Showing papers on "Total electron content published in 1996"

Global ionosphere perturbations monitored by the Worldwide GPS Network

Abstract: 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%). During this particular storm, there is almost no negative phase. A traveling ionospheric disturbance (TID) event is identified that propagates from the northern subauroral region to lower latitudes (down to about 30°N) at a speed of ∼460 m/s. This TID is coincident with significant increases in the TEC around the noon sector. We also find that another strong TEC enhancement occurs in the pre-dawn sector in the northern hemispheric subauroral latitudes, in the beginning of the storm main phase. This enhancement then spreads into almost the entire nightside. The nighttime TEC increase in the subauroral region is also noted in the southern hemisphere, but is less significant. These preliminary results indicate that the differential mapping method, which is based on GPS network measurements, appears to be a powerful tool for studying the global pattern and evolution process of the entire ionospheric perturbation.

GPS phase fluctuations in the equatorial region during the MISETA 1994 campaign

Abstract: In this paper we present the first coordinated use of Global Positioning System (GPS) multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns. Thirty second samples of total electron content (TEC) obtained from GPS phase differences between 1.2- and 1.6-GHz signals are used to study phase fluctuations at several stations. Comparisons were made with various types of ground measurements during the multi-instrument studies of the equatorial thermosphere aeronomy (MISETA) period. Depletions of 6300A airglow emission from Arequipa, Peru, correlated with phase fluctuations recorded at the same site. Phase fluctuations at Arequipa occurred at the times when the Jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes. Levels of phase fluctuations noted at Arequipa varied considerably on nights when only thin layers of irregularities were observed by the Jicamarca radar. Differences of ionospheric conditions between the two sites, separated by only 5.5° geographic longitude, may account for the different behavior patterns of irregularities noted. Similar differences in the general behavior pattern of phase fluctuations were shown when data from Arequipa and Fortaleza, Brazil, were compared. These stations, 33° apart, but at the same dip latitude had different patterns for some days. During a magnetic storm, a very high altitude plume was observed by the radar and by phase fluctuations noted at Santiago at 18° dip latitude. This correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995.

Total Electron Content Obtained by Using the Global Positioning System

Abstract: A procedure is introduced to obtain the balance of measurements of differential group delays and differential carrier phase lead characteristics, both phenomena being due to the ionospheric total electron content(TEC)along the ray path from a Global Positioning System (GPS) satellite. It has been demonstrated that utilizing the measurement of both pseudorange and carrier phase recorded by genetic GPS receivers, the precision of the vertical TEC derived when the anti-spoofing (AS)is on can be as good as that derived when it is off. Combining the data of a network of four GPS receivers, a TEC map is reconstructed which can be employed to examine the ionospheric latitude/longitude structure and dynamics in the Taiwan area.

GPS detection of ionospheric perturbations following a space shuttle ascent

Abstract: The exhaust plume of the Space Shuttle during its ascent is a very powerful source of energy that excites atmospheric acoustic perturbations. Because of the coupling between neutral particles and electrons at ionospheric altitudes, these low frequency acoustic perturbations induce variations of the ionospheric electron density. We computed ionospheric electron content time series using Global Positioning System data collected on Bermuda island during the STS-58 Space Shuttle launch. The analysis of these time series shows a perturbation of the ionospheric electron content following the launch and lasting for 35 mn, with periods less than 10 mn. The perturbation is complex and shows two sub-events separated by about 15 mn at 200 km from the source. The phase velocities and waveform characteristics of the two sub-events lead us to interpret the first impulsive arrival as the direct propagation of the shock wave front, followed by oscillatory guided waves probably excited by the primary shock wave and propagating along horizontal atmospheric interfaces at 120 km altitude and below.

