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The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy
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- PublicationOpen AccessEffects of gradients of the electron density on Earth-space communications(2004)
; ; ; ; ; ;Radicella, S. M.; The Abdus Salam International Centre for Theoretical Physics (ICTP7, Aeronomy and Radiopropagation Laboratory, Trieste, Italy ;Nava, B.; The Abdus Salam International Centre for Theoretical Physics (ICTP7, Aeronomy and Radiopropagation Laboratory, Trieste, Italy ;Coïsson, P.; The Abdus Salam International Centre for Theoretical Physics (ICTP7, Aeronomy and Radiopropagation Laboratory, Trieste, Italy ;Kersley, L.; University of Wales, Aberystwyth, U.K. ;Bailey, G. J.; University of Sheffield, U.K.; ; ; ; This paper is a review of the main results achieved in the framework of COST 271 Action Working Group 4, under the activities of the Work Package 4.4. The first topic treated deals with the influence of ionospheric space and time gradients in the slant to vertical and vertical to slant ionospheric delay conversion when the thin shell approximation of the ionosphere is assumed and with the effects of geomagnetic activity on the errors that this conversion introduces. The second topic is related to the comparison of ionospheric topside models with experimental electron density profiles to check the ability of the models to reproduce the observed topside shape and characteristics that determine the electron density gradients. The analysis that has been done allows pointing out the changes needed to improve the models. Finally a third topic covers a model simulation study of the total electron content that can be encountered in GPS-to-geostationary satellite ray paths. It takes into account that the propagation paths for such satellite-to-satellite links are very long and they have the potential to intersect regions of the ionised atmosphere where the electron density is high when the geometry is close to eclipse.251 722 - PublicationOpen AccessValidation of a method for ionospheric electron density reconstruction by means of vertical incidence data during quiet and storm periods(2005)
; ; ; ; ;Miró Amarante, G.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Radicella, S. M.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;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; ; ; A preliminary validation of the technique developed using the NeQuick ionospheric model and the «effective ionization parameter» Az, based on vertical total electron content data ingestion, was carried out in a previous study. The current study was performed to extend the analyzed conditions and confirm the results. The method to validate this technique is based on a comparison between hourly F2 peak values measured with Vertical Incidence (VI) soundings and those calculated with the new technique. Data corresponding to different hours and seasons (equinox, summer solstice, and winter solstice) during the period 2000-2003 (high and medium solar activity conditions) were compared for all available ionosonde stations. The results show a good agreement between foF2 and hmF2 values obtained with the new technique and measurements from vertical incidence soundings during quiet and storms conditions.247 266 - PublicationOpen AccessComparison of analytical functions used to describe topside electron density profiles with satellite data(2005)
; ; ; ; ;Fonda, C.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Coïsson, P.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Nava, B.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Radicella, S. M.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy; ; ; Electron density models of the ionosphere use different analytical formulations for the electron density vertical profile in the topside. The present paper compares some single-layer topside analytical descriptions (Chapman, Epstein, modified Epstein used in the NeQuick model) with experimental topside profiles obtained from measurements of IK19 and ISIS2 satellites. The limits of height range and shape for each formulation are described and analyzed and suggestions for the use of multiple layers solution to reproduce experimental results are given.241 740 - PublicationOpen AccessOn the link between the topside ionospheric effective scale height and the plasma ambipolar diffusion, theory and preliminary results(2020-10-16)
; ; ; ; ; ; ; Over the years, an amount of models relying on effective parameters were implemented in the challenging issue of the topside ionosphere description. These models are based on different analytical functions, but all of them depend on a parameter called effective scale height, that is deduced from topside electron density measurements. As their names state, they are effective in reproducing the topside electron density profile only when applied to the analytical function used to derive them. Then, in principle, they do not have any physical meaning. It is the goal of this paper to mathematically link the effective scale height modeled through the Epstein layer to the vertical scale height theoretically deduced from the plasma ambipolar diffusion theory. Firstly, effective and theoretical scale heights are linked through a mathematical relation by showing that they tend to each other in the topside ionosphere. Secondly, their connection is preliminarily demonstrated by calculating effective scale height values from the entire COSMIC/FORMOSAT-3 radio occultation dataset. Thirdly, a possible connection between the vertical gradient of the topside scale height (as obtained by COSMIC/FORMOSAT-3 satellites) and the electron temperature (as obtained by ESA Swarm B satellite) is studied by highlighting corresponding similarities in the diurnal, seasonal, solar activity, and latitudinal variability.213 17 - PublicationOpen AccessValidation of the IRI-2020 topside ionosphere options through in-situ electron density observations by low-Earth-orbit satellites(2024)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The topside ionosphere extends from the F2-layer peak, where the electron density reaches its absolute maximum in the ionosphere, to the overlying plasmasphere and magnetosphere. In the topside ionosphere, the electron density decreases with height with a vertical variation rate strongly dependent on height itself. The last