Study of Equatorial Ionospheric Scintillation and TEC characteristics at Solar minimum using GPS-SCINDA data (original) (raw)

Study of the ionospheric scintillation and TEC characteristics at solar minimum in a West African equatorial region using Global Positioning System (GPS) data

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

Ionospheric scintillation is a rapid variation in the amplitude and phase of trans-ionospheric radio signal resulting from density irregularities in the ionosphere. It is referred to us by the index S4. The data used are the scintillation index (S4) and the vertical TEC (VTEC) recorded at the SCINDA (Scintillation Network Decision Aid) GPS station of Abidjan (Latitude = 5.34 o N, Longitude = 3.90 o W). This work covers the period from January 2008 to January 2009, two years of low solar activity with R12 equal to 2.8 and 4.2 respectively. The results show that the scintillation is not intense with S4 values lower than 1 in most of the cases and during the course of the day. However, from 2000 to 0200 there are relatively high values of S4 confirming that scintillation is primarily a nighttime observed phenomenon. The scintillation shows a seasonal effect characterized by intense value in the equinoctial months compare to that of the solstice season. The VTEC in general exhibits a diurnal variation as a function of the solar zenith angle. Higher VTEC values are observed around 1100 and 1800 local time and have the same seasonal variation with the S4 index.

Observation of Ionosphere Scintillation and Total Electron Content (TEC) Characteristic at Equatorial Region

Journal of Physics: Conference Series, 2019

Ionosphere scintillation and total electron content (TEC) measurement were investigated in terms of value at Equatorial based on GPS/GNSS measurement. This paper presents the analysis month-to-month variation of Scintillation (S4) and Total Electron Content (TEC) based on during night time and day time activity. This paper also presents the analysis of scintillation (S4) and Total Electron Content (TEC) during equinox and solstice. The analysis presented from January to December 2016. The measurement and recorded data of scintillation (S4) and Total Electron Content (TEC) was done by GPS Ionosphere Scintillation and TEC Monitoring (GISTM), installed at UKM, Malaysia (2.92°N 101.78°E). Strong Scintillation (S4) was obtained from PRN 135 with S4 ≥ 0.4 (0.430368) on 11:33 UTC (19:33 UT). The maximum Total Electron Content (TEC) was found on midday, generally the daily peak is around 5:00 to 10:00 UTC (13:00 to 18:00LT). April shows that the highest Total Electron Content (TEC) about 152 TECU. For seasonal variation, Scintillation (S4) highest on equinox and lowest on solstice, meanwhile Total Electron Content (TEC) highest on equinox and lowest on solstice. The disturbance will cause error in distance measurement for positioning and navigation.

Total electron content and scintillations over Maseno, Kenya, during high solar activity year

Acta Geophysica, 2019

Proper characterization of total electron content (TEC) and scintillation is very important to global positioning system (GPS) users in communication, navigation, ionospheric or atmospheric studies. Quiet time variation of TEC is useful in the estimation and removal of ionospheric delay for global navigation satellite systems single-frequency positioning. During geomagnetic storms, the variations of ionosphere deviate from their quiet day pattern and can cause significant effects on short-term prediction of various ionospheric parameters. The dynamics of the ionosphere change from region to region; therefore, in order to evaluate and improve the performance of global models of the ionosphere, numerous studies of variations using measured ionospheric parameters from stations globally are useful. This paper presents for the first time variations in the TEC and scintillation at Maseno University (geomagnetic coordinates, 9.64°S, 108.59°E), Kenya, investigated using a NovAtelGSV400B GPS receiver for the high solar activity year 2014. The GPS-measured TEC values were compared with the modeled TEC values by the latest International Reference Ionosphere model (IRI-2016), with a view to evaluate the performance of this version of the model. The largest TEC values were observed from 1300 to 1500 h local time throughout the year with the largest diurnal values occurring in March equinox and smallest during June solstice. The largest TEC values are attributed to extreme ultraviolet radiation coupled with upward ⃗ E × ⃗ B plasma drift velocity. Nighttime enhancements in TEC attributed to the 'fountain' effect occurred during some months. Scintillation correlated with depletions in TEC occurred in the period between 1600 h local time to 1900 h local time (post-sunset) sector during some months, with the strongest value of − 0.91 being experienced in March equinox. Scintillation was absent during geomagnetic storms studied mainly as a result of the time of onset of the recovery phases of the storms. In addition, the geomagnetic storms were manifested in GPS-measured TEC as negative ionospheric storms. The IRI-2016 model gave a good prediction of measured values except for its overestimation of measured TEC in the months of May and June. Further, a new insight shown by the results is the ability of the IRI-2016 model to predict post-sunset TEC enhancements during some months contrary to previous versions reported by other researchers in East Africa. However, model is not quickly sensitive to transitions from one season to another. This result contributes to the improvement of the current IRI model by recommending the introduction of an input into the model that is sensitive to transitions in seasons in future versions of the model.