Relationships between GPS-signal propagation errors and EISCAT observations

Abstract: When travelling through the ionosphere the signals of space-based radio navigation systems such as the Global Positioning System (GPS) are subject to modifica- tions in amplitude, phase and polarization. In particular, phase changes due to refraction lead to propagation er- rors of up to 50 m for single-frequency GPS users. If both the L1 and the L2 frequencies transmitted by the GPS satellites are measured, first-order range error contribu- tions of the ionosphere can be determined and removed by di⁄erence methods. The ionospheric contribution is pro- portional to the total electron content (TEC) along the ray path between satellite and receiver. Using about ten Euro- pean GPS receiving stations of the International GPS Service for Geodynamics (IGS), the TEC over Europe is estimated within the geographic ranges!20i4j440iE and 32.5i4/470iN in longitude and latitude, respec- tively. The derived TEC maps over Europe contribute to the study of horizontal coupling and transport proces- ses during significant ionospheric events. Due to their comprehensive information about the high-latitude ionosphere, EISCAT observations may help to study the influence of ionospheric phenomena upon propagation errors in GPS navigation systems. Since there are still some accuracy limiting problems to be solved in TEC determination using GPS, data comparison of TEC with vertical electron density profiles derived from EISCAT observations is valuable to enhance the accuracy of propagation-error estimations. This is evident both for absolute TEC calibration as well as for the conversion of ray-path-related observations to vertical TEC. The com- bination of EISCAT data and GPS-derived TEC data enables a better understanding of large-scale ionospheric processes.

Solar cycle variations of the equatorial ionospheric anomaly in total electron content in the Asian region

Abstract: Daily equatorial ionospheric anomaly (EIA) contour charts in total electron content (TEG) were obtained by receiving simultaneously two coherent radio signals transmitted from the U.S. Navy Navigation Satellite System satellite at Lunping Observatory (25.00°N, 121.17°E) from September 1985 to December 1994. The latitude, occurrence time, and strength of the most developed EIA crest obtained from daily TEC contour charts have been used to study the solar cycle variations of EIA in the Asian region. No significant solar cycle effect can be seen in the occurrence time and latitude of the most developed EIA crest. Seasonally, the winter crest appears larger and earlier than the summer crest, and the summer crest appears in lower latitude than other seasons. These seasonal changes are mainly accounted for by the effect of daytime meridional wind. The strength of EIA crest increases with the increasing of solar activity and exhibits winter anomaly with the winter strength larger than the summer one Positive correlation is found between the 12-month smoothed EIA crest strength and sunspot number. No saturation effect can be seen during the high solar activity period. The 12-month smoothed EIA crest strength exhibits a hysteresis variation about the solar cycle variation. Monthly mean TEC contour charts for the latitude from 15°N to 35°N are also obtained from those daily contour charts. By using linear regression analysis, the monthly mean TEC I at a given month is linearly correlated with smoothed sunspot number R by a formula I = A + BR. These results can be used to construct the monthly EIA contour chart in TEC for any given sunspot number.

An Assessment of Predicted and Measured Ionospheric Total Electron Content Using a Regional GPS Network

Abstract: The signals from the satellites of the Navstar Global Positioning System (GPS) must travel through the earth's ionosphere on their way to GPS receivers on or near the earth's surface. To achieve the highest possible positioning accuracies from GPS, one must correct for the carrier phase advance and pseudorange group delay imposed on the signals by the ionosphere. Whereas these effects may be considered a nuisance by most GPS users, they will provide the ionospheric community with an opportunity to use GPS as a tool to better understand the plasma surrounding the earth. The dispersive nature of the ionosphere makes it possible to measure its total electron content (TEC) using dualfrequency GPS observations collected by permanent networks of receivers. One such network is that of the International GPS Service for Geodynamics (IGS). We have used dual-frequency GPS pseudorange and carrier phase observations from six European stations in this network to derive regional TEC values. In this research, we investigated the effect of using different elevation cutoff angles and ionospheric shell heights on TEC estimates and satellite-receiver instrumental biases. We found that using different elevation cutoff angles had an impact on TEC estimates at the 2 TEC unit (TECU) level. We also discovered that using different ionospheric shell heights has an effect on the ionospheric TEC estimates at about the 2 TECU level depending on geographic location and time of the day. We found no significant changes in the bias estimates using different elevation cutoff angles. We compared our TEC estimates with TEC predictions obtained by using the International Reference Ionosphere 1990 (IRI90) model. The results of this comparison are similar to those of other studies that were conducted using data sets at low solar activity times. After processing the data from the 6 European stations collected over a 7 day period, we were able to follow highly varying ionospheric conditions associated with geomagnetic disturbances.

