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Showing papers on "Total electron content published in 2002"


Journal ArticleDOI
TL;DR: In this paper, the authors make direct comparisons between GPS maps of total electron content (TEC) over the North American continent, Millstone Hill radar observations of storm enhanced density, and low and high-altitude satellite measurements of the perturbation of the outer plasmasphere during the March 31, 2001 geomagnetic storm.
Abstract: [1] We make direct comparisons between GPS maps of total electron content (TEC) over the North American continent, Millstone Hill radar observations of storm enhanced density, and low and high-altitude satellite measurements of the perturbation of the outer plasmasphere during the March 31, 2001 geomagnetic storm. We find that storm enhanced density (SED) and plumes of greatly-elevated TEC are associated with the erosion of the outer plasmasphere by strong sub-auroral polarization electric fields. The SED/TEC plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by EUV imaging from the IMAGE spacecraft. Characteristics of the SED/TEC plumes/tails for the March 31, 2001 event are: TEC ∼ 100 TECu; F-region sunward velocity ∼1000 m/s; sunward flux ∼5*1024 ions s−1; total transport to dayside magnetopause/merging region (3-hr event) ∼5*1028 ions.

304 citations


Journal ArticleDOI
TL;DR: In this paper, a least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers.
Abstract: The dual frequency radio signals of the Global Positioning System (GPS) allow measurements of the total number of electrons, called total electron content (TEC), along a ray path from GPS satellite to receiver. We have developed a new technique to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers. A least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver. Two-dimensional maps of absolute vertical TEC are derived with time resolution of 30 seconds and spatial resolution of 0.15° × 0.15° in latitude and longitude. Our method is validated in two ways. First, TECs along ray paths from the GPS satellites are simulated using a model for electron contents based on the IRI-95 model. It is found that TEC from our method is underestimated by less than 3 TECU. Then, estimated vertical GPS TEC is compared with ionospheric TEC that is calculated from simultaneous electron density profile obtained with the MU radar. Diurnal and day-to-day variation of the GPS TEC follows the TEC behavior derived from MU radar observation but the GPS TEC is 2 TECU larger than the MU radar TEC on average. This difference can be attributed to the plasmaspheric electron content along the GPS ray path. This method is also applied to GPS data during a magnetic storm of September 25, 1998. An intense TEC enhancement, probably caused by a northward expansion of the equatorial anomaly, was observed in the southern part of Japan in the evening during the main phase of the storm.

250 citations


Journal Article
TL;DR: In this article, a least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers.
Abstract: The dual frequency radio signals of the Global Positioning System (GPS) allow measurements of the total number of electrons, called total electron content (TEC), along a ray path from GPS satellite to receiver. We have developed a new technique to construct two-dimensional maps of absolute TEC over Japan by using GPS data from more than 1000 GPS receivers. A least squares fitting procedure is used to remove instrumental biases inherent in the GPS satellite and receiver. Two-dimensional maps of absolute vertical TEC are derived with time resolution of 30 seconds and spatial resolution of 0.15° × 0.15° in latitude and longitude. Our method is validated in two ways. First, TECs along ray paths from the GPS satellites are simulated using a model for electron contents based on the IRI-95 model. It is found that TEC from our method is underestimated by less than 3 TECU. Then, estimated vertical GPS TEC is compared with ionospheric TEC that is calculated from simultaneous electron density profile obtained with the MU radar. Diurnal and day-to-day variation of the GPS TEC follows the TEC behavior derived from MU radar observation but the GPS TEC is 2 TECU larger than the MU radar TEC on average. This difference can be attributed to the plasmaspheric electron content along the GPS ray path. This method is also applied to GPS data during a magnetic storm of September 25, 1998. An intense TEC enhancement, probably caused by a northward expansion of the equatorial anomaly, was observed in the southern part of Japan in the evening during the main phase of the storm.

