GPS Ionospheric Scintillation Research Articles

Disturbance electric fields and their effect on ionospheric TEC and scintillations over south China

This study investigated both the disturbance electric fields processes including the Interplanetary Electric Field (IEFy) to low-latitude, known as prompt penetration electric field (PPEF) and the disturbance dynamo electric field (DDEF), and their effects on ionospheric TEC and scintillations over south China during four storms of 17 March 2015, 15 July 2012, 7 October 2015 and 20 December 2015. GPS ionospheric and magnetometer data were derived from receiver stations at Guangzhou and Shenzhen, and at Guangdong Zhaoqin (GZH) and equatorial station Dalat, respectively. Results presented that cases of the eastward PPEF on dayside with durations of 3 and 8 h were identified during storm main phases of 17 March 2015 and of 20 December 2015 respectively. DDEFs were found to dominate on nightside during the three main storm phases other than storm of 15 July 2012, and on dayside during the recovery storm phase of 21 December 2015. The responses of positive TEC deviation to the eastward PPEF on dayside were identified during the storm main phase of 20 December 2015 rather than during the storm of 17 March 2015, which showed longitudinal, latitudinal and seasonal dependences as compared to the previous studies. During the storm of 15 July 2012, positive TEC deviations with no response to the eastward PPEF on dayside were identified. Negative TEC deviation responses to the DDEF on dayside were seen during all four storm recovery phases. GPS ionospheric scintillations (S4 ≥ 0.4) dominated in the equinox months before the occurrences of four storms, but were inhibited during the storm of 17 March 2015 over south China, which was attributed to the inhibitions of irregularities caused scintillations.

A model of the deviation between IRI-2016 and ionospheric TEC observation based on GISTM at low latitude Indonesia region

The diurnal variation pattern of total electron content(TEC) from the International Recurrence Ionosphere (IRI-2016) model is generally is good agreement with observational data at all latitudes. However, at low latitudes the IRI TEC is not as accurate as in midlatitudes. Some reports showed that the IRI-2016 TEC model at the maximum and minimum solar activities at low latitudes tends to be underestimate. In this paper, TEC from GISTM (GPS Ionospheric Scintillation and TEC Monitoring) that is installed at Pontianak station (0.03° S;109.33°E geomagnetic latitude 9.7°S ) used for validation and evaluation of IRI-2016 TEC model over the low latitude Indonesian sector. Data from the 2012 - 2014 period representing solar maximum and data from 2018 representing solar minimum, were used in this study. We also developed VTEC deviation (ΔTEC) model by using multiple linear regression and tested the model by using data 2019. Results show that IRI-2016 generally reproduces the diurnal variations pattern but underestimates the observation data for many hours each day especially during maximum solar activity 2012-20114. The highest deviation in the equinoctial months and lowest during the June and December solstice. The deviation (ΔTEC) model showed good agreement with observation data on January and December but not for other months especially on equinox months. Testing of the VTEC deviation model using 2019 data did not show significant improvement compared to the IRI-2016 itself, which generally produces good TEC prediction in most of the months except for equinox months.

Characterization of Ionospheric Delay and Forecasting Using GPS-TEC over Equatorial Region, Malaysia

This paper investigates the characteristic of the ionospheric delay and forecasting using modified statistical Holt-Winter method over Malaysia. This was carried out by using dual frequency GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers installed at the National University of Malaysia (UKM) (geographic coordinates 2.55°N, 101.46°E and geomagnetic coordinates 7.10°S, 174.05°E), and Langkawi national observatory (Langkawi) (geographical coordinates 6.19°N, 99.51°E and geomagnetic coordinates 3.39°S, 172.42°E), during 2011. In this work, the Holt-Winter forecasting method is modified to provide a better forecasting result over Malaysia. The diurnal, monthly, and seasonal variations of actual ionospheric delay have been analyzed and compared with forecasted ionospheric delay. Based on the results, the diurnal variability of ionospheric delay was maximal mostly between 12:00– 17:00 LT, and minimal nearly at 05:00 LT. The maximum monthly ionospheric delays occurred in October, which is attributed to the geomagnetic storm disturbance that caused increase in ionospheric delay. The lowest seasonal ionospheric delay occurred in the summer and the highest was during the equinox. The maximum ionospheric delay on a quiet day was around 41.9 TECU, while it reached up to 86.6 TECU during the geomagnetic storm. The Holt-Winter method exhibited the highest difference between the measurements and the forecasts in March, with an error of 6%. Hence, the modified Holt-Winter method forecast ionospheric delay effectively during quiet and disturbed periods over Malaysia.

