Options
The Abdus Salam International Centre for Theoretical Physics Strada Costiera 11. I-34051, Trieste, Italy
19 results
Now showing 1 - 10 of 19
- PublicationOpen AccessA model assisted ionospheric electron density reconstruction method based on vertical TEC data ingestion(2005)
; ; ; ; ; ;Nava, B.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Coïsson, P.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Miró Amarante, G.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Azpilicueta, F.; Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Argentina ;Radicella, S. M.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy; ; ; ; A technique to reconstruct the electron density of the ionosphere starting from total electron content values has been developed using the NeQuick ionospheric electron density model driven by its effective ionization parameter Az. The technique is based on the computation of Az values for a suitable worldwide grid of points. A simple way to obtain relevant Az grids is to use global vertical Total Electron Content (TEC) maps to define for each grid point as Az value, the one that minimizes the difference between the experimental and the modeled vertical TEC. Having a global grid of Az values it is possible to compute the electron density at any point in the ionosphere using NeQuick. As a consequence, slant TEC values for specific ground station to satellite links or ionosphere peak parameter values at any location can be calculated. The results of the comparisons between experimental and reconstructed slant TEC as well as experimental and reconstructed peak parameters values indicate that the proposed reconstruction method can be used to reproduce the observed ionosphere in a realistic way.225 264 - PublicationOpen AccessComparisons of experimental topside electron concentration profiles with IRI and NeQuick models(2002)
; ; ; ;Coisson, P.; Abdus Salam ICTP, Trieste, Italy ;Radicella, S. M.; Abdus Salam ICTP, Trieste, Italy ;Nava, B.; Abdus Salam ICTP, Trieste, Italy; ; A critical part of the vertical ionospheric electron concentration profile is the region above its maximum (topside ionosphere) and many attempts have been made to model this region because of the limited experimental data available. Recently, many topside electron concentration profiles obtained with the Intercosmos-19 satellite became accessible through the Internet. The period analyzed corresponds to March 1979 - December 1980, a time interval of high solar activity. The present work describes the comparison of these profiles with the IRI and NeQuick model profiles obtained by driving the models with the values of the maximum electron concentration and its height given by the satellite.178 340 - PublicationOpen AccessThe Ionospheric Equivalent Slab Thickness: A Review Supported by a Global Climatological Study Over Two Solar Cycles(2022-06-13)
; ; ; ; ; ; ; ; ; The ionospheric equivalent slab thickness (τ ) is a parameter characterizing both the distribution of the plasma in the ionosphere and the shape of the corresponding vertical electron density profile. It is calculated as the ratio of the vertical total electron content (vTEC) to the ionospheric F2-layer electron density maximum (NmF2). Since its definition dated back in the 60s, a lot of information on the behavior of τ for different helio-geophysical conditions has been cumulated and the connection with several plasma properties has been also demonstrated. The beginning of the Global Positioning System (GPS) era in the 90s had a strong effect on the studies about τ because GPS signals allow to obtain the vTEC up to about 20000 km of altitude. Recently, τ has also found application in many data-assimilation methodologies, especially for the improvement of empirical ionospheric models based on near real-time data. All of these topics are reviewed and discussed in this paper based on the literature published in the last sixty years. Moreover, to highlight and summarize the main global climatological features of τ, in this work we selected thirty-two ionospheric stations globally distributed and co-located with ground-based Global Navigation Satellite System (GNSS) receivers, for the last two solar cycles. This allowed to collect a dataset of NmF2 and vTEC that represents the largest and most complete ever analyzed for studies concerning τ , which gave the chance to deeply investigate its spatial, diurnal, seasonal, and solar activity variations. The corresponding results are presented and discussed in the light of the existing literature.498 19 - PublicationRestrictedMidlatitude climatology of the ionospheric equivalent slab thickness over two solar cycles(2021-10)
