scholarly journals Annual and semiannual variations of vertical total electron content during high solar activity based on GPS observations

2011 ◽  
Vol 29 (5) ◽  
pp. 865-873 ◽  
Author(s):  
M. P. Natali ◽  
A. Meza
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Principal Component ◽  
High Solar Activity ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Total Electron ◽  
Ionospheric Variability ◽  
Low Latitudes ◽  
Sudden Decrease

Abstract. Annual, semiannual and seasonal variations of the Vertical Total Electron Content (VTEC) have been investigated during high solar activity in 2000. In this work we use Global IGS VTEC maps and Principal Component Analysis to study spatial and temporal ionospheric variability. The behavior of VTEC variations at two-hour periods, at noon and at night is analyzed. Particular characteristics associated with each period and the geomagnetic regions are highlighted. The variations at night are smaller than those obtained at noon. At noon it is possible to see patterns of the seasonal variation at high latitude, and patterns of the semiannual anomaly at low latitudes with a slow decrease towards mid latitudes. At night there is no evidence of seasonal or annual anomaly for any region, but it was possible to see the semiannual anomaly at low latitudes with a sudden decrease towards mid latitudes. In general, the semiannual behavior shows March–April equinox at least 40 % higher than September one. Similarities and differences are analyzed also with regard to the same analysis done for a period of low solar activity.

Equatorial total electron content (TEC) at low and high solar activity

2009 ◽  
Vol 43 (11) ◽  
pp. 1757-1761 ◽  
Author(s):  
O.K. Obrou ◽  
M.N. Mene ◽  
A.T. Kobea ◽  
K.Z. Zaka
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
High Solar Activity ◽  
Electron Content ◽  
Total Electron

scholarly journals Accuracy of Global Ionosphere Maps in Relation to Their Time Interval

2021 ◽  
Vol 13 (18) ◽  
pp. 3552
Author(s):  
Beata Milanowska ◽  
Paweł Wielgosz ◽  
Anna Krypiak-Gregorczyk ◽  
Wojciech Jarmołowski
Keyword(s):  
Solar Activity ◽  
Geomagnetic Storms ◽  
High Solar Activity ◽  
Time Interval ◽  
Electron Content ◽  
Dual Frequency ◽  
Total Electron ◽  
Low Latitudes ◽  
Globally Distributed ◽  
Gnss Observations

Global ionosphere maps (GIMs) representing ionospheric total electron content (TEC) are applicable in many scientific and engineering applications. However, the GIMs provided by seven Ionosphere Associated Analysis Centers (IAACs) are generated with different temporal resolutions and using different modeling techniques. In this study, we focused on the influence of map time interval on the empirical accuracy of these ionospheric products. We investigated performance of the high-resolution GIMs during high (2014) and low (2018) solar activity periods as well as under geomagnetic storms (19 February 2014 and 17 March 2015). In each of the analyzed periods, GIMs were also assessed over different geomagnetic latitudes. For the evaluation, we used direct comparison of GIM-derived slant TEC (STEC) with dual-frequency GNSS observations obtained from 18 globally distributed stations. In order to perform a comprehensive study, we also evaluated GIMs with respect to altimetry-derived vertical TEC (VTEC) obtained from the Jason-2 and Jason-3 satellites. The study confirmed the influence of GIMs time interval on the provided TEC accuracy, which was particularly evident during high solar activity, geomagnetic storms, and also at low latitudes. The results show that 120-min interval contributes significantly to the accuracy degradation, whereas 60-min one is sufficient to maintain TEC accuracy.

scholarly journals A Least Squares Solution to Regionalize VTEC Estimates for Positioning Applications

2020 ◽  
Vol 12 (21) ◽  
pp. 3545
Author(s):  
Saeed Farzaneh ◽  
Ehsan Forootan
Keyword(s):  
Solar Activity ◽  
South America ◽  
Least Squares ◽  
High Solar Activity ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Dual Frequency ◽  
Numerical Application ◽  
Total Electron ◽  
Band Limited