194 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a 1-D stratified velocity model of the atmosphere to detect the ionospheric perturbation caused by the Black Thunder mine explosion in eastern Wyoming and showed that linear acoustic ray tracing fits arrival times at all GPS receivers.
Abstract: Sources such as atmospheric or buried explosions and shallow earthquakes are known to produce infrasonic pressure waves in the atmosphere. Because of the coupling between neutral particles and electrons at ionospheric altitudes, these acoustic and gravity waves induce variations of the ionospheric electron density. The Global Positioning System (GPS) provides a way of directly measuring the total electron content in the ionosphere and, therefore, of detecting such perturbations in the upper atmosphere. In July and August 1996, three large surface mine blasts (1.5 Kt each) were detonated at the Black Thunder coal mine in eastern Wyoming. As part of a seismic and acoustic monitoring- experiment, we deployed five dual-frequency GPS receivers at distances ranging from 50 to 200 km from the mine and were able to detect the ionospheric perturbation caused by the blasts. The perturbation starts 10 to 15 min after the blast, lasts for about 30 min, and propagates with an apparent horizontal velocity of 1200 meters per second. Its amplitude reaches 3 x 10 (exp 14) el per square meters in the 7-3 min period band, a value close to the ionospheric perturbation caused by the M = 6.7 Northridge earthquake. The small signal-to-noise ratio of the perturbation can be improved by slant-stacking the electron content time-series recorded by the different GPS receivers taking into account the horizontal propagation of the perturbation. The energy of the perturbation is concentrated in the 200 to 300 second period band, a result consistent with previous observations and numerical model predictions. The 300 second band probably corresponds to gravity modes and shorter periods to acoustic modes, respectively. Using a 1-D stratified velocity model of the atmosphere we show that linear acoustic ray tracing fits arrival times at all GPS receivers. We interpret the perturbation as a direct acoustic wave caused by the explosion itself. This study shows that even relatively small subsurface events can produce ionospheric perturbations that are above the detection threshold of the GPS technique. By sensing derivative signals, which can be detected over a relatively broad region, it appears that GPS might be particularly useful for source characterization within the first acoustic quiet zone where infrasound would probably be ineffective. This suggests that dual-frequency GPS monitoring could contribute to Comprehensive Nuclear Test Ban Treaty verification.

128 citations


Journal ArticleDOI
TL;DR: The performance of different kinds of models are presented in order to determine the accuracy of the different GIMs, and the obtained accuracies range from 54% corresponding to the GPS broadcast model, to about 41%, corresponding to IRI climatological model, and to less than 30% corresponds to GPS data driven models.

110 citations


Journal ArticleDOI
TL;DR: The first observations of GPS L1 amplitude scintillation activity in the midlatitude ionosphere at latitudes corresponding to the northeastern United States have been made as discussed by the authors, where a modified GPS receiver was used to record GPS satellite signal strength at Cornell University (53.2° magnetic latitude).
Abstract: [1] First observations of intense GPS L1 amplitude scintillation activity in the midlatitude ionosphere at latitudes corresponding to the northeastern United States have been made. Moderate to severe, these scintillations result from space weather effects due to a disturbed ionosphere. Moderate to severe scintillations can degrade or even disrupt communication and navigation systems relying upon transionospheric radio wave propagation. A modified GPS receiver was used to record GPS satellite signal strength at Cornell University (53.2° magnetic latitude) during a magnetospheric disturbance on September 25–26, 2001 from 0000–0400 UTC. This disturbance (Kp = 6, minimum Dst = −110 nT) prompted the ionospheric trough to move equatorward over the northeastern U.S. and produced large plasma densities and gradients attributed to storm-time effects. This disturbance resulted in intense L-band amplitude scintillations (≥20 dB, S4 ≈ 0.8) which are highly uncharacteristic at this magnetic latitude. Concurrent measurements of TEC showed steep density gradients (∼30 TEC/deg) and evidence of irregularity structuring.

102 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the data of more than 15 GPS stations of the GPS tracking network of the International GPS Service (IGS), a horizontal resolution in the order of 500 km is achieved, the standard time resolution is 10 min.

