 7.0 earthquakes using data of CODE GIM

NASA Astrophysics Data System (ADS)

Liu, Wenjing; Xu, Liang

2017-07-01

Based on Center of Orbit Determination in Europe (CODE) global ionospheric map (GIM) data, a statistical analysis of local total electron content (TEC) anomalies before 121 low-depth ( D ≤ 100 km) strong ( M w ≥ 7.0) earthquakes has been made using the sliding median differential calculation method combining with a new approach of image processing technique. The results show that significant local TEC anomalies could be observed 0-6 days before 80 earthquakes, about 66.1% out of the total. The positive anomalies occur more often than negative ones. For 26 cases, both positive and negative anomalies are observed before the shock. The pre-earthquake TEC anomalies show local time recurrence for 38 earthquakes, which occur around the same local time on different days. The local time distribution of the pre-earthquake TEC anomalies mainly concentrates between 19 and 06 LT, roughly from the sunset to sunrise. Most of the pre-earthquake TEC anomalies do not locate above the epicenter but shift to the south. The pre-earthquake TEC anomalies could be extracted near the magnetic conjugate point of the epicenter for 40 events, which is 50% out of the total 80 cases with significant local TEC anomalies. In general, the signs of the anomalies around epicenter and its conjugate point are the same, but the abnormal magnitude and lasting time are not.

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.

Plasma density irregularities and Total Electron Content gradients over Europe

NASA Astrophysics Data System (ADS)

Zakharenkova, I.; Kotulak, K.; Cherniak, I.; Krankowski, A.; Froń, A.

2017-12-01

Perturbations of the ionospheric plasma density are crucial from the scientific and application points of view, as they can severe affect radio signals used in the Global Navigation Satellite Systems (GNSS) and low frequency radio astronomy. For several decades the ionospheric irregularities have been extensively studied by different techniques, including ground-based GNSS observations. Spatial distribution of ionospheric disturbances can be specified by horizontal gradients of the ionospheric density (total electron content, TEC). Another, widely used tool in irregularities monitoring is the rate of TEC index (ROTI). Recently, the Northern Hemisphere ROTI product has been implemented to the International GNSS Service (IGS) and available for community. In this study, we present climatology of the spatial TEC gradients occurred over European region at high to middle latitudes. We developed the TEC gradient maps based on the high-resolution (0.5 degree in latitude and longitude) regional TEC maps covering Europe. The obtained climatological characteristics of the spatial TEC gradients are superimposed and analyzed with the global and regional ROTI product in order to reveal development of highly intense plasma irregularities occurred at high and middle latitudes. During geomagnetic storm the complex of physical processes at auroal zone leads to development of intnse ionospheric irregularities and travelling ionospheric disturbances (TIDs). We presents results of the geomagnetic storm analysis including the 2013 and 2015 St. Patrick's Day geomagnetic storms.

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.

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.

Seismo-ionospheric anomalies in total electron content of the GIM and electron density of DEMETER before the 27 February 2010 M8.8 Chile earthquake

NASA Astrophysics Data System (ADS)

Ho, Yi-Ying; Jhuang, Hau-Kun; Su, Yung-Chih; Liu, Jann-Yenq

2013-06-01

In this paper we examine the pre-earthquake ionospheric anomalies by the total electron content (TEC) extracted from GIM (global ionospheric map) and the electron density (Ne) observed by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite during the 2010 M8.8 Chile earthquake. Temporal variations show the nighttime TEC and Ne simultaneously increase 9-19 days before the earthquake. A cross-comparison of data recorded during the period of 1 February to 3 March in 2006-2010 confirms the above temporal anomalies specifically appear in 2010. The spatial analyses show that the anomalies tend to appear over the epicenter.

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.

Thunderstorm-/lightning-induced ionospheric perturbation: An observation from equatorial and low-latitude stations around Hong Kong

NASA Astrophysics Data System (ADS)

Kumar, Sanjay; Chen, Wu; Chen, Mingli; Liu, Zhizhao; Singh, R. P.

2017-08-01

Total electron content (TEC) computed from the network of Global Positioning System over Hong Kong area known as Hong Kong Sat-Ref-network has been used to study perturbation in the ionosphere from thunder storm activity. Data for geomagnetic quiet day (Kp < 4, on 1 April 2014) have been analyzed. The lightning activity was measured from Total Lightning sensor LS8000 over/around the Hong Kong region. Deviation in vertical TEC (DTEC) and the rate of change of TEC index (ROTI) have been derived and compared for lightning day of 1 April 2014 and nonlightning day of 7 April 2014. An analysis showed reduction in TEC during evening hour (up to 1245 UT), whereas an enhancement during nighttime hour on the lightning day is observed. The variations in DTEC during nonlightning day are found to be insignificant in comparison to that during the lightning day. The ionospheric perturbation in TEC has been noticed up to a distance around 500 km and more from the lightning center. ROTI is found to vary from 3 to 60 total electron content unit (TECU)/min (1 TECU = 1016 el m-2) on the day of thunderstorm activity, whereas ROTI is insignificant on nonlightning days. Signature of density bubbles in slant TEC data and periodicities (10-100 min) in DTEC data are observed. For the same pseudorandom numbers (1, 10, 13, 23, and 28) strong amplitude scintillations are also observed at a close by station. Amplitude scintillations are proposed to be caused by plasma bubbles. The results are tentatively explained by thunderstorm-induced electric fields and gravity waves.

Ionospheric Response to the Magnetic Storm of 22 June 2015

NASA Astrophysics Data System (ADS)

Mansilla, Gustavo A.

2018-03-01

A global study is made of the response of the total electron content of the ionosphere (TEC) to the geomagnetic storm occurred on 22 June 2015 (one of the strongest geomagnetic storms of the current Solar Cycle 24). Using data from 44 sites, a hemispheric comparison is made by considering high latitudes (> 50°), middle latitudes (30°-50°) and low latitudes (30°N-30°S). The main features observed were: increases in TEC at high latitudes prior to the storm main phase, a considerable asymmetry of TEC response at middle and low latitudes of the Northern Hemisphere and the Southern Hemisphere and decreases at equatorial latitudes. The long duration enhancements in TEC were well correlated with increases in the O/N2 ratio but decreases in TEC had not associated decreases in the O/N2 ratio as occur with the decreases in the electron density. Besides, prompt penetration electric fields can play an important role in the equatorial and low-latitude ionosphere during main phase of the storm.

Analysis of ionospheric irregularities during total solar eclipse 2016 based on GNSS observation

NASA Astrophysics Data System (ADS)

Husin, A.; Jiyo; Anggarani, S.; Ekawati, S.; Dear, V.

2016-11-01

A total solar eclipse occurred over Indonesia in the morning hours on 9 March 2016. Ionisations in the ionosphere which is associated with the solar radiation during the total eclipse provided a good opportunity to study the ionospheric irregularities. Using global navigation satellite system (GNSS) data taken from dual-frequency receivers in Manado, we investigated and analysed the total electron content (TEC) perturbations with a time resolution of 60 s to reveal ionospheric irregularities during total eclipse. Result showed that TEC conditions based on IPP were decreased during solar eclipse on March 9, comparing with the neighbour day. The maximum percentage deviation (DTEC) from the average value during eclipse period, 00:00 - 02:40 UT reach -41.5%. The duration of maximum decrement in TEC occurs were around 2-30 minutes after the maximum obscuration.

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.

An investigation of solar flares and associated solar radio bursts impact on ionospheric total electron content

NASA Astrophysics Data System (ADS)

Tuyizere, Sarathiel

2016-07-01

Solar transients events such as Coronal Mass Ejections (CMEs) and solar flares represent the cause of various aspects of space weather and can impact the modern man made technological system. Such solar transients are often associated with solar radio bursts (SRBs), particularly of type II and III that , at ground level can be detected by the CALLISTO (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatories) solar spectrometer. The present study aims at investigating solar flares and associated SRBs impact on the ionospheric total electron content (TEC). SRBs data used are dynamic spectra covering the 2014-2015 period and detected by the CALLISTO instrument that is installed at the university of Rwanda, Kigali. To investigate ionospheric impact, we use TEC data from IGS stations located at almost the same universal time zone, and correlate the observed TEC changes to the corresponding observed solar bursts events. Preliminary observations resulting from this study indicate a slight enhancement in TEC during the burst event days. The observed TEC enhancement on the burst day can be associated to increased UV and X-rays radiations and particle acceleration that are associated with SRBs events. This work is a contribution to more understanding of the geo-space impact of solar transients phenomena for modeling and prediction.

An investigation of solar flares and associated solar radio bursts on ionospheric total electron content

NASA Astrophysics Data System (ADS)

Uwamahoro, Jean

2016-07-01

Solar transients events such as Coronal Mass Ejections (CMEs) and solar flares represent are the cause of various aspects of space weather and can impact the modern man made technological system. Such solar transients are often associated with solar radio bursts (SRBs), particularly of type II and III that , at ground level can be detected by the CALLISTO (Compact Astronomical Low-frequency Low-cost Instrument for Spectroscopy and Transportable Observatories) solar spectrometer. The present study aims at investigating solar flares and associated SRBs impact on the ionospheric total electron content (TEC). SRBs data used are dynamic spectra covering the 2014-2015 period and detected by the CALLISTO instrument that is installed at the university of Rwanda, Kigali. To investigate ionospheric impact, we use TEC data from IGS stations located at almost the same universal time zone, and correlate the observed TEC changes to the corresponding observed solar bursts events. Preliminary observations resulting from this study indicate a slight enhancement in TEC during the burst event days. The observed TEC enhancement on the burst day can be associated to increased UV and X-rays radiations and particle acceleration that are associated with SRBs events. This work is a contribution to more understanding of the geo-space impact of solar transients phenomena for modeling and prediction.

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.

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.

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

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.

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.

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.

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.

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.

Performance evaluation of GNSS-TEC estimation techniques at the grid point in middle and low latitudes during different geomagnetic conditions

NASA Astrophysics Data System (ADS)

Abe, O. E.; Otero Villamide, X.; Paparini, C.; Radicella, S. M.; Nava, B.; Rodríguez-Bouza, M.

2017-04-01

Global Navigation Satellite Systems (GNSS) have become a powerful tool use in surveying and mapping, air and maritime navigation, ionospheric/space weather research and other applications. However, in some cases, its maximum efficiency could not be attained due to some uncorrelated errors associated with the system measurements, which is caused mainly by the dispersive nature of the ionosphere. Ionosphere has been represented using the total number of electrons along the signal path at a particular height known as Total Electron Content (TEC). However, there are many methods to estimate TEC but the outputs are not uniform, which could be due to the peculiarity in characterizing the biases inside the observables (measurements), and sometimes could be associated to the influence of mapping function. The errors in TEC estimation could lead to wrong conclusion and this could be more critical in case of safety-of-life application. This work investigated the performance of Ciraolo's and Gopi's GNSS-TEC calibration techniques, during 5 geomagnetic quiet and disturbed conditions in the month of October 2013, at the grid points located in low and middle latitudes. The data used are obtained from the GNSS ground-based receivers located at Borriana in Spain (40°N, 0°E; mid latitude) and Accra in Ghana (5.50°N, -0.20°E; low latitude). The results of the calibrated TEC are compared with the TEC obtained from European Geostationary Navigation Overlay System Processing Set (EGNOS PS) TEC algorithm, which is considered as a reference data. The TEC derived from Global Ionospheric Maps (GIM) through International GNSS service (IGS) was also examined at the same grid points. The results obtained in this work showed that Ciraolo's calibration technique (a calibration technique based on carrier-phase measurements only) estimates TEC better at middle latitude in comparison to Gopi's technique (a calibration technique based on code and carrier-phase measurements). At the same time, Gopi's calibration was also found more reliable in low latitude than Ciraolo's technique. In addition, the TEC derived from IGS GIM seems to be much reliable in middle-latitude than in low-latitude region.

Ionospheric Slant Total Electron Content Analysis Using Global Positioning System Based Estimation

NASA Technical Reports Server (NTRS)

Komjathy, Attila (Inventor); Mannucci, Anthony J. (Inventor); Sparks, Lawrence C. (Inventor)

2017-01-01

A method, system, apparatus, and computer program product provide the ability to analyze ionospheric slant total electron content (TEC) using global navigation satellite systems (GNSS)-based estimation. Slant TEC is estimated for a given set of raypath geometries by fitting historical GNSS data to a specified delay model. The accuracy of the specified delay model is estimated by computing delay estimate residuals and plotting a behavior of the delay estimate residuals. An ionospheric threat model is computed based on the specified delay model. Ionospheric grid delays (IGDs) and grid ionospheric vertical errors (GIVEs) are computed based on the ionospheric threat model.

Investigation of mid-latitude electron density enhancement using total electron content measurements and FORMOSAT-3/COSMIC electron density profiles

NASA Astrophysics Data System (ADS)

Rajesh, P. K.; Nanan, Balan; Liu, Jann-Yenq; Lin, Charles C. H.; Chang, S. Y.; Chen, Chia-Hung

This study investigates the mid-latitude electron density enhancement (MEDE) using global ionospheric map (GIM) total electron content (TEC) measurements and FORMOSAT-3/COSMIC (F3/C) electron density profiles. Diurnal, seasonal, latitudinal, and solar activity variations in the occurrence and strength of MEDE are examined using global GIM TEC data in the years 2002 and 2009. The results show that MEDE occurrence is pronounced during 2200-0400 LT, the feature also appears during day. The strength of MEDE maximizes around 0400 LT, and is very weak during daytime. The occurrence and strength show significant longitude dependence, and vary with season and solar activity. Concurrent F3/C electron density profiles also reveal enhancement of the peak electron density and total electron content. Further studies are carried out by examining the role of neutral wind in re-organizing the plasma using SAMI2 and HWM93 models. The results indicate that meridional neutral wind could cause the plasma to converge over mid-latitudes, and thus support in maintaining the enhancement.

Direct EUV/X-Ray Modulation of the Ionosphere During the August 2017 Total Solar Eclipse

NASA Astrophysics Data System (ADS)

Mrak, Sebastijan; Semeter, Joshua; Drob, Douglas; Huba, J. D.

2018-05-01

The great American total solar eclipse of 21 August 2017 offered a fortuitous opportunity to study the response of the atmosphere and ionosphere using a myriad of ground instruments. We have used the network of U.S. Global Positioning System receivers to examine perturbations in maps of ionospheric total electron content (TEC). Coherent large-scale variations in TEC have been interpreted by others as gravity wave-induced traveling ionospheric disturbances. However, the solar disk had two active regions at that time, one near the center of the disk and one at the edge, which resulted in an irregular illumination pattern in the extreme ultraviolet (EUV)/X-ray bands. Using detailed EUV occultation maps calculated from the National Aeronautics and Space Administration Solar Dynamics Observatory Atmospheric Imaging Assembly images, we show excellent agreement between TEC perturbations and computed gradients in EUV illumination. The results strongly suggest that prominent large-scale TEC disturbances were consequences of direct EUV modulation, rather than gravity wave-induced traveling ionospheric disturbances.

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.

Comparison of Ionospheric TEC Derived from GPS and IRI 2012 Model during Geomagnetic Storms at Indonesia

NASA Astrophysics Data System (ADS)

Marlia, Dessi; Wu, Falin

2016-07-01

This paper investigates the variations of vertical Total Electron Content (VTEC) at Manado, Indonesia (geographic coordinates : lat 1.34 ° S and long 124.82 ° E) for period 2013. The GPS measured TEC is compared with the TEC derived from the IRI (International Reference Ionosphere) 2012 model. Vertical TEC measurements obtained from dual frequency GPS receiver that is GISTM (GPS Ionospheric Scintillations and TEC monitor). Variation of TEC validate to IRI 2012 model at Manado station has been compared with the model for three different topside of electron density namely NeQuick, IRI-01-Corr and IRI2001.There is a need to investigation on diurnal, seasonal variations, solar activity dependence of TEC and including effects of space weather related events to TEC and modeling of TEC. In this paper, diurnal and seasonal variations of VTEC and the effect of VTEC due to space weather events like Geomagnetic storms are analyzed. The result show that the TEC prediction using IRI-2001 model overestimated the GPS TEC measurements, while IRI-NeQuick and IRI-01-corr show a tendency to underestimates the observed TEC during the day time particularly in low latitude region in the maximum solar activity period (2013). The variations of VTEC during 17th March, 2013, 29th June, 2013 storms are analyzed. During 17th March,2013 storm enhancement in VTEC with Kp value 6 and Disturbance storm index (DST) -132 nT. During 29th June, 2013 storm VTEC depletion with value 7 and DST -98 nT. Significant deviations in VTEC during the main phase of the storms are observed. It is found that the response of ionospheric TEC consist of effects of both enhancement and depletions in ionospheric structures (positive and negative storm). Keywords: TEC ionosphere, GPS, GISTM, IRI 2012 model, solar activity, geomagnetic storm

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.

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 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

Characterizing Interplanetary Structures of Long-Lasting Ionospheric Storm Events

NASA Astrophysics Data System (ADS)

Tandoi, C.; Dong, Y.; Ngwira, C. M.; Damas, M. C.

2015-12-01

Geomagnetic storms can result in periods of heightened TEC (Total Electron Content) in Earth's ionosphere. These periods of change in TEC (dTEC) can have adverse impacts on a technological society, such as scintillation of radio signals used by communication and navigation satellites. However, it is unknown which exact properties of a given storm cause dTEC. We are comparing different solar wind properties that result in a significant long-lasting dTEC to see if there are any patterns that remain constant in these storms. These properties, among others, include the interplanetary magnetic field By and Bz components, the proton density, and the flow speed. As a preliminary investigation, we have studied 15 solar storms. Preliminary results will be presented. In the future, we hope to increase our sample size and analyze over 80 different solar storms, which result in significant dTEC.

Investigation of TEC Variations over Mid-Latitude during Quit and Disturbed Days of March 2015

NASA Astrophysics Data System (ADS)

Atıcı, Ramazan; Saǧır, Selçuk; Güzel, Esat

2016-07-01

The variations during 09-14-March-2015 quit days and 15-20 March 2015 disturbed days of Total Electron Content (TEC) values (provided by IONOLAB group) obtained by analysis the data from Ankara Global Position System (GPS) station of Turkey located at mid-latitude, IRI -2012 model the and IRI-PLUS model are investigated. Also, the variations of the geomagnetic, interplanetary and solar wind parameters are examined. As a result of investigations, TEC values from all three models are not change too much at quit days. Unlike, at the disturbed days, although IRI-2012 and IRI-PLUS TEC values are not change too much, a noticeable change in GPS-TEC values is occurred. GPS-TEC values are rapidly increased on 17-March 2015 to be severe magnetic storm (Dst = -124 nT). Then, on following days it was observed to significantly decrease. Thus, it is said that GPS-TEC values are more sensitive than IRI-2012 and IRI-PLUS models to variations occurred on disturbed days.

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.

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.

Improved estimation of Mars ionosphere total electron content

NASA Astrophysics Data System (ADS)

Cartacci, M.; Sánchez-Cano, B.; Orosei, R.; Noschese, R.; Cicchetti, A.; Witasse, O.; Cantini, F.; Rossi, A. P.

2018-01-01

We describe an improved method to estimate the Total Electron Content (TEC) of the Mars ionosphere from the echoes recorded by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) (Picardi et al., 2005; Orosei et al., 2015) onboard Mars Express in its subsurface sounding mode. In particular, we demonstrate that this method solves the issue of the former algorithm described at (Cartacci et al., 2013), which produced an overestimation of TEC estimates on the day side. The MARSIS signal is affected by a phase distortion introduced by the Mars ionosphere that produces a variation of the signal shape and a delay in its travel time. The new TEC estimation is achieved correlating the parameters obtained through the correction of the aforementioned effects. In detail, the knowledge of the quadratic term of the phase distortion estimated by the Contrast Method (Cartacci et al., 2013), together with the linear term (i.e. the extra time delay), estimated through a radar signal simulator, allows to develop a new algorithm particularly well suited to estimate the TEC for solar zenith angles (SZA) lower than 95° The new algorithm for the dayside has been validated with independent data from MARSIS in its Active Ionospheric Sounding (AIS) operational mode, with comparisons with other previous algorithms based on MARSIS subsurface data, with modeling and with modeling ionospheric distortion TEC reconstruction.

