Characteristics Of Ionospheric Scintillations Research Articles

Correction to: Ionospheric scintillation characteristics over Indian region from latitudinally-aligned geodetic GPS observations

AbstractThe article “Ionospheric scintillation characteristics over Indian region from latitudinally-aligned geodetic GPS observations” was originally published Online First without open access. After publication in volume 16, issue 3, page 2675–2691, the author decided to opt for Open Choice and to make the article an open access publication.

Occurrence characteristics of ionospheric scintillations in the civilian GPS signals (L1, L2, and L5) through a dedicated scintillation monitoring receiver at a low-latitude location in India during the 25th solar cycle

Abstract The ionospheric post-sunset irregularities are responsible for the discrepancies in the received global navigation satellite system (GNSS) signals to fluctuate the phase and amplitude resulting in scintillations in the respective components. Ionospheric scintillations reduce the signal quality and alter the signal reception time inducing position errors which is not preferable for the precise position applications. The level of ionospheric amplitude scintillation, quantified by the amplitude scintillation index (S4), is analyzed during the year 2022, which accentuates the ascending phase of solar cycle 25. For this, we analyzed scintillation intensity and occurrence percentage at a low latitude Indian location in India by employing all the available frequencies of the global positioning system (GPS) constellation. The scintillation distribution for each month is also observed which reveals that the autumn equinox seasons has high scintillation occurrence compared to the vernal equinox seasons. The impact of the scintillation on the three civilian signals (L1, L2 and L5) of the GPS constellation is also observed in terms of the scintillation intensity distribution. The cross-correlation of the S4 index for these three signals reveals a strong correlation existing among them during strong scintillations whereas L2 and L5 signals portray a high correlation irrespective of signal intensities. In brief, the strong scintillation occurrence percentage is higher in the L5 signal compared to the L1 and L2 in contrast with weak scintillation, which is high in L1, followed by L2 and L5. Further, the analysis shows that the autumnal equinox has the highest percentage occurrence of strong scintillations (less than 10 % of the scintillation cases) compared to the vernal equinox whereas among solstice seasons June solstice presented the least scintillation occurrence at the location. The outcomes of this study instigate further analysis of scintillation occurrences from diverse GNSS frequencies covering diverse solar activity conditions for complementing the development of robust scintillation mitigation strategies across the low latitudes during the diverse scintillation conditions.

Ionospheric scintillation characteristics over Indian region from latitudinally-aligned geodetic GPS observations

Ionospheric scintillations pose one of the biggest threats to Satellite-Earth communication links in the communication and navigation systems services whose occurrence characteristics could be explained through the strength of fading (amplitude scintillation index; S4) and the rapidity of the fades (decorrelation time; \U0001d70f0). In the present work, we analyzed the S4 index from a latitudinal array of three geodetic global positioning system (GPS) stations along the Indian longitude sector during the descending phase of the 24th solar cycle. The results show predominant occurrences of scintillations during the post-sunset and nighttime periods indicating the level of scintillations close to equatorial, beyond anomaly crest, and near mid-latitude locations. The strong amplitude scintillations during 2014 and 2015 and their lowest magnitudes during 2016 and 2017 reflect the solar activity dependence of the scintillation occurrences. The directional distribution and 2-dimensional surface sky plots of the S4 index substantiate the occurrence of intense scintillation being more prevalent towards the equatorial location, whereas the weak and moderate scintillations are perceived towards the higher low latitude stations. The occurrences of intense scintillations are confirmed in high solar active years and equinox season at all stations, while the equatorial station presents relatively higher occurrences in winter followed by summer. The summer season witnessed intense occurrences even under moderate to low solar activity years (2016–2017), reflecting the post-midnight occurrences due to meridional thermospheric winds. Moreover, maximum percentage occurrences of weak scintillations in all seasons are evident towards the poleward side, far away from the anomaly crest. The amplitude scintillation frequency during the period is further compared with the solar and geomagnetic indices to substantiate the analysis drawn from the variations. The correlation coefficients between the scintillation index occurrence rate with the solar and geomagnetic in-dices at three GNSS stations provide valuable insights into the relationship between solar activity and scintillation. The results show that the strength and direction of the correlation can vary significantly depending on the specific solar index and location. Thus, emphasize further studies on scintillation occurrences for developing effective forecasting and mitigation models over the Indian low-latitude region.

