http://hdl.handle.net/2122/4115 Thu, 23 May 2013 17:43:09 GMT 2013-05-23T17:43:09Z http://hdl.handle.net/2122/8573 Title: Monitoring, tracking and forecasting ionospheric perturbations using GNSS techniques Authors: Jakowski, N.; German Aerospace Center, Institute of Communications and Navigation, Neustrelitz, Germany; Béniguel, Y.; IEEA, Paris, Courbevoie, France; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pajares, M. H.; Universitat Politecnica de Catalunya, Res. group of Astronomy and Geomatics, Barcelona, Spain; Jacobsen, K. S.; Norwegian Mapping Authority, Geodetic Institute, Hønefoss, Norway; Stanislawska, I.; Space Research Center PAS, Warsaw, Poland; Tomasik, L.; Space Research Center PAS, Warsaw, Poland; Warnant, R.; University of Liege, Unit of Geomatics – Geodesy and GNSS, Belgium; Wautelet, G.; University of Liege, Unit of Geomatics – Geodesy and GNSS, Belgium Abstract: The paper reviews the current state of GNSS-based detection, monitoring and forecasting of ionospheric perturbations in Europe in relation to the COST action ES0803 ‘‘Developing Space Weather Products and Services in Europe’’. Space weather research and related ionospheric studies require broad international collaboration in sharing databases, developing analysis software and models and providing services. Reviewed is the European GNSS data basis including ionospheric services providing derived data products such as the Total Electron Content (TEC) and radio scintillation indices. Fundamental ionospheric perturbation phenomena covering quite different scales in time and space are discussed in the light of recent achievements in GNSS-based ionospheric monitoring. Thus, large-scale perturbation processes characterized by moving ionization fronts, wave-like travelling ionospheric disturbances and finally small-scale irregularities causing radio scintillations are considered. Whereas ground and space-based GNSS monitoring techniques are well developed, forecasting of ionospheric perturbations needs much more work to become attractive for users who might be interested in condensed information on the perturbation degree of the ionosphere by robust indices. Finally, we have briefly presented a few samples illustrating the space weather impact on GNSS applications thus encouraging the scientific community to enhance space weather research in upcoming years. Wed, 19 Dec 2012 23:00:00 GMT http://hdl.handle.net/2122/8573 2012-12-19T23:00:00Z http://hdl.handle.net/2122/8500 Title: Space weather challenges of the polar cap ionosphere Authors: Moen, J.; Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway; Oksavik, K.; Department of Physics and Technology, University of Bergen, P.O. Box 7803, NO-5020 Bergen, Norway; Alfonsi, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Daabakk, Y.; Department of Physics, University of Oslo, P.O. Box 1048 Blindern, NO-0316 Oslo, Norway; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: This paper presents research on polar cap ionosphere space weather phenomena conducted during the European Cooperation in Science and Technology (COST) action ES0803 from 2008 to 2012. The main part of the work has been directed toward the study of plasma instabilities and scintillations in association with cusp flow channels and polar cap electron density structures/patches, which is considered as critical knowledge in order to develop forecast models for scintillations in the polar cap. We have approached this problem by multi-instrument techniques that comprise the EISCAT Svalbard Radar, SuperDARN radars, in-situ rocket, and GPS scintillation measurements. The Discussion section aims to unify the bits and pieces of highly specialized information from several papers into a generalized picture. The cusp ionosphere appears as a hot region in GPS scintillation climatology maps. Our results are consistent with the existing view that scintillations in the cusp and the polar cap ionosphere are mainly due to multi-scale structures generated by instability processes associated with the cross-polar transport of polar cap patches. We have demonstrated that the SuperDARN convection model can be used to track these patches backward and forward in time. Hence, once a patch has been detected in the cusp inflow region, SuperDARN can be used to forecast its destination in the future. However, the high-density gradient of polar cap patches is not the only prerequisite for high-latitude scintillations. Unprecedented highresolution rocket measurements reveal that the cusp ionosphere is associated with filamentary precipitation giving rise to kilometer scale gradients onto which the gradient drift instability can operate very efficiently. Cusp ionosphere scintillations also occur during IMF BZ north conditions, which further substantiates that particle precipitation can play a key role to initialize plasma structuring. Furthermore, the cusp is associated with flow channels and strong flow shears, and we have demonstrated that the Kelvin- Helmholtz instability process may be