A study of intense ionospheric scintillation observed during a quiet day in the East African low-latitude region

Radio Science, 2013

Ionospheric plasma density irregularities are a common feature of the equatorial and low-latitude ionosphere. These irregularities are known to cause fading and phase fluctuation (scintillation) of L-band radio navigation signals such as those used by Global Navigation Satellite Systems. This study investigates the occurrence of intense ionospheric scintillation in the postsunset period during a geomagnetically quiet day on 8 April 2011. In particular, we use Global Positioning System (GPS) derived observations, i.e., total electron content (TEC) and amplitude scintillation intensity index, S4, to examine the occurrence of intense scintillations at two low-latitude stations in the East African sector. Deep TEC depletions, in some cases roughly 40 TECU, are observed consistently with the occurrence of intense scintillations. In addition, we compare the GPS-based observations to the Communication/Navigation Outage Forecasting System (C/NOFS) satellite plasma data. The intense scintillation events also correspond well with plasma depletion structures present on the C/NOFS observations and can be attributed to strong plasma bubble activity. The C/NOFS data also provide evidence of strong upward drift velocities (> 60 m/s) associated with the depletions, which may have contributed to the generation of the strong irregularities.

Characteristics of GPS Based Ionospheric Scintillation Observed During Low to Moderate Solar Activity for the Period 2009 to 2011 at Low Latitude Station- Surat

The present paper reports the occurrence of ionospheric scintillation (S4 > 0.2) measured using GPS receiver (GISTM) at Surat, (21.160N, 72.780E) located near the northern crest of equatorial anomaly in India. The results are presented for data collected during di�erent levels of solar activity from Jan-2009 to Dec-2011. These long time observations phenomenon, which covers low to moderate solar activity period, have shown features such as, diurnal, monthly, seasonal, magnetic activity and solar cycle variation in scintillation occurrence. It was observed that the diurnal variation of the amplitude scintillation predominately occurred after sunset time (18:00 to 06:00 LT). Our observation shows that the duration of scintillation occurrence is found to be maximum during moderate solar activity and least during low solar activity. The seasonal variation shows that the occurrence of scintillation is observed to be maximum for equinox months, less in winter months and least in summer...

A study of L-band scintillations and total electron content at an equatorial station, Lagos, Nigeria

Radio Science, 2012

In this paper we present the first results from measurements of scintillation and total electron content (TEC) from an equatorial station, Lagos (Latitude 6.5 N, Longitude 3.4 E, magnetic latitude 3.03 S), Nigeria, using a Novatel GSV4004B GPS ionospheric scintillation and TEC monitor. Details are presented for data collected between February 2010 and August 2010. The results show that the presence of some large scale depletions of TEC or plasma bubbles may be noted during the evening hours and that TEC depletions correspond to increased rate of change of TEC (ROT). This confirms that plasma bubbles are associated with large scale irregularities. It is also established that enhanced amplitude scintillation (S 4) corresponds quite well with TEC depletions and increases in ROT. The diurnal and seasonal percentage occurrence for different levels of scintillation activity has peaks in the equinox months (March and April) at 23:00 LT.

Ionospheric Scintillation Morphological Analysis Using GPS-SCINDA Data at Low Latitude Ground Station

2019

 At our location we have frequent occurrence of weak ionospheric scintillations, while few intense scintillations.  Intense scintillation occurred during the day time with a small frequency and relatively moderate scintillation occurrence during the night time with very frequent occurrence of scintillation.  The maximum numbers of amplitude scintillation events are observed in equinox and minimum in summer.