98 citations


Journal ArticleDOI
TL;DR: In this article, a comparison with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) showed that an enhancement (250-300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes.
Abstract: enhancement of GPS total electron content (� 1.0 � 10 16 m � 2 ). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of � 400–450 m/s. From a comparison with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) we conclude that an enhancement (250–300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes. To investigate generation of the LSTID by auroral energy input, we have used auroral images obtained by the Polar UVI instrument, magnetic field variations obtained at multipoint ground stations, and the empirical Joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. Intense auroral energy input was observed at 0800–1100 UT (4–6 hours before the LSTID), probably causing equatorward neutral wind at lower latitudes. It is likely that the poleward wind pulse that caused the observed LSTID was generated associated with the cessation of this equatorward wind. The effect of Lorentz force is also discussed. INDEX TERMS: 0310 Atmospheric Composition and Structure: Airglow and aurora; 2427 Ionosphere: Ionosphere/atmosphere interactions (0335); 2435 Ionosphere: Ionospheric disturbances; 2437 Ionosphere: Ionospheric dynamics; 2788 Magnetospheric Physics: Storms and substorms; KEYWORDS: large-scale traveling ionospheric disturbance, thermosphere–ionosphere coupling, magnetic storm, airglow imaging, GPS network, ionosonde

94 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the data from about 100 GPS stations located in the neighborhood of the eclipse totality phase in Europe to measure fundamental parameters of the ionospheric response to the 1999 total solar eclipse.

79 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the Scheffield University Plasmasphere Ionosphere Model (SUPIM) to obtain theoretical relationships between the 630 nm airglow intensity and GPS-TEC and between their fluctuation amplitudes.
Abstract: Southwestward-propagating medium-scale traveling ionospheric disturbances (MSTIDs) observed over Shigaraki (34.85°N, 136.10°E) in Japan on the night of May 22, 1998 are analyzed in detail. The MSTIDs were detected with a 630.0 nm (OI) all-sky imager at Shigaraki and a large number of GPS (Global Positioning System) receivers distributed around Shigaraki. Each GPS receiver provided total electron content (TEC) between the GPS altitude (20,200 km) and the ground. MSTID amplitudes varied in space and time, and showed decay and enhancement during the southwestward propagation, suggesting that amplitudes of atmospheric gravity waves and the interaction process between gravity waves and F region plasma were highly variable. It is found that spatial and temporal fluctuations of the 630 nm intensity are well correlated with those of GPS-TEC except for a certain period of time. The Scheffield University Plasmasphere Ionosphere Model (SUPIM) is used to obtain theoretical relationships between the 630 nm airglow intensity and GPS-TEC and between their fluctuation amplitudes. The results indicate that the fluctuation amplitudes observed in weak airglow regions are caused by an electron density fluctuation of about ±20% occurring around an altitude of 250 km, where the 630 nm emission rate reaches a maximum, below the F layer peak altitude. Highly enhanced 630 nm intensity and GPS-TEC within a bright airglow region are due to an electron density enhancement of about 150% occurring at altitudes below 300 km.

73 citations


Journal ArticleDOI
TL;DR: In this article, the authors make use of a 19 h daylight experiment by the EISCAT incoherent scatter radar based in Tromso, Norway, to calculate the total electron content (TEC) and the parameters of the F-region peak, namely its altitude (hmF2) and its density (NmF2).

Journal ArticleDOI
TL;DR: In this article, an all-sky cooled-CCD imager measured 630-nm airglow at a southern island of Japan, Okinawa (26.9°N, 128.3°E, geomagnetic latitude (MLAT) = 17.0°, during the FRONT-2 campaign of August 4-15, 1999.
Abstract: This paper reports the first attempt to observe the equatorward limit of medium-scale traveling ionospheric disturbances (TIDs) in the middle latitudes. The TIDs usually propagate southwestward in the northern hemisphere. An all-sky cooled-CCD imager measured 630-nm airglow at a southern island of Japan, Okinawa (26.9°N, 128.3°E, geomagnetic latitude (MLAT) = 17.0°), during the FRONT-2 campaign of August 4–15, 1999. The TIDs were detected at the mainland of Japan (∼21°–36° MLAT) by the total electron content (TEC) observations of more than 1000 GPS receivers. In the August 4 event, the TIDs moving southwestward was seen only in the northern sky of Okinawa as a depletion band in the 630-nm airglow images. In the August 6 event, the TIDs were not seen in the 630-nm images at Okinawa, although weak TID activity was observed by the GPS network at the mainland of Japan. The TEC data also showed weakening of the TID activity below 18° MLAT. Based on these observations, we suggest that there is a possible limit of medium-scale TID propagation around ∼18° MLAT.