Observing Tsunamis in the Ionosphere Using Ground Based GPS Measurements

NASA Technical Reports Server (NTRS)

Galvan, D. A.; Komjathy, A.; Song, Y. Tony; Stephens, P.; Hickey, M. P.; Foster, J.

2011-01-01

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 recent seismic events, including the Tohoku tsunami of March 11, 2011. We observe fluctuations correlated in time, space, and wave properties with this tsunami in TEC estimates processed using JPL's Global Ionospheric Mapping Software. These TEC estimates were band-pass filtered to remove ionospheric TEC variations with periods outside the typical range of internal gravity waves caused by tsunamis. Observable variations in TEC appear correlated with the Tohoku tsunami near the epicenter, at Hawaii, and near the west coast of North America. Disturbance magnitudes are 1-10% of the background TEC value. Observations near the epicenter 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. The potential exists to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for future early warning systems.

Long Duration Enhancement And Depletion Observed In The Topside Ionospheric Electron Content During The March 2015 Strong Storm

NASA Astrophysics Data System (ADS)

Zhong, J.; Wang, W.; Yue, X.; Burns, A. G.; Dou, X.; Lei, J.

2015-12-01

Up-looking total electron content (TEC) measurements from multiple low Earth orbit (LEO) satellites have been utilized to study the topside ionospheric response to the 17 March 2015 great storm. The combined up-looking TEC observations from these LEO satellites are valuable in addressing the local time and altitudinal dependences of the topside ionospheric response to geomagnetic storms from a global perspective, especially over the southern hemisphere and oceans. In the evening sector, the up-looking TEC showed an obvious long-duration of positive storm effect during the main phase and a long duration of negative storm effect during the recovery phase of this storm. The increases of the topside TEC during the main phase were symmetric with respect to the magnetic equator, which was probably associated with penetration electric fields. Additionally, the up-looking TEC from different orbital altitudes suggested that the negative storm effect at higher altitudes was stronger in the evening sector. In the morning sector, the up-looking TEC also showed increases at low and middle latitudes during the storm main phase. Obvious TEC enhancement can be also seen over the Pacific Ocean in the topside ionosphere during the storm recovery phase. These results imply that the topside ionospheric responses significantly depend on local time. Thus, the LEO-based up-looking TEC provides an important database to study the possible physical mechanisms of the topside ionospheric response to storms.

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.

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.

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.

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.

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.

Long-Term Prediction of the Arctic Ionospheric TEC Based on Time-Varying Periodograms

PubMed Central

Liu, Jingbin; Chen, Ruizhi; Wang, Zemin; An, Jiachun; Hyyppä, Juha

2014-01-01

Knowledge of the polar ionospheric total electron content (TEC) and its future variations is of scientific and engineering relevance. In this study, a new method is developed to predict Arctic mean TEC on the scale of a solar cycle using previous data covering 14 years. The Arctic TEC is derived from global positioning system measurements using the spherical cap harmonic analysis mapping method. The study indicates that the variability of the Arctic TEC results in highly time-varying periodograms, which are utilized for prediction in the proposed method. The TEC time series is divided into two components of periodic oscillations and the average TEC. The newly developed method of TEC prediction is based on an extrapolation method that requires no input of physical observations of the time interval of prediction, and it is performed in both temporally backward and forward directions by summing the extrapolation of the two components. The backward prediction indicates that the Arctic TEC variability includes a 9 years period for the study duration, in addition to the well-established periods. The long-term prediction has an uncertainty of 4.8–5.6 TECU for different period sets. PMID:25369066

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.

Total Electron Content forecast model over Australia

NASA Astrophysics Data System (ADS)

Bouya, Zahra; Terkildsen, Michael; Francis, Matthew

Ionospheric perturbations can cause serious propagation errors in modern radio systems such as Global Navigation Satellite Systems (GNSS). Forecasting ionospheric parameters is helpful to estimate potential degradation of the performance of these systems. Our purpose is to establish an Australian Regional Total Electron Content (TEC) forecast model at IPS. In this work we present an approach based on the combined use of the Principal Component Analysis (PCA) and Artificial Neural Network (ANN) to predict future TEC values. PCA is used to reduce the dimensionality of the original TEC data by mapping it into its eigen-space. In this process the top- 5 eigenvectors are chosen to reflect the directions of the maximum variability. An ANN approach was then used for the multicomponent prediction. We outline the design of the ANN model with its parameters. A number of activation functions along with different spectral ranges and different numbers of Principal Components (PCs) were tested to find the PCA-ANN models reaching the best results. Keywords: GNSS, Space Weather, Regional, Forecast, PCA, ANN.

A statistical study on seismo-ionospheric precursors in the total electron content of global ionosphere map associated with M×6.0 earthquakes in the West Pacific region during 1998-2012

NASA Astrophysics Data System (ADS)

Liu, Jann-Yenq; Chen, Koichi; Tsai, Ho-Fang; Hattori, Katsumi; Le, Huijun

2013-04-01

This paper reports statistical results of seismo-ionospheric precursors (SIPs) of the total electron content (TEC) in the global ionosphere map (GIM) over the epicenter of earthquakes with magnitude 6 and greater in China, Japan, and Taiwan during 1998-2012. To detect SIP, a quartile-based (i.e. median-based) process is performed. The earthquakes are sub-divided into various regions to have a better understanding on SIP characteristics, as well as examined with and without being led by magnetic storms to confirm the SIP existence. Results show that the SIPs mainly are the TEC significant increase in Japan, and decrease in Taiwan and China, respectively, which suggests the latitudinal effect playing an important role. Meanwhile, for a practical application of monitoring SIPs, the GIM TEC at a fixed point is tested. Results show that multi monitoring points and/or a spatial observation are required to enhance the SIP detection.

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.

Seismo-electromagnetic anomalies observed by Fomosat-1 and GIM TEC during January 27 1999 to July 2004

NASA Astrophysics Data System (ADS)

Yu, C. Y.; Liu, J. Y. G.

2014-12-01

In this study, we examine the pre-earthquake ionospheric anomalies (PEIAs) by the electron density (Ne) and ion temperature (Ti) observed by FORMOSAT-1 (ROCSAT-1) satellite during magnitude greater than 7.0 worldwide earthquakes during 1999-2004. Meanwhile, PEIAs is also currently investigated to have a better understanding of the spatial distribution of the ROCSAT-1 SIPs. Total electron density (TEC) of the global ionosphere map (GIM) confirm that the anomalous feature appear near the epicenters before the earthquakes.

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.

Ionospheric TEC Weather Map Over South America

NASA Astrophysics Data System (ADS)

Takahashi, H.; Wrasse, C. M.; Denardini, C. M.; Pádua, M. B.; de Paula, E. R.; Costa, S. M. A.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. Galera; Ivo, A.; Sant'Anna, N.

2016-11-01

Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total 140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m-2 (TECU) <10) to the crest region (TECU > 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

Study of the Total Electron Content in Mars ionosphere from MARSIS data set

NASA Astrophysics Data System (ADS)

Bergeot, Nicolas; Witasse, Olivier; Kofman, Wlodek; Grima, Cyril; Mouginot, Jeremie; Peter, Kerstin; Pätzold, Martin; Dehant, Véronique

2016-04-01

Centimeter level accuracy on the signal delay will be required on X-band radio link for future Mars landers such as InSIGHT, aiming at better determining the interior structure of Mars. One of the main error sources in the estimated signal delay is directly linked to the Total Electron Content (TEC) values at Earth and Mars ionosphere level. While the Earth ionosphere is now well modeled and monitored at regional and global scales, this is not the case concerning the Mars' upper atmosphere. The present paper aims at establishing the basis to model the climatological behavior of the TEC on a global scale in the Mars' ionosphere. For that we analyzed ˜8.5 years of data (mid-2005 to 2014) of the vertical Total Electron Content (vTEC) expressed in TEC units (1 TECu = 1016e-.m-2) from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) radar. Our study takes advantage of the double data set of EUV solar index and Mars vTEC data to develop an empirical Model of Mars Ionosphere (MoMo). The finality of this model is to predict the vTEC at a given latitude, solar zenith angle and season taking only F10.7P solar index as input. To minimize the differences during the least-square adjustment between the modeled and observed vTEC, we considered (1) a 4th-order polynomial function to describe the vTEC diurnal behavior (2) a discretization with respect to Mars seasons (depending on Ls) and (3) two latitudinal sectors (North and South hemispheres). The mean of the differences between the model and the observations is 0.00±0.07 TECu with an error of the model around 0.1 TECu depending on the Solar Zenith Angle (SZA), season and hemisphere of interest (e.g. rms 0.12 TECu for SZA equal to 50°±5° in the Northern hemisphere during the spring season). Additionally, comparison with 250 Mars Express radio occultation data shows differences with MoMo predictions of 0.02±0.06 TECu for solar zenith angles below 50 degrees. Using the model we (1) highlighted different behaviors of Mars ionosphere depending on seasons, solar activity level, and latitudes; (2) estimated a maximum effect on X-Band signal delay (up plus down links) of ˜3 cm during the autumn season and high solar activity at the future InSIGHT lander location.

Total electron content responses to HILDCAAs and geomagnetic storms over South America

NASA Astrophysics Data System (ADS)

Mara de Siqueira Negreti, Patricia; Rodrigues de Paula, Eurico; Nicoli Candido, Claudia Maria

2017-12-01

Total electron content (TEC) is extensively used to monitor the ionospheric behavior under geomagnetically quiet and disturbed conditions. This subject is of greatest importance for space weather applications. Under disturbed conditions the two main sources of electric fields, which are responsible for changes in the plasma drifts and for current perturbations, are the short-lived prompt penetration electric fields (PPEFs) and the longer-lasting ionospheric disturbance dynamo (DD) electric fields. Both mechanisms modulate the TEC around the globe and the equatorial ionization anomaly (EIA) at low latitudes. In this work we computed vertical absolute TEC over the low latitude of South America. The analysis was performed considering HILDCAA (high-intensity, long-duration, continuous auroral electrojet (AE) activity) events and geomagnetic storms. The characteristics of storm-time TEC and HILDCAA-associated TEC will be presented and discussed. For both case studies presented in this work (March and August 2013) the HILDCAA event follows a geomagnetic storm, and then a global scenario of geomagnetic disturbances will be discussed. Solar wind parameters, geomagnetic indices, O / N2 ratios retrieved by GUVI instrument onboard the TIMED satellite and TEC observations will be analyzed and discussed. Data from the RBMC/IBGE (Brazil) and IGS GNSS networks were used to calculate TEC over South America. We show that a HILDCAA event may generate larger TEC differences compared to the TEC observed during the main phase of the precedent geomagnetic storm; thus, a HILDCAA event may be more effective for ionospheric response in comparison to moderate geomagnetic storms, considering the seasonal conditions. During the August HILDCAA event, TEC enhancements from ˜ 25 to 80 % (compared to quiet time) were observed. These enhancements are much higher than the quiet-time variability observed in the ionosphere. We show that ionosphere is quite sensitive to solar wind forcing and considering the events studied here, this was the most important source of ionospheric responses. Furthermore, the most important source of TEC changes were the long-lasting PPEFs observed on August 2013, during the HILDCAA event. The importance of this study relies on the peculiarity of the region analyzed characterized by high declination angle and ionospheric gradients which are responsible for creating a complex response during disturbed periods.

A statistical investigation of z test and ROC curve on seismo-ionospheric anomalies in TEC associated earthquakes in Taiwan during 1999-2014

NASA Astrophysics Data System (ADS)

Shih, A. L.; Liu, J. Y. G.

2015-12-01

A median-based method and a z test are employed to find characteristics of seismo-ionospheric precursor (SIP) of the total electron content (TEC) in global ionosphere map (GIM) associated with 129 M≥5.5 earthquakes in Taiwan during 1999-2014. Results show that both negative and positive anomalies in the GIM TEC with the statistical significance of the z test appear few days before the earthquakes. The receiver operating characteristic (ROC) curve is further applied to see whether the SIPs exist in Taiwan.

Solar Eclipse-Induced Changes in the Ionosphere over the Continental US

NASA Astrophysics Data System (ADS)

Erickson, P. J.; Zhang, S.; Goncharenko, L. P.; Coster, A. J.; Hysell, D. L.; Sulzer, M. P.; Vierinen, J.

2017-12-01

For the first time in 26 years, a total solar eclipse occurred over the continental United States on 21 August 2017, between 16:00-20:00 UT. We report on American solar eclipse observations of the upper atmosphere, conducted by a team led by MIT Haystack Observatory. Efforts measured ionospheric and thermospheric eclipse perturbations. Although eclipse effects have been studied for more than 50 years, recent major sensitivity and resolution advances using radio-based techniques are providing new information on the eclipse ionosphere-thermosphere-mesosphere (ITM) system response. Our study was focused on quantifying eclipse effects on (1) traveling ionospheric disturbances (TIDs) and atmospheric gravity waves (AGWs); (2) spatial ionospheric variations associated with the eclipse; and (3) altitudinal and temporal ionospheric profile variations. We present selected early findings on ITM eclipse response including a dense global network of 6000 GNSS total electron content (TEC) receivers (100 million measurements per day; 1x1 degree spatial grid) and the Millstone Hill and Arecibo incoherent scatter radars. TEC depletions of up to 60% in magnitude were associated with the eclipse umbra and penumbra and consistently trailed the eclipse totality center. TEC enhancements associated with prominent orographic features were observed in the western US due to complex interactions as the lower atmosphere cooled in response to decreasing EUV energy inputs. Strong TIDs in the form of bow waves, stern waves, and a stern wake were observed in TEC data. Altitude-resolved plasma parameter profiles from Millstone Hill saw a nearly 50% decrease in F region electron density in vertical profiles, accompanied by a corresponding 200-250 K decrease in electron temperature. Wide field Millstone Hill radar scans showed similar decreases in electron density to the southwest, maximizing along the line of closest approach to totality. Data is available to the research community through the MIT Haystack Madrigal system. Alongside a summary of observations, we will also present preliminary quantitative comparisons with several ongoing modeling efforts.

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.

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.

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.

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.

Ionospheric effects of sudden stratospheric warmings in eastern Siberia region

NASA Astrophysics Data System (ADS)

Polyakova, A. S.; Chernigovskaya, M. A.; Perevalova, N. P.

2014-12-01

Ionospheric effects observed in Russia's Asia region during sudden stratospheric warmings (SSWs) in the winters 2008/2009 and 2012/2013 corresponding to both extreme solar minimum and moderate solar maximum conditions have been examined. To detect the ionospheric effects which must have been induced by the SSWs, we have carried out a joint analysis of total electron content (TEC) global ionospheric maps (GIM), MLS (Microwave Limb Sounder, EOS Aura) measurements of vertical temperature profiles, as well as NCEP/NCAR and UKMO Reanalysis data. It has been revealed for the first time that during strong SSWs the amplitude of diurnal variation of TEC decreases nearly by half in the mid-latitude ionosphere. Besides, the intensity of TEC deviations from the background level increases during SSWs. It has also revealed that during SSW peak the midday TEC maximum considerably decreases, and the night/morning TEC increases compared to quiet days. The pattern of TEC response to SSW is shown to be identical for both quiet and disturbed geophysical conditions.

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.

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.

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.

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.

First results from the ionospheric tomography experiment using beacon TEC data obtained by means of a network along a longitude of 136°E over Japan

NASA Astrophysics Data System (ADS)

Thampi, Smitha V.; Yamamoto, Mamoru

2010-03-01

A chain of newly designed GNU (GNU is not UNIX) Radio Beacon Receivers (GRBR) has recently been established over Japan, primarily for tomographic imaging of the ionosphere over this region. Receivers installed at Shionomisaki (33.45°N, 135.8°E), Shigaraki (34.8°N, 136.1°E), and Fukui (36°N, 136°E) continuously track low earth orbiting satellites (LEOS), mainly OSCAR, Cosmos, and FORMOSAT-3/COSMIC, to obtain simultaneous total electron content (TEC) data from these three locations, which are then used for the tomographic reconstruction of ionospheric electron densities. This is the first GRBR network established for TEC observations, and the first beacon-based tomographic imaging in Japanese longitudes. The first tomographic images revealed the temporal evolution with all of the major features in the ionospheric electron density distribution over Japan. A comparison of the tomographically reconstructed electron densities with the ƒ o F 2 data from Kokubunji (35°N, 139°E) revealed that there was good agreement between the datasets. These first results show the potential of GRBR and its network for making continuous, unattended ionospheric TEC measurements and for tomographic imaging of the ionosphere.

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).

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.

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.

Three-dimensional ionospheric tomography reconstruction using the model function approach in Tikhonov regularization

NASA Astrophysics Data System (ADS)

Wang, Sicheng; Huang, Sixun; Xiang, Jie; Fang, Hanxian; Feng, Jian; Wang, Yu

2016-12-01

Ionospheric tomography is based on the observed slant total electron content (sTEC) along different satellite-receiver rays to reconstruct the three-dimensional electron density distributions. Due to incomplete measurements provided by the satellite-receiver geometry, it is a typical ill-posed problem, and how to overcome the ill-posedness is still a crucial content of research. In this paper, Tikhonov regularization method is used and the model function approach is applied to determine the optimal regularization parameter. This algorithm not only balances the weights between sTEC observations and background electron density field but also converges globally and rapidly. The background error covariance is given by multiplying background model variance and location-dependent spatial correlation, and the correlation model is developed by using sample statistics from an ensemble of the International Reference Ionosphere 2012 (IRI2012) model outputs. The Global Navigation Satellite System (GNSS) observations in China are used to present the reconstruction results, and measurements from two ionosondes are used to make independent validations. Both the test cases using artificial sTEC observations and actual GNSS sTEC measurements show that the regularization method can effectively improve the background model outputs.

The impact of spherical symmetry assumption on radio occultation data inversion in the ionosphere: An assessment study

NASA Astrophysics Data System (ADS)

Shaikh, M. M.; Notarpietro, R.; Nava, B.

2014-02-01

'Onion-peeling' is a very common technique used to invert Radio Occultation (RO) data in the ionosphere. Because of the implicit assumption of spherical symmetry for the electron density (N(e)) distribution in the ionosphere, the standard Onion-peeling algorithm could give erroneous concentration values in the retrieved electron density profile. In particular, this happens when strong horizontal ionospheric electron density gradients are present, like for example in the Equatorial Ionization Anomaly (EIA) region during high solar activity periods. In this work, using simulated RO Total Electron Content (TEC) data computed by means of the NeQuick2 ionospheric electron density model and ideal RO geometries, we tried to formulate and evaluate an asymmetry level index for quasi-horizontal TEC observations. The asymmetry index is based on the electron density variation that a signal may experience along its path (satellite to satellite link) in a RO event and is strictly dependent on the occultation geometry (e.g. azimuth of the occultation plane). A very good correlation has been found between the asymmetry index and errors related to the inversion products, in particular those concerning the peak electron density NmF2 estimate and the Vertical TEC (VTEC) evaluation.

