Occurrence Of Ionospheric Scintillation Research Articles

Occurrence of ionospheric scintillations under different solar and geomagnetic conditions over low latitude station Varanasi

In the present study, occurrences of amplitude scintillations during the ascending phase of the 25th solar cycle from November 2020 to March 2023 are studied over the equatorial anomaly region Varanasi (latitude 25.31° N, longitude 82.97° E, magnetic dip Lat. 16.2° N). Multi-frequency Global navigation satellite system (GNSS) receiver is used to study the occurrence of amplitude scintillation index S4. Diurnal, monthly, and seasonal occurrence characteristics of the S4 index are presented. The scintillation occurrence is observed during nighttime and daytime but is more probable during nighttime. It is observed that maximum scintillation occurred during the equinox season for the solar moderate period whereas the highest occurrence is in summer during the low solar activity period. The highest scintillation occurrences during the summer solstice for a period of low solar activity condition is rare and could be attributed to the gravity waves (GWs) generation due to the weather phenomena in the lower atmosphere. GWs could act as a seeding perturbation in electron density, affecting the growth of ionospheric irregularities through Rayleigh-Taylor instability. The solar flux index (F10.7) is compared with the percentage occurrence of scintillation for the low and moderate solar activity periods to observe the effect of solar activity on scintillation occurrences. Overall, the scintillation occurrence increases with increasing solar activity. To study the effect of geomagnetic storms on scintillations, we have considered seven moderate and intense geomagnetic storms grouped in three categories that occurred during solar cycle 25. It is observed that the occurrence of scintillations is enhanced for the storms with the recovery phase starting at post-midnight. The probability of occurrence of scintillation during the night hours is decreased when the geomagnetic storm occurs during the daytime.

Ionospheric scintillation and solar activity relation in East Malaysia during solar maximum 2014

Ionospheric scintillation is a common phenomenon in the equatorial, auroral, and polar areas, posing a threat to the Global Navigation Satellite System's (GNSS) operation. This ionospheric effect is thought to impact satellite signal propagation, hence, lowering positioning accuracy. Therefore, detecting ionospheric scintillation is critical in enhancing GNSS performance, particularly at low latitudes with severe amplitude scintillation. This paper investigates the effects of ionospheric scintillation on GPS signals at UNIMAS station, the East part of Malaysia. This study aims to identify the occurrence of ionospheric scintillation by calculating the index of scintillation strength during solar maximum 2014. The amplitude scintillation, which is measured in the S4 index is obtained and classified accordingly from the data recorded at the UNIMAS station. The results have shown that strong scintillation (S4 ≥ 0.5) occurred in the spring (April) and autumn (September and October) seasons, reaching 8 incidents. This paper also presents the diurnal, seasonal, and solar activity dependence of ionospheric scintillation. It is evident that the occurrence of amplitude scintillation is influenced by variations in solar activity, including solar flares and sunspots, as well as diurnal and seasonal changes. These findings provide valuable insights into the behaviour of the ionosphere and its impact on space-based communication and navigation systems.

Effects of the Relative Dynamics of Ionospheric Irregularities and GPS Satellites on Receiver Tracking Loop Performance

AbstractTransionospheric satellite signals are exposed to perturbation, caused by irregularities generated in the ionosphere. However, the characteristics of the satellite motion can have an additional impact on signal perturbation, in addition to the effects of irregularity structures, that drift from west to east during geomagnetic quiet conditions. This paper reports the effect of Global Positioning System satellite geometry, on tracking loop performance of ground‐based receivers, during occurrence of ionospheric scintillations. Observations are made from station Calcutta (22.58°N, 88.38°E geographic; magnetic dip 34.54°), located near the northern crest of Equatorial Ionization Anomaly, during three different solar activity periods (March 2014, March 2015, and March 2022). Efforts have been made to study the correlation of east‐west component of satellite velocity at Ionospheric Pierce Point (IPP) with duration of loss‐of‐lock and rate of signal fading (<−10 dB), from ground scintillation pattern observations. Results of this study show 75%–78% correlation between duration of loss‐of‐lock and eastward component of satellite velocity, for all three period of observation. Subsequently, shorter duration of loss‐of‐lock has been observed corresponding to satellite velocity being westward. Signal fading rate is found to decrease with increasing satellite velocity, having median value of the fading rate cumulative distribution percentage, corresponding to satellite velocity of 16.69, 31.76, and 19.14 m/s respectively during March 2014, March 2015, and March 2022. Results of this study also indicate direction and component of satellite velocity at IPP to be a dominant cause of signal outage, even during periods of weak to moderate scintillations.