A new approach is presented to improve the spatial and temporal resolution of the Vertical Total Electron Content (VTEC) estimates for regional positioning applications. The proposed technique utilises a priori information from the Global Ionosphere Maps (GIMs) of the Center for Orbit Determination in Europe (CODE), provided in terms of Spherical Harmonic (SH) coefficients of up to degree and order 15. Then, it updates the VTEC estimates using a new set of base-functions (with better resolution than SHs) while using the measurements of a regional GNSS network. To achieve the highest accuracy possible, our implementation is based on a transformation of the GIM/CODE VTECs to their equivalent coefficients in terms of (spherical) Slepian functions. These functions are band-limited and reflect the majority of signal energy inside an arbitrarily defined region, yet their orthogonal property is remained. Then, new dual-frequency GNSS measurements are introduced to a Least Squares (LS) updating step that modifies the Slepian VTEC coefficients within the region of interest. Numerical application of this study is demonstrated using a synthetic example and ground-based GPS data in South America. The results are also validated against the VTEC estimations derived from independent GPS stations (that are not used in the modelling), and the VTEC products of international centres. Our results indicate that, by using 62 GPS stations in South America, the ionospheric delay estimation can be considerably improved. For example, using the new VTEC estimates in a Precise Point Positioning (PPP) experiment improved the positioning accuracy compared to the usage of GIM/CODE and Klobuchar models. The reductions in the root mean squared of errors were ∼23% and 25% for a day with moderate solar activity while 26% and ∼35% for a day with high solar activity, respectively.

scholarly journals GPS Total Electron Content measurements at low latitudes in Brazil for low solar activity

2004 ◽  
Vol 43 (1) ◽  
pp. 129-137
Author(s):  
Aracy Mendes da Costa ◽  
J. Williams Vilas Boas ◽  
Edvaldo S. Da Fonseca Junior
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Electron Content ◽  
Total Electron ◽  
Low Latitudes

Se calcularon las variaciones del número total de electrones en la ionosfera (TEC) usando datos de GPS, obtenidos en la estación de baja latitud de Presidente Prudente, Brasil (22.1° S; 51.4° W) en 1997, un periodo de baja actividad solar. Se presentan dos promedios horarios durante este periodo. Se discuten las variaciones diarias, estacionales, debidas a la actividad solar y la Anomalía Ecuatorial. Los promedios diurnos de TEC se comparan con las predicciones del modelo IRI-95 para los meses de los equinoccios y los solsticios y se muestra que IRI-95 sistemáticamente sobreestima los valores observados. Los aumentos prenocturnos de TEC se observaron durante todo el año excepto en mayo y junio. Los valores de TEC medidos reproducen la misma tendencia general de los valores TEC observados en Cachoeira Paulista, Brasil (22.5° S; 45° W). El efecto "fuente" parece ser más efectivo en Presidente Prudente debido a su menor latitud magnética. La correlación entre los valores experimentales de TEC y el flujo solar durante la baja actividad (62 < F10.7 < 116 unidades de flujo) enfatiza que el modelo IRI para bajas latitudes y periodos de baja actividad solar es inadecuado. Los resultados aquí presentados son los primeros obtenidos usando la técnica TEC-GPS sobre la parte suroeste de Brasil.

An Efficient Bayesian Integration Technique to Densify Global Ionospheric Maps using Observations of Local GNSS Networks 

2021 ◽  
Author(s):  
Saeed Farzaneh ◽  
Ehsan forootan
Keyword(s):  
Solar Activity ◽  
South America ◽  
Spherical Harmonics ◽  
Region Of Interest ◽  
High Solar Activity ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Numerical Application ◽  
Local Networks ◽  
Total Electron