Journal ArticleDOI
TL;DR: In this paper, an ionospheric correction technique for single frequency GPS measurements from satellites in low Earth orbit is described. But the method is not suitable for the case of single frequency C}A-code measurements, and the suitability of the model is assessed by comparison with flight data from the Champ satellite that orbits the Earth at an altitude of 450 km.
Abstract: This paper describes an ionospheric correction technique for single frequency GPS measurements from satellites in low Earth orbit. The fractional total electron content (TEC) above the receiver altitude is obtained from global TEC maps of the International GPS Service network and an altitude dependent scale factor. By choosing a suitable eective height of the residual ionosphere, the resulting path delay for positive elevations is then computed from a thin layer approximation. The scale factor can be predicted from the assumption of a Chapman profile for the altitude variation of the electron density or adjusted as a free parameter in the processing of an extended set of single frequency measurements. The suitability of the proposed model is assessed by comparison with flight data from the Champ satellite that orbits the Earth at an altitude of 450 km. For the given test case, a 90% correction of the ionospheric error is achieved in a reduced dynamic orbit determination based on single frequency C}A-code measurements. .

Journal ArticleDOI
TL;DR: In this paper, three main regions may be distinguished from the point of view of geomagnetic storm effects on the midlatitude ionosphere: F2 region (strong effect with positive and negative phases), F1-E region (weak and less known effect), and lower ionosphere (strong positive effect).

Journal ArticleDOI
TL;DR: In this article, the International Reference Ionosphere (IRI) model and ionospheric data deduced from GPS measurements can be combined to improve ionosphere determinations, which can be done by using GPS-derived TEC maps or by using actual GPS measurements of the electron content along the signal path from satellite to ground receiver.

Journal ArticleDOI
TL;DR: In this paper, top-side electron density profiles measured onboard ISIS-1 and ISIS-2 (1969 to 1980) and IK-19 (1979 to 1982) were extended through the plasmasphere using Chasovitin's (1999) model describing the plasma density between the peak of the ionosphere and the Plasmapause.

Journal ArticleDOI
TL;DR: In this article, an experimental method was derived for estimating the effective shell height for electron content measurement by GPS reception using simultaneous vertical and slant observations, and the results indicated that the plasmaspheric effective height used in the oblique-to-zenithal thin shell conversion is considerably greater than the commonly adopted value of 350 km.
Abstract: [1] An experimental method, using simultaneous vertical and slant observations, has been derived for estimating the effective shell height for electron content measurement by GPS reception. At a latitude of approximately 53° north, Lancashire is well placed as an observing site since GPS satellite orbits are inclined at 55° to the Earth's equatorial plane and, as a result, many GPS tracks pass almost directly overhead, giving true zenithal measurements. This paper focuses on the question of oblique-to-zenithal correction and related matters. In particular, plasmaspheric effective height and satellite bias corrections are determined by measuring the total electron content (TEC) from pairs of satellites to a single ground station, each pair giving simultaneous observations of oblique and zenithal TEC. Additional bias corrections are determined by extracting the TEC using pairs of satellites with the same elevation at the same time. The Chapman Production Function Model and the Sheffield University Plasmasphere and Ionosphere Model are both used to determine a theoretical value for the plasmaspheric effective height. The results indicate that the plasmaspheric effective height used in the oblique-to-zenithal thin shell conversion is considerably greater than the commonly adopted value of 350 km. It is suggested, on the basis of all the available evidence, that a value between 600 and 1200 km is preferred. Assuming a lower value could produce an error of 15 to 30% or more in the electron content.

