B. Zolesi

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.

Ionospheric Prediction and Forecasting

Ionospheric Structure.- Ionospheric measurements for prediction and forecasting. Ionospheric prediction for radio propagation purposes.- Total electron content modelling and mapping.- Ionospheric forecasting.- Prediction and forecasting user manual.

Monitoring and Forecasting the Ionosphere Over Europe: The DIAS Project

Knowledge of the state of the upper atmosphere, and in particular its ionospheric part, is very important in several applications affected by space weather, especially the communications and navigation systems that rely on radio transmission. To better classify the ionosphere and forecast its disturbances over Europe, a data collection endeavour called the European Digital Upper Atmosphere Server (DIAS) was initiated in 2004 by a consortium formed around several European ionospheric stations that transmit in real-time ionospheric parameters automatically scaled. The DIAS project is a collaborative venture of eight institutions funded by the European Commission eContent Programme. The project seeks to improve access to digital information collected by public European institutes and to expand its use. The main objective of the DIAS project is to develop a pan-European digital data collection describing the state of the upper atmosphere, based on real-time information and historical data collections provided by most of the operating ionospheric stations in Europe. Various groups of users require data specifying upper atmospheric conditions over Europe for nowcasting and forecasting purposes. The DIAS system is designed to distribute such information. The successful operation of DIAS is based on the effective use of observational data in operational applications through the development of new added-value ionospheric products and services that best fit the needs of the market. DIAS is a unique European system, and its continuous operation will efficiently support radio propagation services with the most reliable information. DIAS began providing services to users in August 2006. The Need for Accurate Ionospheric Products Radio frequency communications and satellite positioning and navigation systems are applications most affected by ionospheric disturbances. Such disturbances can cause drastic and large-scale changes in the usable ranges of high frequency (HF) or below HF bands affecting standard ground-to-ground and submarine communication systems. The characteristics of an ionospheric propagation channel, whether it is HF or transionospheric frequencies, are highly variable on timescales ranging from a few seconds to the 11-year solar cycle. Even during its quietest periods, the Sun produces electromagnetic radiation and solar wind, both of which can affect a variety of geomagnetic and ionospheric phenomena, which in turn affect radio waves propagating through the ionosphere. Hence day-to-day and hour-to-hour changes in propagation channel characteristics can occur.

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.

Estimating the vertical electron density profile from an ionogram: on the passage from true to virtual heights via the target function method

[1] The paper describes a new simple method of calculation by which an artificial ionogram trace is obtained from a given vertical electron density profile. The method is discussed in terms of the target function method used by Autoscala to output a reliable estimation of the real vertical electron density profile associated to the recorded ionogram. This new approach solves the issue of the pole in the calculation of virtual height, and consequently eliminates all the divergence phenomena that sometimes characterized the artificial ionogram traces computed by Autoscala. In contrast to the POLAN procedure, the technique introduced in this paper to pass from true to virtual heights is not based on any arithmetical operation related to changes of integration variables. Since the target function method on which Autoscala is based requires that the passage from a vertical electron density profile to an artificial ionogram be repeated a very large number of times, this new calculation procedure is advantageous in terms of speeding up the associated processing time.

Validation of GPS Ionospheric Radio Occultation results onboard CHAMP by Vertical Sounding Observations in Europe

Ionospheric radio occultation (IRO) measurements have a big potential for monitoring the ionospheric behavior on global scale for now- and forecasting the ionospheric impact on radio systems. In this article we validate the retrieved vertical electron density profiles (EDPs) derived from IRO measurements onboard CHAMP by using vertical sounding measurements at five European vertical sounding stations — Athens, Dourbes, Juliusruh, Rome and Tortosa. Since first IRO measurement onboard CHAMP in April 2001, more than 70000 electron density profiles have been retrieved by a model assisted technique so far. The comparison of IRO retrieved EDPs with ionosonde profiles obtained from the above mentioned stations will be discussed.

European ionospheric forecast and mapping

Abstract A new technique is developed for forecasting and instantaneous mapping of the ionospheric parameters over Europe, based on analytical presentation of the mapped quantities. The diurnal and seasonal variations of the ionospheric foF2 and M(3000)F2 parameters are represented by a modified version of the regional model ISIRM adjusted to the past measured data. An autoregressive extrapolation of the data from the past month enables the 15-day-ahead forecast of the quiet ionospheric distribution to be performed. In addition, the short-term variations due to geomagnetic activity are defined as a plane surface superimposed on the quiet distribution. This correction is obtained by two plane characteristics as functions of the geomagnetic three-hour Kp index. In this way the 24-hour forecast can be obtain during quiet as well as disturbed ionospheric conditions. The corresponding EIFM software provides a variety of options to perform the short-term forecast depending on availability of the measured ionospheric data and predicted Kp values.

On the variability within-the-hour and from hour-to-hour of the F-region characteristics above Rome

Abstract The statistical analysis of daily 5-minutes f 0 F2, M(3000)F2 and MUF values, measured at Rome, leads to interesting results regarding the variability within-the-hour and from hour-to-hour of these parameters. There is evidence that the relative deviations of the 5-minutes values of these characteristics from their corresponding nearest hourly daily value are less than ±0.10 during the post-dawn morning hours up to sunset whereas around dawn and sunset hours they are larger. An “intrinsic” fluctuation of more than 3% is always present.

The SWILM approach for regional long-term modelling of middle/high latitude ionosphere

Abstract The Space - Weighted Ionospheric Local Model, SWILM, is an alternative approach developed for the regional long-term mapping and modelling of the plasma frequency of the F2 layer, foF2, and the M(3000)F2 propagation factor. This model is based on the past monthly medians data from several vertical sounding stations in the region of interest and on the R12 index as indicator of the solar activity. In order to allow users to switch to a planetary scale, a good merge with the global ITU-R (Radiocommunication Sector of the International Telecommunication Union) model is also provided by SWILM with acceptable gradients at the borders of the region. In this paper the basic formulation of the model will be given and the results will be shown as obtained by comparing SWILM and ITU-R performances for mapping and modelling the fbF2 and the M(3000)F2 over a geographic area ranged between 35°–70°N and 10°W–60°E.

REGIONAL MODELLING AND MAPPING OF THE IONOSPHERIC CHARACTERISTIC PARAMETERS BY SPHERICAL CAP HARMONIC EXPANSION

Abstract The method of Spherical Cap Harmonic Analysis, SCHA /1/, has been applied to the critical frequency of the F 2 layer observed at several European vertical incident ionospheric stations. The aim was the regional mapping and modelling of this parameter in Europe. To make it possible a spherical cap including Europe, centred at 50°N, 14°E with the half-angle of 20° has been considered. The model is based on the expansion of Fourier longitudinal series and Legendre colatitudinal functions as the orthogonal basis functions over the caplike region of interest. It has been found that for the modelling of the f 0 F 2, a SCH model with only 9 coefficients (K up to 2) well portrays its basic features.