&lt;p&gt;&lt;strong&gt;Abstract:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Global ionosphere maps (GIM) are generated on daily basis at the Center for Orbit Determination in Europe (CODE) using data from about 200 GNSS sites of the International GNSS Service (IGS) and other institutions. These measurement are used to numerically model the vertical total electron content (VTEC) in a solar-geomagnetic reference frame using a spherical harmonics expansion up to degree and order 15. In this study, an efficient method is developed and applied to densify the GIM model in a region of interest using the TEC measurements of&amp;#160; local networks. Our approach follows a Bayesian updating scheme, where the GIM data are utilized as a prior information in the form of Slepian-coefficients in the region of interest. These coefficients are then updated by the GNSS measurements in a Bayesian framework that considers both the uncertainty of a priori information and the new measurements. Numerical application is demonstrated using a GNSS network in South America. Our results indicate that by using 62 GNSS stations in South America, the ionospheric delay estimation can be considerably improved. For example, using the Bayesian-derived VTEC estimates in a Standard Point Positioning (SPP) experiment improved the positioning accuracy compared to the usage of GIM/CODE and Klobuchar models. The reductions in the root mean squared of errors were found to be &amp;#8764;23% and 25% for a day with moderate solar activity while 26% and &amp;#8764;35% for a day with high solar activity, respectively.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Key words:&lt;/strong&gt; Bayesian densification, Slepian Functions, Spherical Harmonics, Ionospheric modelling, VTEC, SPPs&lt;/p&gt;

scholarly journals SCINDA-GPS derived TEC depletions and amplitude scintillations over Kisumu, Kenya during selected quiet and storm days of 2013 and 2014

2020 ◽  
Vol 8 (1) ◽  
pp. 1
Author(s):  
Uluma Edward ◽  
Ndinya Boniface ◽  
Omondi George
Keyword(s):  
Total Electron Content ◽  
Equatorial Region ◽  
Activity Period ◽  
High Solar Activity ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Gps Receiver ◽  
Total Electron ◽  
Solar Intensity ◽  
Using Data

Total Electron Content (TEC) depletion and amplitude scintillation (S4) can be derived from, SCINDA-GPS receivers situated in various parts of the equatorial region. In this paper we present results of characterization of TEC depletions and amplitude scintillations over Kisumu, Kenya (Geomagnetic coordinates: 9.64o S, 108.59o E; Geographic coordinates: 0.02o S, 34.6o E) for both selected geomagnetically quiet and geomagnetically disturbed conditions between 1st January 2013 and 31st December 2014 using data derived from the Kisumu NovAtel GSV4004B SCINDA-GPS receiver situated at Maseno University. TEC depletions and amplitude scintillations affect Global Positioning System (GPS) signals in the ionosphere as they propagate from the satellite to the receiver. This study aims to investigate day to day variability of TEC depletions and amplitude scintillations over Kisumu, Kenya during both geomagnetically quiet and geomagnetically disturbed days of 2013 and 2014 which was a high solar activity period for Solar Cycle 24. Seasonal variability of TEC depletions and S4 index is also presented. The Receiver Independent Exchange (RINEX) data for the years 2013 and 2014 was retrieved from the Kisumu SCINDA-GPS receiver, processed to obtain Vertical Total Electron Content (VTEC), S4 and Universal Time (UT) and fed into MATLAB to generate VTEC and S4 plots against UT for each selected quiet and storm day within the 2013 and 2014 period. The obtained results showed a diurnal variation of TEC where TEC was minimum at pre-sunrise, maximum during daytime and minimum during nighttime. The minimum TEC during pre-sunrise and nighttime was attributed to reduced solar intensity while maximum TEC during daytime is attributed to increased solar intensity. Most of the selected quiet and storm days of the years 2013 and 2014 showed TEC depletions and TEC enhancements corresponding with enhanced amplitude scintillations between 1800UT and 20:00UT. This might be attributed to the rapid rise of the F-layer and the increase in the vertical E x B plasma drift due to the Pre-reversal Enhancement (PRE) of the eastward electric field. Post-midnight TEC depletions and amplitude scintillations were observed for some days and this was attributed to the effect of zonal winds which brought post-midnight enhancement of the E x B drift. The percentage occurrence of amplitude scintillations for the selected quiet and storm days exhibited a seasonal dependence with equinoctial months having higher occurrences than the solstitial months. The higher average S4 index during equinoctial months might be attributed to increased solar intensity resulting from the close alignment of the solar terminator and the geomagnetic meridian.  

scholarly journals Multifractal analysis of vertical total electron content (VTEC) at equatorial region and low latitude, during low solar activity