Characteristics and coupling mechanism of GPS ionospheric scintillation responses to the tropical cyclones in Australia

The ionospheric scintillation responses to tropical cyclones passing through the ocean near Australia, named as MARCUS in 2018, DEBBIE in 2017, MARCIA in 2015, and YASI in 2011, are investigated using GPS amplitude scintillation S4 index data collected from GPS stations of Ionospheric Scintillation Monitors installed in Darwin, Weipa, and Willis Island of Australia. Based on the data analysis in this study, some significant characteristics of GPS ionospheric scintillation responses to these tropical cyclones are identified as follows: (a) when the tropical cyclone centers are the closest to GPS stations of Ionospheric Scintillation Monitors with less than 500 km distance, more GPS ionospheric scintillations are observed and mostly concentrate above the tropical cyclone paths within 75°S---10.1°S geomagnetic latitude. (b) As a GPS satellite is passing through the tropical cyclone center, the S4 intensity of the GPS ionospheric scintillation is enhanced. (c) Frequency and intensity of GPS ionospheric scintillations are negatively correlated to the ellipsoid distances between GPS ionospheric scintillation observation stations of the Ionospheric Scintillation Monitors and the tropical cyclone centers. Regarding the coupling mechanism of GPS ionospheric scintillations and tropical cyclones, the electric field perturbations due to turbulent top movement from tropical cyclones might generate ionospheric irregularity and disturbance to produce bubbles. When GPS signals encounter these bubbles, GPS ionospheric scintillations occur.

Simultaneous observations of spread F irregularities over Southeast Asia longitude using Sanya VHF radar, GPS and C/NOFS

Through concurrently measurements by Communication/Navigation Outage Forecasting System (C/NOFS), Sanya VHF radar and GPS ionospheric scintillation receiver on 12 March 2010, five plasma bubbles were found and three of them were observed by all those instruments. Two well-developed plumes with strong backscatter echoes were measured by Sanya radar and their corresponding depletions were observed by C/NOFS in Orbit 10317, 10318 and 10319. Broad plasma depletions resulting from merging process were found in orbit of 10318. The occurrence time and geophysical positions of scintillations correlate well with observations implemented by Sanya VHF radar and C/NOFS. Observations from three types of instrument indicate that the spread F irregularities have distinct scale. There were longitudinal differences between Sanya VHF radar and C/NOFS as irregularities measured, and the eastward drift of developed bubbles are responsible for these differences.

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.

Study of GPS Position Error during 16 June, 2005 (Disturb Day) at Bhopal

In order to study GPS position error, the GPS Ionospheric Scintillation and TEC Monitor (GISTM) based GPS receiver was installed at an equatorial station, Bhopal (23.2° N, 77.4° E, Geomagnetic latitude 14.23˚ N), India. We analyzed the horizontal error and the level of confidence in terms of DRMS and CEP and positional error from fixed GPS point for 16 June 2005(disturb day). In order to study the effect of storm on GPS position errors, the latitudinal error and longitudinal error in meter is studied. We observed that the maximum number of error points in the latitudinal error lies between 1.95 to -1.57 meter while longitudinal error points lies between 1.09 to – 1.28 meter. It was observed that some of the error points lie out the 95% error ellipse and it is observed that the error point’s increased in N and N-E direction. The results have been compared with the earlier ones and discussed in terms of possible source mechanism responsible for the position error at anomaly crest region.

Study of GPS scintillation during solar maximum at Malaysia

The global navigation satellite system (GNSS) ionospheric scintillation and total electron content (TEC) monitor (GISTM) receiver has been installed at UTeM, Malaysia (2.3139 °N, 102.3183 °E) for the purpose of monitoring ionospheric scintillation. Ionospheric scintillation data has been collected during solar maximum cycle 2013-2014 for six months. Solar activities significantly impact the ionospheric GPS scintillation, especially in the equatorial region where Malaysia is located. The GPS link is analysed to investigate how the scintillation increases during the solar maximum cycle. The total electrons increased in the ionospheric layer and the scintillation values gradually. In this paper, the GPS ionospheric scintillations are concerned for the dual frequency L1 (ƒL1 = 1.57542 GHz), and L2C (ƒL2 = 1.2276 GHz). The ionospheric amplitude/phase scintillation of GPS satellites is reported. Finally a new algorithm is suggested to enhance the GPS positioning system with availability of GPS and precise point positioning (PPP) approach.