; ; ; ; ; ; ; ; ; Themain climatological features of the ionospheric equivalent slab thickness (τ ) for the Northern hemispheremidlatitudes are analyzed. F2-layer peak electron density values recorded at three midlatitude ionospheric stations (Chilton 51.5° N, 0.6° W, U.K.; Roquetes 40.8° N, 0.5° E, Spain;Wallops Island 37.9° N, 75.5°W, USA) and vertical total electron content values from colocated ground-based Global Navigation Satellite System receivers are used to calculate a dataset of τ values for the last two solar cycles, considering only magnetically quiet periods. Results are presented both as grids of binned medians and as boxplots as a function of local time and month of the year, for different solar activity levels. Corresponding trends are first compared to those output by the midlatitude empirical model developed by Fox et al. (Radio Sci 26:429–438, 1991) and then discussed in the light of what is known so far. From this investigation, the strong need to implement an improved empirical model of τ has emerged. Both Space Weather and Space Geodesy applications might benefit from such model. Therefore, both the dataset and the methodology described in the paper represent a first fundamental step aimed at implementing an empirical climatological model of the ionospheric equivalent slab thickness. The study highlighted also that at midlatitudes τ shows the following main patterns: daytime values considerably smaller than nighttime ones (except in summer); well-defined maxima at solar terminator hours; a greater dispersion during nighttime and solar terminator hours; no clear and evident solar activity dependence.603 1 - PublicationEmbargoOn the low-latitude NeQuick topside ionosphere mismodelling: The role of parameters H0, g, and r(2023-04-17)
; ; ; ; ; This paper deals with the well-known mismodelling characterizing the NeQuick topside ionosphere at low latitudes, i.e., the fact that the model keeps the two electron density humps typical of the equatorial ionization anomaly as the altitude increases from the height of the F2-layer electron density peak, without merging them in a single peak above the geomagnetic equator as expected. This is because the NeQuick topside ionosphere modelling strongly depends on several bottomside ionosphere parameters, which causes an essential coupling between the topside and the bottomside that in many cases behave differently. This means that this kind of topside ionosphere modelling may lead to inaccurate results, as it is the maintenance at low latitudes of the electron density double hump structure in the topside as the altitude increases. On the base of some recently published results, this paper analyzes the role played by the three NeQuick scale height parameters H0, g and r in the description of the electron density above the F2 layer peak height. The results of this work pave the way for a possible solution of this low-latitude NeQuick topside ionosphere mismodelling.190 54 - PublicationRestrictedOptimizing the NeQuick Topside Scale Height Parameters Through COSMIC/FORMOSAT-3 Radio Occultation Data(2021)
; ; ; ; ; In this study, the NeQuick topside scale height empirical parameters H0, g, and r are globally retrieved, for the first time, exploiting a selected dataset of about 1.8M COSMIC/FORMOSAT-3 radio occultation topside electron density profiles. Corresponding spatial, diurnal, seasonal, as well as solar and magnetic activity median trends are studied and discussed. The results of this study could be considered as a baseline for the implementation of an improved NeQuick topside formulation. Indeed, applications relying on single-frequency Global Navigation Satellite System (GNSS) signals would benefit from an ameliorated characterization of the topside ionosphere because empirical ionospheric models, like NeQuick, are used to mitigate the detrimental effect that the ionosphere–plasmasphere system has on GNSS signals.246 3 - PublicationOpen AccessChaos and Predictability in Ionospheric Time SeriesModelling the Earth's ionosphere is a big challenge, due to the complexity of the system. Different first principle models have been developed over the last 50 years, based on ionospheric physics and chemistry, mostly controlled by Space Weather conditions. However, it is not understood in depth if the residual or mismodelled component of the ionosphere's behaviour is predictable in principle as a simple dynamical system, or is conversely so chaotic to be practically stochastic. Working on an ionospheric quantity very popular in aeronomy, we here suggest data analysis techniques to deal with the question of how chaotic and how predictable the local ionosphere's behaviour is. In particular, we calculate the correlation dimension D2 and the Kolmogorov entropy rate K2 for two one-year long time series of data of vertical total electron content (vTEC), collected on the top of the mid-latitude GNSS station of Matera (Italy), one for the year of Solar Maximum 2001 and one for the year of Solar Minimum 2008. The quantity D2 is a proxy of the degree of chaos and dynamical complexity. K2 measures the speed of destruction of the time-shifted self-mutual information of the signal, so that K2-1 is a sort of maximum time horizon for predictability. The analysis of the D2 and K2 for the vTEC time series allows to give a measure of chaos and predictability of the Earth's ionosphere, expected to limit any claim of prediction capacity of any model. The results reported here are preliminary, and must be intended only to demonstrate how the application of the analysis of these quantities to the ionospheric variability is feasible, and with a reasonable output.