efficiently driven by reversed flow events. Mon, 31 Dec 2012 23:00:00 GMT http://hdl.handle.net/2122/8500 2012-12-31T23:00:00Z http://hdl.handle.net/2122/7393 Title: Investigation of low latitude scintillations in Brazil within the cigala project Authors: Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bougard, B.; Septentrio N. V., Leuven, Belgium; Aquino, M.; University of Nottingham, Nottingham, United Kingdom; Galera Monico, J. F.; Univ Estadual Paulista, Faculdade de Ciências e Tecnologia, Pres. Prudente, Brazil; Willems, T.; Septentrio N. V., Leuven, Belgium; Solé, M.; Pildo Consulting S.L., Barcelona, Spain Abstract: Ionospheric scintillations are fluctuations in the phase and amplitude of the signals from GNSS satellites occurring when they cross regions of electron density irregularities in the ionosphere. Such disturbances can cause serious degradation on GNSS system performance, including integrity, accuracy and availability. The two indices internationally adopted to characterize ionospheric scintillations are: the amplitude scintillation index, S4, which is the standard deviation of the received power normalized by its mean value, and the phase scintillation index, σΦ, which is the standard deviation of the de-trended carrier phase. At low latitudes scintillations occur very frequently and can be intense. This is because the low latitudes show a characteristic feature of the plasma density, known as the equatorial anomaly, EA, for which a plasma density enhancement is produced and seen as crests on either side of the magnetic equator. It is a region in which the electron density is considerably high and inhomogeneous, producing ionospheric irregularities causing scintillations. The upcoming solar maximum, which is expected to reach its peak around May 2013, occurs at a time when our reliance on high-precision GNSS (such as GPS, GLONASS and the forthcoming GALILEO) has reached unprecedented proportions. Understanding and monitoring of scintillations are essential, so that warnings and forecast information can be made available to GNSS end users, either for global system or local augmentation network administrators in order to guarantee the necessary levels of accuracy, integrity and availability of high precision and/or safety-of-life applications. Especially when facing severe geospatial perturbations, receiver-level mitigations are also needed to minimize adverse effects on satellite signals tracking availability and accuracy. In this context, the challenge of the CIGALA (Concept for Ionospheric scintillation mitiGAtion for professional GNSS in Latin America) project, co-funded by the European GNSS Agency (GSA) through the European 7th Framework Program, is to understand the causes of ionospheric disturbances and model their effects in order to develop novel counter-measure techniques to be implemented in professional multi-frequency GNSS receivers. This paper describes the scientific advancements made within the project to understand and characterize ionospheric scintillation in Brazil by means of historical and new datasets. Wed, 31 Aug 2011 22:00:00 GMT http://hdl.handle.net/2122/7393 2011-08-31T22:00:00Z http://hdl.handle.net/2122/7272 Title: Interhemispheric comparison of GPS phase scintillation at high latitudes during the magnetic-cloud-induced geomagnetic storm of 5–7 April 2010 Authors: Prikryl, P.; Communications Research Centre Canada, Ottawa, ON, Canada; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Jayachandran, P. T.; Physics Department, University of New Brunswick, Fredericton, NB, Canada; Kinrade, J.; Department of Electronic and Electrical Engineering, University of Bath, Bath, UK; Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, Bath, UK; Ning, B.; Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; Li, G.; Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; Cilliers, P. J.; South African National Space Agency, Hermanus, South Africa; Terkildsen, M.; IPS Radio and Space Services, Bureau of Meteorology, Haymarket, NSW, Australia; Danskin, D. W.; Geomagnetic Laboratory, Natural Resources Canada, ON, Canada; Spanswick, E.; Department of Physics and Astronomy, University of Calgary, AB, Canada; Weatherwax, A. T.; Department of Physics and Astronomy, Siena College, Loudonville, NY, USA; Bristow, W. A.; Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, USA; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ngwira, C. M.; South African National Space Agency, Hermanus, South Africa; Opperman, B. D. L.; South African National Space Agency, Hermanus, South Africa Abstract: Arrays of GPS Ionospheric Scintillation and TEC Monitors (GISTMs) are used in a comparative scintillation study focusing on quasi-conjugate pairs of GPS receivers in the Arctic and Antarctic. Intense GPS phase scintillation and rapid variations in ionospheric total electron content (TEC) that can result in cycle slips were observed at high latitudes with dual-frequency GPS receivers during the first significant geomagnetic storm of solar cycle 24 