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 Monitoring With ROTI From Geodetic Receiver: Limitations and Performance Evaluation

AbstractBy comparing amplitude scintillation index S4 from scintillation receivers and Rate of change of Total electron content Index (ROTI) from nearby geodetic receivers in low latitude region of China during year 2015, this work summarized the limitations of ROTI in indicating ionospheric scintillation and quantitatively evaluated the performance/reliability of ROTI in monitoring ionospheric scintillation in low latitude region. The results indicate that the correlation between ROTI and S4 is lower (higher) when scintillation occurs at lower (higher) satellite elevation angle. Erroneous cycle slips and longer ROTI calculation time interval degrade the integrity of ROTI calculated from 30‐s sampling interval data (abbreviated as 30s‐ROTI). ROTI calculated from 1‐s sampling interval data (abbreviated as 1s‐ROTI) has better integrity (90%) than that of 30s‐ROTI (60%). In addition, we propose a reasonable threshold of 0.25 m for cycle slip detection for the 30‐s cadence observation data to avoid misjudging a large ionospheric variation as a cycle slip and further improve on the integrity of 30s‐ROTI. The deviation of ROTI from S4 decreases the reliability of ROTI in indicating the occurrence of ionospheric scintillation as well as the correlation between ROTI and S4. The reliability of ROTI in indicating the occurrence of scintillation can reach 80% and 88% for 30s ROTI and 1s‐ROTI, respectively. The deviation causes 60% of the correlations between 30s‐ROTI and S4 drop by 0.15 ∼ 0.2 and causes more than 66% of the correlations between 1s‐ROTI and S4 drop by 0.15 ∼ 0.2. These results establish an important reference concerning the reliability of ROTI in indicating the occurrence of ionospheric scintillation.

Statistical study on the characterization of phase and amplitude scintillation events in the high-latitude region during 2014–2020 based on ISMR

A better understanding of the climatology of the ionospheric scintillation in the high-latitude region is beneficial to model the adverse effect of the ionospheric scintillation on the positioning navigation and timing services of Global Navigation Satellite System (GNSS). This paper conducts a statistical study on the characterization of the phase and amplitude scintillation events in the high-latitude region based on scintillation indices provided by ionospheric scintillation monitoring receivers (ISMR) collected during the years of 2014 to 2020. Results of this paper show that phase scintillation dominates in most of the high-latitude regions. The proportion of the phase scintillation with strong magnitude in the middle-high latitude region is greater than that in the high and middle latitude regions, but the duration of the scintillation in the middle-high latitude region is generally shorter, with an average value of about 8 min. The ionospheric scintillation presents seasonal and diurnal dependency due to the effect of the solar radiation and earth orientation. The relationships between the occurrence of ionospheric scintillation and the space weather parameters, Ap and IMF, are also studied, showing that Ap can reflect the intensity of the ionospheric scintillation in the middle-high latitude region, and the ionospheric scintillation occurs more frequently under the condition of the northward IMF.

