Long Term Ionospheric VTEC Variation During Solar cycle 24 as Observed from Indian IGS GPS Station (original) (raw)
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Annales Geophysicae, 2006
With the recent increase in the satellite-based navigation applications, the ionospheric total electron content (TEC) and the L-band scintillation measurements have gained significant importance. In this paper we present the temporal and spatial variations in TEC derived from the simultaneous and continuous measurements made, for the first time, using the Indian GPS network of 18 receivers located from the equator to the northern crest of the equatorial ionization anomaly (EIA) region and beyond, covering a geomagnetic latitude range of 1 • S to 24 • N, using a 16-month period of data for the low sunspot activity (LSSA) years of March 2004 to June 2005.
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.
Variability of ionospheric TEC at low latitude station, Hyderabad during medium solar activity
Russian Journal of Earth Sciences, 2021
The successful operation of communicational and navigational applications requires knowledge of state and behaviour of ionosphere as well as spatial and temporal changes taking place in it. With this view, we have studied the variability and changes in the low latitude ionosphere by considering a low latitude Indian station Hyderabad (17.41 ∘ N, 78.55 ∘ E). The variability is studied during the year 2014, by using the space borne Global Positioning System (GPS) observations. From GPS observations an important parameter; Total Electron Content (TEC) is obtained, which represents the integral electron density of the ionosphere and is widely used in studies concerning ionospheric variability. We have studied how the ionospheric conditions at Hyderabad change from hour to hour, day to day, month to month and season to season. We found that ionosphere over Hyderabad exhibits significant, interesting and regular variability. Although, the trends followed by the ionospheric changes are similar, but the magnitude of peak values differ on different time scales. Finally we have compared the variability of observed or actual values of TEC with the corresponding values predicted by International Reference Ionosphere (IRI) model-2016 and found good agreement between hourly values, while IRI model overestimates or underestimates the daily values.
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 ...
Annales Geophysicae, 2009
The dual frequency signals from the GPS satellites recorded at Rajkot (22.29 • N, 70.74 • E, Geographic, 14.03 • N Geomagnetic) near the Equatorial ionization anomaly crest in India have been analyzed to study the ionospheric variations in terms of Total Electron Content (TEC) for the low solar activity period from April 2005 to December 2007. In this study, we describe the diurnal and seasonal variations of TEC, solar activity dependence of TEC and effects of a space weather related event, a geomagnetic storm on TEC. The diurnal variation of TEC shows pre-dawn minimum for a short period of time, followed by a steep early morning increase and then reaches maximum value between 14:00 LT and 16:00 LT. The mean diurnal variations during different seasons are brought out. It is found that TEC at Rajkot is at its maximum during Equinoctial months (March, April, September, October), and minimum during the Winter months (November, December, January, February), with intermediate values during Summer months (May, June, July, August), showing a semi annual variation. TEC values have been decreasing since 2005, onwards showing positive correlation with solar activity. TEC variations during the geomagnetic storm commencing 24 August 2005 with D st =−216 nT are analysed. TEC shows a positive ionospheric storm effect on the first day of the storm and negative ionospheric storm effect on the next day. The equatorial Electrojet control on the development of the equatorial anomaly is also demonstrated.
Universe
Research on longitudinal discrepancies in local ionospheric variability, especially in equatorial and low-latitude regions, is a focal point of interest for the space weather modeling community. The ionosphere over these regions is influenced by complex electrodynamics, wind, and temperature dynamics that can seriously impact dynamic technological systems such as satellite tracking and positioning, satellite radio communication, and navigation control systems. Here, we researched the longitudinal variability in the ionospheric total electron content (TEC) by analyzing observed global positioning system (GPS)-derived TEC values along with those extracted from the most reliable global ionospheric maps (GIMs) and the International Reference Ionosphere (IRI-2016) model at selected stations in the vicinity of the magnetic equator along the American, African, and Asian longitude sectors. The period of study covered the descending (2016–2017) and deep solar minimum (2018–2019) years in the...