Simultaneous Global Positioning System and radar observations of equatorial spread F at Kwajalein

Abstract: GPS satellites broadcast at two frequencies (Ll of 1575.42 MHz and L2 of 1227.6 MHz). The dispersive property of the ionosphere is frequently used to correct positional measurements for ionospheric effects. Independent measurements at the two frequencies can also be combined to form a relative ionospheric delay and a measure of the total electron content (TEC) which is uncertain by an additive constant. In a previous paper (Musman et al., 1990) estimates of this offset were utilized in constructing models of the time history of the equivalent zenith delay at Westford, Massachusetts. An ionospheric model composed of uniform shells whose electron density changes slowly in a typical diurnal pattern would produce relative ionospheric delays with a simple u-shaped or j-shaped curve. Most of the change in delay would be a result of changes in geometry between the observer and the satellite. Departures from a simple pattern are indicative of ionospheric disturbances and the influence of the protonosphere. From GPS data alone, it is ambiguous whether these disturbances are due to spatial structures, temporal changes, or some combination of the two. Equatorial spread F (ESF) refers to a variety of equatorial ionospheric disturbances, some of which are associated with rising plasma plumes having low electron density and a high degree of turbulence. This phenomenon occurs primarily between local sunset and local midnight at sites within about 15° of the magnetic equator. In some seasons, disturbances can occur during two out of three evenings, while at other times it can be much quieter. GPS observations at Kwajalein (9°N latitude) reported here for August 14, 1990, show severe ionospheric disruption. Two independent and simultaneous sets of radar observations confirm the presence of ESF and reveal quite a bit about the spatial and temporal conditions which affect the system. GPS observations on August 15, 1990, when no ESF was present are much quieter. We find that tens of minute variations in the TEC correspond to the motion of large scale features across the GPS field of view. More severe GPS effects are seen to be collocated with turbulent low density plumes which rise rapidly to high altitudes and drift west to east across the GPS line of sight. Severe disruption can occur in moderately sophisticated GPS systems during such events, at least near solar maximum.

Equatorial plasma depletion precursor signatures and onset observed at 11° south of the magnetic equator

Abstract: Coordinated radio and optical measurements of the structure and dynamics of the postsunset equatorial ionosphere were conducted on October 1, 1994, from Agua Verde, Chile (11.3°S magnetic latitude (MLat)). The measurements clearly show a north-south aligned undulation or ripple on the bottomside of the F layer at 2000 LT, appearing as an eastward propagating decrease in the 630.0-nm airglow, resembling a traveling ionospheric disturbance in the digital portable ionosonde measurements and causing a total electron content decrease in the Global Positioning System (GPS) satellite measurements. The initial development of this feature, toward the east and away from the magnetic equator, took place in an otherwise smooth, unstructured ionosphere. Spread F began to develop in the ionograms at 2020 LT, and, at this same time, local onset of satellite signal scintillation was detected using the multiple ray paths throughout the sky available from the GPS satellite constellation transmitting at L band frequencies. UHF scintillation measurements from Ancon, Peru, along the same magnetic field line, show that intense scintillation and ionospheric irregularities had developed over the magnetic equator almost 60 min prior to their development at 11°S MLat. The observations suggest that the east-west electric field expected to be present within the earlier developed depletion and scintillation region at the magnetic equator mapped along magnetic field lines to lower altitudes and higher latitudes, resulting in an undulation or dome-shaped structure, before evolving into a fully developed depletion (with associated ionospheric irregularities) all along the magnetic flux tube.