on 5–7 April 2010. The impact of a bipolar magnetic cloud of north-south (NS) type embedded in high speed solar wind from a coronal hole caused a geomagnetic storm with maximum 3-hourly Kp = 8- and hourly ring current Dst =−73 nT. The interhemispheric comparison of phase scintillation reveals similarities but also asymmetries of the ionospheric response in the northern and southern auroral zones, cusps and polar caps. In the nightside auroral oval and in the cusp/cleft sectors the phase scintillation was observed in both hemispheres at about the same times and was correlated with geomagnetic activity. The scintillation level was very similar in approximately conjugate locations in Qiqiktarjuaq (75.4° N; 23.4° E CGM lat. and lon.) and South Pole (74.1° S; 18.9° E), in Longyearbyen (75.3° N; 111.2° E) and Zhongshan (74.7° S; 96.7° E), while it was significantly higher in Cambridge Bay (77.0° N; 310.1° E) than at Mario Zucchelli (80.0° S; 307.7° E). In the polar cap, when the interplanetary magnetic field (IMF) was strongly northward, the ionization due to energetic particle precipitation was a likely cause of scintillation that was stronger at Concordia (88.8° S; 54.4° E) in the dark ionosphere than in the sunlit ionosphere over Eureka (88.1° N; 333.4° E), due to a difference in ionospheric conductivity. When the IMF tilted southward, weak or no significant scintillation was detected in the northern polar cap, while in the southern polar cap rapidly varying TEC and strong phase scintillation persisted for many hours. This interhemispheric asymmetry is explained by the difference in the location of solar terminator relative to the cusps in the Northern and Southern Hemisphere. Solar terminator was in the immediate proximity of the cusp in the Southern Hemisphere where sunlit ionospheric plasma was readily convected into the central polar cap and a long series of patches was observed. In contrast, solar terminator was far poleward of the northern cusp thus reducing the entry of sunlit plasma and formation of dense patches. This is consistent with the observed and modeled seasonal variation in occurrence of polar cap patches. The GPS scintillation and TEC data analysis is supported by data from ground-based networks of magnetometers, riometers, ionosondes, HF radars and all-sky imagers, as well as particle flux measurements by DMSP satellites. Tue, 20 Dec 2011 23:00:00 GMT http://hdl.handle.net/2122/7272 2011-12-20T23:00:00Z http://hdl.handle.net/2122/7203 Title: Tackling ionospheric scintillation threat to GNSS in Latin America Authors: Veettil Sreeja, V.; Institute of Engineering Surveying and Space Geodesy, University of Nottingham, Nottingham, NG7 2RD, UK; Aquino, M.; Institute of Engineering Surveying and Space Geodesy, University of Nottingham, Nottingham, NG7 2RD, UK; Forte, B.; Institute of Engineering Surveying and Space Geodesy, University of Nottingham, Nottingham, NG7 2RD, UK; Elmas, Z.; Institute of Engineering Surveying and Space Geodesy, University of Nottingham, Nottingham, NG7 2RD, UK; Hancock, C.; Institute of Engineering Surveying and Space Geodesy, University of Nottingham, Nottingham, NG7 2RD, UK; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bougard, B.; Septentrio N. V., Greenhill Campus, Interleuvenlaan 15G, 3001 Leuven, Belgium; Galera Monico, J. F.; Faculdade de Ciencias e Tecnologia, Departamento de Cartografia, Universidade Estadual Paulista Julio de Mesquita Filho, Rua Roberto Simonsen, 305, Presidente Prudente, SP, Brazil; Wernik, A. W.; Space Research Center, Polish Academy of Sciences, ul. Bartycka18a, 00-716 Warsaw, Poland; Sleewaegen, J. M.; Septentrio N. V., Greenhill Campus, Interleuvenlaan 15G, 3001 Leuven, Belgium; Canto´, A.; Pildo Consulting, SL, Parc Tecnologic de Barcelona Nord Office A216-A220, Marie Curie 8-14, 08042 Barcelona, Spain; Da Silva, E. F.; Consultgel Consultoria em Geomatica Ltda, Rua Jose Tognoli, 238, Presidente Prudente, SP 19060-370, Brazil Abstract: Scintillations are rapid fluctuations in the phase and amplitude of transionospheric radio signals which are caused by small-scale plasma density irregularities in the ionosphere. In the case of the Global Navigation Satellite System (GNSS) receivers, scintillation can cause cycle slips, degrade the positioning accuracy and, when severe enough, can even lead to a complete loss of signal lock. Thus, the required levels of availability, accuracy, integrity and reliability for the GNSS applications may not be met during scintillation occurrence; this poses a major threat to a large number of modern-day GNSS-based applications. The whole of Latin America, Brazil in particular, is located in one of the regions most affected by scintillations. These effects will be exacerbated during solar maxima, the next predicted for 2013. This paper presents initial results from a research work aimed to tackle ionospheric scintillation effects for GNSS users in Latin America. This research is a part of the CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project, co-funded