Journal ArticleDOI
TL;DR: Based on the high time and spatial resolution total electron content (TEC) data, which was estimated from the phase and code observables obtained by using GPS (Global Positioning System) Earth Observation Network (GEONET), the TEC distribution and its time variation over Japanese Islands are scaled into 0.5° × 0. 5° grid data for each 10 minutes.
Abstract: Based on the high time and spatial resolution total electron content (TEC) data, which is estimated from the phase and code observables obtained by using GPS (Global Positioning System) Earth Observation Network (GEONET), the TEC distribution and its time variation over Japanese Islands are scaled into 0.5° × 0.5° grid data for each 10 minutes. The TEC daily map time series are arranged in an array to show the TEC evolution. Based on the spherical harmonics expansion of global ionospheric TEC model (GIM), which is estimated from global GPS observation, the TEC maps are expanded firstly through as high as 60 degrees and orders for a spherical harmonic function as a regional ionosphere map (RIM). The evolution history of medium scale traveling ionospheric disturbances (MSTIDs), i.e. polarward intense TEC enhancement and pre-noon rapid irregular fluctuations near the geomagnetic equator, are identified and confirmed in a quiet geomagnetic period.

Journal ArticleDOI
TL;DR: In this article, the authors discuss some satellite-to-ground propagation problems in the UHF and L bands caused by the Earth's ionosphere, such as signal time delay, signal dispersion, Faraday rotation, and scintillation.
Abstract: Satellite-ground radio systems are now so sensitive that ionospheric changes can disrupt their performance. This paper discusses some satellite-to-ground propagation problems in the UHF and L bands caused by the Earth's ionosphere. Such problems include signal time delay, signal dispersion, Faraday rotation, and scintillation.

Journal ArticleDOI
TL;DR: In this paper, the authors used the Sheffield University plasmasphere-ionosphere model (SUPIM) to estimate the electron content in the plasaspheric sections of GPS ray paths for the three seasons of high solar activity under magnetically quiet conditions.
Abstract: Vertical total electron content (GPS-TEC) data obtained from the dual-frequency GPS receiver network (GEONET) in Japan are compared with those calculated using the Sheffield University plasmasphere-ionosphere model (SUPIM). The model is also used to estimate the electron content in the plasmaspheric sections of GPS ray paths for the three seasons of high solar activity (F10.7 = 165) under magnetically quiet conditions. According to the estimates, the plasmaspheric sections of vertical GPS ray paths over Japan at altitudes above the O+ to H+ transition height and above the upper altitude (2500 km) of Faraday rotation contain up to 11 and 9 TEC units (1 TEC unit = 1016 electrons m−2) of free electrons, respectively. The free electrons present above the Faraday rotation altitude can cause propagation errors of up to 4.9 ns in time delay and 1.6 m in range at the GPS L1 (1.57542 GHz) frequency. The plasmaspheric electron content, PEC, changes appreciably with season and latitude and very little with the time of the day. However, the percentage contribution of PEC to GPS-TEC changes most significantly with the time of the day; the contribution varies from a minimum of about 12% during daytime at equinox to a maximum of about 60% at night in winter.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a new method for estimating the contribution from different ionospheric regions to the response of total electron content variations to the solar flare, based on data from the international network of two-frequency multichannel receivers of the navigation GPS system.
Abstract: . This paper proposes a new method for estimating the contribution from different ionospheric regions to the response of total electron content variations to the solar flare, based on data from the international network of two-frequency multichannel receivers of the navigation GPS system. The method uses the effect of partial "shadowing" of the atmosphere by the terrestrial globe. The study of the solar flare influence on the atmosphere uses GPS stations located near the boundary of the shadow on the ground in the nightside hemisphere. The beams between the satellite-borne transmitter and the receiver on the ground for these stations pass partially through the atmosphere lying in the region of total shadow, and partially through the illuminated atmosphere. The analysis of the ionospheric effect of a powerful solar flare of class X5.7/3B that was recorded on 14 July 2000 (10:24 UT, N22 W07) in quiet geomagnetic conditions (Dst = -10 nT) has shown that about 75% of the TEC increase corresponds to the ionospheric region lying below 300 km and about 25% to regions lying above 300 km. Key words. Ionosphere (solar radiation and cosmic ray effects; instruments and techniques) – Solar physics, astrophysics and astronomy (ultraviolet emissions)

Journal ArticleDOI
TL;DR: In this article, the spatial variations of total electron content (TEC) over the European area for single epochs are examined using a so-called instantaneous mapping procedure applied to simultaneous data collected from a limited number of measuring stations.