Azimuth-dependent elevation threshold (ADET) masks to reduce multipath errors in ionospheric studies using GNSS

Physical structures found in the vicinity of GNSS receivers can introduce multipath interference effects when a signal arrives at the receiver by different routes. Multipath effects are well recognized as one of the most significant sources of error that degrade the accuracy of GNSS signals for navigation and positioning applications. These effects also reduce the quality of GNSS data used for ionospheric studies. The principal cause of multipath effects is proximity of the antenna to reflecting structures and it is more pronounced when the signal comes from a satellite with low elevation. Typically, conservative fixed-elevation thresholds of 20–40° are used to filter out signals from low elevation angles, but this leads to the exclusion of a significant quantity of useable data. In this paper we present a series of azimuth-dependent elevation thresholds that were developed by characterizing the multipath environment of the GPS Ionospheric Scintillation and TEC (Total Electron Content) Monitor (GISTM) receivers installed by SANSA (South African National Space Agency) at Mauritius (20.14°S and 57°E), Marion Island (46.87°S and 37.86°E) and SANAE IV in Antarctica (71.73°S and 2.2°W). The threshold masks were developed from azimuth-elevation maps of the S4 index, σϕ index, the Code-Carrier Divergence Standard Deviation (CC-STDDEV) and the L1 Carrier-to-Noise Density (L1 CNo) from 1-min scintillation data taken over a period of 10–12months at each location to identify signals that are distorted by multipath effects. Using the azimuth-dependent elevation threshold (ADET) mask typically gives 22–28% more useful data than using a fixed-elevation threshold at the sites studied in this paper.

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

Comparison of GPS TEC variations with Holt-Winter method and IRI-2012 over Langkawi, Malaysia

The Total Electron Content (TEC) is the ionospheric parameter that has the main effect on radio wave propagation. Therefore, it is crucial to evaluate the performance of the TEC models for the further improvement of the ionospheric modelling in equatorial regions. This work presents an analysis of the TEC, derived from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver at the Langkawi station, Malaysia, located at the geographic coordinates of 6.19°N, 99.51°E and the geomagnetic coordinates of 3.39°S, 172.42°E. The diurnal, monthly and seasonal variations in 2014 of the observed GPS–TEC were compared with the statistical Holt-Winter method and a recent version of the International Reference Ionosphere model (IRI-2012), using three different topside options of an electron density, which are the IRI-2001, IRI01-corr and NeQuick. The maximum peaks of the GPS–TEC were observed in the post-noon time and the minimum was observed during the early morning time. In addition, in monthly variations the Holt-Winter and the IRI-2012 topside options showed an underestimation that was in agreement with the GPS–TEC, except for the IRI-2001 model which showed an overestimation in June, July and August. Regarding the seasonal variation of the GPS–TEC, the lowest values were observed during summer and it reached its maximum value during the equinox season. The IRI-2001 showed the highest value of percentage deviation compared to the IRI01-corr, NeQuick and Holt-Winter method. Therefore, the accuracy of the models was found to be approximately 95% in the Holt-Winter method, 75% in the IRI01-corr, 73% in the NeQuick and 66% in the IRI-2001 model. Hence, it can be inferred that the Holt-Winter method showed a higher performance and better estimates of the TEC compared to the IRI01-corr and NeQuick, while the IRI-2001 showed a poor predictive performance in the equatorial region over Malaysia.

PREDICTION OF TOTAL ELECTRON CONTENT OF THE IONOSPHERE USING NEURAL NETWORK

This paper presents the prediction of hourly Vertical Total Electron Content (VTEC) using a neural network by utilizing the data from a GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver for six years (from 2005 to 2010) during low to medium solar activity (Sunspot number (SSN) between 0.0 and 42.6). Several network configurations were investigated to observe the effect of the number of neurons, and hidden layers. Overall testing process for several network set-up yielded Root Mean Square Error (RMSE) value of 3 to 7 TECU, absolute error of 2 to 6 TECU and relative error of 8% to 28%. Testing using April 2010 to November 2010 data (SSN from 8.0 to 25.2) produced RMSE value of 2.95 to 3.88 TECU,absolute error of 2.39 to 3.09 TECU and relative error of 8.11% to 16.18%, which are within the acceptable range.

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.

