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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...
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... Diurnal variation of TEC To illustrate the feature of diurnal variation, mean TEC on a particular day is shown in figure 1. It can be seen that the TEC decreases slowly from pre-dawn to sunrise period, reaches its minimum at 05:00 IST (IST = Local Time = UT + 05:30 hrs) and increases steadily till noon, reaches its peak ( ∼ 50 TECU) at 16:00 IST and decreases sharply post-sunset. TEC exhibits the usual diurnal variation of a minimum in the pre-sunrise hours (05:00 IST) and a maximum between 13:00 and 16:00 IST. To illustrate the diurnal variation mass plots of diurnal variations at Surat for different months over a period from August 2008–December 2009 (with an exception of October 2008 and January 2009 when observations were disrupted due to technical problems) is shown in figure 2. 3.2 Seasonal variation of TEC Figure 3 represents monthly mean TEC from February to December 2009 for the region. The morning rise and afternoon decay in TEC is sharp in the equinoxes (March, April, September, and October) 2009. The forenoon rate of production and afternoon decay of ionization is faster in winter (November, December, January, February) 2009 compared to that in summer (May, June, July, August) 2009. The amplitude of the diurnal maximum is higher ( ∼ 40 TECU) in the equinoxes and lower in the winter and summer thus exhibiting the semi-annual variation. In order to clearly analyze the trend of seasonal variations of TEC, the average monthly value of TEC and average peak value of TEC monthly were computed. Figure 4 represents the average of monthly TEC value (upper panel) and average of peak TEC value (middle panel) in light of monthly solar flux 10.7 cm (bottom panel) for a period February 2009 to December 2009. It is observed that annual variation in solar flux 10.7 cm ranges from 68 to 76 s.f.u (solar flux units). Semi-annual trend is observed in both the average value in the top and middle panels of figure 4. To analyze the trend further, similar graphs were plotted by considering average TEC of five internationally disturbed days (D-days) for all the months from February to December 2009 and are presented in figure 5(a) and of five internationally quiet days in figure 5(b). It is observed that for the current low sunspot activity, the D-days and Q-days have followed the trend of seasonal variations. Further, TEC is higher ( ∼ 30 TECU) in the winter than in the summer ( ∼ 25TECU), i.e., the ‘win- ter anomaly’ in seasonal variation is also observed. The time of occurrence of the diurnal maximum varies with season. In the equinoxes, the morning rise and afternoon decay of TEC is sharp compared to that in summer and winter. TEC reaches its day- time peak earlier ( ∼ 13:00 IST) in equinoxes and later ( ∼ 15:00 IST) in summer and winter. In summer, the morning pre-dawn value is high and the peak value is low compared to that in equinoxes. In October, the time of occurrence of maximum TEC is earlier and afternoon decay of TEC is very sharp. The seasonal variations of the ionosphere have been explained in terms of changes in solar zenith angle and thermospheric composition (Rishbeth and Setty 1961) and from global circulations (Millward et al 1996). According to the generally accepted theory, the ionospheric TEC depends ...
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... The season-dependent characteristics of diurnal VTEC fluctuations prominently occur in the lower-mid-latitude region which gradually weaken or disappear towards higher latitudes (Liu et al. 2016). Nevertheless, the day to day variations over the lower middle latitudes are combined consequences of solar zenith angle, meridional wind circulation and compositional changes in the neutral thermospheric composition during the period (Wright 1962;Karia and Pathak 2011). ...
The present study investigates the ionospheric Total Electron Content (TEC) variations
in the lower mid-latitude Turkish region from the Turkish permanent GNSS network
(TPGN) and International GNSS Services (IGS) observations during the year 2016.