Improved short‐term predictions of ƒ0F2 using GPS time delay measurements

Abstract: Reliable HF communications along short-, medium- and long-range paths require propagation assessment. Such assessment could be facilitated with the monitoring of ionospheric characteristics by continuously available passive means, i.e., measurement of the total electron content (TEC) using satellite-emitted signals without a need for burdening the electromagnetic spectrum. With ubiquitous Global Positioning System (GPS) providing instantaneous time delay, or equivalently, TEC, values when needed, an assessment of HF propagation conditions may be available on a near-real-time basis. Both TEC and the peak electron density of the ionosphere, which determines the ordinary upper frequency limit (ƒ0F2( for HF sky wave vertical propagation, vary strongly with solar and geomagnetic parameters. Their ratio, the equivalent slab thickness, may vary to a lesser degree and hence be modeled with greater accuracy. A slab thickness model combined with real-time TEC measurement anywhere on the globe may possibly yield an improved HF parameter prediction algorithm. To test the efficacy of the hypothesis, one has to ascertain the correlation, as exhibited by the correlation coefficient, between the TEC daily variability about the monthly mean and the ƒ0F2 variability. To determine such correlation, a study compared Faraday TEC data as well as GPS-generated TEC data collected in Israel and with corresponding ƒ0F2 values obtained from vertical sounder measurements near the appropriate subionospheric location in Cyprus. The analysis shows that for large percentages of the time, very good correlation exists between TEC and ƒ0F2 short-term variations. The correlation coefficient varies between 0.7 or better during winter and summer months to about 0.5–0.6 during equinox months. A study of the diurnal dependence of the correlation indicates that a better correlation exists during daytime than nighttime. There was no indication that the coefficient is dependent on geomagnetic activity or on protonospheric electron content during the period of this study.

Test of GPS for permanent ionospheric TEC monitoring at high latitudes

Abstract: . The Global Positioning System (GPS) observables are affected by the ionosphere. The dispersive nature of this effect and the use of two frequencies in the GPS observations make possible to measure the ionospheric total electron content (TEC) from dual frequency GPS data. In this work we test the concept of permanent monitoring of TEC using a network of GPS receivers at high latitudes. We have used GPS data from five permanent receivers in Scandinavia, from 1-30 January 1994, with geographic latitudes ranging from 57.4°N to 78.9°N. The results show the capability of the method to monitor the evolution of TEC as a function of time and geographical location. We have detected night-time enhancements almost every night for some of the stations, and we have also been able to produce maps of the instantaneous TEC as a function of both latitude and longitude around the GPS network. We also present some of the current limitations in the use of GPS for estimating TEC at high latitudes such as the difficulties in solving for cycle-slips, and the necessity of reliable values for the receiver and satellite differential instrumental biases.

The Effects of the Ionosphere and C/A Frequency on GPS Signal Shape: Considerations for GNSS-2