GPS phase scintillation at high latitudes during geomagnetic storms of 7–17 March 2012 – Part 2: Interhemispheric comparison

Abstract. During the ascending phase of solar cycle 24, a series of interplanetary coronal mass ejections (ICMEs) in the period 7–17 March 2012 caused geomagnetic storms that strongly affected high-latitude ionosphere in the Northern and Southern Hemisphere. GPS phase scintillation was observed at northern and southern high latitudes by arrays of GPS ionospheric scintillation and TEC monitors (GISTMs) and geodetic-quality GPS receivers sampling at 1 Hz. Mapped as a function of magnetic latitude and magnetic local time (MLT), the scintillation was observed in the ionospheric cusp, the tongue of ionization fragmented into patches, sun-aligned arcs in the polar cap, and nightside auroral oval and subauroral latitudes. Complementing a companion paper (Prikryl et al., 2015a) that focuses on the high-latitude ionospheric response to variable solar wind in the North American sector, interhemispheric comparison reveals commonalities as well as differences and asymmetries between the northern and southern high latitudes, as a consequence of the coupling between the solar wind and magnetosphere. The interhemispheric asymmetries are caused by the dawn–dusk component of the interplanetary magnetic field controlling the MLT of the cusp entry of the storm-enhanced density plasma into the polar cap and the orientation relative to the noon–midnight meridian of the tongue of ionization.

Climatology of GPS phase scintillation at northern high latitudes for the period from 2008 to 2013

Abstract. Global positioning system scintillation and total electron content (TEC) data have been collected by ten specialized GPS Ionospheric Scintillation and TEC Monitors (GISTMs) of the Canadian High Arctic Ionospheric Network (CHAIN). The phase scintillation index σΦ is obtained from the phase of the L1 signal sampled at 50 Hz. Maps of phase scintillation occurrence as a function of the altitude-adjusted corrected geomagnetic (AACGM) latitude and magnetic local time (MLT) are computed for the period from 2008 to 2013. Enhanced phase scintillation is collocated with regions that are known as ionospheric signatures of the coupling between the solar wind and magnetosphere. The phase scintillation mainly occurs on the dayside in the cusp where ionospheric irregularities convect at high speed, in the nightside auroral oval where energetic particle precipitation causes field-aligned irregularities with steep electron density gradients and in the polar cap where electron density patches that are formed from a tongue of ionization. Dependences of scintillation occurrence on season, solar and geomagnetic activity, and the interplanetary magnetic field (IMF) orientation are investigated. The auroral phase scintillation shows semiannual variation with equinoctial maxima known to be associated with auroras, while in the cusp and polar cap the scintillation occurrence is highest in the autumn and winter months and lowest in summer. With rising solar and geomagnetic activity from the solar minimum to solar maximum, yearly maps of mean phase scintillation occurrence show gradual increase and expansion of enhanced scintillation regions both poleward and equatorward from the statistical auroral oval. The dependence of scintillation occurrence on the IMF orientation is dominated by increased scintillation in the cusp, expanded auroral oval and at subauroral latitudes for strongly southward IMF. In the polar cap, the IMF BY polarity controls dawn–dusk asymmetries in scintillation occurrence collocated with a tongue of ionization for southward IMF and with sun-aligned arcs for northward IMF. In investigating the shape of scintillation-causing irregularities, the distributions of scintillation occurrence as a function of "off-meridian" and "off-shell" angles that are computed for the receiver–satellite ray at the ionospheric pierce point are found to suggest predominantly field-aligned irregularities in the auroral oval and L-shell-aligned irregularities in the cusp.

A case study on effect of the magnetic storm of 20 November 2003 on GPS ionospheric scintillation at Vanimo station

The magnetic storm of November 20–21, 2003 was a super storm with minimum Dst −438nT. Using the GPS ionospheric scintillation data recorded at Vanimo station near the magnetic equator, we investigate the behaviors of the ionospheric scintillations during the storm. The amplitude ionospheric scintillations were enhanced evidently at 19:00–20:00LT on November 20 2003, corresponding to the sudden increased solar wind speed, steep increase and reorientation in IMF components, intensification of AE and decreased Dst (Sym-H). Severe density depletion region over Vanimo station, and density enhanced areas adjacent to its northern and southern directions were observed simultaneously. It is the prompt penetration of eastward electric field associated with the southward turning of the IMF and intensification of AE that elevate the ionospheric plasma to certain height through the E×B mechanism, then the plasma drifts along the magnetic lines to low latitude, thus forming the great north–south gradient of electron density. Therefore, the sudden change of the electron density during the period may be responsible for the storm-induced scintillation enhancements at Vanimo station.