The corresponding vertical TEC (VTEC) predicted by Auto Regressive Moving Average
(ARMA) and International Reference Ionosphere 2016 (IRI-2016) models are
evaluated to realize their effectiveness over the region. The spatial, diurnal and
seasonal behavior of VTEC and the relative VTEC variations are modeled with
Ordinary Least Square Estimator (OLSE). The spatial behavior of modeled result
during March equinox and June solstice indicates an inverse relationship of VTEC with
the longitude across the region. On the other hand, the VTEC variation during
September equinox and December solstice including March equinox and June solstice
are decreasing with increase in latitude. The GNSS observed and modeled diurnal
variation of the VTEC show that the VTEC slowly increases with dawn, attains a
broader duration of peak around 09.00 to 12.00 UT, and thereafter decreases
gradually reaching minimum around 21.00 UT. The seasonal variation of VTEC shows
an annual mode, maxima in equinox and minima in solstice. The average value of
VTEC during the June solstice is with slightly higher value than the March equinox
though variations during the latter season is more. Moreover, the study shows
minimum average value during December solstice compared to June solstice at all
stations. The comparative analysis demonstrates the prediction errors by OLSE, ARMA
and IRI remaining between 0.23 to 1.17 %, 2.40 to 4.03 % and 24.82 to 25.79%
respectively. Also, the observed VTEC seasonal variation has good agreement with
OLSE and ARMA models whereas IRI-VTEC often underestimated the observed value
at each location. Hence, the deviations of IRI estimated VTEC compared to ARMA and
OLSE models claim further improvements in IRI model over the Turkish region.
Advanced analysis of TPGN data over the region may comp
... Apart from various locations in globe several researchers have been investigated morphological features of TEC such as the diurnal, monthly, seasonal, latitudinal and solar activity variation using various techniques, e.g. in Africa,[8][13], in South America,[14][15][16][17][18]over China[19][20], Huo et al.[21]and Perevalova et al.[22]over North America, Zakharenkova et al.[23]over Japan; Venkatesh et al.[24][25][26]over Brazil and many more. Ionospheric TEC variations have been investigated in the Indian region, using this data and other separate TEC measurements at Surat[27], Agra[28]and other different stations, namely Trivandrum, Waltair, Raipur and Delhi[6]. The GPS-TEC data for the Surat station (located under the northern crest of the equatorial ionization anomaly in Indian sector) have been analyzed earlier in the year 2009 at low solar activity period[27]. ...
... Ionospheric TEC variations have been investigated in the Indian region, using this data and other separate TEC measurements at Surat[27], Agra[28]and other different stations, namely Trivandrum, Waltair, Raipur and Delhi[6]. The GPS-TEC data for the Surat station (located under the northern crest of the equatorial ionization anomaly in Indian sector) have been analyzed earlier in the year 2009 at low solar activity period[27]. However, the analysis of high solar activity has never been performed for this station. ...
... Thus, the appearance of winter anomaly in EIA crest strength has been attributed to an energy input discrepancy between S-N hemisphere[70]; change in season by a neutral gas composition[43][57]; chemical recombination and solar radiation[67]; solar zenith angle[50][59]; and trans-equatorial summer to winter neutral wind[72]. According to, Karia and Pathak[27]the meridional winds may contribute to the seasonal variations of GPS-TEC, particularly at which the thermospheric wind effects are mainly strong. Research by Kumar et al.[59]reported the presence of winter anomaly in the EIA crest throughout the periodratio is higher in winter season[70]. ...
The measurements of ionospheric TEC (total electron content) are conducted
at a low latitude Indian station Surat (21.16˚N, 72.78˚E Geog.), which lies under
the northern crest of the equatorial anomaly in Indian region. The data
obtained are for a period of five years from low to high solar activity (2010-
2014) using GPS (Global Positioning System) receiver. In this study, we report
the diurnal and seasonal variation of GPS-TEC, dependence of GPS-TEC with
solar activity, geomagnetic condition and EEJ strength. From the seasonal
analysis, it is found that greater values of the GPS-TEC are observed during
equinox season followed by winter and summer. The appearance (in the year
2011 and 2014) and disappearance (in the year 2010 and 2012) of “winter
anomaly” have been observed at the station. From the correlation of GPS-TEC
with different solar indices, i.e. solar EUV flux, F10.7 cm solar radio flux and
Zurich sunspot number (SSN), it is concluded that the solar index EUV flux is
a better controller of GPS-TEC, compared to F10.7 cm and SSN. Further, it is
observed that there is no effect of rising solar activity on correlation. Moreover,
the percentage variability of GPS-TEC and the standard deviation of
GPS-TEC obtained for quiet and disturbed days show that dependence of
GPS-TEC on geomagnetic condition is seasonal. Also, there is a positive correlation
observed between GPS-TEC and EEJ strength.