Ionospheric response over Europe during the solar eclipse of March 20, 2015

NASA Astrophysics Data System (ADS)

Hoque, Mohammed Mainul; Wenzel, Daniela; Jakowski, Norbert; Gerzen, Tatjana; Berdermann, Jens; Wilken, Volker; Kriegel, Martin; Sato, Hiroatsu; Borries, Claudia; Minkwitz, David

2016-10-01

The solar eclipse on March 20, 2015 was a fascinating event for people in Northern Europe. From a scientific point of view, the solar eclipse can be considered as an in situ experiment on the Earth's upper atmosphere with a well-defined switching off and on of solar irradiation. Due to the strong changes in solar radiation during the eclipse, dynamic processes were initiated in the atmosphere and ionosphere causing a measurable impact, for example, on temperature and ionization. We analyzed the behavior of total ionospheric ionization over Europe by reconstructing total electron content (TEC) maps and differential TEC maps. Investigating the large depletion zone around the shadow spot, we found a TEC reduction of up to 6 TEC units, i.e., the total plasma depletion reached up to about 50%. However, the March 20, 2015 eclipse occurred during the recovery phase of a strong geomagnetic storm and the ionosphere was still perturbed and depleted. Therefore, the unusual high depletion is due to the negative bias of up to 20% already observed over Northern Europe before the eclipse occurred. After removing the negative storm effect, the eclipse-induced depletion amounts to about 30%, which is in agreement with previous observations. During the solar eclipse, ionospheric plasma redistribution processes significantly affected the shape of the electron density profile, which is seen in the equivalent slab thickness derived by combining vertical incidence sounding (VS) and TEC measurements. We found enhanced slab thickness values revealing, on the one hand, an increased width of the ionosphere around the maximum phase and, on the other, evidence for delayed depletion of the topside ionosphere. Additionally, we investigated very low frequency (VLF) signal strength measurements and found immediate amplitude changes due to ionization loss at the lower ionosphere during the eclipse time. We found that the magnitude of TEC depletion is linearly dependent on the Sun's obscuration function. By modelling TEC depletion and knowing the Sun's obscuration function in advance, Global Navigation Satellite System (GNSS) operators may improve the broadcast ionospheric correction during a solar eclipse day.

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.

Vertical and Lateral Electron Content in the Martian Ionosphere

NASA Astrophysics Data System (ADS)

Paetzold, M. P.; Peter, K.; Bird, M. K.; Häusler, B.; Tellmann, S.

2016-12-01

The radio-science experiment MaRS (Mars Express Radio Science) on the Mars Express spacecraft sounds the neutral atmosphere and ionosphere of Mars since 2004. Approximately 800 vertical profiles of the ionospheric electron density have been acquired until today. The vertical electron content (TEC) is easily computed from the vertical electron density profile by integrating along the altitude. The TEC is typically a fraction of a TEC unit (1E16 m^-2) and depends on the solar zenith angle. The magnitude of the TEC is however fully dominated by the electron density contained in the main layer M2. The contributions by the M1 layer below M2 or the topside is marginal. MaRS is using two radio frequencies for the sounding of the ionosphere. The directly observed differential Doppler from the two received frequencies is a measure of the lateral electron content that means along the ray path and perpendicular to the vertical electron density profile. Combining both the vertical electron density profile, the vertical TEC and the directly observed lateral TEC describes the lateral electron density distribution in the ionosphere.

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

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.

Detection of Seismic Precursors Using Distance Metrics Between GPS-TEC and IRI-Plas

NASA Astrophysics Data System (ADS)

Necat Deviren, M.; Gulyaeva, Tamara; Sezen, Umut; Arikan, Feza; Arikan, Orhan

Ionosphere is an important layer of atmosphere that varies under solar, geomagnetic, gravitational and seismic activities. Total Electron Content (TEC) is one of the main observables of ionosphere. International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) is accepted by International Organization for Standardization (ISO) as the standard climatic model. IRI-Plas provides TEC up to GPS satellite height. TEC can be estimated using Global Positioning System (GPS) Networks. In this study, TEC is computed using both IRI-Plas and Turkish National Permanent GPS Network as IONOLAB-TEC. In order to detect seismic precursors, three different distance metrics, namely Symmetric Kullback-Liebler Distance (SKLD), Cross-Correlation Coefficient (CC), and L2-Norm (L2N), are implemented between IONOLAB-TEC and IRI-Plas-TEC values. SKLD is also computed between IONOLAB-TEC Maps and IRI-Plas-TEC Maps over Turkey. Between May 2009 and September 2012, it is observed that SKLD metric indicates a disturbance within the period prior to 10 days of earthquake day. The disturbance in SKLD increases for the range of stations in the neighborhood of the epicenter. For strong earthquakes all of the three distance metrics indicate a disturbance before the earthquake, yet SKLD behaves as a more sensitive precursor for earthquakes larger than magnitude 4. This study is supported by the joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

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.

3D tomography of midlatitude sporadic-E in Japan from GNSS-TEC data

NASA Astrophysics Data System (ADS)

Muafiry, Ihsan Naufal; Heki, Kosuke; Maeda, Jun

2018-03-01

We studied ionospheric irregularities caused by midlatitude sporadic-E ( Es) in Japan using ionospheric total electron content (TEC) data from a dense GNSS array, GEONET, with a 3D (three-dimensional) tomography technique. Es is a thin layer of unusually high ionization that appears at altitudes of 100 km. Here, we studied five cases of Es irregularities in 2010 and 2012, also reported in previous studies, over the Kanto and Kyushu Districts. We used slant TEC residuals as the input and estimated the number of electron density anomalies of more than 2000 small blocks with dimensions of 20-30 km covering a horizontal region of 300 × 500 km. We applied a continuity constraint to stabilize the solution and performed several different resolution tests with synthetic data to assess the accuracy of the results. The tomography results showed that positive electron density anomalies occurred at the E region height, and the morphology and dynamics were consistent with those reported by earlier studies.

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.

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.

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.

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.

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.

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.

Statistical Analysis of TEC Anomalies Prior to M6.0+ Earthquakes During 2003-2014

NASA Astrophysics Data System (ADS)

Zhu, Fuying; Su, Fanfan; Lin, Jian

2018-04-01

There are many studies on the anomalous variations of the ionospheric TEC prior to large earthquakes. However, whether or not the morphological characteristics of the TEC anomalies in the daytime and at night are different is rarely studied. In the present paper, based on the total electron content (TEC) data from the global ionosphere map (GIM), we carry out a statistical survey on the spatial-temporal distribution of TEC anomalies before 1339 global M6.0+ earthquakes during 2003-2014. After excluding the interference of geomagnetic disturbance, the temporal and spatial distributions of ionospheric TEC anomalies prior to the earthquakes in the daytime and at night are investigated and compared. Except that the nighttime occurrence rates of the pre-earthquake ionospheric anomalies (PEIAs) are higher than those in the daytime, our analysis has not found any statistically significant difference in the spatial-temporal distribution of PEIAs in the daytime and at night. Moreover, the occurrence rates of pre-earthquake ionospheric TEC both positive anomalies and negative anomalies at night tend to increase slightly with the earthquake magnitude. Thus, we suggest that monitoring the ionospheric TEC changes at night might be a clue to reveal the relation between ionospheric disturbances and seismic activities.

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

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.

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.

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.

Seismo-ionospheric anomalies in ionospheric TEC and plasma density before the 17 July 2006 M7.7 south of Java earthquake

NASA Astrophysics Data System (ADS)

Tao, Dan; Cao, Jinbin; Battiston, Roberto; Li, Liuyuan; Ma, Yuduan; Liu, Wenlong; Zhima, Zeren; Wang, Lanwei; Wray Dunlop, Malcolm

2017-04-01

In this paper, we report significant evidence for preseismic ionospheric anomalies in total electron content (TEC) of the global ionosphere map (GIM) and plasma density appearing on day 2 before the 17 July 2006 M7.7 south of Java earthquake. After distinguishing other anomalies related to the geomagnetic activities, we found a temporal precursor around the epicenter on day 2 before the earthquake (15 July 2006), which agrees well with the spatial variations in latitude-longitude-time (LLT) maps. Meanwhile, the sequences of latitude-time-TEC (LTT) plots reveal that the TECs on epicenter side anomalously decrease and lead to an anomalous asymmetric structure with respect to the magnetic equator in the daytime from day 2 before the earthquake. This anomalous asymmetric structure disappears after the earthquake. To further confirm these anomalies, we studied the plasma data from DEMETER satellite in the earthquake preparation zone (2046.4 km in radius) during the period from day 45 before to day 10 after the earthquake, and also found that the densities of both electron and total ion in the daytime significantly increase on day 2 before the earthquake. Very interestingly, O+ density increases significantly and H+ density decreases, while He+ remains relatively stable. These results indicate that there exists a distinct preseismic signal (preseismic ionospheric anomaly) over the epicenter.

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.

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.

Receiver Operating Characteristic curves of the seismo-ionospheric precursors in GIM TEC associated with magnitude greater than 6.0 earthquakes in China during 1998-2013.

NASA Astrophysics Data System (ADS)

Huang, C. H.; Chen, Y. I.; Liu, J. Y. G.; Huang, Y. H.

2014-12-01

Statistical evidence of the Seismo-Ionospheric Precursors (SIPs) 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 and a z test are employed to detect the overall earthquake signatures. It is found that a reduction of positive signatures and an enhancement of negative signatures appear simultaneously on 3-5 days prior to the earthquakes in China. Finally, receiver operating characteristic (ROC) curves are used to measure the power of TEC for predicting M≥6.0 earthquakes in China.

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).

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.

A statistical study on the F2 layer vertical variation during nighttime medium-scale traveling ionospheric disturbances

NASA Astrophysics Data System (ADS)

Ssessanga, Nicholas; Kim, Yong Ha; Jeong, Se-Heon

2017-03-01

A statistical study on the relationship between the perturbation component (ΔTEC (total electron content)) and the F2 layer peak height (hmF2) during nighttime medium-scale traveling ionospheric disturbances is presented. The results are obtained by using a time-dependent computerized ionospheric tomography (CIT) technique. This was realized by using slant total electron content observations from a dense Global Positioning System receiver network over Japan (with more than 1000 receivers), together with a multiplicative algebraic reconstruction technique. Reconstructions from CIT were validated by using ionosonde and occultation measurements. A total of 36 different time snapshots of the ionosphere when medium-scale traveling ionospheric disturbances (MSTIDs) were eminent were analyzed. These were obtained from a data set covering years from 2011 to 2014. The reconstructed surface wavefronts of ΔTEC and hmF2 structure were found to be aligned along the northwest-southeast direction. These results confirm that nighttime MSTIDs are driven by electrodynamic forces related to Perkins instability which explains the northwest-southeast wavefront alignment based on the F region electrodynamics. Furthermore, from the statistical analysis hmF2 varied quasiperiodically in altitude with dominant peak-to-peak amplitudes between 10 and 40 km. In addition, ΔTEC and hmF2 were 60% anticorrelated.

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.

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).

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.

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.

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.

GIM-TEC adaptive ionospheric weather assessment and forecast system

NASA Astrophysics Data System (ADS)

Gulyaeva, T. L.; Arikan, F.; Hernandez-Pajares, M.; Stanislawska, I.

2013-09-01

The Ionospheric Weather Assessment and Forecast (IWAF) system is a computer software package designed to assess and predict the world-wide representation of 3-D electron density profiles from the Global Ionospheric Maps of Total Electron Content (GIM-TEC). The unique system products include daily-hourly numerical global maps of the F2 layer critical frequency (foF2) and the peak height (hmF2) generated with the International Reference Ionosphere extended to the plasmasphere, IRI-Plas, upgraded by importing the daily-hourly GIM-TEC as a new model driving parameter. Since GIM-TEC maps are provided with 1- or 2-days latency, the global maps forecast for 1 day and 2 days ahead are derived using an harmonic analysis applied to the temporal changes of TEC, foF2 and hmF2 at 5112 grid points of a map encapsulated in IONEX format (-87.5°:2.5°:87.5°N in latitude, -180°:5°:180°E in longitude). The system provides online the ionospheric disturbance warnings in the global W-index map establishing categories of the ionospheric weather from the quiet state (W=±1) to intense storm (W=±4) according to the thresholds set for instant TEC perturbations regarding quiet reference median for the preceding 7 days. The accuracy of IWAF system predictions of TEC, foF2 and hmF2 maps is superior to the standard persistence model with prediction equal to the most recent ‘true’ map. The paper presents outcomes of the new service expressed by the global ionospheric foF2, hmF2 and W-index maps demonstrating the process of origin and propagation of positive and negative ionosphere disturbances in space and time and their forecast under different scenarios.

Profiles of Ionospheric Storm-enhanced Density during the 17 March 2015 Great Storm

NASA Astrophysics Data System (ADS)

Liu, J.; Wang, W.; Burns, A. G.; Yue, X.; Zhang, S.; Zhang, Y.

2015-12-01

Ionospheric F2 region peak densities (NmF2) are expected to show a positive phase correlation with total electron content (TEC), and electron density is expected to have an anti-correlation with electron temperature near the ionospheric F2 peak. However, we show that, during the 17 March 2015 great storm, TEC and F2 region electron density peak height (hmF2) over Millstone Hill increased, but the F2 region electron density peak (NmF2) decreased significantly during the storm-enhanced density (SED) phase of the storm compared with the quiet-time ionosphere. This SED occurred where there was a negative ionospheric storm near the F2 peak and below it. The weak ionosphere below the F2 peak resulted in much reduced downward heat conduction for the electrons, trapping the heat in the topside. This, in turn, increased the topside scale height, so that, even though electron densities at the F2 peak were depleted, TEC increased in the SED. The depletion in NmF2 was probably caused by an increase in the density of the molecular neutrals, resulting in enhanced recombination. In addition, the storm-time topside ionospheric electron density profile was much closer to diffusive equilibrium than non-storm time profile because of less daytime plasma flow from the ionosphere to the plasmasphere.

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.

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.

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.

Comparison of GPS TEC variations with Holt-Winter method and IRI-2012 over Langkawi, Malaysia

NASA Astrophysics Data System (ADS)

Elmunim, N. A.; Abdullah, M.; Hasbi, A. M.; Bahari, S. A.

2017-07-01

The Total Electron Content (TEC) is the ionospheric parameter that has the main effect on radio wave propagation. Therefore, it is crucial to evaluate the performance of the TEC models for the further improvement of the ionospheric modelling in equatorial regions. This work presents an analysis of the TEC, derived from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver at the Langkawi station, Malaysia, located at the geographic coordinates of 6.19°N, 99.51°E and the geomagnetic coordinates of 3.39°S, 172.42°E. The diurnal, monthly and seasonal variations in 2014 of the observed GPS-TEC were compared with the statistical Holt-Winter method and a recent version of the International Reference Ionosphere model (IRI-2012), using three different topside options of an electron density, which are the IRI-2001, IRI01-corr and NeQuick. The maximum peaks of the GPS-TEC were observed in the post-noon time and the minimum was observed during the early morning time. In addition, in monthly variations the Holt-Winter and the IRI-2012 topside options showed an underestimation that was in agreement with the GPS-TEC, except for the IRI-2001 model which showed an overestimation in June, July and August. Regarding the seasonal variation of the GPS-TEC, the lowest values were observed during summer and it reached its maximum value during the equinox season. The IRI-2001 showed the highest value of percentage deviation compared to the IRI01-corr, NeQuick and Holt-Winter method. Therefore, the accuracy of the models was found to be approximately 95% in the Holt-Winter method, 75% in the IRI01-corr, 73% in the NeQuick and 66% in the IRI-2001 model. Hence, it can be inferred that the Holt-Winter method showed a higher performance and better estimates of the TEC compared to the IRI01-corr and NeQuick, while the IRI-2001 showed a poor predictive performance in the equatorial region over Malaysia.

Variations of E-region total electron content and electron density profiles over high latitudes during winter solstice 2007 using radio occultation measurements

NASA Astrophysics Data System (ADS)

Agrawal, Kajli

The space weather phenomenon involves the Sun, interplanetary space and the Earth. Different space weather conditions have diverse effects on the various layers of the Earth's atmosphere Technological advancements have created a situation in which human civilization is not only dependent on resources from deep inside the Earth, but also on the upper atmosphere and outer space region. Therefore, it is essential to improve the understanding of the impacts of space weather conditions on the ionosphere. This research focuses on the variation of total electron content (TEC) and the electron density within the E-region of the ionosphere, which extends from 80-150 km above the surface of the Earth, using radio occultation measurements obtained by COSMIC satellites and using Ionospheric Data Assimilation Four-Dimensional algorithm (IDA4D) which is used to mitigate the effects of F-region in the E-region estimation (Bust, Garner, & Gaussiran, 2004). E-region TEC and the electron density estimation for geomagnetic latitude range of 45°--80°, geomagnetic longitude range of -180°--180° and 1800--0600 MLT (magnetic local time) are presented for two active and two quiet days during winter solstice 2007. Active and quiet days are identified based on the Kp index values. Some of the important findings are (1) E-region electron peak density is higher during active days than during quiet days, and (2) during both types of days, higher density values were found at the magnetic latitude of >60° early morning MLT. Prominent E-region features (TEC and electron density) were observed during most active days over the magnetic latitude range of 60°-70° at ~02:00 MLT.

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.

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.

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.

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.

Spatial analyses on seismo-ionospheric precursors observed by GIM TEC and DEMETER during the 2008 M8.0 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Liu, Jann-Yenq; Chen, Yuh-Ing; Huang, Ching-Chi; Parrot, Michel; Pulinets, Sergey; Ouzounov, Dimitar

2015-04-01

This paper examines seismo-ionospheric precursors (SIPs) in the total electron content (TEC) of the global ionosphere map (GIM) and observations in the French satellite DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) during the 12 May 2008 M8.0 Wenchuan earthquake. The temporal and spatial analyses on the GIM TEC are used to search SIPs of the Wenchuan earthquake. Meanwhile, both daytime and nighttime electron density (Ne), electron temperature (Te), ion density (Ni) and ion temperature (Ti) probed by DEMETER are investigated. A statistical analysis of the box-and-whisker method is utilized to see if the four DEMETER data sets 1-6 days before and after the earthquake are significantly different. The analysis is employed to investigate the epicenter and three reference areas along the same magnetic latitude discriminating the SIPs from global effects. Results show that the nighttime Ne and Ni (daytime Ti) over the epicenter significantly decrease (increase) 1-6 days before the earthquake. The intersections of the global distribution of the significant differences (or anomalous changes) in the nighttime Ne, the nighttime Ni, and the daytime Ti 1-6 days before and after the earthquake specifically appear over the epicenter. The spatial analyses confirm that SIPs of GIM TEC and DEMETER observations appearing 2-6 days before are related to the 2008 M8.0 Wenchuan earthquake.

North-south components of the annual asymmetry in the ionosphere

NASA Astrophysics Data System (ADS)

Gulyaeva, T. L.; Arikan, F.; Hernandez-Pajares, M.; Veselovsky, I. S.

2014-07-01

A retrospective study of the asymmetry in the ionosphere during the solstices is made using the different geospace parameters in the North and South magnetic hemispheres. Data of total electron content (TEC) and global electron content (GEC) produced from global ionospheric maps, GIM-TEC for 1999-2013, the ionospheric electron content (IEC) measured by TOPEX-Jason 1 and 2 satellites for 2001-2012, the F2 layer critical frequency and peak height measured on board ISIS 1, ISIS 2, and IK19 satellites during 1969-1982, and the earthquakes M5+ occurrences for 1999-2013 are analyzed. Annual asymmetry is observed with GEC and IEC for the years of observation with asymmetry index, AI, showing January > July excess from 0.02 to 0.25. The coincident pattern of January-to-July asymmetry ratio of TEC and IEC colocated along the magnetic longitude sector of 270° ± 5°E in the Pacific Ocean is obtained varying with local time and magnetic latitude. The sea/land differences in the F2 layer peak electron density, NmF2, and the peak height, hmF2, gathered with topside sounding data exhibit tilted ionosphere along the seashores with denser electron population at greater peak heights over the sea. The topside peak electron density NmF2, TEC, IEC, and the hemisphere part of GEC are dominant in the South hemisphere which resembles the pattern for seismic activity with dominant earthquake occurrence in the South magnetic hemisphere. Though the study is made for the hemispheric and annual asymmetry during solstices in the ionosphere, the conclusions seem valid for other aspects of seismic-ionospheric associations with tectonic plate boundaries representing zones of enhanced risk for space weather.

Seismo-ionospheric Precursors of the Total Electron Content Associated with Global Large Earthquakes Examined by Using Ground-based and Space-based Radio Occultation GNSS Observations

NASA Astrophysics Data System (ADS)

Liu, J. Y. G.

2017-12-01

To verify seismo-ionospheric precursors (SIPs), statistical analyses are implemented on the relationship between the total electron content (TEC) in the global ionosphere map (GIM) derived from measurements of ground-based GNSS (global navigation satellite system) receivers and worldwide M≥7.0 earthquakes during 2000-2016. A median-based method is employed to determine the characteristic of TEC anomalies related to the earthquakes. It is found that the polarity of both negative (decrease) and positive (increase) in the GIM TEC, which varies location-by location, can be observed few days before the earthquakes. In general, PEIAs with the negative polarity associated with the earthquakes are more frequently detected. Meanwhile, FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) or F3/C in was launched into a circular low-Earth orbit on 15 April 2006. Six F3/C microsatellites with 72-degree inclination angle and 30-degree separation in longitude orbit at 800 km altitude, and conduct the ionospheric radio occultation (RO) observations by receiving signals from GNSS satellites and globally observing about 2500 vertical electron density profiles per day. Both ground-based and space-based RO GNSS observations are used to three dimensionally study SIPs related to the 11 March 2011 M9.0 Tohoku earthquake.

A review of ionospheric effects on Earth-space propagation

NASA Technical Reports Server (NTRS)

Klobuchar, J. A.

1984-01-01

A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

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.

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.

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 Australian Bureau of Meteorology Activities for the Regional Ionosphere Specification and Forcating

NASA Astrophysics Data System (ADS)

Bouya, Z.; Terkildsen, M.; Maher, P.

2016-12-01

Space Weather Services, Australian Bureau of Meteorology, Sydney, Australia Abstract:The Australian Bureau of Meteorology through its Space Weather Service (SWS) provides ionospheric products and services to a diverse group of customers. In this work, we present a regional approach to characterizing the Australian regional Total Electron Content (TEC) and an assimilative model to map the Ionospheric layer parameter foF2. Finally we outline the design of an Australian regional Ionospheric forecast model at SWS. Keywords: TEC, foF2, regional, data assimilation, forecast

South American regional ionospheric maps computed by GESA: A pilot service in the framework of SIRGAS

NASA Astrophysics Data System (ADS)

Brunini, C.; Meza, A.; Gende, M.; Azpilicueta, F.

2008-08-01

SIRGAS (Geocentric Reference Frame for the Americas) is an international enterprise of the geodetic community that aims to realize the Terrestrial Reference Frame in the America's countries. In order to fulfill this commitment, SIRGAS manages a network of continuously operational GNSS receivers totalling around one hundred sites in the Caribbean, Central, and South American region. Although the network was not planed for ionospheric studies, its potential to be used for such a purpose was recently recognized and SIRGAS started a pilot experiment devoted to establish a regular service for computing and releasing regional vertical TEC (vTEC) maps based on GNSS data. Since July, 2005, the GESA (Geodesia Espacial y Aeronomía) laboratory belonging to the Facultad de Ciencias Astronómicas y Geofísicas of the Universidad Nacional de La Plata computes hourly maps of vertical Total Electron Content (vTEC) in the framework of the SIRGAS pilot experiment. These maps exploit all the GNSS data available in the South American region and are computed with the LPIM (La Plata Ionospheric Model). LPIM implements a de-biasing procedure that improves data calibration in relation to other procedures commonly used for such purposes. After calibration, slant TEC measurements are converted to vertical and mapped using local-time and modip latitude. The use of modip latitude smoothed the spatial variability of vTEC, especially in the South American low latitude region and hence allows for a better vTEC interpolation. This contribution summarizes the results obtained by GESA in the framework of the SIRGAS pilot experiment.

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.

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.

A global picture of ionospheric slab thickness derived from GIM TEC and COSMIC radio occultation observations

NASA Astrophysics Data System (ADS)

Huang, He; Liu, Libo; Chen, Yiding; Le, Huijun; Wan, Weixing

2016-01-01

The ionospheric equivalent slab thickness (EST), defined as the ratio of total electron content (TEC) to F2 layer peak electron density (NmF2), describes the thickness of the ionospheric profile. In this study, we retrieve EST from TEC data obtained from Global Ionospheric Map (GIM) and NmF2 retrieved from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data. The diurnal, seasonal, and solar activity variations of global EST are analyzed as the excellent spatial coverage of GIM and COSMIC data. During solstices, daytime EST in the summer hemisphere is larger than that in the winter hemisphere, except in some high-latitude regions, and the reverse is true for the nighttime EST. The peaks of EST often appear at 0400 local time. The presunrise enhancement in EST appears in all seasons, while the postsunset enhancement in EST is not readily observed in equinox. Both enhancements are attributed to the more remarkable electron density decay of NmF2 compared to that of TEC. The dependence of EST on solar activity is related to the inconsistent solar activity dependences of electron density at different altitudes. Furthermore, it is interesting that EST is enhanced from 0° to 120°E in longitude and 30° to 75°S in latitude during nighttime, just to the east of Weddell Sea Anomaly, during equinox and the Southern Hemisphere summer. This phenomenon is supposed to be related to the effects of geomagnetic declination-related plasma vertical drifts.

Analysis of FORTE data to extract ionospheric parameters

NASA Astrophysics Data System (ADS)

Roussel-Dupré, Robert A.; Jacobson, Abram R.; Triplett, Laurie A.

2001-01-01

The ionospheric transfer function is derived for a spherically symmetric ionosphere with an arbitrary radial electron density profile in the limit where the radio frequencies of interest ω are much larger than the plasma frequency ωpe. An expansion of the transfer function to second order in the parameter X (= ω2pe/ω2) is carried out. In this limit the dispersive properties of the ionosphere are manifested as a frequency-dependent time of arrival that includes quadratic, cubic, and quartic terms in 1/ω. The coefficients of these terms are related to the total electron content (TEC) along the slant path from transmitter to receiver, the product of TEC and the longitudinal magnetic field strength along the slant path, and refractive bending and higher-order electron density profile effects, respectively. By fitting the time of arrival versus frequency of a transionospheric signal to a polynomial in 1/ω it is possible to extract the TEC, the longitudinal magnetic field strength, the peak electron density, and an effective thickness for the ionosphere. This exercise was carried out for a number of transionospheric pulses measured in the VHF by the FORTE satellite receiver and generated by the Los Alamos Portable Pulser. The results are compared with predictions derived from the International Reference Ionosphere and the United States Geological Survey geomagnetic field model.

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.

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.

Global features of ionospheric slab thickness derived from JPL TEC and COSMIC observations

NASA Astrophysics Data System (ADS)

Huang, He; Liu, Libo

2016-04-01

The ionospheric equivalent slab thickness (EST) is the ratio of total electron content (TEC) to F2-layer peak electron density (NmF2), describing the thickness of the ionospheric profile. In this study, we retrieve EST from Jet Propulsion Laboratory (JPL) TEC data and NmF2 retrieved from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data. The diurnal, seasonal and solar activity variations of global EST are analyzed as the excellent spatial coverage of JPL TEC and COSMIC data. During solstices, daytime EST in the summer hemisphere is larger than that in the winter hemisphere, except in some high-latitude regions; and the reverse is true for the nighttime EST. The peaks of EST often appear at 0400 local time. The pre-sunrise enhancement in EST appears in all seasons, while the post-sunset enhancement in EST is not readily observed in equinox. The dependence of EST on solar activity is very complicated. Furthermore, an interesting phenomenon is found that EST is enhanced from 0° to 120° E in longitude and 30° to 75° S in latitude during nighttime, just to the east of Weddell Sea Anomaly, during equinox and southern hemisphere summer.

A real-time ionospheric model based on GNSS Precise Point Positioning

NASA Astrophysics Data System (ADS)

Tu, Rui; Zhang, Hongping; Ge, Maorong; Huang, Guanwen

2013-09-01

This paper proposes a method of real-time monitoring and modeling the ionospheric Total Electron Content (TEC) by Precise Point Positioning (PPP). Firstly, the ionospheric TEC and receiver’s Differential Code Biases (DCB) are estimated with the undifferenced raw observation in real-time, then the ionospheric TEC model is established based on the Single Layer Model (SLM) assumption and the recovered ionospheric TEC. In this study, phase observations with high precision are directly used instead of phase smoothed code observations. In addition, the DCB estimation is separated from the establishment of the ionospheric model which will limit the impacts of the SLM assumption impacts. The ionospheric model is established at every epoch for real time application. The method is validated with three different GNSS networks on a local, regional, and global basis. The results show that the method is feasible and effective, the real-time ionosphere and DCB results are very consistent with the IGS final products, with a bias of 1-2 TECU and 0.4 ns respectively.

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.

Case Studies of Forecasting Ionospheric Total Electron Content

NASA Astrophysics Data System (ADS)

Mannucci, A. J.; Meng, X.; Verkhoglyadova, O. P.; Tsurutani, B.; McGranaghan, R. M.

2017-12-01

We report on medium-range forecast-mode runs of ionosphere-thermosphere coupled models that calculate ionospheric total electron content (TEC), focusing on low-latitude daytime conditions. A medium-range forecast-mode run refers to simulations that are driven by inputs that can be predicted 2-3 days in advance, for example based on simulations of the solar wind. We will present results from a weak geomagnetic storm caused by a high-speed solar wind stream on June 29, 2012. Simulations based on the Global Ionosphere Thermosphere Model (GITM) and the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) significantly over-estimate TEC in certain low latitude daytime regions, compared to TEC maps based on observations. We will present the results from a more intense coronal mass ejection (CME) driven storm where the simulations are closer to observations. We compare high latitude data sets to model inputs, such as auroral boundary and convection patterns, to assess the degree to which poorly estimated high latitude drivers may be the largest cause of discrepancy between simulations and observations. Our results reveal many factors that can affect the accuracy of forecasts, including the fidelity of empirical models used to estimate high latitude precipitation patterns, or observation proxies for solar EUV spectra, such as the F10.7 index. Implications for forecasts with few-day lead times are discussed

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.

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.

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.

Imaging Global Electron Content backwards in time more than 160 years ago

NASA Astrophysics Data System (ADS)

Gulyaeva, T. L.; Veselovsky, I. S.

2014-02-01

The Global Electron Content, GEC, represents the total number of electrons in the spherical layer over the Earth restricted by orbit of Global Positioning Satellite system (20,200 km). GEC is produced from Global Ionospheric Map of Total Electron Content, GIM-TEC, transformed to the electron density varying with height using the International Reference Ionosphere and Plasmasphere model, IRI-Plas. The climatologic GEC model is developed from GIM-TEC maps for a period 1999-2012 including the solar activity, annual and semiannual cycles as the most important factors affecting daily GEC variation. The proxy Rzp of the international sunspot numbers, Ri, is used as a measure of solar activity composed of 3 day smoothed Ri, 7 day and 81 day backwards mean of Ri scaled to the range of 1-40 proxy units, p.u. The root mean square error of the GEC climatologic model is found to vary from 8% to 13% of GEC. Taking advantage of a long history of sunspot numbers, the climatologic GEC model is applied for GEC reconstruction backwards in time for more than 160 years ago since 1850. The extended set of GEC values provides the numerical representation of the ionosphere and plasmasphere electron content coherent with variations of solar activity as a potential proxy index driving the ionosphere models.

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.

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.

Correction of Single Frequency Altimeter Measurements for Ionosphere Delay

NASA Technical Reports Server (NTRS)

Schreiner, William S.; Markin, Robert E.; Born, George H.

1997-01-01

This study is a preliminary analysis of the accuracy of various ionosphere models to correct single frequency altimeter height measurements for Ionospheric path delay. In particular, research focused on adjusting empirical and parameterized ionosphere models in the parameterized real-time ionospheric specification model (PRISM) 1.2 using total electron content (TEC) data from the global positioning system (GPS). The types of GPS data used to adjust PRISM included GPS line-of-sight (LOS) TEC data mapped to the vertical, and a grid of GPS derived TEC data in a sun-fixed longitude frame. The adjusted PRISM TEC values, as well as predictions by IRI-90, a climatotogical model, were compared to TOPEX/Poseidon (T/P) TEC measurements from the dual-frequency altimeter for a number of T/P tracks. When adjusted with GPS LOS data, the PRISM empirical model predicted TEC over 24 1 h data sets for a given local time to with in a global error of 8.60 TECU rms during a midnight centered ionosphere and 9.74 TECU rms during a noon centered ionosphere. Using GPS derived sun-fixed TEC data, the PRISM parameterized model predicted TEC within an error of 8.47 TECU rms centered at midnight and 12.83 TECU rms centered at noon. From these best results, it is clear that the proposed requirement of 3-4 TECU global rms for TOPEX/Poseidon Follow-On will be very difficult to meet, even with a substantial increase in the number of GPS ground stations, with any realizable combination of the aforementioned models or data assimilation schemes.

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.

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 network technology for studying the ionosphere

NASA Astrophysics Data System (ADS)

Yasyukevich, Yury; Zhivetiev, Ilya

2015-09-01

One of the key problems of ionosphere physics is the coupling between different ionospheric regions. We apply networks technology for studying the coupling of changing ionospheric dynamics in different regions. We used data from global ionosphere maps (GIM) of total electron content (TEC) produced by CODE for 2005-2010. Distribution of cross-correlation function maxima of TEC variations is not simple. This distribution allows us to reveal two levels of ionosphere coupling: "strong" (r>0.9) and "weak" (r>0.72). The ionosphere of the Arctic region upper 50° magnetic latitude is characterized by a "strong" coupling. In the Southern hemisphere, a similar region is bigger. "Weak" coupling is typical for the whole Southern hemisphere. In North America there is an area where TEC dynamics is "strongly" correlated inside and is not correlated with other ionospheric regions.

Effect of geomagnetic storms of different solar origin on the ionospheric TEC

NASA Astrophysics Data System (ADS)

Mansoori, Azad A.; Khan, Parvaiz A.; Purohit, P. K.

2018-05-01

We have studied the behaviour of ionospheric Total Electron Content (TEC) at a mid latitude station Usuda (36.130N, 138.360E), Japan during intense geomagnetic storms which were observed during 23 solar cycle (1998-2006). For the present study we have selected 47 intense geomagnetic storms (Dst≤-100nT), for the given period, which were then categorised into four categories depending upon their solar and interplanetary sources like Magnetic Cloud (MC), Co-rotating Interaction Region (CIR), Sheath driven Interplanetary Coronal Mass Ejection (SH+ICME) and Sheath driven Magnetic cloud (SH+MC). From our study we found that the geomagnetic storms significantly affect the ionosphere having any of the solar origin. However the geomagnetic storms which are either caused by SH+MC or SH+ICME produced maximum effect in TEC.

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)

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.

Global empirical model of TEC response to geomagnetic activity

NASA Astrophysics Data System (ADS)

Mukhtarov, P.; Andonov, B.; Pancheva, D.

2013-10-01

global total electron content (TEC) model response to geomagnetic activity described by the Kp index is built by using the Center for Orbit Determination of Europe (CODE) TEC data for a full 13 years, January 1999 to December 2011. The model describes the most probable spatial distribution and temporal variability of the geomagnetically forced TEC anomalies assuming that these anomalies at a given modified dip latitude depend mainly on the Kp index, local time (LT), and longitude. The geomagnetic anomalies are expressed by the relative deviation of TEC from its 15 day median and are denoted as rTEC. The rTEC response to the geomagnetic activity is presented by a sum of two responses with different time delay constants and different signs of the cross-correlation function. It has been found that the mean dependence of rTEC on Kp index can be expressed by a cubic function. The LT dependence of rTEC is described by Fourier time series which includes the contribution of four diurnal components with periods 24, 12, 8, and 6 h. The rTEC dependence on longitude is presented by Fourier series which includes the contribution of zonal waves with zonal wave numbers up to 6. In order to demonstrate how the model is able to reproduce the rTEC response to geomagnetic activity, three geomagnetic storms at different seasons and solar activity conditions are presented. The model residuals clearly reveal two types of the model deviation from the data: some underestimation of the largest TEC response to the geomagnetic activity and randomly distributed errors which are the data noise or anomalies generated by other sources. The presented TEC model fits to the CODE TEC input data with small negative bias of -0.204, root mean squares error RMSE = 4.592, and standard deviation error STDE = 4.588. The model offers TEC maps which depend on geographic coordinates (5° × 5° in latitude and longitude) and universal time (UT) at given geomagnetic activity and day of the year. It could be used for both science and possible service (nowcasting and short-term prediction); for the latter, a detailed validation of the model at different geophysical conditions has to be performed in order to clarify the model predicting quality.

A new short-term forecasting model for the total electron content storm time disturbances

NASA Astrophysics Data System (ADS)

Tsagouri, Ioanna; Koutroumbas, Konstantinos; Elias, Panagiotis

2018-06-01

This paper aims to introduce a new model for the short-term forecast of the vertical Total Electron Content (vTEC). The basic idea of the proposed model lies on the concept of the Solar Wind driven autoregressive model for Ionospheric short-term Forecast (SWIF). In its original version, the model is operationally implemented in the DIAS system (http://dias.space.noa.gr) and provides alerts and warnings for upcoming ionospheric disturbances, as well as single site and regional forecasts of the foF2 critical frequency over Europe up to 24 h in advance. The forecasts are driven by the real time assessment of the solar wind conditions at ACE location. The comparative analysis of the variations in foF2 and vTEC during eleven geomagnetic storm events that occurred in the present solar cycle 24 reveals similarities but also differences in the storm-time response of the two characteristics with respect to the local time and the latitude of the observation point. Since the aforementioned dependences drive the storm-time forecasts of the SWIF model, the results obtained here support the upgrade of the SWIF's modeling technique in forecasting the storm-time vTEC variation from its onset to full development and recovery. According to the proposed approach, the vTEC storm-time response can be forecasted from 1 to 12-13 h before its onset, depending on the local time of the observation point at storm onset at L1. Preliminary results on the assessment of the performance of the proposed model and further considerations on its potential implementation in operational mode are also discussed.

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;

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.

Ionospheric tomography using Faraday rotation of Automatic Dependent Surveillance Broadcast (UHF) signals Ionospheric Measurement From ADS-B Signals

NASA Astrophysics Data System (ADS)

Cushley, Alex Clay

The proposed launch of a CubeSat carrying the first space-borne ADS-B receiver by RMCC will create a unique opportunity to study the modification of radio waves following propagation through the ionosphere as the signals propagate from the transmitting aircraft to the passive satellite receiver(s). Experimental work is described which successfully demonstrated that ADS-B data can be used to reconstruct two-dimensional electron density maps of the ionosphere using techniques from computerized tomography. Ray-tracing techniques are used to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modelled Faraday rotation is determined and converted to TEC along the ray-paths. The resulting TEC is used as input for CIT using ART. This study concentrated on meso-scale structures 100--1000 km in horizontal extent. The primary scientific interest of this thesis was to show the feasibility of a new method to image the ionosphere and obtain a better understanding of magneto-ionic wave propagation. Keywords: Automatic Dependent Surveillance-Broadcast (ADS-B), Faraday rotation, electromagnetic (EM) waves, radio frequency (RF) propagation, ionosphere (auroral, irregularities, instruments and techniques), electron density profile, total electron content (TEC), computer ionospheric tomography (CIT), algebraic reconstruction technique (ART).

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.

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).

Morphology of high-latitude plasma density perturbations as deduced from the total electron content measurements onboard the Swarm constellation

NASA Astrophysics Data System (ADS)

Park, Jaeheung; Lühr, Hermann; Kervalishvili, Guram; Rauberg, Jan; Stolle, Claudia; Kwak, Young-Sil; Lee, Woo Kyoung

2017-01-01

In this study, we investigate the climatology of high-latitude total electron content (TEC) variations as observed by the dual-frequency Global Navigation Satellite Systems (GNSS) receivers onboard the Swarm satellite constellation. The distribution of TEC perturbations as a function of geographic/magnetic coordinates and seasons reasonably agrees with that of the Challenging Minisatellite Payload observations published earlier. Categorizing the high-latitude TEC perturbations according to line-of-sight directions between Swarm and GNSS satellites, we can deduce their morphology with respect to the geomagnetic field lines. In the Northern Hemisphere, the perturbation shapes are mostly aligned with the L shell surface, and this anisotropy is strongest in the nightside auroral (substorm) and subauroral regions and weakest in the central polar cap. The results are consistent with the well-known two-cell plasma convection pattern of the high-latitude ionosphere, which is approximately aligned with L shells at auroral regions and crossing different L shells for a significant part of the polar cap. In the Southern Hemisphere, the perturbation structures exhibit noticeable misalignment to the local L shells. Here the direction toward the Sun has an additional influence on the plasma structure, which we attribute to photoionization effects. The larger offset between geographic and geomagnetic poles in the south than in the north is responsible for the hemispheric difference.

Operation and Maintenance Manual, TECS 18.

DTIC Science & Technology

1978-11-01

width modulated variable output voltage and frequency using a three-phase transistor bridge circuit . Reduced power line electromagnetic interference...Description 3-1 Section II. Circuit Fundamentals 3-1 Section III. System Description 3-2 CHAPTER 4. Protection and Maintenance 4-1 Section I. Internal...Number I-la TECS 18 Electronic Module Location-Evaporator Side 1-3 1-lb TECS 18 Electronic Module Location-Condenser Side 1-4 1-2 Remote Control Panel 1-5

Ionospheric Tomography Using Faraday Rotation of Automatic Dependant Surveillance Broadcast UHF Signals

NASA Astrophysics Data System (ADS)

Cushley, A. C.

2013-12-01

The proposed launch of a satellite carrying the first space-borne ADS-B receiver by the Royal Military College of Canada (RMCC) will create a unique opportunity to study the modification of the 1090 MHz radio waves following propagation through the ionosphere from the transmitting aircraft to the passive satellite receiver(s). Experimental work successfully demonstrated that ADS-B data can be used to reconstruct two dimensional (2D) electron density maps of the ionosphere using computerized tomography (CT). The goal of this work is to evaluate the feasibility of CT reconstruction. The data is modelled using Ray-tracing techniques. This allows us to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modelled Faraday rotation (FR) is determined and converted to total electron content (TEC) along the ray-paths. The resulting TEC is used as input for computerized ionospheric tomography (CIT) using algebraic reconstruction technique (ART). This study concentrated on meso-scale structures 100-1000 km in horizontal extent. The primary scientific interest of this thesis was to show the feasibility of a new method to image the ionosphere and obtain a better understanding of magneto-ionic wave propagation. Multiple feature input electron density profile to ray-tracing program. Top: reconstructed relative electron density map of ray-trace input (Fig. 1) using TEC measurements and line-of-sight path. Bottom: reconstructed electron density map of ray-trace input using quiet background a priori estimate.

GNSS Derived Ionospheric TEC Observed Through Different TEC Calibration Techniques in the Brazilian Sector

NASA Astrophysics Data System (ADS)

Becker-Guedes, F.; Carmo, C. S.; Camargo, P. O.; Monico, J. F. G.; Nicoli Candido, C. M.

2017-12-01

Global Navigation Satellite System (GNSS) is becoming a reliable tool for use in air navigation systems. Its use as the main technology for determination of airplanes positioning has various economic and logistic benefits but it depends strongly on the ionospheric layer influences. The Brazilian sector ionosphere, mainly over the equatorial ionization anomaly (EIA), presents remarkable errors in the GNSS signal as compared to North America and Europe. In order to study the total electron content latitudinal variation of the Brazilian ionosphere we used a pair of GNSS receivers on the ground, one located in the equatorial region (Sao Luis) and other in the southern crest of the EIA (Cachoeira Paulista), to collect the GNSS observables and calculate the vertical TEC using different methods that has proven to work well to describe the ionospheric behavior in the North America and in Europe. We compared this results with a modified Nagoya TEC calculation method used by the EMBRACE (Estudo e Monitoramento BRAsileiro do Clima Espacial - Brazilian Study and Monitoring of Space Weather) program. This work intends to follow the performance of different TEC tuning methods to evaluate the spurious effects of the ionospheric EIA gradients in the TEC determination under typical conditions of the low-latitudes ionosphere in the Brazilian sector. The calculated TEC under different solar cycle conditions, geomagnetic activity, and seasonal variations show deviations in the performance of each method and stress the importance of well adjust the GNSS observations to local conditions in order to optimize the TEC evaluation. This study contributes to a better understanding of local GNSS signal errors in the global intent of offering conditions to improve the accuracy, integrity, availability, and continuity requirements for the use of GNSS for air navigation in South America.

Analysis of rocket beacon transmissions for computerized reconstruction of ionospheric densities

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.; Huba, J. D.; Chaturvedi, P. K.; Fulford, J. A.; Forsyth, P. A.; Anderson, D. N.; Zalesak, S. T.

1993-01-01

Three methods are described to obtain ionospheric electron densities from transionospheric, rocket-beacon TEC data. First, when the line-of-sight from a ground receiver to the rocket beacon is tangent to the flight trajectory, the electron concentration can be obtained by differentiating the TEC with respect to the distance to the rocket. A similar method may be used to obtain the electron-density profile if the layer is horizontally stratified. Second, TEC data obtained during chemical release experiments may be interpreted with the aid of physical models of the disturbed ionosphere to yield spatial maps of the modified regions. Third, computerized tomography (CT) can be used to analyze TEC data obtained along a chain of ground-based receivers aligned along the plane of the rocket trajectory. CT analysis of TEC data is used to reconstruct a 2D image of a simulated equatorial plume. TEC data is computed for a linear chain of nine receivers with adjacent spacings of either 100 or 200 km. The simulation data are analyzed to provide an F region reconstruction on a grid with 15 x 15 km pixels. Ionospheric rocket tomography may also be applied to rocket-assisted measurements of amplitude and phase scintillations and airglow intensities.

Complex analysis of the ionospheric response to operation of ``Progress'' cargo spacecraft according to the data of GNSS receivers in Baikal region

NASA Astrophysics Data System (ADS)

Ishin, Artem; Voeykov, Sergey; Perevalova, Natalia; Khakhinov, Vitaliy

2017-12-01

As a part of the Plasma-Progress and Radar-Progress space experiments conducted from 2006 to 2014, effects of the Progress spacecraft engines on the ionosphere have been studied using data from Global Navigation Satellite System (GNSS) receivers. 72 experiments have been carried out. All these experiments were based on data from the International GNSS Service (IGS) to record ionospheric plasma irregularities caused by engine operation. 35 experiments used data from the ISTP SB RAS network SibNet. The analysis of the spatio-temporal structure of total electron content (TEC) variations has shown that the problem of identifying the TEC response to engine operation is complicated by a number of factors: 1) the engine effect on ionospheric plasma is strongly localized in space and has a relatively low intensity; 2) a small number of satellite-receiver radio rays due to the limited number of GNSS stations, particularly before 2013; 3) a potential TEC response is masked with background ionospheric disturbances of various intensities. However, TEC responses are identified with certainty when a satellite-receiver radio ray crosses a disturbed region within minutes after the impact. TEC responses have been registered in 7 experiments (10 % of cases). The amplitude of ionospheric response (0.3-0.16 TECU) exceeded the background TEC variations (~0.25 TECU) several times. The TEC data indicate that the ionospheric irregularity lifetime is from 4 to 10 minutes. According to the estimates we made, the transverse size of irregularities is from 12 to 30 km.

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.

TEC data ingestion into IRI and NeQuick over the antarctic region

NASA Astrophysics Data System (ADS)

Nava, Bruno; Pezzopane, Michael; Radicella, Sandro M.; Scotto, Carlo; Pietrella, Marco; Migoya Orue, Yenca; Alazo Cuartas, Katy; Kashcheyev, Anton

2016-07-01

In the present work a comparative analysis to evaluate the IRI and NeQuick 2 models capabilities in reproducing the ionospheric behaviour over the Antarctic Region has been performed. A technique to adapt the two models to GNSS-derived vertical Total Electron Content (TEC) has been therefore implemented to retrieve the 3-D ionosphere electron density at specific locations where ionosonde data were available. In particular, the electron density profiles used in this study have been provided in the framework of the AUSPICIO (AUtomatic Scaling of Polar Ionograms and Cooperative Ionospheric Observations) project applying the Adaptive Ionospheric Profiler (AIP) to ionograms recorded at eight selected mid, high-latitude and polar ionosondes. The relevant GNSS-derived vertical TEC values have been obtained from the Global Ionosphere Maps (GIM) produced by the Center for Orbit Determination in Europe (CODE). The effectiveness of the IRI and NeQuick 2 in reconstructing the ionosphere electron density at the given locations and epochs has been primarily assessed in terms of statistical comparison between experimental and model-retrieved peak parameters values (foF2 and hmF2). The analysis results indicate that in general the models are equivalent in their ability to reproduce the critical frequency of the F2 layer and they also tend to overestimate the height of the peak electron density, especially during high solar activity periods. Nevertheless this tendency is more noticeable in NeQuick 2 than in IRI. For completeness, the statistics indicating the models bottomside reconstruction capabilities, computed as height integrated electron density profile mismodeling, will also be discussed.

Ionospheric tomography using ADS-B signals

NASA Astrophysics Data System (ADS)

Cushley, A. C.; Noël, J.-M.

2014-07-01

Numerical modeling has demonstrated that Automatic Dependent Surveillance Broadcast (ADS-B) signals can be used to reconstruct two-dimensional (2-D) electron density maps of the ionosphere using techniques for computerized tomography. Ray tracing techniques were used to determine the characteristics of individual waves, including the wave path and the state of polarization at the satellite receiver. The modeled Faraday rotation was computed and converted to total electron content (TEC) along the raypaths. The resulting TEC was used as input for computerized ionospheric tomography (CIT) using algebraic reconstruction technique. This study concentrated on reconstructing mesoscale structures 25-100 km in horizontal extent. The primary scientific interest of this study was to show that ADS-B signals can be used as a new source of data for CIT to image the ionosphere and to obtain a better understanding of magneto-ionic wave propagation.

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

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.

Ionospheric effects during severe space weather events seen in ionospheric service data products

NASA Astrophysics Data System (ADS)

Jakowski, Norbert; Danielides, Michael; Mayer, Christoph; Borries, Claudia

Space weather effects are closely related to complex perturbation processes in the magnetosphere-ionosphere-thermosphere systems, initiated by enhanced solar energy input. To understand and model complex space weather processes, different views on the same subject are helpful. One of the ionosphere key parameters is the Total Electron Content (TEC) which provides a first or-der approximation of the ionospheric range error in Global Navigation Satellite System (GNSS) applications. Additionally, horizontal gradients and time rate of change of TEC are important for estimating the perturbation degree of the ionosphere. TEC maps can effectively be gener-ated using ground based GNSS measurements from global receiver networks. Whereas ground based GNSS measurements provide good horizontal resolution, space based radio occultation measurements can complete the view by providing information on the vertical plasma density distribution. The combination of ground based TEC and vertical sounding measurements pro-vide essential information on the shape of the vertical electron density profile by computing the equivalent slab thickness at the ionosonde station site. Since radio beacon measurements at 150/400 MHz are well suited to trace the horizontal structure of Travelling Ionospheric Dis-turbances (TIDs), these data products essentially complete GNSS based TEC mapping results. Radio scintillation data products, characterising small scale irregularities in the ionosphere, are useful to estimate the continuity and availability of transionospheric radio signals. The different data products are addressed while discussing severe space weather events in the ionosphere e.g. events in October/November 2003. The complementary view of different near real time service data products is helpful to better understand the complex dynamics of ionospheric perturbation processes and to forecast the development of parameters customers are interested in.

Feasibility study of short-term earthquake prediction using ionospheric anomalies immediately before large earthquakes

NASA Astrophysics Data System (ADS)

Heki, K.; He, L.

2017-12-01

We showed that positive and negative electron density anomalies emerge above the fault immediately before they rupture, 40/20/10 minutes before Mw9/8/7 earthquakes (Heki, 2011 GRL; Heki and Enomoto, 2013 JGR; He and Heki 2017 JGR). These signals are stronger for earthquake with larger Mw and under higher background vertical TEC (total electron conetent) (Heki and Enomoto, 2015 JGR). The epicenter, the positive and the negative anomalies align along the local geomagnetic field (He and Heki, 2016 GRL), suggesting electric fields within ionosphere are responsible for making the anomalies (Kuo et al., 2014 JGR; Kelley et al., 2017 JGR). Here we suppose the next Nankai Trough earthquake that may occur within a few tens of years in Southwest Japan, and will discuss if we can recognize its preseismic signatures in TEC by real-time observations with GNSS.During high geomagnetic activities, large-scale traveling ionospheric disturbances (LSTID) often propagate from auroral ovals toward mid-latitude regions, and leave similar signatures to preseismic anomalies. This is a main obstacle to use preseismic TEC changes for practical short-term earthquake prediction. In this presentation, we show that the same anomalies appeared 40 minutes before the mainshock above northern Australia, the geomagnetically conjugate point of the 2011 Tohoku-oki earthquake epicenter. This not only demonstrates that electric fields play a role in making the preseismic TEC anomalies, but also offers a possibility to discriminate preseismic anomalies from those caused by LSTID. By monitoring TEC in the conjugate areas in the two hemisphere, we can recognize anomalies with simultaneous onset as those caused by within-ionosphere electric fields (e.g. preseismic anomalies, night-time MSTID) and anomalies without simultaneous onset as gravity-wave origin disturbances (e.g. LSTID, daytime MSTID).

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.

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.

Variation of GPS-TEC in a low latitude Indian region during the year 2012 and 2013

NASA Astrophysics Data System (ADS)

Patel, Nilesh C.; Karia, Sheetal P.; Pathak, Kamlesh N.

2018-05-01

The paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the period from January 2012 to December 2013 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Surat (21.16°N, 72.78°E Geog.), situated under the northern crest of the equatorial ionization anomaly region (EIA) and other three International GNSS Service (IGS) stations Bangalore (13.02°N, 77.57°E Geog.), Hyderabad (17.25°N, 78.30°E Geog.), and Lucknow (26.91°N, 80.95°E Geog.) in India. We describe the diurnal and seasonal characteristics. It was observed that GPS-TEC reaches its maximum value between 12:00 and 16:00 IST. Further, Seasonal variations of GPS-TEC is categorized into four seasons, i.e., March equinox (February, March, and April), June solstice (May, June, and July), September equinox (August, September, and October) and December solstice (November, December and January). The forenoon rate of production in Lucknow (beyond EIA crest) is faster than Bangalore, Hyderabad and Surat station. It is found that September equinox shows GPS-TEC slightly higher than the March equinox, followed by June solstice and the lowest GPS-TEC are in winter solstice at four stations. The equinoctial asymmetry clearly observed in the current study. Also GPS-TEC shows a semiannual variation.

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.

Observation and simulation of the ionosphere disturbance waves triggered by rocket exhausts

NASA Astrophysics Data System (ADS)

Lin, Charles C. H.; Chen, Chia-Hung; Matsumura, Mitsuru; Lin, Jia-Ting; Kakinami, Yoshihiro

2017-08-01

Observations and theoretical modeling of the ionospheric disturbance waves generated by rocket launches are investigated. During the rocket passage, time rate change of total electron content (rTEC) enhancement with the V-shape shock wave signature is commonly observed, followed by acoustic wave disturbances and region of negative rTEC centered along the trajectory. Ten to fifteen min after the rocket passage, delayed disturbance waves appeared and propagated along direction normal to the V-shape wavefronts. These observation features appeared most prominently in the 2016 North Korea rocket launch showing a very distinct V-shape rTEC enhancement over enormous areas along the southeast flight trajectory despite that it was also appeared in the 2009 North Korea rocket launch with the eastward flight trajectory. Numerical simulations using the physical-based nonlinear and nonhydrostatic coupled model of neutral atmosphere and ionosphere reproduce promised results in qualitative agreement with the characteristics of ionospheric disturbance waves observed in the 2009 event by considering the released energy of the rocket exhaust as the disturbance source. Simulations reproduce the shock wave signature of electron density enhancement, acoustic wave disturbances, the electron density depletion due to the rocket-induced pressure bulge, and the delayed disturbance waves. The pressure bulge results in outward neutral wind flows carrying neutrals and plasma away from it and leading to electron density depletions. Simulations further show, for the first time, that the delayed disturbance waves are produced by the surface reflection of the earlier arrival acoustic wave disturbances.

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.

New aspects of the ionospheric response to the October 2003 superstorms from multiple-satellite observations

NASA Astrophysics Data System (ADS)

Lei, Jiuhou; Wang, Wenbin; Burns, Alan G.; Yue, Xinan; Dou, Xiankang; Luan, Xiaoli; Solomon, Stanley C.; Liu, Yong C.-M.

2014-03-01

The total electron content (TEC) data measured by the Jason, CHAMP, GRACE, and SAC-C satellites, the in situ electron densities from CHAMP and GRACE, and the vertical E × B drifts from the ROCSAT, have been utilized to examine the ionospheric response to the October 2003 superstorms. The combination of observations from multiple satellites provides a unique global view of ionospheric storm effects, especially over the Pacific Ocean and American regions, which were under sunlit conditions during the main phases of the October 2003 superstorms. The main results of this study are as follows: (1) There were substantial increases in TEC in the daytime at low and middle latitudes during both superstorms. (2) The enhancements were greater during the 30 October superstorm and occurred over a wider range of local times. (3) They also tended to peak at earlier local times during this second event. (4) These TEC enhancement events occurred at the local times when there were enhancements in the upward vertical drift. (5) The strong upward vertical drifts are attributed to penetration electric fields, suggesting that these penetration electric fields played a significant role in the electron density enhancements during these superstorms. Overall, the main contribution of this study is the simultaneous view of the storm time ionospheric response from multiple satellites, and the association of local time differences in ionospheric plasma response with measured vertical drift variations.

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.

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.

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.

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.

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.

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.

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.

Analysis of ionosphere variability over low-latitude GNSS stations during 24th solar maximum period

NASA Astrophysics Data System (ADS)

Venkata Ratnam, D.; Sivavaraprasad, G.; Latha Devi, N. S. M. P.

2017-07-01

Global Positioning System (GPS) is a remote sensing tool of space weather and ionospheric variations. However, the interplanetary space-dependent drifts in the ionospheric irregularities cause predominant ranging errors in the GPS signals. The dynamic variability of the low-latitude ionosphere is an imperative threat to the satellite-based radio communication and navigation ranging systems. The study of temporal and spatial variations in the ionosphere has triggered new investigations in modelling, nowcasting and forecasting the ionospheric variations. Hence, in this paper, the dynamism in the day-to-day, month-to-month and seasonal variability of the ionospheric Total Electron Content (TEC) has been explored during the solar maximum period, January-December 2013, of the 24th solar cycle. The spatial and temporal variations of the ionosphere are analysed using the TEC values derived from three Indian low-latitude GPS stations, namely, Bengaluru, Guntur and Hyderabad, separated by 13-18° in latitude and 77-81° in longitude. The observed regional GPS-TEC variations are compared with the predicted TEC values of the International Reference Ionosphere (IRI-2012 and 2007) models. Ionospheric parameters such as Vertical TEC (VTEC), relative TEC deviation index and monthly variations in the grand-mean of ionosphere TEC and TEC intensity, along with the upper and lower quartiles, are adopted to investigate the ionosphere TEC variability during quiet and disturbed days. The maximum ionospheric TEC variability is found during March and September equinoxes, followed by December solstice while the minimum variability is observed during June solstice. IRI models are in reasonable agreement with GPS TEC but are overestimating during dawn hours (01:00-06:00 LT) as compared to the dusk hours. Higher percentage deviations are observed during equinoctial months than summer over EIA stations, Guntur and Hyderabad. GPS TEC variations are overestimated during dawn hours for all the seasons over Bengaluru. It has also been observed that positive storm effect (enhancement of TEC) is observed during the main phase of the March storm, 2013 (March 16-18, 2013) while both positive and negative storm effects (depletion of TEC) are registered during the main phase of the June storm, 2013 (June 28-30, 2013) at Bengaluru and Guntur, respectively. IRI-2012 model has slightly large discrepancies with the GPS-VTEC compared with the IRI-2007 model during the June storm, 2013 over Guntur station. This analysis highlights the importance of upgrading the IRI models due to their discrepancies during quiet and disturbed states of the ionosphere and developing an early warning forecast system to alert about ionosphere variability.

