ALBERT

Description: 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, rU, 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”.

Description: Published

Description: 1237-1246

Description: 2A. Fisica dell'alta atmosfera

Description: JCR Journal

Description: Under perturbed conditions caused by intense solar wind-magnetosphere coupling, the ionosphere may become highly turbulent and irregularities, typically enhancements or depletions of the electron density embedded in the ambient ionosphere, can form causing diffraction effects on the satellites signals passing through them. Such effects can cause GPS navigation errors and outages, abruptly jeopardizing its performance. Due to the morphology of the geomagnetic field, whose lines are almost vertical at high latitude, polar areas are characterized by the presence of significant ionospheric irregularities. The understanding and consequent mitigation of the effect of the scintillation phenomena is important, not only in preparation for the next solar cycle, whose maximum is expected in 2013, but also for a deeper comprehension of the dynamics of the high-latitude ionosphere. We analyze data of ionospheric scintillation over North European regions under different geomagnetic condition, to characterize the GPS scintillation phenomena under different forcing conditions of the near-Earth environment and to develop a “scintillation climatology” of the high and mid latitude ionosphere. The scintillation occurrence as a function of the magnetic local time and of the altitude adjusted corrected magnetic latitude is analysed, together with the Total Electron Content (TEC) information, to put in evidence the link between electron density gradients and ionospheric irregularities causing scintillation. The results shown herein are obtained merging observations from a network of GISTMs (GPS Ionospheric Scintillation and TEC Monitor) located over a wide range of latitudes in the Northern hemisphere. Findings confirm the associations of the occurrence of the ionospheric irregularities with the position of the auroral oval and of the ionospheric trough walls and show the contribution of the polar cap patches even under solar minimum conditions. This work could contribute to the development of forecasting tools for GPS ionospheric scintillation prediction.

Description: Unpublished

Description: Oslo - Norway

Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale

Description: open

Description: The aim of this study is to investigate the performance of a method based on improving the stochastic model to mitigate ionospheric scintillation effects on GNSS positioning by processing experimental data from GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers, which are capable of computing amplitude and phase scintillation parameters from GPS signals. We applied the approach to mitigate ionospheric scintillation effects on GNSS positioning, in conjunction with the estimation of an ionospheric parameter, considered as a stochastic process. This approach produced, in a single epoch point positioning solution, an improvement on height and 3D accuracy of the order of 31% and of 45%, respectively, when applied in a northern high latitude GISTM network under a moderate scintillation scenario. In this project we investigated the case study of 21 November 2009 using data from GISTM stations located in Antarctica and applying the same scintillation mitigation approach to a Precise Point Positioning (PPP) solution. We used an in-house software under development at Unesp. Despite the solar activity being very low, observations from ACE indicated the influence of a recurrent coronal hole high speed stream. Solar wind speed ranged from 430 to 575 km/s, with Bz fluctuations from -8 to +9 nT, generally leading to the formation of ionospheric irregularities responsible of scintillation effects on GNSS signals. Preliminary results from this case study in the PPP mode are encouraging, showing improvements of the order of 26% in 3D accuracy when applying the proposed scintillation stochastic modeling.

Description: Unpublished

Description: Buenos Aires - Argentina

Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale

Description: open

Description: The ionosphere is characterized by a highly variable degree of ionization maintained by a wide range of solar radiation and by electrons and protons originating from Sun. This plasma is under the permanent solar forcing, and interacts with the geomagnetic and interplanetary magnetic fields. The ionosphere shows diurnal and seasonal variations, together with a 11-year period variability related to the solar cycle. Sporadic events due to the intermittent behaviour of the Sun are superimposed to these quasi-periodic trends: coronal mass ejections, particle and radiation bursts (flares) yield impulsive perturbations in the Sun-Earth environment and to magnetic storms and substorms in the near-Earth region. By consequence, under these perturbed conditions coming from the outer space, the ionosphere may become highly turbulent and the probability of irregularities formation, typically enhancements or depletions of the electron density embedded in the ambient ionosphere, increases. Such irregularities cause diffraction effects, mainly due to the random fluctuations of the refractive index of the ionosphere, on the satellites signals passing through them and consequent perturbations may cause GNSS navigation errors and outages, abruptly corrupting its performance. Due to the morphology of the geomagnetic field, whose lines are almost vertical at high latitude, polar areas are characterized by the presence of significant ionospheric irregularities having scale sizes ranging from hundreds of kilometres down to a few centimetres and with highly dynamic structures. The understanding and consequent mitigation of the effect of such phenomena is important, in preparation for the next solar cycle (24), whose maximum is expected in 2012. We analyse the fluctuations in the carrier frequency of the radio waves received on the ground, commonly referred to as ionospheric amplitude and phase scintillations, to investigate the physical processes causing them and, conversely, to understand how these processes affect the operational capabilities of GNSS receivers under different geomagnetic conditions. The phase scintillations on GNSS signals are likely caused by ionospheric irregularities of scale size of hundreds of meters to few kilometers. The amplitude scintillations on GNSS signals are caused by ionospheric irregularities of scale size smaller than the Fresnel radius, which is of the order of hundreds of meters for GNSS signals, typically embedded into the patches. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham manage the same kind of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers over the European high and mid latitude regions and over Antarctica. The GISTM receivers consist of NovAtel OEM4 dual-frequency receivers with special firmware specifically able to compute in near real time the amplitude and the phase scintillation from the GPS L1 frequency signals, and the ionospheric TEC (Total Electron Content) from the GPS L1 and L2 carrier phase signals. From this ground-based network, we are able to capture the dynamics of ionospheric plasma in a wide latitudinal range, from auroral to cusp/cap regions, considering the contribution of both hemispheres, in a bi-polar framework. In particular, the stations considered in our analysis are located at Ny-Ålesund (78.9°N, 11.9°E), Hammerfest (70.7°N, 23.7°E), Brønnøysund (65.5°N, 12.2°E) in the Northern hemisphere and at Mario Zucchelli Station (74.7°S, 164.1°E) and Concordia Station (75.1°S, 123.2°E) in Antarctica. The data collection started in 2001 and is still in progress. The results, obtained by statistically analyzing a large data sample over a wide period, show the effect of ionospheric disturbances on the GNSS signals, evidencing the different contributions of the auroral and the cusp/cap ionosphere and highlighting possible scintillation scenarios over polar regions.