Abstract: By greatly increasing the chipping rate of the pseudo random noise (prn) code, it may be possible to measure the ionosphere (TEC) in near real time, by exploiting the dispersive nature of the ionosphere. The ionosphere is a major source of error for all stand alone GPS based navigation, and spatial decorrelation limits the accuracy of differential GPS users. The ionospheric distortion of the C/A code (1.023 Mbps), and P code (10.23 Mbps) may be too small to measure. However, the use of a faster (40-100 Mbps) chipping frequency for GNSS2, may permit measurement of the ionosphere’s Total Electron Content (TEC) using only a single frequency receiver. Currently, we can only ‘measure’ the ionosphere by using a dual frequency receiver (limited to military users), or with a cross correlating receiver (limited by poor signal to noise) or by observing ‘code-carrier divergence’ (limited by long observation times). The diurnal model of the atmosphere is only capable of removing 50-60% of the error. This investigation is based on the standard model of the ionosphere, which assumes negligible attenuation in the L-band, but does produce a time advance proportional to k/f*2. Expanding in a Taylor Series about Ll, the first two terms of this model lead to code-carrier divergence. The next term is quadratic in frequency and produces both amplitude and phase modulation of the received signal. The higher order terms produce relatively insignificant changes. Although these variations are present in the signal received from GPS, it is quite small and has previously been unmeasured. A computer simulation was developed to analytically determine the shape of the GPS signal after passing through the ionosphere, and to determine the effect of faster chipping frequency on the shape of the received signal. The GPS signal is expressed in the frequency domain, then phase shifts, proportional to k/f, were applied. The signal was then transformed into the time domain, and this signal was compared with the original signal. This paper will present analytical results from the simulation. The benefits of a faster chipping frequency for GNSS2 will be explored. Time domain plots of the modified signal will be presented, illustrating the changes in both amplitude and phase due tot he ionosphere. The limits imposed by the presence of atmospheric noise and receiver noise will not be discussed. This paper will not discuss other aspects of GNSS2 design, such as constellation selection. Although greater spreading requires greater bandwidth, the quadratic dependence of this distortion on frequency may justify the additional bandwidth if it allows us to directly measure, rather than estimate, the ionosphere with a single frequency receiver. GNSS2 should be designed with a much faster code frequency (40-100 Mbps) since it would improve code positioning accuracy, would reduce the carrier ambiguity space, and may permit real- time ionospheric measurements.

Ionospheric predictions for South American latitudes

Abstract: Experimental values of the critical frequencies of the ionosphere (ƒ0E,ƒ0F1 and ƒ0F2) obtained at South American stations for different solar conditions and seasons are used to check the validity of the international reference ionosphere model to predict these ionospheric variables in this region. The results obtained show that, in general, for ƒ0E and ƒ0F1 there is good agreement between the predicted and experimental values when compared. The model predicts ƒ0F1 for periods when F1 was not present. The degree of accuracy among experimental and predicted ƒ0F2 values is lower than those observed for the other characteristics, and cases with strong disagreement are observed. It is shown that in some cases a large error would be produced if the predictedƒ0F2 is used as an input to a total electron content model.

Toward ionospheric tomography in Antarctica: first steps and comparison with dynasonde observations

Abstract: Total electron content (TEC) measurements obtained at two Antarctic stations over nine months beginning early in 1994 have been analysed as a first step to performing ionospheric tomography. Two receiving systems were deployed at the Faraday and Halley research stations operated by the British Antarctic Survey to monitor signals from a random selection of passes of satellites in the Navy Navigational Satellite System. The resultant measurements of total electron content have been inverted and combined with ionosonde measurements of true height and foF2 to yield two-dimensional contour maps of ionospheric electron density. In spite of the poor geometry of the observations, some 130 satellite passes were found to be suitable for reconstruction using the techniques developed for ionospheric tomography. The contour maps of plasma density have been compared with independent observations of the vertical electron density profile measured by the dynasonde ionospheric sounder located at Halley. An example is presented of a deep trough investigated by the technique, illustrating the potential of the tomographic method for study of an extended spatial region of the ionosphere over inhospitable terrain.

About the Use of GPS Measurements for Ionospheric Studies

Abstract: Radio beacon measurements have effectively been used in exploring the temporal and spatial structure of the ionosphere since nearly 3 decades.