... Apart from various locations in globe several researchers have been investigated morphological features of TEC such as the diurnal, monthly, seasonal, latitudinal and solar activity variation using various techniques, e.g. in Africa,[8][13], in South America,[14][15][16][17][18]over China[19][20], Huo et al.[21]and Perevalova et al.[22]over North America, Zakharenkova et al.[23]over Japan; Venkatesh et al.[24][25][26]over Brazil and many more. Ionospheric TEC variations have been investigated in the Indian region, using this data and other separate TEC measurements at Surat[27], Agra[28]and other different stations, namely Trivandrum, Waltair, Raipur and Delhi[6]. The GPS-TEC data for the Surat station (located under the northern crest of the equatorial ionization anomaly in Indian sector) have been analyzed earlier in the year 2009 at low solar activity period[27]. ...
... Ionospheric TEC variations have been investigated in the Indian region, using this data and other separate TEC measurements at Surat[27], Agra[28]and other different stations, namely Trivandrum, Waltair, Raipur and Delhi[6]. The GPS-TEC data for the Surat station (located under the northern crest of the equatorial ionization anomaly in Indian sector) have been analyzed earlier in the year 2009 at low solar activity period[27]. However, the analysis of high solar activity has never been performed for this station. ...
... Thus, the appearance of winter anomaly in EIA crest strength has been attributed to an energy input discrepancy between S-N hemisphere[70]; change in season by a neutral gas composition[43][57]; chemical recombination and solar radiation[67]; solar zenith angle[50][59]; and trans-equatorial summer to winter neutral wind[72]. According to, Karia and Pathak[27]the meridional winds may contribute to the seasonal variations of GPS-TEC, particularly at which the thermospheric wind effects are mainly strong. Research by Kumar et al.[59]reported the presence of winter anomaly in the EIA crest throughout the periodratio is higher in winter season[70]. ...
The measurements of ionospheric TEC (total electron content) are conducted
at a low latitude Indian station Surat (21.16˚N, 72.78˚E Geog.), which lies under
the northern crest of the equatorial anomaly in Indian region. The data
obtained are for a period of five years from low to high solar activity (2010-
2014) using GPS (Global Positioning System) receiver. In this study, we report
the diurnal and seasonal variation of GPS-TEC, dependence of GPS-TEC with
solar activity, geomagnetic condition and EEJ strength. From the seasonal
analysis, it is found that greater values of the GPS-TEC are observed during
equinox season followed by winter and summer. The appearance (in the year
2011 and 2014) and disappearance (in the year 2010 and 2012) of “winter
anomaly” have been observed at the station. From the correlation of GPS-TEC
with different solar indices, i.e. solar EUV flux, F10.7 cm solar radio flux and
Zurich sunspot number (SSN), it is concluded that the solar index EUV flux is
a better controller of GPS-TEC, compared to F10.7 cm and SSN. Further, it is
observed that there is no effect of rising solar activity on correlation. Moreover,
the percentage variability of GPS-TEC and the standard deviation of
GPS-TEC obtained for quiet and disturbed days show that dependence of
GPS-TEC on geomagnetic condition is seasonal. Also, there is a positive correlation
observed between GPS-TEC and EEJ strength.
... Also, significant day-to-day variations are seen at all the stations, predominantly during the daytime hours, with a higher value at the EIA crest regions corresponding to the equatorial electrojet (EEJ) strength. Subsequently, Bagiya et al. [3](2005 − 2007), Chauhan et al. [13](2006 − 2009), Galav et al. [23](2005 − 2010), Karia and Pathak [33](2008 − 2009) have studied the TEC variation at the respective near anomaly crest stations at Rajkot, Agra, Udaipur, and Surat, confirming similar behavior of TEC as studied by the previous researchers. Reports of Panda et al. [42] [43] from studies of a chain of stations over the Indian region during 2011 − 2012, also suggests comparatively broader and longer duration of the day maximum TEC towards equator, while converse effect is observed beyond the anomaly crest station. ...
... A difference of 1 TEC unit (TECU, with 1 TECU equal to 10 16 electrons/(column m 2 )) corresponds to a difference of 0.16 m along the slant direction between the GNSS satellite and a ground receiver (range delay). If a ground GNSS receiver utilizes a single frequency and correction for ionospheric range delay is not performed, the positioning error becomes significant (Karia and Pathak, 2011). In addition to these TEC variations, plasma bubbles cause radio wave scintillation, which deteriorates radio wave quality and sometimes causes phase unlocking at the receiving system. ...