The Prediction of Day‐to‐Day Occurrence of Low Latitude Ionospheric Strong Scintillation Using Gradient Boosting Algorithm

AbstractIonospheric scintillations caused by equatorial plasma bubbles (EPBs) can seriously affect various high technology systems based on Global Navigation Satellite System (GNSS) signals at equatorial and low latitudes. A reliable prediction of ionospheric scintillation occurrence is critical to relieve the effect. Using the long‐term ground‐based GNSS receiver and ionosonde data collected in the Brazilian longitude sector during 2012–2020, an ionospheric strong scintillation prediction model based on the gradient boosting algorithms extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM), and CatBoost is created and tested. It is for the first time that the XGBoost, LightGBM, and CatBoost are utilized to predict the day‐to‐day occurrence of regional ionospheric scintillation during post‐sunset hours. The relative importance of different parameters affecting EPB/scintillation occurrence for building the prediction model is examined. A comparison of daily scintillation occurrence from the modeled and observed results during 2014 (solar maximum) and 2020 (solar minimum) shows that the gradient boosting algorithms are effective for predicting strong scintillations over low latitude, with a prediction accuracy of ∼85%. The results suggest that the trained model with input of total electron content, equatorial F layer peak height and critical frequency before sunset could be well employed to predict the occurrence/nonoccurrence of intense scintillations over low latitude after sunset on a daily basis.

Remote sensing ionospheric variations due to total solar eclipse, using GNSS observations

For years great interest has been taken in the effects of physical phenomena on ionosphere structure. A total solar eclipse was visible in North America on August 21st, 2017. This event offered a great opportunity for remote sensing the ionospheric behavior under the eclipse condition. In this study we investigated the effects of total solar eclipse on variations of Total Electron Content (TEC), and consequently deviations on regional models of Vertical TEC (VTEC), as well as variations in ionospheric scintillation occurrence. Although variations of TEC due to total solar eclipse are studied thoroughly by many authors, but the effect of solar eclipse on ionospheric scintillation has never been considered before. Our study is based on measurements from a high-rate GPS network over North America on the day of eclipse, a day before and after its occurrence, on the other hand, GPS measurements from ground-based stations on similar days were used to model TEC on the day of event, and also one day before and after it. The results of this study demonstrate that solar eclipse reduced scintillation occurrence at the totality region up to 28 percent and TEC values showed a decrease of maximum 7 TECU. Considering TEC models, our study showed apparent variations in the regional models, which confirms previous studies on ionospheric responses to eclipse as well as theoretical assumptions.

Ionospheric scintillation intensity fading characteristics and GPS receiver tracking performance at low latitudes

Ionospheric scintillation refers to rapid fluctuations in signal amplitude/phase when radio signals propagate through irregularities in the ionosphere. The occurrence of ionospheric scintillation can severely degrade the Global Navigation Satellite System (GNSS) receiver tracking loop performance, with consequential effects on positioning. Under strong scintillation conditions, receivers can even lose lock on satellites, which poses serious threats to safety–critical GNSS applications and precise positioning. The characteristics of intensity fading on Global Positioning System (GPS) L1 C/A signals during the peak of the last solar cycle at the low latitude station of Presidente Prudente (Lat. 22.12°S, Long. 51.41°W, Magnetic Lat. 12.74°S) are investigated. The results show that the occurrence of scintillation at this station is extremely frequent. An analysis of the fading events revealed an inverse relationship between fading depth and duration. Mathematical models are built to investigate and explain the statistical relationship between intensity fading and the commonly used amplitude scintillation index S4. Then the GPS receiver tracking loop performance is studied in relation to fading. A conclusion can be drawn that both fading depth and duration can affect the tracking loop performance, but the tracking error variance is more strongly related to fading speed, defined as the ratio of fading depth to fading duration. The proposed study is of great significance for better understanding the ionospheric scintillation intensity fading characteristics at low latitudes. It can also contribute to the research on the effects of scintillation on GNSS as well as support the design and development of scintillation robust GNSS receivers.