Ionospheric scintillation characteristics from GPS observations over Malaysian region after the 2011 Valentine’s day solar flare

Abstract Ionospheric scintillations due to plasma irregularities can severely affect the modern dynamic and technological systems whose operations rely on satellite-based navigation systems. We investigate the occurrence of ionospheric scintillation in the equatorial and low latitude region over Malaysia after the 2011 Valentine’s Day solar flare. A network of three Global Ionospheric Scintillation and Total Electron Content Monitor (GISTM) GSV4004B receivers with increasing latitudes from the magnetic equator were used to monitor ionospheric TEC, rate of change of TEC index (ROTI), and amplitude (S4) as well as phase (σ φ) scintillation indices. The results show a simultaneous sudden rise in S4 and σ φ along with a significant depletion of TEC at all three locations. However, the largest enhancement of scintillation indices accompanying a substantial TEC depletion is observed at the farthest low latitude station (UNIMAS) from the equator with values around 0.5, 0.3 rad, and 1 TECU, respectively. The corresponding values at the near-equatorial station (Langkawi; 0.4, 0.2 rad, and 3 TECU) and intermediate station (UKM; 0.45, 0.3 rad, and 5 TECU) are examined along with ROTI variations, confirming the simultaneous occurrence of kilometer-scale and sub kilometer scale irregularities during 17 and 18 February 2011. The radiation effects of the solar flare on the ionosphere were prominently recognized at the local nighttime hours (around 14:00 to 17:00 UT) coinciding with the equatorial prereversal enhancement (PRE) time to seed the equatorial plasma bubbles (EPBs) enhancement that resulted in ionospheric irregularities over the low latitudes. The significant TEC depletion seen in the signals from selected GPS satellites (PRNs 11, 19, 23, and 32) suggests plausible degradation in the performance of GPS-based services over the Malaysian region. The study provides an effective understanding of the post-flare ionospheric irregularities during an episode of minor geomagnetic storm period and aligns with the efforts for mitigating the scintillation effects in space-based radio services over low latitudes.

Ionospheric scintillation characteristics and their effects over GNSS signal and position and navigation systems in the Brazilian region

The ionosphere is an ionized layer extending from about 50 km to 1,000 km of altitude. When an electromagnetic signal cross this layer it suffers a delay in its group velocity and an advance in its phase velocity. The ionosphere is very dynamics and after the sunset its F region equatorial bottomside is lifted up by the intensified eastward electric field, giving origin to an steep plasma gradient. This configurates an unstable condition with higher density plasma standing over lower density one. This instability pushes rarified plasma upward giving origin to large regions named Equatorial Plasma Bubbles (EPB) that rise at equatorial regions and map to low latitudes along the magnetic field lines and can reach continental extension. Through cascating process small scale irregularities (cm to km) are generated inside the EPBs. Due to refractive effects amplitude and phase scintillations are generated in the signal crossing these irregularities. Trans-ionospheric signals used in telecommunication links and in the GNSS applications are severely affected during ionospheric scintillations. In this work we will present the ionospheric scintillation morphology over Brazilian longitudinal sector, its effects over positioning and navigation systems and the existing methodology to mitigate them.

Spectral characteristics of ionospheric scintillations of VHF radiosignal near magnetic zenith

We present the results of observing the Cygnus-A radio source scintillation in the Earth's ionosphere under quiet and disturbed geomagnetic conditions by using the Irkutsk incoherent scattering radar (IISR). The scintillation method applied for ionosphere testing at IISR confidently determines the Fresnel frequency and power cutoff, the spectral characteristics usually related to the velocities and spatial spectra of ionospheric plasma irregularities. We also use the IGRF magnetic field model to show the relation between the shape of discrete radio source scintillation spectra and the direction to the radio source with respect to the geomagnetic field. The S4 index increase within the magnetic zenith is observed to be conditioned by the scintillation spectrum widening. We also evaluate the zonal velocity of observed ionospheric irregularities as ∼10 m/sec assuming the irregularity height to be equal to the F2-layer maximum height in the ionosphere.