Description: Unpublished

Description: Padua - Italy

Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale

Description: open

Description: We analyze data of GNSS ionospheric scintillation over polar regions of both hemispheres, to characterize the scintillation phenomena under quiet conditions of the near‐Earth environment through the development of a “scintillation climatology” of the high and mid latitude ionosphere. Maps of scintillation occurrence as a function of the magnetic local time and of the altitude adjusted corrected magnetic latitude are then analysed, together with the Total Electron Content (TEC) information, to put in evidence the strong link between the electron density gradients and the ionospheric irregularities causing scintillation. The results shown herein are obtained by merging observations from a network of GISTMs (GPS Ionospheric Scintillation and TEC Monitor) located over a wide range of latitudes in the Northern hemisphere and in Antarctica. Data samples refers to a period of very quiet conditions of the geospace in the last solar cycle. Findings confirm the association of the occurrence of the ionospheric irregularities with respect to the electron density gradients in correspondence of the boundaries of the auroral oval and of the ionospheric trough walls and show the contribution of the polar cap patches even under solar minimum conditions. This work aims to contribute to the development of nowcasting and forecasting tools for GNSS ionospheric scintillation prediction.

Description: Unpublished

Description: Buenos Aires - Argentina

Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale

Description: open

Description: Under perturbed conditions coming from the outer space, the ionosphere may become highly turbulent and small scale (from centimeters to meters) irregularities, typically enhancements or depletions of the electron density embedded in the ambient ionosphere, can form causing diffraction effects on the satellites signals passing through them. Such effect can abruptly corrupt the performance of the positioning systems affecting, in turn, the awareness and safety of the modern devices. In this paper we analyze data of ionospheric scintillation in the latitudinal range 57°- 88° N during the period October, November and December 2003 as a first step to develop a “scintillation climatology” over the Northern Europe. The behavior of the scintillation occurrence as function of the magnetic local time and of the corrected magnetic latitude is investigated to characterize the scintillation conditions. The Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the Institute of Engineering Surveying and Space Geodesy (IESSG) of the University of Nottingham manage the same kind of GISTM (GPS Ionospheric Scintillation and TEC monitor) receivers over the European middle and high latitude regions. The results here shown and obtained merging observations from three GISTM, highlight also the possibility to investigate the dynamics of irregularities causing scintillation by combining the information coming from auroral to cusp latitudes. The findings, even if at a very preliminary stage, are here presented also in the frame of possible Space Weather implications.

Description: Unpublished

Description: Vienna - Austria

Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale

Description: open

Description: The global coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has made the development of a vaccine a top biomedical priority. In this study, we developed a series of DNA vaccine candidates expressing different forms of the SARS-CoV-2 spike (S) protein and evaluated them in 35 rhesus macaques. Vaccinated animals developed humoral and cellular immune responses, including neutralizing antibody titers at levels comparable to those found in convalescent humans and macaques infected with SARS-CoV-2. After vaccination, all animals were challenged with SARS-CoV-2, and the vaccine encoding the full-length S protein resulted in 〉3.1 and 〉3.7 log10 reductions in median viral loads in bronchoalveolar lavage and nasal mucosa, respectively, as compared with viral loads in sham controls. Vaccine-elicited neutralizing antibody titers correlated with protective efficacy, suggesting an immune correlate of protection. These data demonstrate vaccine protection against SARS-CoV-2 in nonhuman primates.