version of the International Reference Ionosphere (IRI) model, i.e., IRI-2020, describes this complex behavior through four topside options based on different sub-models (i.e., options) developed from the 1970s to the present. All these options have in common the F2-layer peak as an anchor point, while they differ in their topside electron density profile and/or plasma effective scale height formulations. In this work, we perform a validation of the accuracy of the four IRI-2020 topside options based on the comparison against in-situ electron density observations by Gravity Recovery and Climate Experiment (GRACE), Ionospheric Connection Explorer (ICON), and Defense Meteorological Satellite Program (DMSP) F15 low-Earth-orbit satellites. Datasets used in this study encompass observations recorded from 1999 to 2022, covering different diurnal, seasonal, and solar activity conditions, on a global basis and for the height range 400–850 km above the ground. The nearly two solar cycles dataset facilitated the evaluation of IRI-2020 topside options ability to reproduce the spatial and time variations of the topside ionosphere for different solar activity conditions. The weaknesses and strengths of each IRI-2020 topside option are highlighted and discussed, and suggestions on how to improve the modeling of the challenging topside ionosphere region within the IRI model are provided for future reference.43 21 - PublicationOpen AccessOn the Analytical Description of the Topside Ionosphere by NeQuick: Modeling the Scale Height Through COSMIC/FORMOSAT-3 Selected Data(2020-05)
; ; ; ; ; ; ; ; ; ; ; The analytical description of the topside ionosphere included in the NeQuick model is studied in detail. First, the modeled scale height behavior is analyzed at infinity and for the lowest part of the topside region; in the latter case, the analysis is done through an expansion in Taylor series near the F2-layer peak. Moreover, the significant influence of the three NeQuick topside parameters in the modeling of the topside profile is investigated in detail and, in particular, it is shown that for the lowest part of the topside the model assumes a linearly increasing trend of the topside scale height. Second, the topside formulation is inverted to derive a fully analytical expression of the topside scale height as a function of the electron density and F2-layer peak parameters. This expression has been applied to a selected and very reliable dataset of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)/FORMOSAT-3 radio occultation profiles. Statistical analyses strongly support the hypothesis embedded in NeQuick regarding the linear trend of the topside scale height for the lowest part of the topside.195 20 - 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 AccessIonospheric topside models compared with experimental electron density profiles(2005)
; ; ;Coïsson, P.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy ;Radicella, S. M.; The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy; Recently an increasing number of topside electron density profiles has been made available to the scientific community on the Internet. These data are important for ionospheric modeling purposes, since the experimental information on the electron density above the ionosphere maximum of ionization is very scarce. The present work compares NeQuick and IRI models with the topside electron density profiles available in the databases of the ISIS2, IK19 and Cosmos 1809 satellites. Experimental electron content from the F2 peak up to satellite height and electron densities at fixed heights above the peak have been compared under a wide range of different conditions. The analysis performed points out the behavior of the models and the improvements needed to be assessed to have a better reproduction of the experimental results. NeQuick topside is a modified Epstein layer, with thickness parameter determined by an empirical relation. It appears that its performance is strongly affected by this parameter, indicating the need for improvements of its formulation. IRI topside is based on Booker's approach to consider two parts with constant height gradients. It appears that this formulation leads to an overestimation of the electron density in the upper part of the profiles, and overestimation of TEC.210 461 - 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 AccessIonospheric equivalent slab thickness ingestion into the NeQuick model(2023)
; ; ; ; ; ; ; ; ; ; ; The ionospheric equivalent slab thickness (𝜏), defined as the ratio of the vertical total electron content (vTEC) to the ionospheric F2‑layer electron density maximum (NmF2), is a parameter providing useful information on the shape of the vertical electron density profile. However, the use of this information is of difficult practical application in empirical ionosphere models, such as the NeQuick, because by design they do not explicitly include 𝜏 as a modelling parameter. In this work, we investigated the opportunity of using measured 𝜏 values to improve the empirical modelling of the ionosphere vertical electron density profile by NeQuick. Measured 𝜏 values were obtained through NmF2 observations and vTEC measurements obtained between 2001 and 2019 by an ionosonde and a ground-based GNSS receiver, respectively, co‑located at Rome ionospheric station (41.8° N, 12.5° E; Italy). NeQuick 𝜏 was obtained as the ratio between modelled NmF2 and vTEC values, the latter calculated by integration of the vertical profile. As a first step, 𝜏 values modelled by NeQuick were compared with corresponding values measured at Rome station to highlight diurnal, seasonal, and solar activity differences. Then, measured 𝜏 values were ingested in NeQuick through a three-parameter assimilation procedure which first assimilates F2‑layer peak characteristics to constrain the F2‑layer anchor point, and then assimilates vTEC to optimize the F2‑layer shape through the NeQuick F2‑layer thickness parameter, namely B2bot. The assimilation procedure provides information on how the NeQuick B2bot has to be modified to match measured 𝜏 values, and then on how the shape of the F2‑layer profile has to be changed accordingly. Our results highlight that, in many cases, the NeQuick B2bot has to be increased to match observations, which has implications on the modelling of the NeQuick bottomside and topside effective scale heights.134 31