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Showing papers on "Total electron content published in 1995"


Journal ArticleDOI
TL;DR: The parameterized ionospheric model (PIM) as mentioned in this paper is a global model of theoretical ionosphere climatology based on diurnally reproducible runs of four physics-based numerical models of the ionosphere.
Abstract: We describe a parameterized ionospheric model (PIM), a global model of theoretical ionospheric climatology based on diurnally reproducible runs of four physics based numerical models of the ionosphere. The four numerical models, taken together, cover the E and F layers for all latitudes, longitudes, and local times. PIM consists of a semianalytic representation of diurnally reproducible runs of these models for low, moderate, and high levels of both solar and geomagnetic activity and for June and December solstice and March equinox conditions. PIM produces output in several user selectable formats including global or regional latitude/longitude grids (in either geographic or geomagnetic coordinates), a set of user specified points (which could lie along a satellite orbital path), or an altitude/azimuth/elevation grid for a user-specified location. The user selectable output variables include profile parameters (ƒ0F2, hmF2, total electron content, etc.), electron density profiles, and ion composition (O+, NO+, and O2+).

269 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a simple ionospheric shell model to derive a map of the ionosphere in the northern hemisphere every 12 hours during the January 1-15, 1993, period.
Abstract: Ionospheric total electron content (TEC) data derived from dual- frequency Global Positioning System (GPS) signals from 30 globally distributed network sites are fit to a simple ionospheric shell model, yielding a map of the ionosphere in the northern hemisphere every 12 hours during the January 1-15, 1993, period.

128 citations


Journal ArticleDOI
TL;DR: In this article, the authors present the final formulation of the DGR model and give a brief re- view of tests of the improved model done by different authors, including the results of different experiments.
Abstract: Tests of the analytical model of the electron density profile originally proposed by G, Di Giovanni and SM Radicella (DGR model) have shown the need to introduce improvements in order to obtain a model able to reproduce the ionosphere in a larger spectrum of geophysical and time conditions The present paper reviews the steps toward such progress and presents the final formulation of the model It gives also a brief re- view of tests of the improved model done by different authors

120 citations


Journal ArticleDOI
TL;DR: In this article, a baseline interferometer array at a northern midlatitude site, illuminated by VHF radio beacons from two geosynchronous satellites, quasi-continuously for over a year was used to detect and measure the trace velocity of traveling ionospheric disturbances via their signatures in the line-of-sight total electron content (TEC).
Abstract: We have operated a very long baseline interferometer array at a northern midlatitude site, illuminated by VHF radio beacons from two geosynchronous satellites, quasi-continuously for over a year. The array can detect and measure the trace velocity of traveling ionospheric disturbances (TIDs) via their signatures in the line-of-sight total electron content (TEC). The system noise level is of the order of 1013 m−2 in the TEC, so that even very weak perturbations can be studied. We have used the year-long TID detection/velocimetry data set to describe local time and seasonal dependences of the wave parameters. The most striking finding is that the preferred azimuths of TIDs in the data set tend to belong to either of two modes: The first mode, strongest at midday and in the early afternoon, particularly around winter equinox, propagates southward. The second mode, strongest in the evening, especially during summer solstice through autumn equinox, propagates west-northwestward. The two modes are disposed in local time such as to suggest the agency of clockwise rotation of the TID preferred azimuths versus time, as expected by wind filtering in the thermospheric diurnal tide. However, there is a gap between the two modes' azimuth bands. Moreover, the two modes exist in all trace-speed quartiles of the data set TIDs, a finding which is at variance with the hypothesis of wind filtering being the primary explanation of these modes.