Study of ionospheric scintillation characteristics in Australia with GNSS during 2011–2015

Ionospheric scintillation has a great impact on radio propagation and electronic system performance, thus is extensively studied currently. The influence of ionospheric scintillation on Global Navigation Satellite System (GNSS) is particularly evident, making GNSS an effective method to study characteristics of scintillation. In this paper, spatial-temporal statistical features of ionospheric scintillation are intensively studied based on GNSS scintillation data provided by Space Weather Service (SWS) in Australia. Most scintillation data are measured by observation stations in Australia region during 2011–2015. A data processing and analyzing framework is proposed to investigate scintillation features in this paper. General pictures of amplitude scintillation activities observed at different stations are first explored. It is found that scintillation activity presents a manifest seasonal variation at most stations during the researched time spans. The probabilities of amplitude scintillation of different intensities are also evaluated. In the experiment to investigate signal amplitude distributions, Nakagami-m and α-μ distribution models are applied to describe the measured amplitude distribution curves. The result shows that the α-μ model provides a more approximate description for the measured distributions. Kurtosis and information entropy are also calculated to further verify this conclusion. The proposed study is of great significance for a better understanding of ionospheric scintillation in the region of Australia, and for discovering the effects of scintillation on GNSS signals.

Analysis of Ionospheric Scintillation Characteristics in Sub-Antarctica Region with GNSS Data at Macquarie Island.

Ionospheric scintillation has a great impact on radio propagation and electronic system performance, thus is extensively studied currently. The influence of scintillation on Global Navigation Satellite System (GNSS) is particularly evident, making GNSS an effective medium to study characteristics of scintillation. Ionospheric scintillation varies greatly in relation with temporal and spatial distribution. In this paper, both temporal and spatial characteristics of scintillation are investigated based on Macquarie Island’s GNSS scintillation data collected from 2011 to 2015. Experiments demonstrate that occurrence rates of amplitude scintillation have a close relationship with solar activity, while phase scintillation is more likely to be generated by geomagnetic activity. In addition, scintillation distribution behaviors related to elevation and azimuth angles are statistically analyzed for both amplitude and phase scintillation. The proposed work is valuable for a deeper understanding of theoretical mechanisms of ionospheric scintillation in this region, and provides a reference for GNSS applications in certain regions around sub-Antarctica.

On the occurrence of F region irregularities over Haikou retrieved from COSMIC GPS radio occultation and ground‐based ionospheric scintillation monitor observations

AbstractIn this paper, the amplitude scintillation index (s4) derived from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) radio occultation (RO) technique and ground‐based Ionospheric Scintillation Monitor (ISM) at Haikou station (geographic latitude: 20.0°N, geographic longitude: 110.3°E, and geomagnetic latitude: 10.02°N) is used to investigate the morphology of F region irregularities in the low latitudes of China. The RO events of tangent point within the range of 10–30°N latitude, 70–160°E longitude, and 150–500 km altitude are adopted to analyze the ionospheric scintillation characteristics. The percentage of ionospheric scintillation occurrence is computed to obtain its diurnal variations, seasonal trends, and the dependence on solar and geomagnetic activities. Based on a statistical analysis of a long‐term period data set (years 2007 to 2013), we found that the ionospheric scintillation occurrence from both techniques show similar variations. After sunset (18 LT), the scintillation occurrence increases rapidly and reaches the maximum 3 h later. Then it decreases rapidly till 04 LT and remains low level during the daytime. The ionospheric scintillation tends to occur more frequently during vernal and autumnal equinoxes, especially in March–April and September–October. The equinoctial asymmetry could be seen clearly from the ground‐based ISM observations. The peak ionospheric scintillation occurrence time varies with seasons. It is reached latest in summer, while in spring it is very close to that in autumn. The nighttime ionospheric scintillation occurrence tends to increase with increasing solar activities. The increasing tendency is more prominent in vernal and autumnal equinoxes than that in summer and winter. In general, the control of geomagnetic activities is apt to inhibit ionospheric scintillation at equinox nighttime. In summer and winter, the geomagnetic activities could either trigger or inhibit the generation of ionospheric irregularities in a much more complicated way. Thus, it can be concluded that the tangent point location does accurately represent the scattering region, at least in an average sense. The RO technique is demonstrated to be a useful tool for remotely sensing the terrestrial ionosphere on a global scale down to the regional scale in terms of scintillation occurrence.

Observational Analysis of Variation Characteristics of GPS-Based TEC Fluctuation over China

In this study, the characteristics of the total electron content (TEC) fluctuations and their regional differences over China were analyzed by utilizing the rate of the TEC index (ROTI) based on GPS data from 21 reference stations across China during a solar cycle. The results show that there were significant regional differences at different latitudes. Strong ionospheric TEC fluctuations were usually observed at lower latitudes in southern China, where the occurrence of TEC fluctuations demonstrated typical nighttime- and season-dependent (equinox months) features. This phenomenon was consistent with the ionospheric scintillation characteristics of this region. Additionally, compared to low-latitude China, the intensity of TEC fluctuations over mid-latitude China was significantly weaker, and the occurrence of TEC fluctuations was not a nighttime-dependent phenomenon. Moreover, the intensity of TEC fluctuations was much stronger during high solar activity than during low solar activity. Furthermore, the summer-dependent characteristics of TEC fluctuations gradually emerged over lower mid-latitude areas as equinox characteristics weakened. Similar to the equinox characteristics, the summer-dependent characteristics gradually weakened or even disappeared with the increasing latitude. Relevant discussions of this phenomenon are still relatively rare, and it requires further study and analysis.