GPS scintillations and total electron content climatology in the southern low, middle and high latitude regions

In recent years, several groups have installed high-frequency sampling receivers in the southern middle and high latitude regions, to monitor ionospheric scintillations and the total electron content (TEC) changes. Taking advantage of the archive of continuous and systematic observations of the ionosphere on L-band by means of signals from the Global Positioning System (GPS), we present the first attempt at ionospheric scintillation and TEC mapping from Latin America to Antarctica. The climatology of the area considered is derived through Ground-Based Scintillation Climatology, a method that can identify ionospheric sectors in which scintillations are more likely to occur. This study also introduces the novel ionospheric scintillation 'hot-spot' analysis. This analysis first identifies the crucial areas of the ionosphere in terms of enhanced probability of scintillation occurrence, and then it studies the seasonal variation of the main scintillation and TEC-related parameters. The results produced by this sophisticated analysis give significant indications of the spatial/ temporal recurrences of plasma irregularities, which contributes to the extending of current knowledge of the mechanisms that cause scintillations, and consequently to the development of efficient tools to forecast space-weather-related ionospheric events.

Characterization of GPS-TEC over African equatorial ionization anomaly (EIA) region during 2009–2016

This study characterizes total electron content (TEC) measured by Global Positioning System (GPS) over African equatorial ioniza-tion anomaly (EIA) region for 2009–2016 period during both quiet geomagnetic conditions (Kp 1) and normal conditions (1 > Kp 4). GPS-TEC data from four equatorial/low-latitude stations, namely, Addis Ababa (ADIS: 9.04°N, 38.77°E, mag. lat: 0.2°N) [Ethiopia]; Yamoussoukro (YKRO: 6.87°N, 5.24°W, mag. lat: 2.6°S) [Ivory Coast]; Malindi (MAL2; 3.00°S, 40.19°E, mag. lat: 12.4°S) [Kenya] and Libreville (NKLG; 0.35°N, 9.67°W, mag. lat: 13.5°S) [Gabon] were used for this study. Interesting features like noontime TEC bite-out, winter anomaly during the ascending and maximum phases of solar cycle 24, diurnal and seasonal variations with solar activity have been observed and investigated in this study. The day-today variations exhibited ionospheric TEC asymmetry on an annual scale. TEC observed at equatorial stations (EIA-trough) and EIA-crest reach maximum values between 1300–1600LTand1300–1600 LT and 1300–1600LTand1300–1600 LT, respectively. About 76% of the high TEC values were recorded in equinoctial months while the June solstice predominantly exhibited low TEC values. Yearly, the estimated TEC values increases or decreases with solar activity, with 2014 having the highest TEC value. Solar activity dependence of TEC within the EIA zone reveals that both F10.7 cm index and EUV flux (24–36 nm) gives a stronger correlation with TEC than Sunspot Number (SSN). A slightly higher degree of dependence is on EUV flux with the mean highest correlation coefficient (R) value of 0.70, 0.83, 0.82 and 0.88 for quiet geomagnetic conditions (Kp 1) at stations ADIS, MAL2, NKLG, and YKRO, respectively. The correlation results for the entire period consequently reveals that SSN and solar flux F10.7 cm index might not be an ideal index as a proxy for EUV flux as well as to measure the variability of TEC strength within the EIA zone. The estimated TEC along the EIA crest (MAL2 and NKLG) exhibited double-hump maximum, as well as post-sunset peaks (night time enhancement of TEC) between $2100 and 2300 LT. EIA formation was prominent during evening/post-noon hours.

Irregularities in the African ionosphere associated with total electron content anomalies observed during high solar activity levels

Frontiers in Astronomy and Space Sciences

In this paper, we investigate anomalies in total electron content (TEC) from 7 stations of the Africa Geodetic Reference Frame (AFREF) during the initial and recovery stages of the geomagnetic storm of 19 February 2014. Additionally, we study geomagnetic storms under the solar activity ascending period of March 2012 and low solar activity of May 2017 to emphasize scintillation effects, especially during the nighttime. We employ a 15-days median-average sliding window to study the latitudinal patterns of relative TEC (rTEC) and determine the storm ionospheric irregularities using the rate of TEC index (ROTI). The low-latitude stations show larger rTEC variations during the storm than the midlatitude stations. ROTI strength >1 TECU/min is found at low latitude stations during postsunset and <1 TECU/min at mid latitudes during daytime. The results from this study show that rTEC differences between midlatitude stations may be caused by dynamo of the electric field originating from...

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

International Journal of Advanced Astronomy, 2020

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 ...