A study of GPS ionospheric scintillations observed at Shenzhen

Ionospheric scintillation variations are studied using GPS measurements at the low latitude station of Shenzhen (22.59°N,113.97°E), situated under the northern crest of the equatorial anomaly region, from the Chinese Meridian Project. The results are presented for data collected during the current phase of rising solar activity (low to high solar activity) from December 2010 to April 2014. The results show that GPS scintillation events were largely a nighttime phenomenon during the whole observation period. Scintillation events mainly occurred along the inner edge of the northern crest of the equatorial anomaly in China. The occurrence of scintillations in different sectors of the sky was also investigated, and the results revealed that it is more likely for the scintillations to be observed in the west sector of the sky above Shenzhen. During the present period of study, a total number of 512 total electron content (TEC) depletions and 460 lock loss events were observed. In addition, both of these events are likely to increase during periods of high solar activity, especially because the strong scintillations are often simultaneously accompanied by TEC depletions and lock losses by GPS receivers.

On the second order statistics for GPS ionospheric scintillation modeling

AbstractEquatorial ionospheric scintillation is a phenomenon that occurs frequently, typically during nighttime, affecting radio signals that propagate through the ionosphere. Depending on the temporal and spatial distribution, ionospheric scintillation can represent a problem in the availability and precision for the Global Navigation Satellite System's users. This work is concerned with the statistical evaluation of the amplitude ionospheric scintillation fading events, namely, level crossing rate (LCR) and average fading duration (AFD). Using α‐μ model, the LCR and AFD are validated against experimental data obtained in São José dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, a station located near the southern crest of the ionospheric equatorial ionization anomaly. The amplitude scintillation data were collected between December 2001 and January 2002, a period of high solar flux conditions. The obtained results with the proposed model fitted quite well with the experimental data and performed better when compared to the widely used Nakagami‐m model. Additionally, this work discusses the estimation of α and μ parameters, and the best fading coefficients found in this analysis are related to scintillation severity. Finally, for theoretical situations in which no set of experimental data are available, this work also presents parameterized equations to describe these fading statistics properly.

GNSS station characterisation for ionospheric scintillation applications

Ionospheric scintillations are fluctuations in the phase and amplitude of the signals from GNSS (Global Navigation Satellite Systems) occurring when they cross regions of electron density irregularities in the ionosphere. Such disturbances can cause serious degradation of several aspects of GNSS system performance, including integrity, accuracy and availability. The two indices adopted worldwide to characterise ionospheric scintillations are: the amplitude scintillation index, S4, which is the standard deviation of the received power normalised by its mean value, and the phase scintillation index, σΦ, which is the standard deviation of the de-trended carrier phase. Collaborative work between NGI and INGV supports a permanent network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers that covers a wide range of latitudes in the northern European sector. Data from this network has contributed significantly to several papers during the past few years (see e.g. De Franceschi et al., 2008; Aquino et al., 2009; Spogli et al., 2009, 2010; Alfonsi et al., 2011). In these investigations multipath effects and noise that contaminate the scintillation measurements are largely filtered by applying an elevation angle threshold. A deeper analysis of the data quality and the development of a more complex filtering technique can improve the results obtained so far. The structures in the environment of each receiver in the network which contaminate scintillation measurements should be identified in order to improve the quality of the scintillation and TEC data by removing error sources due to the local environment. The analysis in this paper considers a data set characterised by quiet ionospheric conditions of the mid-latitude station located in Nottingham (UK), followed by a case study of the severe geomagnetic storm, which occurred in late 2003, known generally as the “Halloween Storm”.

Comparative analysis of spread‐F signature and GPS scintillation occurrences at Tucumán, Argentina

AbstractWe analyze data recorded from October 2010 to September 2011, during the ascending phase of the 24th solar cycle, from an Advanced Ionospheric Sounder‐Istituto Nazionale di Geofisica e Vulcanologia ionosonde and a GPS Ionospheric Scintillation and total electron content (TEC) monitor scintillation receiver, colocated at low latitude in the Southern American longitudinal sector (Tucumán, 26.9°S, 294.6°E, magnetic latitude 15.5°S, Argentina). The site offers the opportunity to perform spread‐F and GPS scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly. Spread‐F signatures, classified into four types (strong range spread‐F (SSF), range spread‐F, frequency spread‐F (FSF), and mixed spread‐F), the phase and amplitude scintillation index (σΦ and S4, respectively), the TEC, and the rate of TEC parameter, marker of the TEC gradients, that can cause scintillations, are considered. The seasonal behavior results as follows: the occurrence of all four types of spread‐F is higher in summer and lower in winter, while the occurrence of scintillations peaks at equinoxes in the postsunset sector and shows a minimum in winter. The correspondence between SSF and scintillations seems to be systematic, and a possible correlation between S4 and FSF peaks is envisaged at the terminator. The investigation focused also on two particular periods, from 12 to 16 March 2011 and from 23 to 29 September 2011, both characterized by the simultaneous presence of SSF signatures and scintillation phenomena, allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities.