Occurrences of Regional Strong E s Irregularities and Corresponding Scintillations Characterized Using a High-Temporal-Resolution GNSS Network (original) (raw)
Related papers
2013
The rate of TEC index (ROTI) is a measurement that characterizes ionospheric irregularities. It can be obtained from standard GNSS dual-frequency phase data collected using a geodetic type of GNSS receiver. By processing GPS data from ground-based networks of International GNSS Service and Continuously Operating Reference Station (CORS), ROTI maps have been produced to observe global and regional scintillation activities. A major mid-latitude scintillation event in the contiguous United States is reported here that was captured in ROTI maps produced using CORS GPS data collected during a space weather storm. The analyses conducted in this work and previously by another group indicate that ROTI is a good occurrence indicator of both amplitude and phase scintillations of GPS L-band signals, even though the magnitudes of ROTI, S4, and sigma(sub phi) can be different. For example, our analysis indicates that prominent ROTI and the L1 phase scintillation (sigma(sub phi)) are well correla...
Climatology of GNSS ionospheric scintillation at high latitudes
2009
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. 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 kilometers down to a few centimeters and with highly dynamic structures. The understanding of the effect of such phenomena is important, not only in preparation for the next solar cycle (24), whose maximum is expected in 2012, but also for a deeper comprehension of the dynamics of the high-latitude ionosphere. We analyze 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. 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. 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.
2020
The Earth's Ionosphere frequently disrupts Space to Earth communication such as Global Navigation Satellite Systems (GNSS) and international telecommunications critical to a modern technological world. As human society has become heavily dependent on GNSS services, timely and accurate space weather characterization and forecasts are needed. This is particularly true at mid-latitudes, such as the contiguous United States (US), where population density is greatest, hence technological interruptions most impactful. As a conducting layer, the ionosphere delays radio signals by refraction, and in some circumstances causes wave interference due to diffraction off density irregularities. Ionospheric refraction can be used to estimate the path-integrated plasma density, referred to as the Total Electron Content (TEC). Maps of TEC constructed from ground-based receiver networks provide a global and time-dependent image of ionospheric dynamics. While refraction scales with radiofrequency and dual-frequency GNSS receivers routinely compensate for this effect. Radio receivers, including GNSS monitors, are being used to monitor and quantify these effects, producing climatological maps of ionospheric irregularities. However, vi
GPS observations of medium-scale traveling ionospheric disturbances over Europe
Annales Geophysicae, 2013
Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70 % at lower latitudes over Europe, whereas it is approximately 45 % at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50 % at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E-and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.
Detection of Low-Latitude Ionospheric Irregularities From GNSS Observations
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015
The equatorial and low-latitude regions, from 20 • N to 20 • S, frequently experience strong ionospheric disturbances which affect the signals from global navigation satellite systems (GNSS). The satellite signals propagating through ionospheric irregularities undergo scattering and dispersion, resulting in the amplitude and phase scintillation of the signal. The signals from some of the satellites may encounter plasma irregularities along their path, causing them to be corrupted. In this paper, a fast Fourier transform (FFT)-based irregularity detecting algorithm called FFT averaging ratio (FAR) algorithm and an enhanced FAR algorithm have been implemented as postprocessing techniques to identify the satellite PRNs which were corrupted by the ionospheric irregularities. GNSS data was collected using a Novatel GPStation-6 receiver located at Koneru Lakshmaiah University (16 • 10 N/80 • 62 E) in Guntur, Andhra Pradesh, in the southern part of India during the solar maximum year of 2013. FAR algorithm detected 991 events and enhanced FAR detected 954 events in 2013. Most of the disturbances were detected in the months of vernal equinox. The number of disturbances detected in the autumnal equinox months was small due to missing data over 46% of the total number of days in September and October. The summer solstice months showed very few events. A large number of disturbances were detected during the winter solstice month of December which is 43% higher than that of July. The outcome of this research work is compliant with the existing ionospheric climatological model for low-latitude regions.
Ionospheric scintillations by sporadic-E irregularities over low latitude
2007
The observations of daytime ionospheric scintillation are attributed to E-region irregularities at high and equatorial latitudes. In this paper, VHF amplitude scintillations recorded during the daytime period from 1991 to 1999 at low latitude station Varanasi (geomag. lat. = 14 • 55 N, long. = 154 0 E) are analyzed to study the behaviour of sporadic-E irregularities during the active solar and magnetic periods. The daytime digital scintillation data have been analyzed to study some important parameters of scintillation producing sporadic-E irregularities like auto-correlation function, power spectral densities, signal de-correlation time etc. We report the behaviour of these parameters under weak and strong scintillation conditions. The results are also discussed in the light of recent works.
Remote Sensing
The storm onset on 7 September 2017, triggered several variations in the ionospheric electron density, causing severe phase fluctuations at polar latitudes in both hemispheres. In addition, although quite rare at high latitudes, clear amplitude scintillations were recorded by two Global Navigation Satellite System receivers during the main phase of the storm. This work attempted to investigate the physical mechanisms triggering the observed amplitude scintillations, with the aim of identifying the conditions favoring such events. We investigated the ionospheric background and other conditions that prevailed when the irregularities formed and moved, following a multi-observations approach. Specifically, we combined information from scintillation parameters and recorded by multi-constellation (GPS, GLONASS and Galileo) receivers located at Concordia station (75.10°S, 123.35°E) and SANAE IV base (71.67°S, 2.84°W), with measurements acquired by the Special Sensor Ultraviolet Spectrograp...
Ionospheric scintillation calculations based on in situ irregularity spectra
Radio Science, 1977
Recent results from rocket, satellite, and radar experiments have greatly increased our understanding of equatorial spread-F and its effects upon communication systems. In situ measurements have shown that the typical irregularity spectrum is a power law with a one-dimensional index of -2. Previous applications of scintillation theory to such irregularities have utilized an anisotropic power law, in an effort to model elongation of irregularities along the magnetic field, and have found approximate solutions for the scintillation index S 4, the rms phase deviation, and the characteristic scale size of the scintillation spectrum. We present here rigorous closed-form solutions for these quantities which are valid to the extent that weak scattering thin screen theory allows. In addition we introduce a second "hybrid" form for irregularity spectra which is gaussian along the magnetic field and a power law in the perpendicular plane. The index is chosen in such a way that a one-dimensional spectrum obtained on a spacecraft whose velocity •s makes a reasonable angle to the magnetic field and varies as k -2. Such a spectrum is introduced since it seems likely that at least at long wavelengths equatorial spread-F is an interchange instability and that the density variation along /• is that of the zero-order density variation. One-dimensional spectra for small angles between •s and/• would hence be steeper than k -2 at intermediate k values, a result consistent with some in situ measurements. If particle precipitation is responsible for high latitude irregularities at long wavelengths, the hybrid spectrum might also be more appropriate for their characterization.
Journal of Space Weather and Space Climate
We analyze the amplitude scintillation on L-band signals over San Miguel de Tucumán (Argentina), focusing on the multi-scale variability and speculating on the possible relationship between forcing factors from the geospace and the ionospheric response. The site is nominally located below the expected position of the southern crest of the Equatorial Ionospheric Anomaly (EIA). For this scope, we concentrate on the period 1–31 March 2011, during which one minor and one moderate storm characterize the first half of the month, while generally quiet conditions of the geospace stand for the second half. By leveraging on the Adaptive Local Iterative Filtering (ALIF) signal decomposition technique, we investigate the multi-scale properties of Global Navigation Satellite Systems (GNSS) amplitude scintillation and helio-geophysical parameters, looking for possible cause-effect mechanisms relating the former to the latter. Namely, we identify resonant modes in the Akasofu (ε) parameter as like...