Ionospheric disturbances during low‐latitude auroral events and their association with magnetospheric processes

Abstract: Ionospheric disturbances associated with low-latitude auroral events that occurred during geomagnetic storms on October 21, 1989, and May 10, 1992, are investigated from measurements of the total electron content (TEC) by the U.S. Navy Navigation Satellite System (NNSS) and ionosonde data from the Japanese meridian chain. Features of the ionospheric disturbances are then associated with the progression of geomagnetic disturbances during the storms. After the onset of the main phase of each storm, anomalous TEC distributions characterized by depressed TEC distributions on the high-latitude side (> 35° geographic latitude) and an enhanced equatorial ionization anomaly (EIA) on the low-latitude side (<35° geographic latitude) were observed over Japan both by the NNSS and by the meridian chain of ionosonde stations. This enhancement of the EIA suggests the penetration of magnetospheric electric fields during the storms. Corresponding to the anomalous TEC decreases in the northern part of Japan, ionosonde stations in this region observed specific disturbances of ionospheric variation characterized by simultaneous decreases of ƒ0F2 and increases of h′F. These features of ionospheric variations on the high-latitude side can be attributed to the upward escape of ionospheric plasma caused by the heating and evacuation mechanisms, which are induced by depletion of the plasmasphere and the resulting access of ring current particles to low latitudes. After the appearance of the characteristic ionospheric variations mentioned above, low-latitude aurorae were observed at the maximum development stage of the Dst, associated with the recovery of midlatitude geomagnetic horizontal (H) components. Prior to the appearance of the low-latitude aurorae, magnetic disturbances in the auroral region increased with the decrease of midlatitude H components, as a natural consequence of magnetic storms. However, they showed a recovery before the start of the low-latitude aurorae, while the magnitude of the low-latitude magnetic field continued to decrease. These observed features of the magnetic disturbances suggest that the position of the auroral oval shifted toward the equator before the appearance of the low-latitude aurorae. Consequently, these observations are consistent with the plasmapause and auroral zone moving toward the equator before the onset of low-latitude aurorae. We conclude that the convection electric field penetrating toward low latitudes causes the enhancement of the EIA, the shrinkage of the plasmasphere, and the penetration of high-energy particles toward the low-latitude region.

Electron density profile modeling

Abstract: The Base Point Model (BPM) is used to model the electron density (N) profile in the ionosphere, This model assumes two Chapman profile expressions one for the bottomside and one for the topside, and requires a characteristic point called "F region base point". The comparison among the modeled and experimental bottom-side N profiles obtained from Tucuman (26,9°S; 65.4°W) ionosonde shows that, in general, there is a very good agreement within 30 km below the height of the maximum N(hm). Cases with a very good agreement for the entire N-profile are observed. The study of the electron content below hm and the Total Electron Content (TEC) measured over Tucuman shows that, the difference among predicted and measured TEC is due to the disagreement in the topside N-profile more than that observed in the bottomside N-profile.

A method for deducing the topside ionospheric profile from ionograms and tec measurements

Abstract: A method is presented in this paper for deducing the topside ionospheric electron concentration profile from THC measurements and ionograms obtained by ionosonds, in which the calculated profile by IRI─90 is corrected by a supposed scale height to fit the actual topside profile. Such a correcting scale height is obtained by forcing the integration of the corrected topside profile equal to the measured topside electron content, which is obtained with measured TEC eliminating the sub-peak electron content, an integration of the sub-peak electron concentration profile deduced from ionograms.

On Atmospheric Effects on GPS Surveying

Abstract: The aim of this paper is to study the atmospheric effects and the mechanics of delay of radio signals, and to search for a better approach for reducing the effects of the atmosphere on GPS surveying. The stresses of our investigations are put on cases with low elevation angles and single-frequency receivers. Several important models, widely used, are tested by direct comparison of their effects on positioning with the real GPS measurement data, instead of comparison of compensation or characteristic quantities, such as TEC, etc.