by the EC Seventh Framework Program and supervised by the GNSS Supervisory Authority (GSA), which aims to develop and test ionospheric scintillation countermeasures to be implemented in multi-frequency, multi-constellation GNSS receivers. Fri, 30 Sep 2011 22:00:00 GMT http://hdl.handle.net/2122/7203 2011-09-30T22:00:00Z http://hdl.handle.net/2122/7069 Title: L'osservatorio ionosferico in Artide e Antartide: osservazioni sperimentali e risultati scientifici Authors: De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The Italian Upper Atmosphere Observatory at polar latitude was firstly established during the Antarctic campaign 1990-1991 to support the telecommunication logistic activity of the National Program for Antarctic Research (PNRA). The Istituto Nazionale di Geofisica e Vulcanologia (INGV), formerly Istituto Nazionale di Geofisica (ING), was involved in this action as the long time experience in HF radar, ionospheric sounding and ionospheric prediction services for radio communication purposes, managing two of the most important and historical ionospheric observatories all over the world: Rome (41.8N, 12.5E) and Gibilmanna (37.9 N, 14.0 E). Since that time, starting from 1993 up to now, several research projects have been carried on focusing on the multi instruments upper atmosphere observations in Arctic and Antarctica with the aim to study the polar ionosphere in different time and space domains, contributing both to the Global Change and to the emerging Space Weather needs. Here we briefly report on the experimental activities as well on the main scientific results obtained highlighting the latest findings in the field of bipolar GNSS (Global Navigation Satellite Systems) ionospheric scintillation measurements and investigation. Thu, 31 Dec 2009 23:00:00 GMT http://hdl.handle.net/2122/7069 2009-12-31T23:00:00Z http://hdl.handle.net/2122/7037 Title: Bipolar climatology of GPS ionospheric scintillation at solar minimum Authors: Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Aquino, M.; Institute of Engineering Surveying and Space Geodesy (IESSG), University of Nottingham, Triumph Road, Nottingham NG7 2TU, United Kingdom; Dodson, A.; Institute of Engineering Surveying and Space Geodesy (IESSG), University of Nottingham, Triumph Road, Nottingham NG7 2TU, United Kingdom; Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, University of Bath, BA2 7AY, Bath, United Kingdom Abstract: High-rate sampling data of GNSS (Global Navigation Satellite Systems) ionospheric scintillation acquired by a network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers located in the Svalbard Islands, in Norway and in Antarctica have been analyzed. The aim is to describe the “scintillation climatology” of the high latitude ionosphere over both the poles under quiet conditions of the near-Earth environment. For climatology we mean to assess the general recurrent features of the ionospheric irregularities dynamics and temporal evolution on long data series, trying to catch eventual correspondences with scintillation occurrence. In spite of the fact that the sites are not geomagnetically conjugate, long series of data recorded by the same kind of receivers provide a rare opportunity to draw a picture of the ionospheric features characterizing the scintillation conditions over high latitudes. The method adopted is the Ground Based Scintillation Climatology, which produces maps of scintillation occurrence and of TEC relative variation to investigate ionospheric scintillations scenario in terms of geomagnetic and geographic coordinates, Interplanetary Magnetic Field conditions and seasonal variability. By means of such a novel and original description of the ionospheric irregularities, our work provides insights to speculate on the cause-effect mechanisms producing scintillations, suggesting the roles of the high latitude ionospheric trough, of the auroral boundaries and of the polar cap ionosphere in hosting those irregularities causing scintillations over both the hemispheres at high latitude. The method can constitute a first step towards the development of new algorithms to forecast the scintillations during space weather events. Thu, 23 Jun 2011 22:00:00 GMT http://hdl.handle.net/2122/7037 2011-06-23T22:00:00Z http://hdl.handle.net/2122/7022 Title: Optimum parameter for estimating phase fluctuations on transionospheric signals at high latitudes Authors: Forte, B.; Centre for Atmospheric Research, University of Nova Gorica, Vipavska 13, SI-5000 Nova Gorica, Slovenia; Materassi, M.; Istituto dei Sistemi Complessi, CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spalla, P.; Istituto di Fisica Applicata “Nello Carrara”, CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy Abstract: Transionospheric radio signals may experience fluctuations in their amplitude and phase due to irregularity in the spatial electron density distribution, referred to as scintillation. Ionospheric scintillation is responsible for transionospheric signal degradation that can affect the performance of satellite based navigation systems. Usually, the scintillation activity is measured by means of indices such as the normalised standard deviation of the received intensity S4 and the standard deviation of the received phase r/ typically calculated over 1 min of data. Data from a GPS scintillation monitor based on 50 Hz measurements recorded at Dirigibile Italia Station (Ny-Alesund, Svalbard), in the frame of the ISACCO project (De Franceschi et al., 2006) are used to investigate possible adoption of an alternative parameter for the estimate of phase fluctuations: i.e., the standard deviation of the phase rate of change S/. This parameter is shown to better correlate with S4 being much less detrending dependent than r/. The couple (S4, S/) should be then considered a more physical proxy of radio scintillation than the couple (S4, r/). Tue, 14 Jun 2011 22:00:00 GMT http://hdl.handle.net/2122/7022 2011-06-14T22:00:00Z http://hdl.handle.net/2122/7017 Title: Turbulent times in the northern polar ionosphere? Authors: Burston, R.; University of Bath, Bath, United Kingdom; Astin, I.; University of Bath, Bath, United Kingdom; Mitchell, C.; University of Bath, Bath, United Kingdom; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pedersen, T.; Space Vehicles Directorate, Air Force Research Laboratory, Hanscom Air Force Base, Massachusetts, USA; Skone, S.; Department of Geomatics Engineering, Schulich School of Engineering, University of Calgary, Calgary, Canada Abstract: A model is presented of the growth rate of turbulently generated irregularities in the electron concentration of northern polar cap plasma patches. The turbulence is generated by the short‐term fluctuations in the electric field imposed on the polar cap ionosphere by electric field mapping from the magnetosphere. The model uses an ionospheric imaging algorithm to specify the state of the ionosphere throughout. The growth rates are used to estimate mean amplitudes for the irregularities, and these mean amplitudes are compared with observations of the scintillation indices S4 and s by calculating the linear correlation coefficients between them. The scintillation data are recorded by GPS L1 band receivers stationed at high northern latitudes. A total of 13 days are analyzed, covering four separate magnetic storm periods. These results are compared with those from a similar model of the gradient drift instability (GDI) growth rate. Overall, the results show better correlation between the GDI process and the scintillation indices than for the turbulence process and the scintillation indices. Two storms, however, show approximately equally good correlations for both processes, indicating that there might be times when the turbulence process of irregularity formation on plasma patches may be the controlling one. Thu, 29 Apr 2010 22:00:00 GMT http://hdl.handle.net/2122/7017 2010-04-29T22:00:00Z http://hdl.handle.net/2122/7015 Title: GPS scintillation and TEC gradients at equatorial latitudes in April 2006 Authors: Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Tong, J. R.; Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY, United Kingdom; De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Bourdillon, A.; Institut d’Electronique et de Te´ le´communications de Rennes (IETR), University of Rennes, Baˆt11D, Campus de Beaulieu 35042 Rennes Cedex, France; Le Huy, M.; Vietnam Academy of Science and Technology (VAST), Institute of Geophysics, Box 411 Buudien Boho, Hanoi, Vietnam; Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY, United Kingdom Abstract: We use observations of ionospheric scintillation at equatorial latitudes from two GPS receivers specially modified for recording, at a sampling rate of 50 Hz, the phase and the amplitude of the L1 signal and the Total Electron Content (TEC) from L1 and L2. The receivers, called GISTM (GPS Ionospheric Scintillation and TEC Monitor), are located in Vietnam (Hue, 16.4 N, 107.6 E; Hoc Mon, 10.9 N, 106.6 E). These experimental observations are analysed together with the tomographic reconstruction of the ionosphere produced by the Multi-Instrument Data Analysis System (MIDAS) for investigating the moderate geomagnetic storm which occurred on early April 2006, under low solar activity. The synergic adoption of the ionospheric imaging and of the GISTM measurements supports the identification of the scale-sizes of the ionospheric irregularities causing scintillations and helps the interpretation of the physical mechanisms generating or inhibiting the appearance of the equatorial F layer irregularities. In particular, our study attributes to the turning of the IMF (Interplanetary Magnetic Field) between northward and southward direction an important role in the inhibition of the generation of spread F irregularities resulting in a lack of scintillation enhancement in the post-sunset hours. 2010 COSPAR. Published by Elsevier Ltd. All rights reserved. Mon, 16 May 2011 22:00:00 GMT http://hdl.handle.net/2122/7015 2011-05-16T22:00:00Z