27 Sep 2002
TL;DR: It is shown that a carefully designed estimation algorithm based on kriging could provide confidence bounds on the ionospheric delay corrections allowing WAAS to meet the GNSS Landing System requirements.
Abstract: GPS alone cannot provide the integrity needed for air navigation. Several error sources deteriorate the precision of the position estimate. One of the largest and more unpredictable sources of error for single frequency users is the ionosphere. For this reason, ionospheric behavior drives the performance of the Wide Area Augmentation System (WAAS). At any given time, the only information we have of the ionosphere is a limited amount of Total Electron Content (TEC) measurements. As a consequence, in order to estimate the ionospheric delay and get a confidence bound on such an estimate, we need to understand the spatial structure of the ionosphere over the region of interest. Using the thin shell model framework, where each TEC measurement is identified as a location on the thin shell, labeled the Ionospheric Pierce Point (IPP), the problem is reduced to a 2-dimensional problem. Once we have a good description of a nominal ionosphere, there are two questions that need to be answered before estimating the delay at a given IPP: Are the IPP measurements compatible with the assumed nominal model of the ionosphere? How relevant are the IPP measurements to the location we need to estimate? To answer the first one, an accurate characterization of the ionosphere in nominal conditions is needed. The large observed stationarity violations make this latter question very difficult. A worst case based method to determine the spatial structure of the nominal ionosphere in terms of the variogram, or, equivalently, the covariance is presented. The technique called "kriging" produces at each location an estimate and a confidence bound on the estimate, the kriging variance. The particular behavior of the kriging variance at the edge of coverage allows us to intuitively define the "well sampled" region. We show that a carefully designed estimation algorithm based on kriging could provide confidence bounds on the ionospheric delay corrections allowing WAAS to meet the GNSS Landing System requirements.

Journal ArticleDOI
TL;DR: In this paper, an empirical model of total electron content (TEC) for a low-latitude station, Palehua, has been developed using harmonic analysis of TEC data measured at this station during the period 1980-1990; the TEC values were obtained from Faraday rotation measurements of linearly polarised signals transmitted by geostationary satellites.

Journal ArticleDOI
TL;DR: In this paper, the multiplicative algebraic reconstruction technique (MART) was used to reconstruct and compare two-dimensional ionospheric structures from measured TECs through the receptions of the GPS signals, the NNSS signals, and/or both of the systems.

Journal ArticleDOI
TL;DR: In this article, GPS data from over 60 GPS stations were used to study the ionospheric effects of the 12-16 September 1999 magnetic storm over Europe, including the positive and negative phases.
Abstract: . TEC data, obtained from over 60 GPS stations, were used to study the ionospheric effects of the 12–16 September 1999 magnetic storm over Europe. The spatial and temporal changes of the ionosphere were analysed as a time series of TEC maps, which present 15 min averages of TEC. The data set consisting of GPS observations, collected by a dense network of European stations, with sampling rate of 30 s, enable the creation of TEC maps with high spatial and temporal resolution. The storm included the positive as well as the negative phase. The positive phase took place during the first storm day of 12 September 1999. The short-lived daytime TEC enhancement was observed at all latitudes. The maximal enhancement reached a factor of 1.3–1.5. On the second and third days, the negative phase of the storm developed. The TEC decrease was registered regardless of time of the day. The TEC depression exceeded 70% relative to quiet days. On the following days (15 and 16 September), a significant daytime enhancement of TEC was observed once again. The complex occurrence of the ionospheric storm was probably related to the features of development of the magnetic storm. We found out that during the storm the large and medium-scale irregularities developed in the high-latitude ionosphere. The multi-stations technique, employed to create TEC maps, was particularly successful while studying the mid-latitude ionospheric trough. We found out that the essential changes of TEC during the storm, which were registered at the auroral and sub-auroral ionosphere, were connected with the effect of the trough and its dynamics, which depends on geomagnetic activity. Key words. Ionosphere (ionospheric disturbances; auroral ionosphere; mid-latitude ionosphere)