Traveling ionospheric disturbances observed in digitized polarimeter data

Abstract: Faraday rotation data from a pair of polarimeters located in Tucson, Arizona during the first half of 1990 have been examined for evidence of traveling ionospheric disturbances. With the use of digital filtering techniques, oscillations in total electron content (TEC) with periods ranging from 20 to 90 minutes and amplitudes of 1–5 × 1016 m−2 have been detected in the data. When present, the oscillations persist for varying time intervals (usually several hours) and show considerable variation from day to day. Although the viewing geometry (nearly along the local magnetic field line) is not ideal for observation of TIDs, these oscillations do appear to be real ionospheric oscillations. We have examined the possibility that the oscillations are not caused by actual changes in electron content but rather are due to changes in the Faraday rotation resulting from the motion of the ionospheric plasma along a magnetic field line and the resulting change in effective magnetic field strength. Our calculations indicate waves with displacement amplitudes of a few tens of kilometers would be sufficient to explain the observations. We also examined the possibility that the oscillations could be due to actual changes in TEC by using a one-dimensional F region model and imposing a plausible wind oscillation (simulating a gravity wave). We found that a wave with a velocity amplitude of 15 m s−1 was also sufficient to explain the observations. We expect that the observations are best explained by a combination of the two effects, that is, an actual oscillation in electron content and an oscillation in Faraday rotation, both caused by gravity waves in the thermosphere. We estimate that for the 90-min oscillations, 25% of the amplitude is due to the Faraday rotation effect and 75% is due to an actual change in TEC.

On the minimum ground-based observable frequency of the Jovian decametric emission imposed by the terrestrial ionosphere

Abstract: For experimental observation of the Jovian decametric emission, it is important to know the low-frequency limit of the received radiation, which depends on the Jovian elevation (angular position from the local horizon) and the ionospheric electron density distribution. We develop the corresponding analysis and present results for different Jovian positions and different models of the ionospheric electron density profile. This consideration is of special interest for the periods 1993 to 1997 and also 2005 to 2009, years for low Jovian positions observed from northern hemisphere observatories where Jupiter is in the southern hemisphere in the celestial equatorial coordinate system. For several ionospheric models we determine the using range which depends on the Jovian elevations. By the use of empirical ionospheric models from Feichter and Leitinger, [1990, 1993] of the total electron content (TEC) from which an electron density maximum can be derived, we found that the solar activity highly influences the electron peak density which, in turn, acts on the low-frequency limit of the detectable Jovian decametric emission from ground-based observatories.

Spatial shape and development dynamics of auroral scintillation patches

Abstract: Results of simultaneous measurements of altitude distribution of auroral small-scale irregularities and total electron content by the method of radio illumination of the ionosphere by signals from an orbital satellite at 150–400 MHz are presented. It is shown that under magnetically quiet conditions the small-scale irregularities (l⊥∼1km) tend to occupy local regions, which extend over ≲ 100– 200 km along the geomagnetic fieldB with ≲ 5– 20 km from the North to South. Characteristic times of formation and collapse of such local structures under the conditions of weak geomagnetic activity are of the order of more than one hour.

Dst and SD Variations of Total Electron Content around Equatorial Anomaly Crest Region

Abstract: The D st and SD variations of ionospheric total electron content (TEC) around equatorial anomaly crest region during SC geomagnetic storms have been statistically analyzed by using the continuous measurements oftotal electron content at Lunping Observatory (25.00°N, 121.17°E geographic, 14.3°N, 191.3°E geomagnetic) from March 1977 to December 1993. The characteristic variations of D st and SD of TEC are described and compared with the D st and SD variations obtained from geomagnetic horizontal component recorded at Lunping Observatory. Some qualitative explanations are also attempted.

Deriving Ionospheric TEC from GPS Observations

Abstract: Global Positioning Satellites (GPS) broadcast at two different frequencies. These are usually used to correct positional measurements for ionospheric effects. Alternately information can be obtained about the ionosphere. A method for deriving total electron content (TEC) will be described. Observations taken in Boulder during January 1995 will be utilized and compared with Faraday rotation Both carrier phase and group delay will be used