The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 min and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (EIA) and post-sunset plasma enhancement (PS-EIA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in EIA and PS-EIA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles.
... Under quite geomagnetic condition the variation in TEC could be attributed to the earthquake preparation. The vertical TEC were calculated first as explained in [14] . In the second step the percentage deviation from the monthly mean was calcu- lated: ...
The present paper reports the modification in GPS TEC (total electron content) and atmospheric refractivity prior to the Iran earthquake that had occurred on 16 April 2013 in Iran (28.10°N, 62.05°E). The analysis of GPS-based TEC from two GPS receivers, Surat (21.16°N, 72.78°E) and Lucknow (26.91°N, 80.95°E ) and results of atmospheric refractivity profile for radiosonde observation stations (Shiraz, Iran and Delhi, India) around the fault line are presented in this paper. It is seen that atmospheric refractivity gets modified from 8 to 6 days prior to the earthquake at Shiraz, Iran and Delhi, India. The GPS TEC showed variations a few days prior to the earthquake. We conclude that in search of precursory signatures for an earthquake, both GPS TEC and refractivity are important parameters.
We analyze the behavior of Total Electron Content (TEC) in the Ionosphere using the GPS data between 2009 and 2017 towards the western part of India. The GPS data used in the present study consists of 22 Continuously Operating Reference Sites (CORS), bounded between 20⁰- 24⁰ N Latitude and 68⁰ - 74⁰ E Longitude. All the GPS data used in the study are generated using the Leica 1200 receivers and AX1202GG antennas with a sampling interval of 0.03 Hz. The TEC value of this study is calculated using the L-band GPS frequencies L1 (1575.42 MHz) and L2 (1227.36 MHz). The results reveal maximum TEC values during the daytime (03.30–04.30 IST) for all the years and a maximum of 120 TECu (TEC unit) was observed during the year 2014. The reflection of seasonal variation was visible in the time-series of TEC in all the years, while E season (March, April, September and October) observed maximum TEC values in all the stations. The mean monthly TEC values of the present study illustrate the solar cycle-24 and the coefficient of correlation (r²) of 0.74 indicates a close relationship between the sunspot number and TEC values. A fall of 35% TECu was observed on the annular solar eclipse day on 15 January 2010.
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.
We investigated total electron content (TEC) at Ilorin (8.50° N
4.65° E, dip lat. 2.95) for the year 2010, a year of low solar
activity in 2010 with Rz = 15.8. The investigation involved the use of TEC
derived from GPS, estimated TEC from digisonde portable sounder data (DPS),
and the International Reference Ionosphere (IRI) and NeQuick 2 (NeQ) models.
During the sunrise period, we found that the rate of increase in DPS TEC, IRI
TEC, and NeQ TEC was higher compared with GPS TEC. One reason for this can be
attributed to an overestimation of plasmaspheric electron content (PEC)
contribution in modeled TEC and DPS TEC. A correction factor around the
sunrise, where our finding showed a significant percentage deviation between
the modeled TEC and GPS TEC, will correct the differences. Our finding
revealed that during the daytime when PEC contribution is known to be absent
or insignificant, GPS TEC and DPS TEC in April, September, and December
predict TEC very well. The lowest discrepancies were observed in May, June,
and July (June solstice) between the observed values and all the model values
at all hours. There is an overestimation in DPS TEC that could be due to
extrapolation error while integrating from the peak electron density of F2
(NmF2) to around ∼ 1000 km in the Ne profile. The
underestimation observed in NeQ TEC must have come from the inadequate
representation of contribution from PEC on the topside of the NeQ model
profile, whereas the exaggeration of PEC contribution in IRI TEC amounts to
overestimation in GPS TEC. The excess bite-out observed in DPS TEC and
modeled TEC indicates over-prediction of the fountain effect in these models.
Therefore, the daytime bite-out observed in these models requires a modifier
that could moderate the perceived fountain effect morphology in the models
accordingly. The daytime DPS TEC performs better than the daytime IRI TEC and
NeQ TEC in all the months. However, the dusk period requires attention due to
the highest percentage deviation recorded, especially for the models, in
March, November, and December. Seasonally, we found that all the TECs
maximize and minimize during the March equinox and June solstice,
respectively. Therefore, GPS TEC and modeled TEC reveal the semiannual
variations in TEC.