Polar traveling ionospheric disturbances inferred with the B-spline method and associated scintillations in the Southern Hemisphere

A new method for analyzing travelling ionospheric disturbances (TIDs) is developed by using two B-spline basis functions of degree 4 on the Total Electron Content (TEC) data from the ground-based Global Positioning System (GPS) receivers. This method enhances the spatial resolution to about 0.1° (geographic latitude) × 0.1° (geographic longitude), which is useful in studying all scales (small, medium and large) TIDs. Using this method, we investigated TIDs and their associated scintillation on 18–19 July 2013 at Southern Hemisphere and found phase scintillation is more sensitive than amplitude scintillation to the TIDs at South Pole. To see the full impact of TIDs on scintillation, we have used a proxy phase scintillation index, calculated using geodetic GPS receivers over Antarctica. We have verified the presence of TIDs during these two days by using a Global Navigation Satellite System (GNSS)-TEC single station approach and SuperDARN slant range signals. Our results show the TEC fluctuations are associated with ionospheric scintillation. The shape of TIDs, their elongation and flattening along/across the geographic latitude/longitude, seems to be related to the magnitude and occurrence of ionospheric scintillations. Magnetospheric particle precipitation boost TEC gradients and generate stronger amplitude scintillation, however, large-scale plasma irregularities cause overall enhancement in magnitude of the phase scintillation index. Due to the high turbulence in the polar ionosphere, TIDs change their shapes quite quickly and/or may disappear in the background ionosphere. B-spline TIDs analysis method is very useful in identifying the visible as well as hidden TIDs parts in the polar ionosphere. For the first time, ionospheric scintillation has been investigated in the vicinity of TIDs at high- latitude in the southern hemisphere. Further, the presented B-spline TIDs analysis method is unique and simple in itself as it uses GPS receiver processed TEC data as the primary input. Our results show that at polar latitude it is not necessary that TIDs always appear near the high TEC regions. Usefulness of the B-spline TIDs detection method has been demonstrated in analyzing TIDs at all geographic locations and different solar activity conditions by comparing B-spline TIDs method produced results with the previous case studies.

Simulation and analysis of chemical release in the ionosphere

Ionospheric inhomogeneous plasma produced by single point chemical release has simple space-time structure, and cannot impact radio wave frequencies higher than Very High Frequency (VHF) band. In order to produce more complicated ionospheric plasma perturbation structure and trigger instabilities phenomena, multiple-point chemical release scheme is presented in this paper. The effects of chemical release on low latitude ionospheric plasma are estimated by linear instability growth rate theory that high growth rate represents high irregularities, ionospheric scintillation occurrence probability and high scintillation intension in scintillation duration. The amplitude scintillations and the phase scintillations of 150 MHz, 400 MHz, and 1000 MHz are calculated based on the theory of multiple phase screen (MPS), when they propagate through the disturbed area.

Statistical characteristics of locally generated ESF during equinoctial months over Sanya

Understanding the local generation rate of equatorial spread-F (ESF) is important for forecasting ionospheric scintillation. Using the GPS ionospheric scintillation/TEC and VHF radar data during March-April and September-October from 2010 to 2014, the occurrence of ionospheric scintillation, TEC fast fluctuation, and backscatter plume were studied. Through analyzing the simultaneous occurrence of ionospheric scintillation, TEC fast fluctuation and backscatter plume, the local generation rate of ESF over Sanya was investigated. The results show that the monthly generation rate varies between 0% and 68%. A significant equinoctial asymmetry of local generation rate of ESF can be found in 2010, 2013 and 2014. The local generation rate of ESF increases from 2010 to 2014 during March-April, while it does not have similar trend during September-October. The plasma vertical drift influenced by solar activity has a significant impact on the monthly generation rate. The equinoctial asymmetry of plasma vertical drift may contribute a lot to the equinoctial asymmetry of the generation rate of ESF.

