Predicted and measured total electron content at both peaks of the equatorial anomaly (original) (raw)
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VALIDATION OF TEC MODELS OVER AN EQUATORIAL STATION
Total electron content (TEC) data obtained by the Faraday technique at Ghana (5.63°N, 359.81 °E) have been used for the validation of two ionospheric models for the purpose of TEC prediction in the equatorial region. The two models considered are the international Reference Ionosphere (IRI) and the NeQuick. Predicted values from both models for a year each of high and low solar activities are presented. The results
Journal of Space Weather and Space Climate, 2016
We present a geomagnetic quiet time (Dst > À50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980-1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58°N, 88.38°E geographic; 12.09°N, 160.46°E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F 10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89-0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of 50-100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400-0500 LT) minimum and near-noon (1300-1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-r range from the observed mean values.
Latitudinal variation of Ionospheric TEC at northern hemispheric region
Russian Journal of Earth Sciences, 2019
This paper includes the study of diurnal, monthly, annual and seasonal variation of total electron content (TEC) at low, mid and high latitude in the Northern Hemispheric region. We have also correlated the TEC variation with the solar proxies (viz. , index, F10.7 cm and sunspot number). This study was carried out during low solar activity period of 24th solar cycle i.e. from January 2016 to December 2016, at the three latitudes namely Mangilao, US (GUUG) at 13.44 ∘ N, 144.80 ∘ E, Urumqi, China (URUM) at 43.82 ∘ N, 87.60 ∘ E, and Ny-Alesund, Norway (NYAL) at 78.92 ∘ N, 11.86 ∘ E. We observed some unique feature like sinusoidal pattern of diurnal TEC and semiannual oscillation of seasonal TEC. We also observed that the highest values of diurnal and monthly TEC were obtained at low latitude station GUUG Mangilao. It is also seen that maximum seasonal TEC at low, mid and high latitudes was obtained during equinox.
Total Electron Content(TEC) and Model Validation at an Equatorial Region
2008
The ionosphere has practical importance in GPS applications because it influences transionospheric radio wave propagation. The parameter of ionosphere that produces most of the effects on radio signals is Total Electron Content (TEC). By modelling this TEC parameter, the evaluation of the ionospheric error and the correction of these ionospheric errors for differential GPS can be done. A new approach in the determination of the differential ionospheric error to sub-centimeter accuracy is described in this paper utilizing a developed model. An ionospheric delay model was developed to accurately determine the difference in ionospheric delay expected over a short baseline so that a more accurate differential GPS correction could be made. An ionospheric error correction model should be made applicable to any location including the equatorial region. The results showed that the developed algorithm is a function of elevation angle and TEC from the reference station path to the satellite and could give differential ionospheric delay in sub-centimetre accuracy.
Study of Ionospheric TEC Variability over Low , Mid and High Latitudes during Solar Maximum
2015
Total electron content (TEC) is a key ionospheric parameter that describes the major impact of the ionosphere on the propagate on of radio waves which is crucial for terrestrial and space communication. The present investigation is dedicated to study the latitudinal variability of ionosphere. The study is carried out by taking three stations one each in low, mid and high latitude regions namely IISC, Bangalore, India (13.02 0 N, 77.57 0 E), GUAO, Urumqi, China (43.82 0 N, 87.60 0 E) and NYAL, NY-Alesund, Norway (78.92 0 N, 11.86 0 E) respectively. To study the changes in the ionosphere at three selected station we have considered the GPS observations. The GPS derived TEC values have been collected from the SOPAC (Scripps Orbits and Permanent Array Center) data archive of the IGS (International GPS service). The study is carried out during the high solar activity period of 24 th solar cycle i.e. during January 2012 to December 2012. We also studied the behaviour of ionospheric Total ...
The measurements of total electron content (TEC) are conducted at Surat (21° 9 0 N, 72° 47 0 E) in India, which lies under the northern crest of the equatorial anomaly region, for a period of four years from low to moderate solar activity (2009–2012) using a Global Positioning System (GPS) receiver. These results are compared with the TEC derived from IRI-2012 using three different options of topside electron density: NeQuick, IRI01-corr and IRI-2001. As there is difference between the upper limit of integration in the GPS TEC (20,200 km) and the IRI model (2000 km), to have a fair comparison of measured TEC with that of modeled TEC, the plasmaspheric contribution to the GPS TEC is removed. The measured TEC are compared with the model derived TEC for different times of the day for all months of four years (2009–2012). The IRI-2012 estimates the TEC well for the dusk hours 1800LT and noon hour 1200LT from 2010 to 2012. However, the estimation shows discrepancies with the observed TEC in the year 2009. For 0600LT it is observed that, from 2009 to 2011 the predictions made by IRI-2012 (options NeQuick and IRI01-corr) shifts from over estimation (0–50%) to under estimation (50–75%) and estimate the TEC well in the year 2012. In general, from 2009 to 2012, it is observed that with ascending phase of solar cycle the discrepancies in IRI prediction decreases for 0600LT, 1200LT and 1800LT hours of the day. Further, the comparison is also done for TEC at peak hour 1430LT for four months i.e. April, June, October and December (representing four seasons). It is observed that the peak hour TEC obtained by model overestimates the TEC for a low solar activity year 2009 but estimates well in 2010 and 2012 (except June). Further, model underestimates the peak hour TEC for moderate solar activity year 2011.
Journal of Earth System Science, 2011
In recent years, measurements of total electron content (TEC) have gained importance with increasing demand for the GPS-based navigation applications in trans-ionospheric communications. To study the variation in ionospheric TEC, we used the data obtained from GPS Ionospheric Scintillation and TEC monitoring (GISTM) system which is in operation at SVNIT, Surat, India (21.16 • N, 72.78 • E) located at the northern crest of equatorial anomaly region. The data collected (for the low sunspot activity period from August 2008-December 2009) were used to study the diurnal, monthly, seasonal semi-annual and annual variations of TEC at Surat. It was observed that the diurnal variation at the region reaches its maximum value between 13:00 and 16:00 IST. The monthly average diurnal variations showed that the TEC maximizes during the equinox months followed by the winter months, and are lowest during the summer months. The ionospheric range delay to TEC for the primary GPS signal is 0.162 m per TECU.
A numerical model for low-latitude ionospheric TEC
Indian Journal of Radio and Space Physics
A numerical model of total electron content (TEC) at low latitudes has been constructed from the Faraday rotation data recorded at a number of locations in India during the period Oct. 1975-July 1976 when the geostationary~atellite ATS-6 was located at 35°E. In all, 36 coefficients for each season are required to represent the model. The model can be used for satellite tracking systems in estimating quickly the range, range rate and angular refraction errors. The present model is an improvement over the previously constructed model based on orbiting satellite data.