104 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used incoherent scatter radar data collected at Millstone Hill and total electron content data from a north-south chain of stations during the May 26-27, 1990, storm.
Abstract: The initial ionospheric storm positive phase often appears as a large enhancement in F region electron density at middle latitudes in the evening hours following a storm sudden commencement. The cause of this dusk effect is still not well understood, though several mechanisms have been proposed. This phenomenon is studied using incoherent scatter radar data collected at Millstone Hill and total electron content data from a north-south chain of stations during the May 26-27, 1990, storm. Nine-position Millstone Hill radar data allows estimation of gradients in electron density and in velocity components above the station. From these the motion term in the continuity equation is calculated and used along with wind, electric field data, and modeling to assess the relative importance of the proposed mechanisms during this storm. It is shown that a combination of mechanisms appear to have been involved, including a traveling atmospheric disturbance, advection of high-density plasma from lower latitudes, and neutral composition changes.

49 citations


Journal Article
TL;DR: In this article, an experiment designed to image the ionospheric electron density above the UK using tomographic techniques is presented. But the results of the experiment are limited due to the limitation of the tomographic method in the context of modelling studies.
Abstract: Results are presented from an experiment designed to image the ionospheric electron density above the UK using tomographic techniques. Total electron content measurements were made using radio signals from the Navy Navigational Satellite System. The transmissions were monitored simultaneously at four receiving stations aligned in longitude and covering some 9 degrees in latitude. Inversion of the data using suitable reconstruction algorithms yielded tomographic images of the mid-latitude ionosphere. Reconstructed images are presented in this paper showing density perturbations due to travelling ionospheric disturbances which allow the propagation characteristics of the waves to be inferred. Some limitations of the imaging method are also discussed in the context of modelling studies. The work provides further demonstration of the potential and versatility of the application of tomographic methods to ionospheric imaging.

48 citations


Journal Article
TL;DR: In this paper, a modified truncated singular value decomposition (MTSVD) method was applied to actual TEC data in a magnetically disturbed period, revealing a large-scale structure of electron density in the disturbed ionosphere.
Abstract: A computerized tomography technique was applied to reconstruct two-dimensional electron density distributions from measurements of total electron content (TEC). We found that the modified truncated singular value decomposition (MTSVD) method, which is usually effective in ill-posed inversion problems, is effective in the ionospheric application. Furthermore, a main control parameter for a good reconstruction was examined by using several density distribution models, and the effects of noise in TEC and discretization error were also investigated. After the simulation study, the MTSVD method was applied to actual TEC data in a magnetically disturbed period. Total electron contents were observed, at four receiving stations covering a latitudinal range of 9.7 degrees with a longitudinal range of 2.2 degrees over Japan, by using signals transmitted from a Navy Navigational Satellite System (NNSS) satellite. The tomographic reconstruction revealed a large-scale structure of electron density in the disturbed ionosphere.

48 citations


Journal ArticleDOI
TL;DR: In this article, a technique for using GPS total electron content (TEC) data to detect auroral-E ionization (AEI) at all satellite line-of-sight elevations is presented.
Abstract: GPS (Global Positioning System) satellites and a receiver located at Fairbanks, Alaska are used to detect auroral activity. A technique for using GPS total electron content (TEC) data to detect auroral-E ionization (AEI) at all satellite line-of-sight elevations is presented. The location of AEI during auroral substorms is determined and is consistent with simultaneous magnetometer data. Maps of detected AEI events reveal the distribution of AEI in space and time. Additionally, a technique is presented for identifying the effects of the auroral oval E-layer on the TEC data. Particle precipitation measured by the TIROS satellite is closely related to variations in the TEC data. The effects of the oval are consistently seen in the TEC data for a variety of magnetic conditions. The location of the equatorward edge of the oval is determined during auroral substorms and compares well with a model of the oval and with individual TIROS passes.

43 citations


Journal ArticleDOI
TL;DR: In this paper, a preliminary analysis was made of ionospheric slab thickness, τ, and total electron content, TEC, for southern Australia using GPS satellite measurements, and it was concluded that as few as four GPS receivers could provide TEC for the whole of Australia in real-time, though approximately six receivers in convenient locations would be required in practice.

34 citations


Journal ArticleDOI
TL;DR: In this article, the authors analyzed the solar cycle variations of total electron content (TEC) around equatorial anomaly crest region in East Asia using the ETS2 satellite beacon signal during the period from March 1977 to December 1990.