Journal of Geophysical Research: Atmospheres, 2010
The aim of this work is the analysis of the annual, semiannual, and seasonal effects in the total electron content (TEC) of the terrestrial atmosphere during low solar activity. Spatial and temporal ionospheric variability are investigated from global International Global Navigation Satellite System Service (IGS) VTEC maps during low solar activity in 2006. Two different techniques, principal component analysis (PCA) and Fourier analysis, are applied to the data set. Applying the PCA technique on a time series of global IGS VTEC maps gives us a method to analyze the main ionospheric anomalies on a global scale. The Fourier series provide us a comparison with the results obtained with PCA. The behavior of VTEC variations at 2 h periods centered at 1200 and 2200 local time (LT) are analyzed. Particular characteristics associated with each period and with the geomagnetic region are highlighted. All the stations show an annual behavior, which means that the maxima variations of the VTEC...
Advances in Space Research, 2013
Total electron content (TEC) data obtained from GPS dual frequency measurements during the ascending half of the solar cycle 24 from 2009 to 2012 over Dibrugarh (27.5°N, 94.9°E; 17.6°N MLAT) have been used to study the diurnal, seasonal, annual and solar cycle variation of TEC. The measurements reported here are for the first time from the location situated at the poleward edge of the northern equatorial ionization anomaly (EIA) and within the peak region of the longitudinal wave number 4 (WN4) structure in EIA crest TEC. TEC exhibits a minimum around 0600 LT and diurnal maximum around 1300-1600 LT. In the low and moderate solar activity years 2009-2010 and 2010-2011, average daytime (1000-1600 LT) TEC in summer was higher (25.4 and 36.6 TECU) compared to that in winter (21.5 and 26.1 TECU). However, at the peak of the solar cycle in 2011-2012, reversal in the level of ionization between winter and summer takes place and winter TEC becomes higher (50.6 TECU) than that in summer (45.0 TECU). Further, TEC in spring (34.1, 49.9 and 63.3 TECU respectively in 2009-10, 2010-11 and 2011-12) is higher than that in autumn (24.2, 32.3 and 51.9 TECU respectively) thus showing equinoctial asymmetry in all the years of observation. The winter anomaly in high solar activity years and equinoctial asymmetry all throughout may be largely attributed to changes in the thermospheric O/N 2 density ratio. A winter to summer delay of $1 h in the time of occurrence of the diurnal maximum has also been observed. Daytime maximum TEC bears a nonlinear relationship with F 10.7 cm solar flux. TEC increases linearly with F 10.7 cm solar flux initially up to about 140 sfu (1 sfu = 10 À22 W m À2 Hz À1) after which it tends to saturate. On the contrary, TEC increases linearly with solar EUV flux (photons cm À2 s À1 , 0.5-50 nm) during the same period. TEC predicted by the IRI 2012 are lower than the measured TEC for nearly 90% of the time.
Journal of Energy Engineering and Thermodynamics
The Total Electron Content (TEC) measurements from two stations in the Indian sector, namely the equatorial station Bangalore (Geographic latitude 12°, 58' N, longitude 77°, 35' E) and the equatorial ionization anomaly (EIA) station Varanasi (Geographic latitude 25°, 19' N, longitude 82°, 59' E), are used to examine the variations of the TEC. In comparison to Varanasi, Bangalore has greater daytime TEC values. At the anomalous crest locations, significant daily changes in the TEC values are seen. Three distinct possibilities for the topside electron density present in the model (IRI-2001, IR01-Corr, and Ne-Quick) have been taken into consideration when comparing the observed GPS-TEC with the IRI-2016 model-derived TEC. While the TEC using the IRI01-Corr and IRI-2001 approach exhibits greater variances, the TEC obtained using the Ne-Quick options exhibits better agreement with GPS-TEC.