2013 ◽  
Vol 31 (1) ◽  
pp. 127-133 ◽  
Author(s):  
M. J. A. Bolzan ◽  
A. Tardelli ◽  
V. G. Pillat ◽  
P. R. Fagundes ◽  
R. R. Rosa
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Solar Rotation ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
X Rays ◽  
Equilibrium System ◽  
Equatorial Anomaly ◽  
Total Electron ◽  
Small Scales

Abstract. This paper analyses the multifractal aspects of the GPS data (measured during a period of low solar activity) obtained from two Brazilian stations: Belém (01.3° S, 48.3° W) and São José dos Campos (SJC) (23.2° S, 45.9° W). The results show that the respective geographic sites show important scaling differences as well as similarities when their multifractal signatures for vertical total electron content (VTEC) are compared. The f(α) spectra have a narrow shape for great scales, which indicates the predominance of deterministic phenomena, such as solar rotation (27 days) over intermittent phenomena. Furthermore, the f(α) spectra for both sites have a strong multifractality degree at small scales. This strong multifractality degree observed at small scales (1 to 12 h) at both sites is because the ionosphere over Brazil is a non-equilibrium system. The differences found were that Belém presented a stronger multifractality at small scales (1 h to 12 h) compared with SJC, particularly in 2006. The reason for this behaviour may be associated with the location of Belém, near the geomagnetic equator, where at this location the actions of X-rays, ultraviolet, and another wavelength from the Sun are more direct, strong, and constant throughout the whole year. Although the SJC site is near ionospheric equatorial anomaly (IEA) peaks, this interpretation could explain the higher values found for the intermittent parameter μ for Belém compared with SJC. Belém also showed the presence of one or two flattening regions for f(α) spectra at the same scales mentioned before. These differences and similarities also were interpreted in terms of the IEA content, where this phenomenon is an important source of intermittence due the presence of the VTEC peaks at ±20° geomagnetic latitudes.

Variability of the Vertical Total Electron Content, from GPS data, during 2 to 8 November 2015, Using Oukaimeden and Rabat Stations in Morocco

2017 ◽  
Vol 13 (S335) ◽  
pp. 159-161
Author(s):  
Khaoula El bouyahyaoui ◽  
Aziza Bounhir ◽  
Zouhair Benkhaldoun ◽  
Rolland FLEURY ◽  
Christine Amory-Mazaudier ◽  
...  
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Gps Data ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Gps Measurements ◽  
Total Electron

AbstractIn this work we present a method for detecting the activity of the ionosphere (TEC) and we illustrate the signature of the solar activity on the vertical total electron content VTEC, during 02 to 08 November 2015, using GPS measurements obtained from two stations in Morocco, the first one in Marrakech at Observatory of Oukaimeden OUCA (31°12′23.3″ N 7°51′58.8″ W), the second in Rabat, Rabt (33.9981°N;353.1457°E, geographic).

VARIATIONS IN TOTAL ELECTRON CONTENT DURING THE PHASES OF LOW AND HIGH SOLAR ACTIVITIES

2016 ◽  
Vol 78 (5-8) ◽  
Author(s):  
Mariyam Jamilah Homam ◽  
Mohamad Aizat Ezri Ahmad Hapizudin
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Solar Minimum ◽  
Solar Maximum ◽  
High Solar Activity ◽  
Electron Content ◽  
Minimum Phase ◽  
Maximum Phase ◽  
Total Electron ◽  
Value Changes

Variations in the Total Electron Content of the ionosphere were studied by utilizing data from the GISTM receiver installed at Universiti Tun Hussein Onn Malaysia. The study was conducted during periods of low solar activity (July 2007–July 2008) and high solar activity (July 2013–July 2014). Results show that the TEC are dependent on the solar activity.The values during high solar activity were significantly higher than that obtained during the solar minimum phase. The minimum TEC values for both phases varied between 89% and 97%, and the maximum TEC values varied between 70% and 81%. The pattern of daily TEC value changes was constant, and TEC peaked in the afternoon at ~14 LT. The highest TEC recorded during the solar maximum phase was 144.5 TEC Unit (TECU) in April 2014, whereas the highest TEC recorded during the solar minimum phase was 36.3 TECU in April 2008. TEC was maximized from March to May under both solar maximum and minimum phases.

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