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

Optimal Integration of Cascade Thermoelectric Cooler into Electronic Housing: Experimental Approach

NASA Astrophysics Data System (ADS)

Semeniuk, V.; Protsenko, D.

2018-06-01

The problem of the optimal integration of thermoelectrically cooled optoelectronic components into an electronic housing is studied with the emphasis on practical implementation. The lines of 2-stage and 3-stage thermoelectric coolers (TECs) compatible with TO8 housing have been developed, and their parameters are measured in a wide range of heat sink temperatures. The TECs are optimized to receive a temperature difference of 100-110 K under a heat load from 70 mW to 100 mW with minimal power consumption. To fit into a standard housing interior, all the TECs have the same overall dimensions, regardless of the number of stages. Details of the TEC configurations and their performance characteristics are presented and discussed.

Optimal Integration of Cascade Thermoelectric Cooler into Electronic Housing: Experimental Approach

NASA Astrophysics Data System (ADS)

Semeniuk, V.; Protsenko, D.

2018-03-01

The problem of the optimal integration of thermoelectrically cooled optoelectronic components into an electronic housing is studied with the emphasis on practical implementation. The lines of 2-stage and 3-stage thermoelectric coolers (TECs) compatible with TO8 housing have been developed, and their parameters are measured in a wide range of heat sink temperatures. The TECs are optimized to receive a temperature difference of 100-110 K under a heat load from 70 mW to 100 mW with minimal power consumption. To fit into a standard housing interior, all the TECs have the same overall dimensions, regardless of the number of stages. Details of the TEC configurations and their performance characteristics are presented and discussed.

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.

Optical signature of an ionospheric hole

NASA Technical Reports Server (NTRS)

Mendillo, M.; Baumgardner, J.

1982-01-01

Simultaneous radio and optical diagnostics of a large, artificially-induced ionospheric modification were conducted during the June 1981 launch of a weather satellite. Intensified imaging and photometer observations at 6300 A, along the same ray path as VHF polarimeter measurements of the ionosphere's total electron content (TEC), were made while the rocket plume caused disturbances. A rapid TEC chemical depletion, on the order of -16.8 x 10 to the 12th el/sq cm, caused a burst of 6300 A radiation which expanded over 60 deg of the sky, with a peak intensity of almost 9 k R. Atmospheric diffusion and O(1D) quenching rate theoretical estimates were then tested, using the event as an active space plasma experiment.

Study of ionospheric anomalies due to impact of typhoon using Principal Component Analysis and image processing

NASA Astrophysics Data System (ADS)

LIN, JYH-WOEI

2012-08-01

Principal Component Analysis (PCA) and image processing are used to determine Total Electron Content (TEC) anomalies in the F-layer of the ionosphere relating to Typhoon Nakri for 29 May, 2008 (UTC). 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 is highly localized; however, it becomes more intense and widespread with height. Potential causes of these results are discussed with emphasis given to acoustic gravity waves caused by wind force.

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.

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.

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.

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.

Characteristics of equatorial plasma bubbles observed by TEC map based on ground-based GNSS receivers over South America

NASA Astrophysics Data System (ADS)

Barros, Diego; Takahashi, Hisao; Wrasse, Cristiano M.; Figueiredo, Cosme Alexandre O. B.

2018-01-01

A ground-based network of GNSS receivers has been used to monitor equatorial plasma bubbles (EPBs) by mapping the total electron content (TEC map). The large coverage of the TEC map allowed us to monitor several EPBs simultaneously and get characteristics of the dynamics, extension and longitudinal distributions of the EPBs from the onset time until their disappearance. These characteristics were obtained by using TEC map analysis and the keogram technique. TEC map databases analyzed were for the period between November 2012 and January 2016. The zonal drift velocities of the EPBs showed a clear latitudinal gradient varying from 123 m s-1 at the Equator to 65 m s-1 for 35° S latitude. Consequently, observed EPBs are inclined against the geomagnetic field lines. Both zonal drift velocity and the inclination of the EPBs were compared to the thermospheric neutral wind, which showed good agreement. Moreover, the large two-dimensional coverage of TEC maps allowed us to study periodic EPBs with a wide longitudinal distance. The averaged values observed for the inter-bubble distances also presented a clear latitudinal gradient varying from 920 km at the Equator to 640 km at 30° S. The latitudinal gradient in the inter-bubble distances seems to be related to the difference in the zonal drift velocity of the EPB from the Equator to middle latitudes and to the difference in the westward movement of the terminator. On several occasions, the distances reached more than 2000 km. Inter-bubble distances greater than 1000 km have not been reported in the literature.

Concentric waves and short-period oscillations observed in the ionosphere after the 2013 Moore EF5 tornado

NASA Astrophysics Data System (ADS)

Nishioka, Michi; Tsugawa, Takuya; Kubota, Minoru; Ishii, Mamoru

2013-11-01

We detected clear concentric waves and short-period oscillations in the ionosphere after an Enhanced Fujita scale (EF)5 tornado hit Moore, Oklahoma, U.S., on 20 May 2013 using dense wide-coverage ionospheric total electron content (TEC) observations in North America. These concentric waves were nondispersive, with a horizontal wavelength of ~120 km and a period of ~13 min. They were observed for more than 7 h throughout North America. TEC oscillations with a period of ~4 min were also observed to the south of Moore for more than 8 h. A comparison between the TEC observations and infrared cloud image from the GOES satellite indicates that the concentric waves and short-period oscillations are caused by supercell-induced atmospheric gravity waves and acoustic resonances, respectively. 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.

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.

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.

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.

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.

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.

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.

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.

Firefly Algorithm in detection of TEC seismo-ionospheric anomalies

NASA Astrophysics Data System (ADS)

Akhoondzadeh, Mehdi

2015-07-01

Anomaly detection in time series of different earthquake precursors is an essential introduction to create an early warning system with an allowable uncertainty. Since these time series are more often non linear, complex and massive, therefore the applied predictor method should be able to detect the discord patterns from a large data in a short time. This study acknowledges Firefly Algorithm (FA) as a simple and robust predictor to detect the TEC (Total Electron Content) seismo-ionospheric anomalies around the time of the some powerful earthquakes including Chile (27 February 2010), Varzeghan (11 August 2012) and Saravan (16 April 2013). Outstanding anomalies were observed 7 and 5 days before the Chile and Varzeghan earthquakes, respectively and also 3 and 8 days prior to the Saravan earthquake.

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.

Longitudinal structure of the equatorial ionosphere: Time evolution of the four-peaked EIA structure

NASA Astrophysics Data System (ADS)

Lin, C. H.; Hsiao, C. C.; Liu, J. Y.; Liu, C. H.

2007-12-01

Longitudinal structure of the equatorial ionosphere during the 24 h local time period is observed by the FORMOSAT-3/COSMIC (F3/C) satellite constellation. By binning the F3/C radio occultation observations during September and October 2006, global ionospheric total electron content (TEC) maps at a constant local time map (local time TEC map, referred as LT map) can be obtained to monitor the development and subsidence of the four-peaked longitudinal structure of the equatorial ionosphere. From LT maps, the four-peaked structure starts to develop at 0800-1000 LT and becomes most prominent at 1200-1600 LT. The longitudinal structure starts to subside after 2200-2400 LT and becomes indiscernible after 0400-0600 LT. In addition to TEC, ionospheric peak altitude also shows a four-peaked longitudinal structure with variation very similar to TEC during daytime. The four-peaked structure of the ionospheric peak altitude is indiscernible at night. With global local time maps of ionospheric TEC and peak altitude, we compare temporal variations of the longitudinal structure with variations of E × B drift from the empirical model. Our results indicate that the observations are consistent with the hypothesis that the four-peaked longitudinal structure is caused by the equatorial plasma fountain modulated by the E3 nonmigrating tide. Additionally, the four maximum regions show a tendency of moving eastward with propagation velocity of several 10 s m/s.

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.

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.

(abstract) A Comparison Between Measurements of the F-layer Critical Frequency and Values Derived from the PRISM Adjustment Algorithm Applied to Total Electron Content Data in the Equatorial Region

NASA Technical Reports Server (NTRS)

Mannucci, A. J.; Anderson, D. N.; Abdu, A. M.

1994-01-01

The Parametrized Real-Time Ionosphere Specification Model (PRISM) is a global ionospheric specification model that can incorporate real-time data to compute accurate electron density profiles. Time series of computed and measured data are compared in this paper. This comparison can be used to suggest methods of optimizing the PRISM adjustment algorithm for TEC data obtained at low altitudes.

Observation of TEC perturbation associated with medium-scale traveling ionospheric disturbance and possible seeding mechanism of atmospheric gravity wave at a Brazilian sector

NASA Astrophysics Data System (ADS)

Jonah, O. F.; Kherani, E. A.; De Paula, E. R.

2016-03-01

In the present study, we document daytime total electron content (TEC) disturbances associated with medium-scale traveling ionospheric disturbances (MSTIDs), on few chosen geomagnetically quiet days over Southern Hemisphere of Brazilian longitude sector. These disturbances are derived from TEC data obtained using Global Navigation Satellite System (GNSS) receiver networks. From the keograms and cross-correlation maps, the TEC disturbances are identified as the MSTIDs that are propagating equatorward-eastward, having most of their average wavelengths longer in latitude than in longitude direction. These are the important outcomes of the present study which suggest that the daytime MSTIDs over Southern Hemisphere are similar to their counterparts in the Northern Hemisphere. Another important outcome is that the occurrence characteristics of these MSTIDs and that of atmospheric gravity wave (AGW) activities in the thermosphere are found to be similar on day-to-day basis. This suggests a possible connection between them, confirming the widely accepted AGW forcing mechanism for the generation of these daytime MSTIDs. The source of this AGW is investigated using the Geostationary Operational Environmental Satellite system (GOES) and Constellation Observing System for Meteorology, Ionosphere, and Climate satellite data. Finally, we provided evidences that AGWs are generated by convection activities from the tropospheric region.

Investigation of ionospheric precursors related to deep and intermediate earthquakes based on spectral and statistical analysis

NASA Astrophysics Data System (ADS)

Oikonomou, Christina; Haralambous, Haris; Muslim, Buldan

2017-01-01

Ionospheric TEC (Total Electron Content) variations prior to the deep (≈600 km) earthquake doublet close to magnetic equator in Peru (M = 7.6) and to the intermediate (≈200 km) earthquake in Afghanistan (M = 7.5) during 2015 were investigated using measurements from Global Navigation Satellite System (GNSS) network with the aim to detect possible ionospheric precursors of these events. For this we applied both statistical and spectral analysis. Ionospheric anomalies related to both earthquakes were observed few hours and few days prior to the earthquakes during daytime localized mainly near the epicenter. These were large-scale positive TEC anomalies and small-scale TEC oscillations with periods of 20 min and duration around 2-4 h appearing at the same local time each day. Several days prior to the earthquake in Peru a significant phenomenon was observed during afternoon time related to the modification of the Equatorial Ionization Anomaly (EIA) structure. During nighttime, however, it was not possible to identify any ionospheric earthquake precursor due to the concurrence of various phenomena, such as Equatorial Plasma Bubbles and pre- and post-midnight TEC peaks prior to Peru earthquake, and solar terminator transition prior to both earthquakes which could induce resembling ionospheric anomalies.

Genetic algorithm for TEC seismo-ionospheric anomalies detection around the time of the Solomon (Mw = 8.0) earthquake of 06 February 2013

NASA Astrophysics Data System (ADS)

Akhoondzadeh, M.

2013-08-01

On 6 February 2013, at 12:12:27 local time (01:12:27 UTC) a seismic event registering Mw 8.0 struck the Solomon Islands, located at the boundaries of the Australian and Pacific tectonic plates. Time series prediction is an important and widely interesting topic in the research of earthquake precursors. This paper describes a new computational intelligence approach to detect the unusual variations of the total electron content (TEC) seismo-ionospheric anomalies induced by the powerful Solomon earthquake using genetic algorithm (GA). The GA detected a considerable number of anomalous occurrences on earthquake day and also 7 and 8 days prior to the earthquake in a period of high geomagnetic activities. In this study, also the detected TEC anomalies using the proposed method are compared to the results dealing with the observed TEC anomalies by applying the mean, median, wavelet, Kalman filter, ARIMA, neural network and support vector machine methods. The accordance in the final results of all eight methods is a convincing indication for the efficiency of the GA method. It indicates that GA can be an appropriate non-parametric tool for anomaly detection in a non linear time series showing the seismo-ionospheric precursors variations.

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.

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.

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.

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.

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.

Efficient Usage of Dense GNSS Networks in Central Europe for the Visualization and Investigation of Ionospheric TEC Variations

PubMed Central

Zanimonskiy, Yevgen M.; Yampolski, Yuri M.; Figurski, Mariusz

2017-01-01

The technique of the orthogonal projection of ionosphere electronic content variations for mapping total electron content (TEC) allows us to visualize ionospheric irregularities. For the reconstruction of global ionospheric characteristics, numerous global navigation satellite system (GNSS) receivers located in different regions of the Earth are used as sensors. We used dense GNSS networks in central Europe to detect and investigate a special type of plasma inhomogeneities, called travelling ionospheric disturbances (TID). Such use of GNSS sensors allows us to reconstruct the main TID parameters, such as spatial dimensions, velocities, and directions of their movement. The paper gives examples of the restoration of dynamic characteristics of ionospheric irregularities for quiet and disturbed geophysical conditions. Special attention is paid to the dynamics of ionospheric disturbances stimulated by the magnetic storms of two St. Patrick’s Days (17 March 2013 and 2015). Additional opportunities for the remote sensing of the ionosphere with the use of dense regional networks of GNSS receiving sensors have been noted too. PMID:28994718

Efficient Usage of Dense GNSS Networks in Central Europe for the Visualization and Investigation of Ionospheric TEC Variations.

PubMed

Nykiel, Grzegorz; Zanimonskiy, Yevgen M; Yampolski, Yuri M; Figurski, Mariusz

2017-10-10

The technique of the orthogonal projection of ionosphere electronic content variations for mapping total electron content (TEC) allows us to visualize ionospheric irregularities. For the reconstruction of global ionospheric characteristics, numerous global navigation satellite system (GNSS) receivers located in different regions of the Earth are used as sensors. We used dense GNSS networks in central Europe to detect and investigate a special type of plasma inhomogeneities, called travelling ionospheric disturbances (TID). Such use of GNSS sensors allows us to reconstruct the main TID parameters, such as spatial dimensions, velocities, and directions of their movement. The paper gives examples of the restoration of dynamic characteristics of ionospheric irregularities for quiet and disturbed geophysical conditions. Special attention is paid to the dynamics of ionospheric disturbances stimulated by the magnetic storms of two St. Patrick's Days (17 March 2013 and 2015). Additional opportunities for the remote sensing of the ionosphere with the use of dense regional networks of GNSS receiving sensors have been noted too.

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.

Analysis and validation of different global ionospheric maps (GIMs) over China

NASA Astrophysics Data System (ADS)

Xiang, Yan; Yuan, Yunbin; Li, Zishen; Wang, Ningbo

2015-01-01

We assess four different global ionospheric maps (GIMs) over the area of China based on internal consistency (W.r.t.GNSS-derived total electron content (TEC)) and external accuracy (W.r.t.Topex/Poseidon-derived TEC). The results of relevance would serve as references for single-frequency GNSS Positioning, Navigation and Timing (PNT) users to flexibly determine which GIM is to be based on to get the more efficient ionospheric delay corrections service. Performance of these four GIMs sources are validated during high level (2003) as well as low level (2009) solar activity and even 10 years data is tested against GNSS-derived TEC over China and its neighborhood. Results show that UPC GIMs outperform all the rest of GIMs when ionospheric gradients are large, and there is marginally difference in low solar activity or middle latitude among these GIMs since 2006. Hence, we suggest that the UPC GIMs should be used in solar maximum and low latitude. It is also reasonable to apply any GIMs in low solar activity and middle latitude.

Ionosphere of Mars observed by Mars Express.

NASA Astrophysics Data System (ADS)

Dubinin, Eduard; Fraenz, Markus; Andrews, Dave; Morgan, Dave

2016-04-01

The Martian ionosphere is studied at different solar zenith angles using the local electron number densities and total electron content (TEC) derived from the observations by MARSIS onboard Mars Express. The data are complemented by the ASPERA-3 observations which provide us with the information about upward/downward velocity of the low-energy ions and electron precipitation. We consider the Mars Express observations at different solar cycle intervals. Different factors which influence the ionosphere dynamics are analyzed. The focus is made on a role of the crustal magnetic field on the Martian ionosphere and its influence on ion escape.

Simultaneous Ground- and Space-Based Observations of the Plasmaspheric Plume and Reconnection

NASA Technical Reports Server (NTRS)

Walsh, B. M.; Foster, J. C.; Erickson, P. J.; Sibeck, D. G.

2014-01-01

Magnetic reconnection is the primary process through which energy couples from the solar wind into Earth's magnetosphere and ionosphere. Conditions both in the incident solar wind and in the magnetosphere are important in determining the efficiency of this energy transfer. In particular, the cold, dense plasmaspheric plume can substantially impact the coupling in the dayside reconnection region. Using ground-based total electron content (TEC) maps and measurements from the THEMIS spacecraft, we investigated simultaneous ionosphere and magnetosphere observations of the plasmaspheric plume and its involvement in an unsteady magnetic reconnection process. The observations show the full circulation pattern of the plasmaspheric plume and validate the connection between signatures of variability in the dense plume and reconnection at the magnetopause as measured in situ and through TEC measurements in the ionosphere.

Simultaneous ground- and space-based observations of the plasmaspheric plume and reconnection.

PubMed

Walsh, B M; Foster, J C; Erickson, P J; Sibeck, D G

2014-03-07

Magnetic reconnection is the primary process through which energy couples from the solar wind into Earth's magnetosphere and ionosphere. Conditions both in the incident solar wind and in the magnetosphere are important in determining the efficiency of this energy transfer. In particular, the cold, dense plasmaspheric plume can substantially impact the coupling in the dayside reconnection region. Using ground-based total electron content (TEC) maps and measurements from the THEMIS spacecraft, we investigated simultaneous ionosphere and magnetosphere observations of the plasmaspheric plume and its involvement in an unsteady magnetic reconnection process. The observations show the full circulation pattern of the plasmaspheric plume and validate the connection between signatures of variability in the dense plume and reconnection at the magnetopause as measured in situ and through TEC measurements in the ionosphere.