44 7 - PublicationRestrictedNeQuick2 and IRI2012 models applied to mid and high latitudes, and the Antarctic ionosphere(2017-01)
; ; ; ; ; ; ;Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Nava, B.; The Abdus Salam International Centre for Theoretical Physics Strada Costiera 11. I-34051, Trieste, Italy ;Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Migoya Orue, Y.; The Abdus Salam International Centre for Theoretical Physics Strada Costiera 11. I-34051, Trieste, Italy ;Ippolito, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; ; Within the framework of the AUSPICIO (AUtomatic Scaling of Polar Ionograms and Co-operative Ionospheric Observations) project, a limited sample of ionograms recorded mostly in 2001 and 2009, and to a lesser extent in 2006–07 and 2012–15, at the ionospheric observatories of Hobart and MacquarieIsland (mid-latitude), Comandante FerrazandLivingstoneIsland(high latitude),andCasey, Mawson, Davis and Scott Base (inside the Antarctic Polar Circle (APC)) were considered to study the capability of the NeQuick2 and IRI2012 models for predicting the behaviour of the ionosphere at mid- and high latitudes and over the Antarctic area. The applicability of NeQuick2 and IRI2012 was evaluated as i) climatological models taking as input the F 10.7 solar activity index and ii) assimilative models ingesting the foF2 and hmF2 measurements obtained from the electron density profiles provided bytheAdaptiveIonosphericProfiler(AIP). Thestatisticalanalysisresults reveal thatthe bestdescription of the ionosphere’s electron density is achieved when the AIP measurements are ingested into the NeQuick2 and IRI2012 models. Moreover, NeQuick2 performance is far better than IRI2012 performance outside the APC. Conversely, the IRI2012 model performs better than the NeQuick2 model inside the APC.309 7 - PublicationOpen AccessAn Update of the NeQuick-Corr Topside Ionosphere Modeling Based on New Datasets(2024-04-18)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; A new analytical formula for H0, one of the three parameters (H0, g, and r) on which the NeQuick model is based to describe the altitude profile of the electron density above the F2-layer peak height hmF2, has recently been proposed. This new analytical representation of H0, called H0,corr, relies on numerical grids based on two different types of datasets. On one side, electron density observations by the Swarm satellites over Europe from December 2013 to September 2018, and on the other side, IRI UP (International Reference Ionosphere UPdate) maps over Europe of the critical frequency of the ordinary mode of propagation associated with the F2 layer, foF2, and hmF2, at 15 min cadence for the same period. The new NeQuick topside representation based on H0,corr, hereafter referred to as NeQuick-corr, improved the original NeQuick topside representation. This work updates the numerical grids of H0,corr by extending the underlying Swarm and IRI UP datasets until December 2021, thus allowing coverage of low solar activity levels, as well. Moreover, concerning Swarm, besides the original dataset, the calibrated one is considered, and corresponding grids of H0,corr calculated. At the same time, the role of g is investigated, by considering values different from the reference one, equal to 0.125, currently adopted. To understand what are the best H0,corr grids to be considered for the NeQuick-corr topside representation, vertical total electron content data for low, middle, and high latitudes, recorded from five low-Earth-orbit satellite missions (COSMIC/FORMOSAT-3, GRACE, METOP, TerraSAR-X, and Swarm) have been analyzed. The updated H0,corr grids based on the original Swarm dataset with a value for g = 0.15, and the updated H0,corr grids based on the calibrated Swarm dataset with a value for g = 0.14, are those for which the best results are obtained. The results show that the performance of the different NeQuick-corr models is reliable also for low latitudes, even though these are outside the spatial domain for which the H0,corr grids were obtained, and are dependent on solar activity.83 26 - PublicationOpen AccessModeling the Topside Ionosphere Effective Scale Height through In Situ Electron Density Observations by Low-Earth-Orbit Satellites(2023-06-09)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; In this work, we aim to characterize the effective scale height at the ionosphere F2-layer peak (H0) by using in situ electron density (Ne) observations by Langmuir Probes (LPs) onboard the China Seismo-Electromagnetic Satellite (CSES—01). CSES—01 is a sun-synchronous satellite orbiting at an altitude of ~500 km, with descending and ascending nodes at ~14:00 local time (LT) and ~02:00 LT, respectively. Calibrated CSES—01 LPs Ne observations for the years 2019–2021 provide information in the topside ionosphere, whereas the International Reference Ionosphere model (IRI) provides Ne values at the F2-layer peak altitude for the same time and geographical coordinates as CSES—01. CSES—01 and IRI Ne datasets are used as anchor points to infer H0 by assuming a linear scale height in the topside representation given by the NeQuick model. COSMIC/FORMOSAT—3 (COSMIC—1) radio occultation (RO) data are used to constrain the vertical gradient of the effective scale height in the topside ionosphere in the linear approximation. With the CSES—01 dataset, we studied the global behavior of H0 for daytime (~14:00 LT) and nighttime (~02:00 LT) conditions, different seasons, and low solar activity. Results from CSES—01 observations are compared with those obtained through Swarm B satellite Ne-calibrated measurements and validated against those from COSMIC—1 RO for similar diurnal, seasonal, and solar activity conditions. H0 values modeled by using CSES—01 and Swarm B-calibrated observations during daytime both agree with corresponding values obtained directly from COSMIC—1 RO profiles. Differently, H0 modeling for nighttime conditions deserves further investigation because values obtained from both CSES—01 and Swarm B-calibrated observations show remarkable and spatially localized differences compared to those obtained through COSMIC—1. Most of the H0 mismodeling for nighttime conditions can probably to be attributed to a sub-optimal spatial representation of the F2-layer peak density made by the underlying IRI model. For comparison, H0 values obtained with non-calibrated CSES—01 and Swarm B Ne observations are also calculated and discussed. The methodology developed in this study for the topside effective scale height modeling turns out to be applicable not only to CSES—01 satellite data but to any in situ Ne observation by low-Earth-orbit satellites orbiting in the topside ionosphere.368 31