Regional Ionospheric Model Research Articles

Perspectives on updated ƒoF2 maps for IRI

The separate uses of the electron-density element of the IRI for aeronomy studies and as aids to telecommunications planningand operation are briefly reviewed. In these respective roles it is confirmed that both near-real-time (‘nowcast’) and long-term smoothed models are needed. Requirements for global and regional ionosphere models are considered. The F2-region peak density, proportional to critical frequency ƒ oF22, is a key model parameter and how accurately electron densities are determined over all F-region heights is critically dependent on how well this quantity can be estimated for different places and times. Present available ƒ oF2 long-term prediction maps are described and the needs and potential for updating these are addressed. Options for the generation of nowcast regional models based on the use of the IRI are also examined.

Intercomparison of TEC obtained from the IRI model to the one derived from GPS measurements

IRI (International Reference Ionosphere) is a well-known standard of the ionosphere, but nowadays GPS permanent observations are also the base of the regional and global ionosphere models. In this paper, comparison of TEC (Total Electron Content) derived from the IRI model to the global TEC parameters derived from GPS measurements is presented. Global TEC maps show, that GPS derived ionosphere models, in opposition to the IRI, give possibilities to investigate ionospheric response to the solar activity on the global and regional scale. The comparison results show a dynamic problem at high latitudes in IRI model.

Regional and local ionospheric models based on Millstone Hill incoherent scatter radar data

Local and regional statistical models to describe Millstone Hill incoherent scatter radar observations of electron density, electron temperature and ion temperature since 1976 are developed using a bin‐fit technique. The local models generate ionospheric variations with local time, day number, and altitude from 150–1000 km. The prior day's F107 and the Ap index from the previous 3 hour period are keyed inputs to specify solar and geomagnetic activity. The regional models have a latitude coverage of 32–55° geodetic and an altitude coverage of 200–600 km. These climatology models are capable of reproducing primary ionospheric variation features seen in previous studies as well as several newly revealed features, such as the semiannual variation of electron density. They are accessible through the World Wide Web at the URL http://www.openmadrigal.org.

Wide-Area, Carrier-Phase Ambiguity Resolution Using a Tomographic Model of the Ionosphere

: A method for resolving GPS carrier-phase ambiguities exactly at hundreds of kilometers from the nearest reference site has been tested under a variety of operating conditions, with help from a computed tomography model of the ionosphere. The objective is decimeter-level (root mean square) wide area kinematic positioning in real time using broadcast orbits, and subdecimeter-level positioning using precise orbits. This work is relevant to surveying and navigation, as well as to newer real-time uses of GPS, such as monitoring of atmospheric water vapor. The paper shows how this objective could be achieved using GPS data from a wide area network to obtain a regional ionospheric model. Information from the model would then be transmitted to users so they could apply precise ionospheric corrections to their data at the approximately known locations of their rovers. Test results are summarized, including detailed results of one test involving a large-area network and an active ionosphere.

The evolution of the DGR approach to model electron density profiles

Abstract The paper describes the evolution of the “profiler” proposed by Di Giovanni and Radicella (1990) to calculate the electron density distribution with height up to the F2 peak based on the Epstein layer introduced originally by Rawer. Such model uses ionospheric characteristics routinely scaled from ionograms or models of such characteristics. Radicella and Zhang (1995) presented an improved version of the profiler able to give the electron density distribution on both the bottom and topside of the ionosphere and the ionospheric total electron content (TEC) by introducing a constant shape factor for the semi-Epstein layer above the F2 peak. This version of the DGR model was adopted by the European COST 238 action as the basis for its regional model of the ionosphere. Further efforts were made to improve the topside part of the profiler by taking into account the contribution of the plasmaspherie electron density. The three separate solutions that have been implemented are described. One of them was adopted by the European COST 251 as basis for its regional ionospheric model. Another one developed partially with European Space Agency (ESA) support has been adopted in the ESA European Geostationary Navigation Overlay System project ionospheric specifications. A modified version of this profiler has been implemented to forecast TEC values over Europe as a joint effort with the CLRC Rutherford Appleton Laboratory in the United Kingdom and the Geophysical Institute, Sofia, Bulgaria.

Easy to use Global and Regional Ionospheric Models — A Report on Approaches Used in Graz

Out of the necessity to provide quick access to ionospheric model data from various computer programs written in different languages (PASCAL, FORTRAN, IDL, etc.) we developed a “data box” approach in the following way: grid point values are calculated from an existing global or regional model and written into a data file. Good values for grid point distances are 5 degrees in latitude, 10 degrees in longitude and 10 km in height. Third order interpolation is used in all grid variables to find the model value where needed. For ray tracing applications splines can be used over the region of interest instead of simple interpolation.

Correction to “On the potential applicability of the simplified ionospheric regional model to different midlatitude areas” by Bruno Zolesi, Ljiljana R. Cander, and Giorgiana De Franceschi

Correction to “On the potential applicability of the simplified ionospheric regional model to different midlatitude areas” by Bruno Zolesi, Ljiljana R. Cander, and Giorgiana De Franceschi

On the potential applicability of the simplified ionospheric regional model to different midlatitude areas

The simplified ionospheric regional model (SIRM) was originally developed for modeling the most relevant ionospheric characteristics over Europe for radiocommunication purposes. The model, based mainly on the Fourier expansion of a reference past data set, is here adapted and applied to different sets of dishomogeneous periods of observed data coming from a sparse network of ionospheric stations in midlatitude areas, that is, northeastern North America, southeastern South America, northeast Asia, and southeast Australia. Notwithstanding the simple SIRM formulation and the reduced number of numerical coefficients involved, a good agreement has been found between modeled and observed monthly median values of ƒ0F2 and M(3000)F2 under different heliogeophysical conditions.

Enhancing differential GPS using regional ionospheric error models

Distance-dependent errors due to ionospheric refraction complicate ambiguity resolution and limit the accuracy attainable in GPS baseline determination. This paper presents an approach for modelling these errors from the observations of several permanent GPS-stations surrounding the area of interest. Regional ionospheric correction models are produced epoch-by-epoch and satellite-by-satellite. It is shown that after their application, observation residuals, fractional parts of estimated ambiguities, and single-frequency coordinate errors are greatly reduced, thus improving ambiguity resolution even under disturbed ionospheric conditions, with short observation sessions, in the case of baseline lengths of more than 10 km, and with singlefrequency and dual-frequency data.

Simplified ionospheric regional model for telecommunication applications

A simplified model of the key ionospheric characteristics of vertical incidence such as fo F2 M(3000)F2, h′F, foF1, and f0E that are used for prediction of operational parameters of HF telecommunication systems in a restricted area has been developed. The simplified ionospheric regional model (SIRM), is based upon the Fourier analysis of the monthly median values of these characteristics from seven ionospheric stations in Europe. It is shown that only 12 dominant Fourier coefficients, expressed as a function of local time (LT), solar activity and geographic latitude are sufficient to reproduce the main features of the diurnal, seasonal, and solar cycle behavior of the mid‐latitude ionosphere under median conditions. The model is in a very suitable form for digital computer calculation of the characteristics for a given position, instant of time, and solar activity.