27 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the Base Point Model (BPM) to predict the total electron content (TEC) at the southern crest of the equatorial anomaly region at Tucuman.

Journal ArticleDOI
TL;DR: In this article, longitudinal differences in total electron content (TEC) in summer in the northern equatorial-anomaly region are studied using observations from Wuhan (an east-Asian longitude station) and Palehua (a mid-Pacific longitude stations), and values from the Sheffield University Plasmasphere-Ionosphere Model.

Journal Article
TL;DR: In this article, the total electron content (TEC) data and reconstructed tomographic images from the Mid-America CIT (computerized ionospheric tomography) Experiment (MACE '93) were examined for structure and irregularities on top of the smooth background data.
Abstract: Analysis of the total electron content (TEC) data and reconstructed tomographic images from the Mid-America CIT (computerized ionospheric tomography) Experiment (MACE '93) is presented with the intent of examining and characterizing ionospheric irregularities. The TEC data and tomographic images are examined for structure and irregularities on top of the smooth background data. Structures seen in the TEC data by neighboring receivers over a single Transit pass are then correlated to obtain information about the approximate size and location of the structure. An attempt is made to analyze temporal and spatial evolution of structures from the TEC data using sequential satellite passes. The tomographic images generated from the TEC data are then examined for similar structures, with structure characteristics such as structure size and degree of electron density enhancement and depletion considered.

Journal ArticleDOI
TL;DR: In this article, a passive sporadic E detection technique based on a Global Positioning System (GPS) receiving system has been developed and tested in a midlatitude environment, which detects the small-scale total electron content (TEC) variations believed to be produced by electron density structures associated with sporadic E. The current GPS detection technique was able to detect ionosonde-detected sporadic E conditions for 73% of the cases at high-elevation look angles in a set of mid-latitude summer observations.
Abstract: A passive sporadic E detection technique based on a Global Positioning System (GPS) receiving system has been developed and tested in a midlatitude environment. This system detects the small-scale total electron content (TEC) variations believed to be produced by electron density structures associated with sporadic E. The current GPS detection technique was able to detect ionosonde-detected sporadic E conditions for 73% of the cases at high-elevation look angles in a set of midlatitude summer observations. Several approaches have been identified that may significantly improve this detection ratio. These approaches include reducing GPS phase multipath, implementing time and space averaging, and investigating the use of high-speed GPS TEC measurements. This technique provides a basic sporadic E detection functionality for applications where an ionosonde is not available. It also provides complementary ionospheric information in regions outside the ionosonde viewing area for applications where an ionosonde is available.

Journal ArticleDOI
TL;DR: In this article, measurements of total electron content made with a radio interferometer reveal weak but frequent outbursts of totalelectron-content disturbances with trace azimuths roughly westward, with trace speeds up to ∼2 km/s, and with temporal periods in the range 100-500 seconds.
Abstract: Measurements of fluctuations in total electron content made with a radio interferometer reveal weak but frequent outbursts of total-electron-content disturbances, with trace azimuths roughly westward, with trace speeds up to ∼2 km/s, and with temporal periods in the range 100–500 seconds. Statistical tests of the dataset suggest that these disturbances are due to drift of plasmaspheric irregularities past the radio lines-of-sight. The phenomenon is likely to provide a new passive tracer of zonal convection in the inner magnetosphere.

Journal ArticleDOI
TL;DR: In this paper, an ionospheric model is used to simulate total electron content (TEC) disturbance events observed at middle and lower latitude sites near 75○W and 7○E longitudes.
Abstract: An ionospheric model is used to simulate total electron content (TEC) disturbance events observed at middle and lower latitude sites near 75○W and 7○E longitudes. Within this longitudinal range, daytime TEC disturbances show patterns that are correlated with substrom activity seen in both auroral electrojet and ring current behavior. In modeling studies of the observed ionospheric effects, both electric field and neutral wind perturbations are examined as possible mechanisms. The morphological features of the required electric field perturbations near drawn and dusk are compared with those at other times to examine the local time characteristics of magnetospheric influence. Large-scale traveling atmospheric disturbances (TADs), an alternative candidate for the disturbance source, are also characterized and compared with known thermospheric behavior.