Regional 3-D ionospheric electron density specification on the basis of data assimilation of ground-based GNSS and radio occultation data

NASA Astrophysics Data System (ADS)

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

2016-06-01

In this paper, a regional 3-D ionospheric electron density specification over China and adjacent areas (70°E-140°E in longitude, 15°N-55°N in latitude, and 100-900 km in altitude) is developed on the basis of data assimilation technique. The International Reference Ionosphere (IRI) is used as a background model, and a three-dimensional variational technique is used to assimilate both the ground-based Global Navigation Satellite System (GNSS) observations from the Crustal Movement Observation Network of China (CMONOC) and International GNSS Service (IGS) and the ionospheric radio occultation (RO) data from FORMOSAT-3/COSMIC (F3/C) satellites. The regional 3-D gridded ionospheric electron densities can be generated with temporal resolution of 5 min in universal time, horizontal resolution of 2° × 2° in latitude and longitude, and vertical resolution of 20 km between 100 and 500 km and 50 km between 500 and 900 km. The data assimilation results are validated through extensive comparison with several sources of electron density information, including (1) ionospheric total electron content (TEC); (2) Abel-retrieved F3/C electron density profiles (EDPs); (3) ionosonde foF2 and bottomside EDPs; and (4) the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) under both geomagnetic quiet and disturbed conditions. The validation results show that the data assimilation procedure pushes the climatological IRI model toward the observation, and a general accuracy improvement of 15-30% can be expected. Thecomparisons also indicate that the data assimilation results are more close to the Center for Orbit Determination of Europe (CODE) TEC and Madrigal TEC products than USU-GAIM. These initial results might demonstrate the effectiveness of the data assimilation technique in improving specification of local ionospheric morphology.

Solar eclipses at high latitudes: ionospheric effects in the lower ionosphere

NASA Astrophysics Data System (ADS)

Cherniakov, S.

2017-12-01

The partial reflection facility of the Polar Geophysical Institute (the Tumanny observatory, 69.0N, 35.7E) has observed behavior of the high-latitude lower ionosphere during the 20 March 2015 total solar eclipse. There were several effects during the eclipse. At the heights of 60-80 km the ionosphere has shown the effect of a "short night", but at the higher altitudes local enhanced electron concentration had a wave-like form. Data received by the riometer of the Tumanny observatory have also shown wave-like behavior. The behavior can be explained by influence of acoustic-gravity waves which originated after cooling of the atmosphere during the lunar shadow supersonic movement, and transport processes during the eclipse. During the 21 August 2017 solar eclipse there was a substorm at the high latitudes. But after the end of the substorm in the region of the Tumanny observatory the observed amplitudes of the reflected waves had wave effects which could be connected with the coming waves from the region of the eclipse. The wave features were also shown in the behavior of the total electron content (TEC) of the lower ionosphere. During several solar eclipses it was implemented observations of lower ionosphere behavior by the partial reflection facility of the Tumanny observatory. The consideration of the lower ionosphere TEC had revealed common features in the TEC behavior during the eclipses. The photochemical theory of processes in the lower ionosphere is very complicated and up to now it is not completely developed. Therefore introduction of the effective coefficients determining the total speed of several important reactions has been widely adopted when modeling the D-region of the ionosphere. However, experimental opportunities for obtaining effective recombination coefficients are rather limited. One of the methods to estimate effective recombination coefficients uses the phenomenon of a solar eclipse. During solar eclipses at the partial reflection facility of the Tumanny observatory observations were carried out. It gave possibility to obtain the behavior of the electron concentration in time at the selected heights. Using the obtained experimental profiles, the effective recombination coefficients at the D-region heights of the ionosphere have been evaluated.

The Electronic Health Literacy and Utilization of Technology for Health in a Remote Hawaiian Community: Lana‘i

PubMed Central

Humphry, Joseph

2018-01-01

The Lana‘i Community Health Center (LCHC) like other health care organizations, is striving to implement technology-enabled care (TEC) in the clinical setting. TEC includes such technological innovations as patient portals, mobile phone applications, wearable health sensors, and telehealth. This study examines the utilization of communication technology by members of the Lana‘i community and LCHC staff and board members in the home and in their daily lives and evaluates the community's electronic health literacy. Quantitative surveys and qualitative focus groups were utilized. These revealed that members of the Lana‘i community and LCHC staff and board members regularly utilize technology, in the form of smart cell phones, WiFi, and internet texting. This community has integrated technology into their daily lives, even though they live on an isolated island with 3,102 people; however, despite this integration, the electronic health literacy of this population appears insufficient for proper understanding and utilization of TEC, limiting the potential of patient portals or remote monitoring of patient generated data for chronic disease prevention and management without additional education and mentoring. It is therefore in the best interest of the LCHC and other health organizations wishing to implement TEC in a rural community such as Lana‘i to include a strong educational component with use of TEC, and perhaps establish a mentor/partnership program for the highly-challenged patient. PMID:29541550

The Electronic Health Literacy and Utilization of Technology for Health in a Remote Hawaiian Community: Lana'i.

PubMed

Witten, Nash Ak; Humphry, Joseph

2018-03-01

The Lana'i Community Health Center (LCHC) like other health care organizations, is striving to implement technology-enabled care (TEC) in the clinical setting. TEC includes such technological innovations as patient portals, mobile phone applications, wearable health sensors, and telehealth. This study examines the utilization of communication technology by members of the Lana'i community and LCHC staff and board members in the home and in their daily lives and evaluates the community's electronic health literacy. Quantitative surveys and qualitative focus groups were utilized. These revealed that members of the Lana'i community and LCHC staff and board members regularly utilize technology, in the form of smart cell phones, WiFi, and internet texting. This community has integrated technology into their daily lives, even though they live on an isolated island with 3,102 people; however, despite this integration, the electronic health literacy of this population appears insufficient for proper understanding and utilization of TEC, limiting the potential of patient portals or remote monitoring of patient generated data for chronic disease prevention and management without additional education and mentoring. It is therefore in the best interest of the LCHC and other health organizations wishing to implement TEC in a rural community such as Lana'i to include a strong educational component with use of TEC, and perhaps establish a mentor/partnership program for the highly-challenged patient.

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.

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.

Impact of the quasi-two-day traveling planetary wave on the ionosphere

NASA Astrophysics Data System (ADS)

Yue, J.; Wang, W.; Richmond, A. D.; Liu, H.; Chang, L. C.

2012-12-01

The Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is used to simulate the quasi-two-day wave (QTDW) modulation of the ionospheric dynamo and electron density. The QTDW can directly penetrate into the lower thermosphere and modulate the neutral winds at a period of two days. On the other hand, the QTDW can change the tidal amplitudes. The QTDW in zonal and meridional winds results in a quasi-two-day oscillation (QTDO) of the dynamo electric fields. The QTDO of the electric fields in the E-region is transmitted along the magnetic field lines to the F-region and leads to the QTDOs of the vertical ion drift and total electron content (TEC) at low and mid latitudes, leading to the 2-day oscillation of the fountain effect. Since the Earth's magnetic field has zonal wavenumber 1 and higher structures in geographic coordinates, the neutral wind dynamo and its associated vertical ion drift can be influenced by the wavenumber interaction between the QTDW and the magnetic field. Thus, longitudinal structures with other wavenumbers in the ionospheric fields, such as electric field, vertical ion drifts, electron densities and TEC, emerge from this interaction. Additionally, because the tides are damped/enhanced during a strong QTDW event, the overall fountain effect and the ionospheric morphology are changed.Amplitude (TECU) and phase (UT hour) of the QTDO of TEC as a function of day and latitude. The contour interval is 0.02 TECU and 4 hr, respectively. The color scale for the amplitude and phase is 0-0.3 TECU and 0 to 48 hr.

Nonlinear ionospheric responses to large-amplitude infrasonic-acoustic waves generated by undersea earthquakes

NASA Astrophysics Data System (ADS)

Zettergren, M. D.; Snively, J. B.; Komjathy, A.; Verkhoglyadova, O. P.

2017-02-01

Numerical models of ionospheric coupling with the neutral atmosphere are used to investigate perturbations of plasma density, vertically integrated total electron content (TEC), neutral velocity, and neutral temperature associated with large-amplitude acoustic waves generated by the initial ocean surface displacements from strong undersea earthquakes. A simplified source model for the 2011 Tohoku earthquake is constructed from estimates of initial ocean surface responses to approximate the vertical motions over realistic spatial and temporal scales. Resulting TEC perturbations from modeling case studies appear consistent with observational data, reproducing pronounced TEC depletions which are shown to be a consequence of the impacts of nonlinear, dissipating acoustic waves. Thermospheric acoustic compressional velocities are ˜±250-300 m/s, superposed with downward flows of similar amplitudes, and temperature perturbations are ˜300 K, while the dominant wave periodicity in the thermosphere is ˜3-4 min. Results capture acoustic wave processes including reflection, onset of resonance, and nonlinear steepening and dissipation—ultimately leading to the formation of ionospheric TEC depletions "holes"—that are consistent with reported observations. Three additional simulations illustrate the dependence of atmospheric acoustic wave and subsequent ionospheric responses on the surface displacement amplitude, which is varied from the Tohoku case study by factors of 1/100, 1/10, and 2. Collectively, results suggest that TEC depletions may only accompany very-large amplitude thermospheric acoustic waves necessary to induce a nonlinear response, here with saturated compressional velocities ˜200-250 m/s generated by sea surface displacements exceeding ˜1 m occurring over a 3 min time period.

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.

Ionospheric Anomalies Related to the (M = 7.3), August 27, 2012, Puerto Earthquake, (M = 6.8), August 30, 2012 Jan Mayen Island Earthquake, and (M = 7.6), August 31, 2012, Philippines Earthquake: Two-Dimensional Principal Component Analysis

PubMed Central

Lin, Jyh-Woei

2013-01-01

Two-dimensional principal component analysis (2DPCA) and principal component analysis (PCA) are used to examine the ionospheric total electron content (TEC) data during the time period from 00:00 on August 21 to 12: 45 on August 31 (UT), which are 10 days before the M = 7.6 Philippines earthquake at 12:47:34 on August 31, 2012 (UT) with the depth at 34.9 km. From the results by using 2DPCA, a TEC precursor of Philippines earthquake is found during the time period from 4:25 to 4:40 on August 28, 2012 (UT) with the duration time of at least 15 minutes. Another earthquake-related TEC anomaly is detectable for the time period from 04:35 to 04:40 on August 27, 2012 (UT) with the duration time of at least 5 minutes during the Puerto earthquake at 04: 37:20 on August 27, 2012 (UT) (M w = 7.3) with the depth at 20.3 km. The precursor of the Puerto earthquake is not detectable. TEC anomaly is not to be found related to the Jan Mayen Island earthquake (M w = 6.8) at 13:43:24 on August 30, 2012 (UT). These earthquake-related TEC anomalies are detectable by using 2DPCA rather than PCA. They are localized nearby the epicenters of the Philippines and Puerto earthquakes. PMID:23844386

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.

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.

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.

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).

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.

Impact of the Lower Atmosphere on the Ionosphere Response to a Geomagnetic Superstorm

NASA Astrophysics Data System (ADS)

Pedatella, N. M.

2016-12-01

Numerical simulations in the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) are performed to elucidate the impacts of lower atmosphere forcing on the ionosphere response to a geomagnetic superstorm. In particular, how the ionosphere variability due to the October 2003 Halloween storm would be different if it occurred in January coincident with a major sudden stratosphere warming (SSW) event is investigated. The TIE-GCM simulations reveal that the E x B vertical drift velocity and total electron content (TEC) respond differently to the geomagnetic disturbance when the lower atmosphere forcing is representative of SSW conditions compared to climatological lower atmosphere forcing conditions. Notably, the storm time variations in the E x B vertical drift velocity differ when the effects of the SSW are considered, and this is in part due to effects of the SSW on the equatorial ionosphere being potentially misinterpreted as being of geomagnetic origin. Differences in the TEC response to the geomagnetic storm can be up to 100% ( 30 TECU) of the storm induced TEC change, and the temporal variability of the TEC during the storm recovery phase is considerably different if SSW effects are considered. The results demonstrate that even during periods of extreme geomagnetic forcing it is important to consider the effects of lower atmosphere forcing on the ionosphere variability.

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.

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.

Finding Multi-scale Connectivity in Our Geospace Observational System: A New Perspective for Total Electron Content Data Through Network Analysis

NASA Astrophysics Data System (ADS)

McGranaghan, R. M.; Mannucci, A. J.; Verkhoglyadova, O. P.; Malik, N.

2017-12-01

How do we evolve beyond current traditional methods in order to innovate into the future? In what disruptive innovations will the next frontier of space physics and aeronomy (SPA) be grounded? We believe the answer to these compelling, yet equally challenging, questions lies in a shift of focus: from a narrow, field-specific view to a radically inclusive, interdisciplinary new modus operandi at the intersection of SPA and the information and data sciences. Concretely addressing these broader themes, we present results from a novel technique for knowledge discovery in the magnetosphere-ionosphere-thermosphere (MIT) system: complex network analysis (NA). We share findings from the first NA of ionospheric total electron content (TEC) data, including hemispheric and interplanetary magnetic field clock angle dependencies [1]. Our work shows that NA complements more traditional approaches for the investigation of TEC structure and dynamics, by both reaffirming well-established understanding, giving credence to the method, and identifying new connections, illustrating the exciting potential. We contextualize these new results through a discussion of the potential of data-driven discovery in the MIT system when innovative data science techniques are embraced. We address implications and potentially disruptive data analysis approaches for SPA in terms of: 1) the future of the geospace observational system; 2) understanding multi-scale phenomena; and 3) machine learning. [1] McGranaghan, R. M., A. J. Mannucci, O. Verkhoglyadova, and N. Malik (2017), Finding multiscale connectivity in our geospace observational system: Network analysis of total electron content, J. Geophys. Res. Space Physics, 122, doi:10.1002/2017JA024202.

The plasmasphere electron content paradox

NASA Astrophysics Data System (ADS)

Krall, J.; Huba, J. D.

2016-09-01

Measurements show that plasmasphere refilling rates decrease with increasing solar activity, while paradoxically, the vertical integration of the plasmasphere electron density (pTEC) increases with increasing solar activity. Using the Naval Research Laboratory SAMI2 (Sami2 is Another Model of the Ionosphere) and SAMI3 (Sami3 is Also a Model of the Ionosphere) codes, we simulate plasmasphere refilling following a model storm, reproducing this observed phenomenon. In doing so, we find that the refilling rate and resulting pTEC values are sensitive to the oxygen profile in the thermosphere and exosphere: the supply of H+ in the topside ionosphere is limited by the local O+ density, through H+O+→H++O charge exchange. At solar minimum, the O+ supply simply increases with the O density in the exosphere. At solar maximum, we find that O-O+ collisions limit the O+ density in the topside ionosphere such that it decreases with increasing O density. The paradox occurs because the pTEC metric gives electrons in the topside ionosphere more weight than electrons in the plasmasphere.

Ionospheric Profiling Through Nonlinear Dielectric Response to Electron Density*

NASA Astrophysics Data System (ADS)

Moses, R. W.; Jacobson, A. R.

2002-12-01

It is well known that the total electron content (TEC) along a line of sight in the ionosphere can be extracted from the frequency-dependent time lag measured in transionospheric RF signals [1]. For five years the FORTE satellite has been used to develop a substantial data base of transionospheric signals originating in both lightning and man-made sources. Here, we use signals generated by the Los Alamos Portable Pulser (LAPP) [2] and recorded by FORTE as input to a multi-layer computer model of RF wave propagation in the ionosphere, including Faraday rotation in the Earth's magnetic field. Nonlinearities in both the frequency dependence of the group velocity and the optical pathlength are modeled and matched to FORTE data to infer details of the vertical profile of electron density. Using the International Reference Ionosphere [3] as a profile model, we show how the vertical TEC, peak electron density, and ionospheric thickness can be extracted even at large transmitter-to-satellite separations. [1] Roussel-Dupre, R. A., A. R. Jacobson, and L. A. Triplett, Radio Sci., 36, 1615 (2001). [2] Massey, R.S., S.O. Knox, R.C. Franz, D.N. Holden, and C.T. Rhodes, Radio Sci., 33, 1739 (1998). [3] Bilitza, D., "International Reference Ionosphere 1990," NSSDC/WDC-A-R&S 90-92. *Work supported by USDOE

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.

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.

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.

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.

Reliable prediction intervals with regression neural networks.

PubMed

Papadopoulos, Harris; Haralambous, Haris

2011-10-01

This paper proposes an extension to conventional regression neural networks (NNs) for replacing the point predictions they produce with prediction intervals that satisfy a required level of confidence. Our approach follows a novel machine learning framework, called Conformal Prediction (CP), for assigning reliable confidence measures to predictions without assuming anything more than that the data are independent and identically distributed (i.i.d.). We evaluate the proposed method on four benchmark datasets and on the problem of predicting Total Electron Content (TEC), which is an important parameter in trans-ionospheric links; for the latter we use a dataset of more than 60000 TEC measurements collected over a period of 11 years. Our experimental results show that the prediction intervals produced by our method are both well calibrated and tight enough to be useful in practice. Copyright © 2011 Elsevier Ltd. All rights reserved.

Digital beacon receiver for ionospheric TEC measurement developed with GNU Radio

NASA Astrophysics Data System (ADS)

Yamamoto, M.

2008-11-01

A simple digital receiver named GNU Radio Beacon Receiver (GRBR) was developed for the satellite-ground beacon experiment to measure the ionospheric total electron content (TEC). The open-source software toolkit for the software defined radio, GNU Radio, is utilized to realize the basic function of the receiver and perform fast signal processing. The software is written in Python for a LINUX PC. The open-source hardware called Universal Software Radio Peripheral (USRP), which best matches the GNU Radio, is used as a front-end to acquire the satellite beacon signals of 150 and 400 MHz. The first experiment was successful as results from GRBR showed very good agreement to those from the co-located analog beacon receiver. Detailed design information and software codes are open at the URL http://www.rish.kyoto-u.ac.jp/digitalbeacon/.

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.

Thermal and TEC anomalies detection using an intelligent hybrid system around the time of the Saravan, Iran, (Mw = 7.7) earthquake of 16 April 2013

NASA Astrophysics Data System (ADS)

Akhoondzadeh, M.

2014-02-01

A powerful earthquake of Mw = 7.7 struck the Saravan region (28.107° N, 62.053° E) in Iran on 16 April 2013. Up to now nomination of an automated anomaly detection method in a non linear time series of earthquake precursor has been an attractive and challenging task. Artificial Neural Network (ANN) and Particle Swarm Optimization (PSO) have revealed strong potentials in accurate time series prediction. This paper presents the first study of an integration of ANN and PSO method in the research of earthquake precursors to detect the unusual variations of the thermal and total electron content (TEC) seismo-ionospheric anomalies induced by the strong earthquake of Saravan. In this study, to overcome the stagnation in local minimum during the ANN training, PSO as an optimization method is used instead of traditional algorithms for training the ANN method. The proposed hybrid method detected a considerable number of anomalies 4 and 8 days preceding the earthquake. Since, in this case study, ionospheric TEC anomalies induced by seismic activity is confused with background fluctuations due to solar activity, a multi-resolution time series processing technique based on wavelet transform has been applied on TEC signal variations. In view of the fact that the accordance in the final results deduced from some robust methods is a convincing indication for the efficiency of the method, therefore the detected thermal and TEC anomalies using the ANN + PSO method were compared to the results with regard to the observed anomalies by implementing the mean, median, Wavelet, Kalman filter, Auto-Regressive Integrated Moving Average (ARIMA), Support Vector Machine (SVM) and Genetic Algorithm (GA) methods. The results indicate that the ANN + PSO method is quite promising and deserves serious attention as a new tool for thermal and TEC seismo anomalies detection.

Empirical forecast of the quiet time Ionosphere over Europe: a comparative model investigation

NASA Astrophysics Data System (ADS)

Badeke, R.; Borries, C.; Hoque, M. M.; Minkwitz, D.