Journal ArticleDOI
TL;DR: In this paper, the ionospheric response to an X5.7/3B solar flare that occurred at 10:03 UT on 14 July 2000 was studied, and it was found that dayside TEC values were enhanced during the flare event, which could be as large as 5 TECU in regions with small solar zenith angles.
Abstract: [1] This paper studies the ionospheric response to an X5.7/3B solar flare that occurred at 10:03 UT on 14 July 2000. With Global Positioning System (GPS) observations, temporal evolution of the ionospheric total electron content (TEC) values was obtained within the latitude range of 30°N ∼ 45°N and the longitude range of 15°E ∼ 45°E. It was found that dayside TEC values were enhanced during the flare event, which could be as large as 5 TECU (1 TECU = 1016/m2) in regions with small solar zenith angles. The enhancement tended to depend on latitude, longitude and the solar zenith angle of the subionospheric point. However, the TEC enhancement derived from the latitude belt between 30°N and 45°N was not symmetrical about either the longitude or the local hour; it was smaller in the local morning than in the afternoon. The TEC enhancement in the Southern Hemisphere seems to be larger than that in the Northern Hemisphere for the same solar zenith angle. This implies that the background levels of the ionosphere and thermosphere had some influence on the TEC enhancement. The temporal variation of TEC shows minor correlative disturbances from 10:15 UT to 10:27 UT when the solar flare was in the maximum phase. It is likely that the minor disturbances resulted from the evolution of flare emission in the EUV domain.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effects of the total electron content in the ionosphere accompanying the launches of the Proton, Soyuz, and Space Shuttle space vehicles from the Baikonur cosmodrome and Kennedy Space Center launch site in 1998-2000, as well as the earthquakes in Turkey on August 17 and November 12, 1999, were analyzed.
Abstract: Shock–acoustic waves generated during rocket launches and earthquakes are investigated by a method developed earlier for processing data from a global network of receivers of the GPS navigation system Disturbances of the total electron content in the ionosphere accompanying the launches of the Proton, Soyuz, and Space Shuttle space vehicles from the Baikonur cosmodrome and Kennedy Space Center launch site in 1998–2000, as well as the earthquakes in Turkey on August 17 and November 12, 1999, were analyzed It was shown that, regardless of the source type, the impulsive disturbance has the character of an N-wave with a period of 200–360 s and an amplitude exceeding background fluctuations under moderate geomagnetic conditions by a factor of 2–5 as a minimum The elevation angle of the disturbance wave vector varies from 25° to 65°, and the phase velocity (900–1200 m/s) approaches the speed of sound at heights of the ionospheric F-region maximum The source location corresponds to a segment of the booster trajectories at a distance of no less than 500–1000 km from the start position and to a flight altitude of no less than 100 km In the case of earthquakes the source location approximately coincides with the epicenter

Journal ArticleDOI
TL;DR: In this article, an enhanced version of the self-calibration of range errors (SCORE) was proposed to determine the ionospheric and plasmaspheric charge column densities.
Abstract: [1] The plasmasphere (also denoted as the protonosphere) is a large toroidal domain of light ionized particles situated above the ionosphere and confined by the Earth's magnetic field. While plasmaspheric charge densities are considerably less than those of the ionosphere, the large extent of the plasmasphere can produce significant charge column densities, or total electron content (TEC), for lines-of-sight passing through the plasmasphere. A method for Self-Calibration of Range Errors (SCORE) has been developed previously both to determine combined bias calibration values for GPS receivers and satellites and to calculate absolute TEC values for the ionosphere. An enhanced SCORE process, described here, retains the “self-calibration” feature of the original SCORE process, by not requiring any measurements beyond those performed by the GPS receiver system being calibrated. The enhanced SCORE process also determines a characteristic plasmasphere amplitude parameter, thus providing an autonomous determination of both the ionospheric and plasmaspheric TEC. Case studies for a near-equatorial site are presented, with model parameters derived from 1998 data being applied to determine ionospheric and plasmaspheric TEC for measurements made in 1999.