Ionospheric topside models compared with experimental electron density profiles

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

Comparing TOPEX TEC measurements with IRI predictions

TEC values obtained from TOPEX satellite were compared with the International Reference Ionosphere (IRI) 2001 model estimates. The present work also shows results of the IRI model with the option of a new topside electron density distribution (NeQuick model). TOPEX TEC measurements, which include years of high and middle to low solar activity (2000 and 2004), were analyzed by binning the region covered by the satellite (±66°) every five degrees of modip. In general, there is good agreement between IRI predictions and Topex measurements. Cases with large disagreements are observed at low and high latitudes during high solar activity. Comparing the model predictions using the default IRI2001 model and the NeQuick topside option show that the default IRI 2001 version represents the observed data in a more realistic way, but appears to be less reliable at high and low latitudes in some cases.Fil: Migoya Orue, Yenca Olivia. Universidad Tecnológica Nacional; ArgentinaFil: S.M. Radicella. Aeronomy and Radiopropagation Laboratory; ItaliaFil: P. Coïsson. Aeronomy and Radiopropagation Laboratory; ItaliaFil: Ezquer, Rodolfo Gerardo. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Ionósfera; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; ArgentinaFil: Nava, B.. Aeronomy and Radiopropagation Laboratory; Itali

Experimental insight into the magnetic and electrical properties of amorphous Ge1-xMnx

We present a study of the electrical and magnetic properties of the amorphous Ge1-xMnx.DMS, with 2% ≤ x ≤ 17%, by means of SQUID magnetometry and low temperature DC measurements. The thin films were grown by physical vapour deposition at 50°C in ultrahigh vacuum. The DC electrical characterizations show that variable range hopping is the main mechanism of charge transport below room temperature. Magnetic characterization reveals that a unique and smooth magnetic transition is present in our samples, which can be attributed to ferromagnetic percolation of bound magnetic polarons

Comparison of analytical functions used to describe topside electron density profiles with satellite data

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

Effects of gradients of the electron density on Earth-space communications

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

Validation of a method for ionospheric electron density reconstruction by means of vertical incidence data during quiet and storm periods

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

A model assisted ionospheric electron density reconstruction method based on vertical TEC data ingestion

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

low latitude ionospheric effects of major geomagnetic storms observed using topex tec data

Abstract. Low latitude ionospheric effects of two major geomagnetic storms are analysed using TOPEX TEC data for specific satellite passes. The storms are the one that started on 15 July 2000 and the one that started on 8 November 2004. The variation of vertical TEC as a function of latitude along the satellite passes during day-time mostly in the region of the Pacific Ocean have been analysed comparing the storm period with quiet conditions. It has to be noted that for obvious reasons the TEC behaviour over this region cannot be observed using ground-based instruments but TOPEX data give a reasonable overall view of the region covered by the Equatorial Anomaly, just as the storms were developing. The performance of vertical TEC obtained from GPS derived TEC of global ionospheric maps (GIMs) are compared with the TOPEX data in order to determine their accuracy when storms of this type take place. The results show that the Equatorial Anomaly TEC peaks move towards the poles by several degrees and increase their intensity with respect to the quiet conditions behaviour for both storms that occurred at different seasons and solar activity level. This behaviour is not well represented by the maps of the different GIMs used in this study. The rate of change obtained from TOPEX TEC were computed to look for vertical TEC spatial gradients variations

Effects of gradients of the electron density on Earth-space communications

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

Vulnerability Assessment of Italian Rationalist Architecture: Two Case Studies

The work is focused on the structural vulnerability assessment of two historical constructions, chosen as case-studies representative of a recurrent typology of Italian rationalist architecture, dating back to the Fascist period, often hosting public offices. Both examined buildings have similar dimensions and geometry, being characterised by five/six storeys and by an almost square plan with an inner courtyard, and are located in EmiliaRomagna, in zones of medium seismic hazard. The older building, dating back to the Thirties and located in Ravenna, has a mixed masonry-reinforced concrete structure, while the other one, built in the late forties and located in Parma, is characterised by an unreinforced masonry structure with some limited reinforced concrete elements. For the vulnerability assessment of the two buildings, a multi-disciplinary approach was followed, including the historical documents search concerning both the investigated buildings and the surrounding areas, the detailed geometrical and structural survey, the identification of materials, and in situ and laboratory tests to evaluate materials mechanical properties. These activities allowed reaching an adequate level of knowledge about the present conditions of the structures and their critical deficiencies. This knowledge path is not only necessary for the subsequent numerical analyses, but is also important as it allows targeting the repairing interventions, possibly reducing their final costs, in agreement with the “minimum intervention” approach for heritage buildings