Journal ArticleDOI
TL;DR: In this article, the authors examined 58 passes of GPS satellites whose E-layer penetration points lie close to the midpoint of the Wales-Fairbanks path and found that there is a threshold value of TEC above which auroral-E (AE) propagation occurs.
Abstract: VHF propagation on /spl les/5300 km polar paths has been documented during the maximum phase of sunspot cycle 19. Mode analysis on these polar paths has shown that auroral-E ionization (AEI) supported some modes. Electron densities and plasma frequencies which could support AEI modes at frequencies up to 46 MHz have also been measured. Long distance VHF propagation from AEI has also been reported by radio amateurs using frequencies in the 2 m band in a "sidescatter mode". An AEI experiment has been in operation between Wales (Alaska) and Fairbanks (Alaska) where a 75-watt CW transmitter located in Wales transmits the Morse letter "R" every 5 s, and a receiver in Fairbanks detects the 25.5 MHz signal whenever AEI is present near the midpoint of the 960 km path. Another experiment is underway using a GPS total electron content (TEC) receiving station at Fairbanks also using AEI data from the Wales-Fairbanks experiment. From this, the authors examine 58 passes of GPS satellites whose E-layer penetration points lie close to the midpoint of the Wales-Fairbanks path and find that there is a threshold value of TEC above which auroral-E (AE) propagation occurs. They also find that AEI propagation is strongly correlated with large- and medium-scale E-region structures in TEC determined by the GPS measurements. When TEC ionospheric structures are not present near the Wales-Fairbanks path midpoint, no AEI signal is received. The authors tentatively conclude that the occurrence of these specific TEC signatures may be utilized as predictors of AEI forward propagation on paths within and parallel to the auroral oval. >

Journal ArticleDOI
TL;DR: In this paper, the authors compared the variability of total electron content (TEC) observed by the Faraday rotation method at Florence with the same technique applied independently to the ionospheric parameters of the ground-based vertical-incidence sounding database (VID).
Abstract: Variability of total electron content (TEC) observed by the Faraday rotation method at Florence has been stud- ied with the same technique applied independently to the ionospheric parameters foF2 and M(3000)F2 of the ground-based vertical-incidence sounding database (VID). Results of daily and monthly TEC disturbance indices at sub-ionospheric point are compared with variability of the ionosphere at Rome and Gibilmanna (de- duced from VID) for a period of 1976 to 1991. During moderate and high solar activity the variability of TEC is greater than the variability of VID, whereas during solar minimum the situation is opposite. In this context joint TEC and VID observations distinguish either the F region peak or the topside ionosphere heights where the dynamic processes dominate at different times.

01 Jul 1995
TL;DR: In this article, the shape and behavior of the phase-scintillation power-density spectrum (PDS) over a scale-size range of 1Os to 1OOs of kilometers was investigated.
Abstract: : Many military systems used for communications, command and control, navigation, tracking, and surveillance depend on reliable and relatively noise-free transmission of radiowave signals through the earth's ionosphere. These systems can be affected by both large-scale features (> 1,000 km) and small-scale structures (> few hundred km) in the ionosphere, often leading to degraded operations. This report documents the results of the first year of a three-year investigation of various facets of this problem. Two study areas are reported on: (1) an investigation of methods for using signals from Global Positioning System (GPS) satellites to measure ionospheric Total Electron Content (TEC), and (2) a study of the shape and behavior of the phase-scintillation power-density spectrum (PDS) over a scale-size range of 1Os to 1OOs of kilometers. The TEC studies are still on-going; the phase PDS study found that the slope of the phase PDS at these scale sizes is steeper than those found in earlier studies at shorter scales.