PERBANDINGAN KARAKTERISTIK AKTIVITAS SINTILASI IONOSFER DI ATAS MANADO, PONTIANAK DAN BANDUNG DARI DATA PENERIMA GPS (CHARACTERISTICS COMPARISON OF IONOSPHERIC SCINTILLATION ACTIVITIES OVER MANADO, PONTIANAK AND BANDUNG BASED ON GPS RECEIVER DATA)

Ionospheric scintillation activity on certain region need to be known its characteristics since its occurrence can degrade satellite signal quality of global satellite navigation system (GNSS) and also satellite communication that works at L-band frequency. The occurrence of ionospheric scintillation varies with location. Therefore, this paper aimed to determine comparative charasteristics of ionospheric scintillation activity over Manado, Pontianak and Bandung from amplitude scintillation index S4 data derived from GPS receiver. The data obtained from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) at Manado station (1.48o N; 124.85oE geomagnetic latitude 7.7oS), at Pontianak station (0.03o S;109.33oE geomagnetic latitude 9.7oS) and at Bandung (-6.90oS;107.6oE geomagnetic latitude 16.54oS) on July 2014 to June 2015. The data were classified into three categores : quiet, moderate and strong based on s4 index. Then we calculated percentage occurrence of scintillation monthly from each observation stastions and mapping of S4 index over Manado, Pontianak and Bandung. The results show that the presentage of strong scintillation (S4>0.5) above Manado is always lower than the other stastions. Strong scintillation was detected at one stations may not also detected at other stations. For very strong scintillastion event, the occurrence of strong scintillation could be detected by all observation stastions but vary in duration. Duration of strong scintillation over Bandung was the longest (up to 4 hours) compared to Pontianak (less than 2 hours) and Manado (less than 1 hour). Based on map of distribution scintillastion occurrence, strong scintillation occurs more intensively over Bandung than over Pontianak and Manado.

Climatology of ionospheric scintillation over the Vietnam low-latitude region for the period 2006–2014

This paper presents the characteristics of the occurrence of ionospheric scintillations at low-latitude, over Vietnam, by using continuous data of three GSV4004 receivers located at PHUT/Hanoï (105.9°E, 21.0°N; magnetic latitude 14.4°N), HUES/Hue (107.6°E, 16.5°N; magnetic latitude 9.5°N) and HOCM/Ho Chi Minh city (106.6°E, 10.8°N; magnetic latitude 3.3°N) for the period 2006–2014. The results show that the scintillation activity is maximum during equinox months for all the years and depends on solar activity as expected. The correlations between the monthly percentage scintillation occurrence and the F10.7 flux are of 0.40, 0.52 and 0.67 for PHUT, HUES and HOCM respectively. The distribution of scintillation occurrences is dominant in the pre-midnight sector and around the northern crest of the equatorial ionization anomaly (EIA), from the 15°N to 20°N geographic latitude with a maximum at 16°N. The results obtained from the directional analysis show higher distributions of scintillations in the southern sky of PHUT and in the northern sky of HUES and HOCM, and in the elevation angles smaller than 40°. The correlation between ROTI and S4 is low and rather good at PHUT (under EIA) than HOCM (near equator). We found better correlation in the post-midnight hours and less correlation in the pre-midnight hours for all stations. When all satellites are considered during the period of 2009–2011, the range of variation of the ration between ROTI and S4 is from 1 to 7 for PHUT, from 0.3 to 6 for HUES and from 0.7 to 6 for HOCM.

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.

Avoiding the Ionospheric Scintillation Interference on Geosynchronous SAR by Orbit Optimization

L-band geosynchronous synthetic aperture radar (GEO SAR) images will most likely deteriorate in the presence of ionosphere scintillation interference due to the low carrier frequency of GEO SAR. Meanwhile, because of the high orbit and the long working time above the region with the active ionosphere, GEO SAR will experience ionospheric scintillation with a higher probability. To make the GEO SAR avoid being interfered by ionospheric scintillation, we propose an orbit-optimization strategy by utilizing the diurnal and geographical pattern of the ionospheric scintillation occurrence in this letter. As the equatorial region is likely to experience ionospheric scintillation during the specified time window from the early evening after sunset to midnight, the orbit can be optimized by tuning the GEO SAR orbit parameters (e.g., a proper time past perigee) to avoid imaging over the equatorial region during the specified time window. Finally, simulation is conducted to verify the effectiveness of the method under the proposed three types of GEO SAR orbits, and the corresponding effective sets of time past perigee are obtained.

Onset location of scintillation-producing spread-F plume over Sanya

Equatorial spread-F (ESF) backscatter plumes are often observed in radar range-time-intensity (RTI) maps at low latitude. Except case studies, few statistical investigations on the onset locations of scintillation-producing ESF plumes at given sites have been conducted. In this study, a statistical analysis is carried out on onset locations of ESF backscatter plumes observed at a low-latitude location Sanya (18.4°N, 109.6°E; dip lat 12.8°N) during equinoctial months of 2013. By employing a tracing method to locate backscatter plumes, we estimate the onset longitudes of periodic plumes obtained from the Sanya VHF radar five-beam steering measurements. The results show that the inter-plume distances (in longitude) are mostly confined within 200–600 km, and the ESF plumes producing ionospheric scintillations over Sanya are almost exclusively generated at the longitudes of 94°–110°E. The results indicate the necessity to monitor ESF plume initial generation in the longitude region of 94°–110°E to better understand the day-to-day variability in the occurrence of ionospheric scintillations over Sanya.

The occurrence characteristics of ionospheric scintillation over Vietnam region during 2009-2012 period

The statistic characteristics of ionospheric scintillation occurrence over Vietnam region have been studied using the continuous data from three GSV4004 receivers at Hanoi, Hue and Ho Chi Minh city during 2009-2012 period. The local time variation, seasonal variation and directional variation of scintillation occurrences in each stations were considered. The obtained results showed that the ionospheric scintillation over Vietnam region, mainly occurred at night time between 20 to 24 local time. The occurrence of ionospheric scintillation depend on the season and solar activity, with the maximum occurrence frequency on the equinox months (March, April and September, October) and significant enhancements on the strong active solar years (2011-2012). Over Vietnam region, ionospheric scintillation occurs concentratively on the equatorial ionisation anomaly crest, from the 13oN to 21oN geographic latitude with maximum at about 15oN. The ionospheric scintillation occurs mainly within the elevation angle smaller 40o and concentrate on some deterministic azimuth angles at each station.ReferencesAarons J.,1982: Global morphology of ionospheric scintillations, Proc. IEEE, 70, 360-378.Abadi P., Saito S., and Srigutomo W., 2014: Low-latitude scintillation occurrences around the equatorial anomaly crest over Indonesia, Annales Geophys., 32, 7-17.Basu, S., S. Basu, J. Aarons, J.P. McClure, and M.D. Cousins, 1978: On the coexistence of kilometer- and meter-scale irregularities in the nighttime equatorial F region, Journal of Geophysical Research, 83 (A9), pp. 4219 - 4226.Basu S., E. Kudeki, S. Basu, C. E. Valladares and E. J. Weber, 1996: Scintillation, plasma drifts, and neutral winds in the equatorial ionosphere after sunset, Journal of Geophysical Research, Vol. 101, N.A12, 26795-26809.Beniguel Y., and Adam JP, 2007: Ionosphere Scintillation and their Effect on the Positioning Errors, IEEA, proccesding, France.Cervera M. A. and R. M. Thomas, 2006: Latitudinal and temporal variation of equatorial ionospheric irregularities determined from GPS scintillation observations, Ann.Geophys.,N.24, 3329-3341.Dierendonck V., A.J, John Klobuchar, Quyen Hua, 1993: Ionospheric Scintillation monitoring using commercial single frequency C/A code receivers, Proceedings of ION GPS-93.Kintner P. M., Ledvina B. M., and Paula E. R, 2007: GPS and ionospheric scintillations, Space weather, Vol.5, S09003, doi:10.1029/2007W000260.Trần Thị Lan, Lê Huy Minh, R. Fleury, P. Lassudrie Duchesne, A. Bourdillon, 2009: Bước đầu nghiên cứu nồng độ điện tử tổng cộng và nhấp nháy điện ly sử dụng số liệu các trạm thu GPS liên tuc ở Việt Nam, Tạp chí Các khoa học về Trái Đất. T. 31, 3, 212-223.Trần Thị Lan, Lê Huy Minh, 2011: Biến thiên theo thời gian của nồng độ điện tử tổng cộng và nhấp nháy điện ly theo số liệu GPS liên tuc ở Việt Nam, Tạp chí Các khoa học về Trái Đất. T. 33, N4, 681-689.Le Huy Minh, Amory-Mazaudier C.,Fleury R., Bourdillon A., Lassudrie-Duchesne P., L. Tran Thi, T. Nguyen Chien and T. Nguyen Ha, P. Vila, 2014 : Time variations of the total electron content in the Southeast Asian equatorial ionization anomaly for the period 2006-2011, Advances in Space Research, 54, 355-368.Rama Rao, P. V. S., Gopi Krishna, S., Niranjan, and Prasad, D. S. V. V. D, 2006: Study of spatial and temporal characteristics of L-band scintillation over the Indian low latitude region and their possible effects on GPS navigation, Ann. Geophys., 24, 1567-1580.Saito S., Maruyama T., Ishii M., Kubota M., Ma G., Chen Y., Li J., Duyen C. H., Truong T. L., 2008: Observation of small to large scale ionospheric irregularities associated with plasma bubbles with a transequatorial HF propagation experiment and spaced GPS receivers, Journal of Geophysical research, V.113, A12313.Valladares C. E., Villalobos J., Sheehan R., and Hagan M.P., 2004: Latitudinal extension of low laititude scintillations measured with a network of GPS receivers, Ann. Geophys., 22, 3155-3175.GSV GPS Silicon Valley, 2005: GSV4004/GSV4004A - GPS Ionospheric Scintillation & TEC Monitor, USER’S MANUAL.