Statistics of GNSS amplitude scintillation occurrences over Dakar, Senegal at varying elevation angles during the maximum phase of solar cycle 24

Space Weather, 2016

This study characterizes Global Navigation Satellite System amplitude scintillation over Dakar (14.75°N, 17.45°W, magnitude latitude: 5.88°N), Senegal. The data, which we arranged on daily and monthly scales, cover 14 months: September-November 2012; February-December 2013; and January-February 2014. The data were further binned into three levels of scintillation using the S4 index: weak (0.3 ≤ S4 < 0.4), moderate (0.4 ≤ S4 < 0.7), and intense (S4 ≥ 0.7), over varying elevation angles (10°, 20°, and 30°). Daily occurrences of scintillation were most frequent around 22-02 LT. On a month-by-month basis, October recorded the highest occurrences of scintillations, while June recorded the least. Furthermore, contrary to Akala et al. (2014, 2015) who earlier reported January as off season for scintillation occurrences at some sites in Africa, namely, Lagos (Central West Africa), Nairobi, and Kampala (East Africa), the current study recorded some scintillation occurrences at Dakar (far west of West Africa) in January. It therefore implies that longitudinal variations do exist in the climatology of ionospheric scintillations over Africa. Consequently, detailed understanding of the climatology and daily distributions of ionospheric scintillations over equatorial Africa, which is our key objective in this study (from the perspective of Dakar), is the basic requirement for developing robust physics-based scintillation models for the African equatorial region. Finally, we noted that the conventional adoption of high-elevation masking angles during scintillation data processing, with a view to suppressing multipath effects usually hid important ionospheric-induced scintillation data. Paradoxically, Africa, with a vast ionospheric data gap, has the largest landmass under the global equatorial ionization anomaly (EIA), a region 15°below and above the magnetic equator. Earlier studies [e.g., Burke et al., 2004;

Instantaneous Ionospheric Scintillation Mapping over the East African Region by use of GPS Derived Amplitude Scintillation Proxy

American Journal of Roentgenology, 2021

Ionospheric scintillation activity over the East African region is often monitored using measurements from the SCIntillation Network Decision Aid (SCINDA) receivers. Many of the SCINDA receivers over East Africa are currently not archiving data and therefore a large part of the region remain un sampled. We investigated the possibility to use dual frequency receivers of the Global Navigation Satellite System (GNSS) network for scintillation mapping. A proxy for amplitude scintillation was first derived by scaling the rate of change of total electron content index (ROTI). The proxy was validated against S4 derived from nearly collocated SCINDA receivers over the region. A good correlation was observed between the proxy and S4. The proxy was then used to map the occurrence of amplitude scintillation over East Africa based on semivariogram modeling and Kriging interpolation technique. The results indicate that the S4 values had a good positive correlation with

Solar activity dependence of total electron content derived from GPS observations over Mbarara

Advances in Space Research, 2012

Vertical total electron content (VTEC) observed at Mbarara (geographic coordinates: 0.60°S, 30.74°E; geomagnetic coordinates: 10.22°S, 102.36°E), Uganda, for the period 2001-2009 have been used to study the diurnal, seasonal and solar activity variations. The daily values of the 10.7 cm radio flux (F 10.7) and sunspot number (R) were used to represent Solar Extreme Ultraviolet Variability (EUV). VTEC is generally higher during high solar activity period for all the seasons and increases from 0600 h LT and reaches its maximum value within 1400 h-1500 h LT. All analysed linear and quadratic fits demonstrate positive VTEC-F 10.7 and positive VTEC-R correlation, with all fits at 0000 h and 1400 h LT being significant with a confidence level of 95% when both linear and quadratic models are used. All the fits at 0600 h LT are insignificant with a confidence level of 95%. Generally, over Mbarara, quadratic fit shows that VTEC saturates during all seasons for F 10.7 more than 200 units and R more than 150 units. The result of this study can be used to improve the International Reference Ionosphere (IRI) prediction of TEC around the equatorial region of the African sector.

Studies of ionospheric variations during geomagnetic activities at the low-latitude station, Ile-Ife, Nigeria

Acta Geophysica, 2013

The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from −40 to 0 nT) and during geomagnetic storm events (with Dst about −100 nT). Seasonal variations of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted dat...

Temporal and spatial variations in TEC using simultaneous measurements from the Indian GPS network of receivers during the low solar activity period of 2004–2005

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.