2016-12-01

The purpose of this work is to find the best empirical model for a reliable 24 hour forecast of the ionospheric Total Electron Content (TEC) over Europe under geomagnetically quiet conditions. It will be used as an improved reference for the description of storm-induced perturbations in the ionosphere. The observational TEC-data were obtained from the International GNSS Service (IGS). Four different forecast model approaches were validated with observational IGS TEC-data: a 27 day median model (27d), a Fourier Analysis (FA) approach, the Neustrelitz TEC global model (NTCM-GL) and NeQuick 2. Two years were investigated depending on the solar activity: 2015 (high activity) and 2008 (low avtivity) The time periods of magnetic storms, which were identified with the Dst index, were excluded from the validation. For both years the two models 27d and FA show better results than NTCM-GL and NeQuick 2. For example for the year 2015 and 15° E / 50° N the difference between the IGS data and the predicted 27d model shows a mean value of 0.413 TEC units (TECU), a standard deviation of 3.307 TECU and a correlation coefficient of 0.921, while NTCM-GL and NeQuick 2 have mean differences of around 2-3 TECU, standard deviations of 4.5-5 TECU and correlation coefficients below 0.85. Since 27d and FA predictions strongly depend on observational data, the results confirm that data driven forecasts perform better than the climatological models NTCM-GL and NeQuick 2. However, the benefits of NTCM-GL and NeQuick 2 are actually the lower data dependency, i.e. they do not lack on precision when observational IGS TEC data are unavailable. Hence a combination of the different models is recommended reacting accordingly to the different data availabilities.

Aerosols and seismo-ionosphere coupling: A review

NASA Astrophysics Data System (ADS)

Namgaladze, Aleksandr; Karpov, Mikhail; Knyazeva, Maria

2018-06-01

The role of atmosphere aerosols in the global electric circuit, particularly during earthquakes preparation periods, is discussed in this review paper. Aerosols participate in production and transport of electric charges as well as in clouds formation. Satellite imagery shows increased aerosol optical depth over the tectonic faults and formation of the anomalous clouds aligned with the faults shortly before the earthquake shocks. At the same time variations of the ionospheric electric field and total electron content (TEC) are observed. We assume that the vertical electric current is generated over the fault due to the separation and vertical transport of charges with different masses and polarities. This charges the ionosphere positively relative to the Earth in the same way as the thunderstorm currents do. The resulting electric field in the ionosphere drives F2-layer plasma via the electromagnetic [E→ ×B→ ] drift and decreases or increases electron density depending on the configuration of the electric field, thus, creating observed negative or positive TEC disturbances. The important role of the electric dynamo effect in these processes is underlined.

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.

GNSS-ISR data fusion: General framework with application to the high-latitude ionosphere

NASA Astrophysics Data System (ADS)

Semeter, Joshua; Hirsch, Michael; Lind, Frank; Coster, Anthea; Erickson, Philip; Pankratius, Victor

2016-03-01

A mathematical framework is presented for the fusion of electron density measured by incoherent scatter radar (ISR) and total electron content (TEC) measured using global navigation satellite systems (GNSS). Both measurements are treated as projections of an unknown density field (for GNSS-TEC the projection is tomographic; for ISR the projection is a weighted average over a local spatial region) and discrete inverse theory is applied to obtain a higher fidelity representation of the field than could be obtained from either modality individually. The specific implementation explored herein uses the interpolated ISR density field as initial guess to the combined inverse problem, which is subsequently solved using maximum entropy regularization. Simulations involving a dense meridional network of GNSS receivers near the Poker Flat ISR demonstrate the potential of this approach to resolve sub-beam structure in ISR measurements. Several future directions are outlined, including (1) data fusion using lower level (lag product) ISR data, (2) consideration of the different temporal sampling rates, (3) application of physics-based regularization, (4) consideration of nonoptimal observing geometries, and (5) use of an ISR simulation framework for optimal experiment design.

Application of generalized singular value decomposition to ionospheric tomography

NASA Astrophysics Data System (ADS)

Bhuyan, K.; Singh, S.; Bhuyan, P.

2004-10-01

The electron density distribution of the low- and mid-latitude ionosphere has been investigated by the computerized tomography technique using a Generalized Singular Value Decomposition (GSVD) based algorithm. Model ionospheric total electron content (TEC) data obtained from the International Reference Ionosphere 2001 and slant relative TEC data measured at a chain of three stations receiving transit satellite transmissions in Alaska, USA are used in this analysis. The issue of optimum efficiency of the GSVD algorithm in the reconstruction of ionospheric structures is being addressed through simulation of the equatorial ionization anomaly (EIA), in addition to its application to investigate complicated ionospheric density irregularities. Results show that the Generalized Cross Validation approach to find the regularization parameter and the corresponding solution gives a very good reconstructed image of the low-latitude ionosphere and the EIA within it. Provided that some minimum norm is fulfilled, the GSVD solution is found to be least affected by considerations, such as pixel size and number of ray paths. The method has also been used to investigate the behaviour of the mid-latitude ionosphere under magnetically quiet and disturbed conditions.

Analysis of the 20th November 2003 Extreme Geomagnetic Storm using CTIPe Model and GNSS Data

NASA Astrophysics Data System (ADS)

Fernandez-Gomez, I.; Borries, C.; Codrescu, M.

2016-12-01

The ionospheric instabilities produced by solar activity generate disturbances in ionospheric density (ionospheric storms) with important terrestrial consequences such as disrupting communications and positioning. During the 20th November 2003 extreme geomagnetic storm, significant perturbations were produced in the ionosphere - thermosphere system. In this work, we replicate how this system responded to the onset of this particular storm, using the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics physics based model. CTIPe simulates the changes in the neutral winds, temperature, composition and electron densities. Although modelling the ionosphere under this conditions is a challenging task due to energy flow uncertainties, the model reproduces some of the storm features necessary to interpret the physical mechanisms behind the Total Electron Content (TEC) increase and the dramatic changes in composition during this event.Corresponding effects are observed in the TEC simulations from other physics based models and from observations derived from Global Navigation Satellite System (GNSS) and ground-based measurements.The study illustrates the necessity of using both, measurements and models, to have a complete understanding of the processes that are most likely responsible for the observed effects.

A study on ionospheric scintillation near the EIA crest in relation to equatorial electrodynamics

NASA Astrophysics Data System (ADS)

Chatterjee, S.; Chakraborty, S. K.; Veenadhari, B.; Banola, S.

2014-02-01

Equatorial electrojet (EEJ) data, which are considered as a proxy index of equatorial electric field, are analyzed in conjunction with equatorial ionosonde, total electron content (TEC) and scintillation data near the equatorial ionization anomaly (EIA) crest for the equinoctial months of high solar activity years (2011-2012) to identify any precursor index of postsunset evolution of equatorial electron density irregularities and subsequent occurrence of scintillation near the northern EIA crest. Only geomagnetically quiet and normal electrojet days are considered. The diurnal profiles of EEJ on the scintillation days exhibit a secondary enhancement in the afternoon to presunset hours following diurnal peaks. A series of electrodynamical processes conducive for generation of irregularities emerge following secondary enhancement of EEJ. Latitudinal profile of TEC exhibits resurgence in EIA structure around the postsunset period. Diurnal TEC profile near the EIA crest resembles postsunset secondary enhancement on the days with afternoon enhancement in EEJ. Occurrence of equatorial spread F and postsunset scintillation near the EIA crest seems to follow the secondary enhancement events in EEJ. Both the magnitude and duration of enhanced EEJ are found to be important for postsunset intensification of EIA structure and subsequent occurrence of equatorial irregularities. A critical value combining the two may be considered an important precursor for postsunset occurrence of scintillation near the EIA crest. The results are validated using archived data for the years 1989-1990 and explained in terms of modulation effects of enhanced equatorial fountain.

Quasi-two-day wave coupling of the mesosphere and lower thermosphere-ionosphere in the TIME-GCM: Two-day oscillations in the ionosphere

NASA Astrophysics Data System (ADS)

Yue, Jia; Wang, Wenbin; Richmond, Arthur D.; Liu, Han-Li

2012-07-01

The Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is used to simulate the quasi-two-day wave (QTDW) modulation of the ionospheric dynamo and electron density. The QTDW can directly penetrate into the lower thermosphere and modulate the neutral winds at a period of two days. The QTDW modulation of the tidal amplitudes is not evident. The QTDW in zonal and meridional winds results in a quasi-two-day oscillation (QTDO) of the dynamo electric fields at southern midlatitudes, which is mapped into the conjugate northern magnetic midlatitudes. The QTDO of the electric fields in the E region is transmitted along the magnetic field lines to the F region and leads to the QTDOs of the vertical ion drift and total electron content (TEC) at low and mid latitudes. The QTDO of the vertical ion drift near the magnetic equator leads to the 2-day oscillation of the fountain effect. The QTDO of the TEC has two peaks at ±25 magnetic latitude (Mlat) and one near the dip equator. The equatorial peak is nearly out of phase with the ones at ±25 Mlat. The vertical ion drift at midlatitudes extends the QTDW response of the TEC to midlatitudes from the Equatorial Ionospheric Anomaly (EIA). Most differently from previous reports, we discover that the QTDW winds couple into the F region ionosphere through both the fountain effect and the middle latitude dynamos.

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.

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.

Ionosphere monitoring and forecast activities within the IAG working group "Ionosphere Prediction"

NASA Astrophysics Data System (ADS)

Hoque, Mainul; Garcia-Rigo, Alberto; Erdogan, Eren; Cueto Santamaría, Marta; Jakowski, Norbert; Berdermann, Jens; Hernandez-Pajares, Manuel; Schmidt, Michael; Wilken, Volker

2017-04-01

Ionospheric disturbances can affect technologies in space and on Earth disrupting satellite and airline operations, communications networks, navigation systems. As the world becomes ever more dependent on these technologies, ionospheric disturbances as part of space weather pose an increasing risk to the economic vitality and national security. Therefore, having the knowledge of ionospheric state in advance during space weather events is becoming more and more important. To promote scientific cooperation we recently formed a Working Group (WG) called "Ionosphere Predictions" within the International Association of Geodesy (IAG) under Sub-Commission 4.3 "Atmosphere Remote Sensing" of the Commission 4 "Positioning and Applications". The general objective of the WG is to promote the development of ionosphere prediction algorithm/models based on the dependence of ionospheric characteristics on solar and magnetic conditions combining data from different sensors to improve the spatial and temporal resolution and sensitivity taking advantage of different sounding geometries and latency. Our presented work enables the possibility to compare total electron content (TEC) prediction approaches/results from different centers contributing to this WG such as German Aerospace Center (DLR), Universitat Politècnica de Catalunya (UPC), Technische Universität München (TUM) and GMV. DLR developed a model-assisted TEC forecast algorithm taking benefit from actual trends of the TEC behavior at each grid point. Since during perturbations, characterized by large TEC fluctuations or ionization fronts, this approach may fail, the trend information is merged with the current background model which provides a stable climatological TEC behavior. The presented solution is a first step to regularly provide forecasted TEC services via SWACI/IMPC by DLR. UPC forecast model is based on applying linear regression to a temporal window of TEC maps in the Discrete Cosine Transform (DCT) domain. Performance tests are being conducted at the moment in order to improve UPC predicted products for 1-, 2-days ahead. In addition, UPC is working to enable short-term predictions based on UPC real-time GIMs (labelled URTG) and implementing an improved prediction approach. TUM developed a forecast method based on a time series analysis of TEC products which are either B-spline coefficients estimated by a Kalman filter or TEC grid maps derived from the B-spline coefficients. The forecast method uses a Fourier series expansion to extract the trend functions from the estimated TEC product. Then the trend functions are carried out to provide predicted TEC products. The forecast algorithm developed by GMV is based on the ionospheric delay estimation from previous epochs using GNSS data and the main dependence of ionospheric delays on solar and magnetic conditions. Since the ionospheric behavior is highly dependent on the region of the Earth, different region-based algorithmic modifications have been implemented in GMV's magicSBAS ionospheric algorithms to be able to estimate and forecast ionospheric delays worldwide. Different TEC prediction approaches outlined here will certainly help to learn about forecasting ionospheric ionization.

Variability of Thermosphere and Ionosphere Responses to Solar Flares

NASA Technical Reports Server (NTRS)

Qian, Liying; Burns, Alan G.; Chamberlin, Philip C.; Solomon, Stanley C.

2011-01-01

We investigated how the rise rate and decay rate of solar flares affect the thermosphere and ionosphere responses to them. Model simulations and data analysis were conducted for two flares of similar magnitude (X6.2 and X5.4) that had the same location on the solar limb, but the X6.2 flare had longer rise and decay times. Simulated total electron content (TEC) enhancements from the X6.2 and X5.4 flares were 6 total electron content units (TECU) and approximately 2 TECU, and the simulated neutral density enhancements were approximately 15% -20% and approximately 5%, respectively, in reasonable agreement with observations. Additional model simulations showed that for idealized flares with the same magnitude and location, the thermosphere and ionosphere responses changed significantly as a function of rise and decay rates. The Neupert Effect, which predicts that a faster flare rise rate leads to a larger EUV enhancement during the impulsive phase, caused a larger maximum ion production enhancement. In addition, model simulations showed that increased E x B plasma transport due to conductivity increases during the flares caused a significant equatorial anomaly feature in the electron density enhancement in the F region but a relatively weaker equatorial anomaly feature in TEC enhancement, owing to dominant contributions by photochemical production and loss processes. The latitude dependence of the thermosphere response correlated well with the solar zenith angle effect, whereas the latitude dependence of the ionosphere response was more complex, owing to plasma transport and the winter anomaly.

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.

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.

Investigation of Ionospheric Anomalies related to moderate Romanian earthquakes occurred during last decade using VLF/LF INFREP and GNSS Global Networks

NASA Astrophysics Data System (ADS)

Moldovan, Iren-Adelina; Oikonomou, Christina; Haralambous, Haris; Nastase, Eduard; Emilian Toader, Victorin; Biagi, Pier Francesco; Colella, Roberto; Toma-Danila, Dragos

2017-04-01

Ionospheric TEC (Total Electron Content) variations and Low Frequency (LF) signal amplitude data prior to five moderate earthquakes (Mw≥5) occurred in Romania, in Vrancea crustal and subcrustal seismic zones, during the last decade were analyzed using observations from the Global Navigation Satellite System (GNSS) and the European INFREP (International Network for Frontier Research on Earthquake Precursors) networks respectively, aiming to detect potential ionospheric anomalies related to these events and describe their characteristics. For this, spectral analysis on TEC data and terminator time method on VLF/LF data were applied. It was found that TEC perturbations appeared few days (1-7) up to few hours before the events lasting around 2-3 hours, with periods 20 and 3-5 minutes which could be associated with the impending earthquakes. In addition, in all three events the sunrise terminator times were delayed approximately 20-40 min few days prior and during the earthquake day. Acknowledgments This work was partially supported by the Partnership in Priority Areas Program - PNII, under MEN-UEFISCDI, DARING Project no. 69/2014 and the Nucleu Program - PN 16-35, Project no. 03 01

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 the Rice Convection Model as a Space Weather Tool

DTIC Science & Technology

2015-05-31

coupled to the ionosphere that is suitable for both scientific studies as well as a prediction tool. We are able to run the model faster than “real...of work by finding ways to fund a more systematic effort in making the RCM a space weather prediction tool for magnetospheric and ionospheric studies...convection electric field, total electron content, TEC, ionospheric convection, plasmasphere 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT

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.

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.

Ionospheric redistribution during geomagnetic storms

PubMed Central

Immel, T J; Mannucci, A J

2013-01-01

[1]The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dst<−100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation but follows it by 3–6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow. PMID:26167429

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.

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.

Ionospheric redistribution during geomagnetic storms.

PubMed

Immel, T J; Mannucci, A J

2013-12-01

[1]The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active ( D s t <-100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation but follows it by 3-6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.

Performance of MIDAS Over East African Longitude Sector: Case Study During 4-14 March 2012 Quiet to Disturbed Geomagnetic Conditions

NASA Astrophysics Data System (ADS)

Giday, Nigussie M.; Katamzi-Joseph, Zama T.

2018-02-01

This study investigates the performance of a tomographic algorithm, Multi-Instrument and Data Analysis System (MIDAS), during an extended period of 4-14 March 2012, containing moderate and strong geomagnetic storms conditions, over an understudied and data scarce Eastern African longitude sector. Nonetheless, a relatively better distribution of Global Navigation Satellite Systems stations exists along a narrow longitude sector between 30°E and 44°E and latitude range of 30°S and 36°N that spans the equatorial, middle-, and low-latitude ionosphere. Then results are compared with independent global models such as International Reference Ionosphere 2012 (IRI-2012) and global ionosphere map (GIM). MIDAS performance was better than that of the IRI-2012 and GIM models in terms of capturing the diurnal trends as well as the short temporal total electron content (TEC) structures, with least root-mean-square errors (RMSEs). Overall, MIDAS results showed better agreement with the observation vertical TEC (VTEC) with computed maximum correlation coefficient (r) of 0.99 and minimum root-mean-square error (RMSE) of 2.91 TEC unit (1 TECU = 1,016 el m-2 over all the test stations and the validation days. Conversely, for the IRI-2012 and GIM TEC estimates, the corresponding maximum computed r values were 0.93 and 0.99, respectively, while the minimum RMSEs were 13.03 TECU and 6.52 TECU, respectively, for all the test stations and the validation days.

Performance of ionospheric maps in support of long baseline GNSS kinematic positioning at low latitudes

NASA Astrophysics Data System (ADS)

Park, J.; Sreeja, V.; Aquino, M.; Cesaroni, C.; Spogli, L.; Dodson, A.; De Franceschi, G.

2016-05-01

Ionospheric scintillation occurs mainly at high and low latitude regions of the Earth and may impose serious degradation on GNSS (Global Navigation Satellite System) functionality. The Brazilian territory sits on one of the most affected areas of the globe, where the ionosphere behaves very unpredictably, with strong scintillation frequently occurring in the local postsunset hours. The correlation between scintillation occurrence and sharp variations in the ionospheric total electron content (TEC) in Brazil is demonstrated in Spogli et al. (2013). The compounded effect of these associated ionospheric disturbances on long baseline GNSS kinematic positioning is studied in this paper, in particular when ionospheric maps are used to aid the positioning solution. The experiments have been conducted using data from GNSS reference stations in Brazil. The use of a regional TEC map generated under the CALIBRA (Countering GNSS high-Accuracy applications Limitations due to Ionospheric disturbances in BRAzil) project, referred to as CALIBRA TEC map (CTM), was compared to the use of the Global Ionosphere Map (GIM), provided by the International GNSS Service (IGS). Results show that the use of the CTM greatly improves the kinematic positioning solution as compared with that using the GIM, especially under disturbed ionospheric conditions. Additionally, different hypotheses were tested regarding the precision of the TEC values obtained from ionospheric maps, and its effect on the long baseline kinematic solution evaluated. Finally, this study compares two interpolation methods for ionospheric maps, namely, the Inverse Distance Weight and the Natural Neighbor.

(Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC submillimetre galaxies. I. Multiwavelength identifications and redshift distribution

NASA Astrophysics Data System (ADS)

Miettinen, O.; Smolčić, V.; Novak, M.; Aravena, M.; Karim, A.; Masters, D.; Riechers, D. A.; Bussmann, R. S.; McCracken, H. J.; Ilbert, O.; Bertoldi, F.; Capak, P.; Feruglio, C.; Halliday, C.; Kartaltepe, J. S.; Navarrete, F.; Salvato, M.; Sanders, D.; Schinnerer, E.; Sheth, K.

2015-05-01

We used the Plateau de Bure Interferometer (PdBI) to map a sample of 15 submillimetre galaxies (SMGs) in the COSMOS field at the wavelength of 1.3 mm. The target SMGs were originally discovered in the James Clerk Maxwell Telescope (JCMT)/AzTEC 1.1 mm continuum survey at S/N1.1 mm = 4-4.5. This paper presents, for the first time, interferometric millimetre-wavelength observations of these sources. The angular resolution of our observations, 1''&dotbelow;8, allowed us to accurately determine the positions of the target SMGs. Using a detection threshold of S/N1.3 mm> 4.5 regardless of multiwavelength counterpart association, and 4