L-band scintillations and calibrated total electron content gradients over Brazil during the last solar maximum

This work presents a contribution to the understanding of the ionospheric triggering of L-band scintillation in the region over São Paulo state in Brazil, under high solar activity. In particular, a climatological analysis of Global Navigation Satellite Systems (GNSS) data acquired in 2012 is presented to highlight the relationship between intensity and variability of the total electron content (TEC) gradients and the occurrence of ionospheric scintillation. The analysis is based on the GNSS data acquired by a dense distribution of receivers and exploits the integration of a dedicated TEC calibration technique into the Ground Based Scintillation Climatology (GBSC), previously developed at the Istituto Nazionale di Geofisica e Vulcanologia. Such integration enables representing the local ionospheric features through climatological maps of calibrated TEC and TEC gradients and of amplitude scintillation occurrence. The disentanglement of the contribution to the TEC variations due to zonal and meridional gradients conveys insight into the relation between the scintillation occurrence and the morphology of the TEC variability. The importance of the information provided by the TEC gradients variability and the role of the meridional TEC gradients in driving scintillation are critically described.

Correlation analysis between the occurrence of ionospheric scintillation at the magnetic equator and at the southern peak of the Equatorial Ionization Anomaly

AbstractIonospheric scintillation refers to amplitude and phase fluctuations in radio signals due to electron density irregularities associated to structures named ionospheric plasma bubbles. The phenomenon is more pronounced around the magnetic equator where, after sunset, plasma bubbles of varying sizes and density depletions are generated by plasma instability mechanisms. The bubble depletions are aligned along Earth's magnetic field lines, and they develop vertically upward over the magnetic equator so that their extremities extend in latitude to north and south of the dip equator. Over Brazil, developing bubbles can extend to the southern peak of the Equatorial Ionization Anomaly, where high levels of ionospheric scintillation are common. Scintillation may seriously affect satellite navigation systems, such as the Global Navigation Satellite Systems. However, its effects may be mitigated by using a predictive model derived from a collection of extended databases on scintillation and its associated variables. This work proposes the use of a classification and regression decision tree to perform a study on the correlation between the occurrence of scintillation at the magnetic equator and that at the southern peak of the equatorial anomaly. Due to limited size of the original database, a novel resampling heuristic was applied to generate new training instances from the original ones in order to improve the accuracy of the decision tree. The correlation analysis presented in this work may serve as a starting point for the eventual development of a predictive model suitable for operational use.