01 Jul 1995
TL;DR: In this article, the shape and behavior of the phase-scintillation power-density spectrum (PDS) over a scale-size range of 1Os to 1OOs of kilometers was investigated.
Abstract: Many military systems used for communications, command and control, navigation, tracking, and surveillance depend on reliable and relatively noise-free transmission of radiowave signals through the earth`s ionosphere This report documents the results of the first year of a three-year investigation of various facets of this problem Two study areas are reported on: (1) an investigation of methods for using signals from Global Positioning System (GPS) satellites to measure ionospheric Total Electron Content (TEC), and (2) a study of the shape and behavior of the phase-scintillation power-density spectrum (PDS) over a scale-size range of 1Os to 1OOs of kilometers The phase PDS study found that the slope of the phase PDS at these scale sizes is steeper than those found in earlier studies at shorter scales

Proceedings ArticleDOI
05 Sep 1995
TL;DR: In this paper, the history of ground-based vertical-incidence sounding of the ionosphere is outlined, and the ionosonde network serves for the patrol of the quiet or disturbed state of ionosphere.
Abstract: The history of ground-based vertical-incidence sounding of the ionosphere is outlined. The ionosonde network serves for the patrol of the quiet or disturbed state of the ionosphere. Duration of the ionosphere F region peak parameters disturbance is compared with total electron content quiet times and sudden ionospheric disturbances detected by radio signal deterioration.

01 Mar 1995
TL;DR: A data archive of total electron content CIEC data was developed through operation and maintenance of GPS satellite receiver equipment at Shemya, AK; Hanscom AFB, MA; Thule AB, Greenland; Tucuman, Argentina; and Agua Verde, Chile.
Abstract: A data archive of Total Electron Content CIEC data was developed through operation and maintenance of GPS satellite receiver equipment at Shemya, AK; Hanscom AFB, MA; Thule AB, Greenland; Tucuman, Argentina; and Agua Verde, Chile. Scintillation data can be extracted from much of this database. The Shemya, AK, data provide a valuable source for characterizing TEC morphology and variability with look direction at this site. The Shemya data were also used in an initial assessment of the seasonal and directional specification accuracy of the Bent ionospheric model, specific to this site. Analysis of an existing NWRA database has produced ionospheric trough boundary signatures in the sub auroral European sector. These signatures will support studies aimed at real time detection of the trough boundary. Innovative software techniques were developed to improve data quality in the areas of multipath integration (the Multipath Template Technique) and the automated calibration of an installed receiver system for the combination of all system components` contributions to pseudorange error (SCORE:: Self-Calibration Of pseudoRange Errors).

ReportDOI
28 Feb 1995
TL;DR: In this paper, the Phillips Laboratory Global Theoretical Ionosphere Model (GLIMM) was used to model high-latitude large-scale plasma structures using two separate mechanisms (time-varying global convection and meso-scale convection events).
Abstract: : In the last year, we have studied several issues that are critical for understanding ionospheric weather. Work on global F-region modeling has consisted of testing the Phillips Laboratory Global Theoretical Ionosphere Model. Comparisons with both data and other theoretical models have been successfully conducted and are ongoing. GPS observations, as well as data analysis, are also ongoing. Data have been collected for a study on the limitations in making absolute ionospheric measurements using GPS. Another study on ionospheric variability is the first of its kind using GPS data. The observed seasonal total electron content behavior is consistent with that determined from the Faraday rotation technique. Work on the FAA's Phase 1 Wide Area Differential GPS (WADGPS) Satellite Navigation Testbed Experiment also continues. Initial results indicate that stations using operational WADGPS should be located no greater than 430 km apart. Work comparing our electron-proton-H atom model to both observations and other models has been generally successful. We have successfully modeled the creation of high-latitude large-scale plasma structures using two separate mechanisms (time-varying global convection and meso-scale convection events). Ionospheric weather, Global F-region modeling, Total electron content, GPS, TEC, Aurora, Electron transport, Proton-H atom transport, Plasma structure, Patches