The statistical investigation of amplitude Scintillations at Indian high latitude Station Maitri, Antarctica

We have investigated the occurrence characteristics of ionospheric scintillations, using dual frequency GPS receiver, installed and operated at Indian scientific base station Maitri (71.45S and 11.45E) Antarctica, during December 2009 to December 2010. The scintillation morphology is described in terms of S4 Index. The scintillations are classified into four main categories as Weak (0.2<S4<0.4), Moderate (0.4<S4<0.6), Strong (0.6<S4<1.0) and Saturated (S4>1.0). From the analysis we found that the percentage of weak, moderate, strong and saturated scintillations were 96%, 80%, 58% and 7% respectively. The maximum percentage of all types of scintillation was observed in the summer season, followed by equinox and the least in winter season. As the year 2010 was a low solar activity period, consequently the maximum occurrences of scintillations were those of weak and moderate and only four cases of saturated scintillation were observed.

Characteristics of VHF scintillations in the equatorial anomaly crest region in India

Abstract. The characteristics of ionospheric scintillations at Rajkot in the equatorial anomaly crest region in India are described for the years 1987–1991 by monitoring the 244-MHz transmission from the satellite FLEETSAT. This period covers the ascending phase of solar cycle 22. Scintillations occur predominantly in the pre-midnight period during equinoxes and winter seasons and in the post-midnight period during summer season. During equinoxes and winter, scintillation occurrence increases with solar activity, whilst in summer it is found to decrease with solar activity. Statistically, scintillation occurrence is suppressed by magnetic activity. The characteristics observed during winter and equinoxes are similar to those seen at the equatorial station, Trivandrum. This, coupled with the nature of the post-sunset equatorial F-region drift and h'F variations, supports the view that at the anomaly crest station, scintillations are of equatorial origin during equinox and winter, whilst in summer they may be of mid-latitude type. The variations in scintillation intensity (in dB) with season and solar activity are also reported.

Characteristics of VHF scintillations in the equatorial anomaly crest region in India

<strong class="journal-contentHeaderColor">Abstract.</strong> The characteristics of ionospheric scintillations at Rajkot in the equatorial anomaly crest region in India are described for the years 1987–1991 by monitoring the 244-MHz transmission from the satellite FLEETSAT. This period covers the ascending phase of solar cycle 22. Scintillations occur predominantly in the pre-midnight period during equinoxes and winter seasons and in the post-midnight period during summer season. During equinoxes and winter, scintillation occurrence increases with solar activity, whilst in summer it is found to decrease with solar activity. Statistically, scintillation occurrence is suppressed by magnetic activity. The characteristics observed during winter and equinoxes are similar to those seen at the equatorial station, Trivandrum. This, coupled with the nature of the post-sunset equatorial F-region drift and <i>h</i>'<i>F</i> variations, supports the view that at the anomaly crest station, scintillations are of equatorial origin during equinox and winter, whilst in summer they may be of mid-latitude type. The variations in scintillation intensity (in dB) with season and solar activity are also reported.

Ionospheric scintillation measurements at 1.5 GHz in mid‐latitude region

Anomalous signal fluctuations due to ionospheric scintillation at 1.5 GHz appear occasionally on earth‐space paths in maritime satellite communication. With regard to the characteristics of ionospheric scintillations at gigahertz frequencies, few data are available in the middle latitude region. This paper describes the results of 1.5‐GHz scintillation measurements at Yamaguchi, Japan. Measurements were carried out by receiving a 1.5‐GHz beacon signal from the MARISAT satellite over the Indian Ocean with an elevation angle of 17.3°. In 13 months of measurements, very severe scintillation with peak‐to‐peak fluctuations exceeding 30 dB was observed in the equinoctial month, and a number of spike‐type scintillations were also observed, particularly at night. Scintillation characteristics, such as diurnal and seasonal variations, amplitude distribution, spectrum, and depolarization are discussed.