S.M. Radicella

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.

AN ANALYTICAL MODEL OF THE ELECTRON DENSITY PROFILE IN THE IONOSPHERE

Abstract Electron density height profiles and their first derivatives with height from the E region to the peak of the F2 layer, as calculated by inversion of ionogram traces, are reproduced with good accuracy by formally identical simple analytical functions, different from those used by other authors. The resulting electron density profile is continuous and without gradient discontinuities in the fist and second derivatives with height. The function chosen is such that the entire profile from the E to the F2 layer, can be calculated by knowing only the values of the electron density and height of: The peak of the F2 layer, the point of inflection below that peak, the maximum or point of inflection in the F1 layer, and the peak of the E region. It is shown that the empirical relations in /1/, found between the coordinates of a characteristic point below the F2 layer peak and ionospheric parameters read in the ionograms, can also be derived from the analytical function adopted to describe the electron density profile.

A family of ionospheric models for different uses

Abstract Empirical models of three dimensional electron density distributions in the ionosphere have been constructed for global as well as regional use. The models differ by their degree of complexity and calculation time and therefore have different uses. All are based on “ionogram parameter” (critical frequencies foE, foF1, foF2 and the F2 region transfer parameter M(3000)F2). The models allow the use of global or regional maps for foF2 and M(3000)F2 and use built-in formulations for foE and foF1. Update (instantaneous mapping / nowcasting) versions exist which take foF2 and M(3000)F2 or F2 region peak height and electron density as input. The ground to F2 layer peak part of the profile is identical for all three models and is based on an Epstein formulation. The “quick calculationr” model NeQuick uses a simple formulation for the topside F layer, which is essentially a semi-Epstein layer with a thickness parameter which increases linearly with height. The “ionospheric model” COSTprof is the model which was adopted by COST 251 in its regional “monthly median” form. Its topside F layer is based on O + -H + diffusive equilibrium with built-in maps for three parameters, namely the oxygen scale height at the F2 peak, its height gradient and the O + -H + transition height. The “ionosphere-plasmasphere” model NeUoG-plas uses a magnetic field aligned “plasmasphere” above COSTprof Typical uses of the models and comparison among them are discussed.

EQUATORIAL F2-PEAK PARAMETERS,IN THE IRI MODEL

We have used measurements of an ionosonde station near the magnetic equator in Ouagadougou, Burkina Faso to evaluate the ability of the International Reference Ionosphere (IRI) model to correctly represent ionospheric F2 peak parameters in this region. The data represent conditions of high and low solar activity. Comparing the URSI and CCIR option for the F2 plasma frequency, foF2, we find that for low solar activity both options agree quite well with the ionosonde foF2 values and overall the CCIR maps show a slightly better fit. During high solar activity discrepancies are found during nighttime and the URSI maps providing the overall better fit. The measured F2 peak height values, hmF2, are compared on one hand with IRI predictions that are obtained based on the CCIR model for the propagation factor M(3OOO)F2 and on the other hand with the ionosonde-measured M(3OOO)F2 values. As expected using the measured values results in more accurate predictions. It is important to note that with the measured M(3OOO)F2 values IRI predicts the characteristic post-sunset that is seen in the measurements but not in the IRI predictions with the CCIR-M(3OOO)F2 model. 0 2003 COSPAR. Published by Elsevier Science Ltd. All

New B0 and B1 models for IRI

Abstract The electron density profile in the F region bottomside is described in the International Reference Ionosphere (IRI) by two parameters: a thickness parameter B 0 and a shape parameter B 1. The models used for B 0 and B 1 in IRI are based on ionosonde data from magnetic mid-latitude stations. Comparisons with ionosonde data from several stations close to the magnetic equator show large discrepancies between the model and the data. We propose new models for B 0 and B 1 based on data from several ionosondes including low and mid latitude stations. Close to the magnetic dip equator the new B 0 model provides an improvement over the current IRI model by a factor of up to 1.5.

Middle and low latitude ionosphere response to 2015 St. Patrick's Day geomagnetic storm

This paper presents a study of the St Patricks Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earths magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the B z component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earths magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.

EQUATORIAL F2-LAYER PEAK HEIGHT AND CORRELATION WITH VERTICAL ION DRIFT AND M(3000)F2

Ionosonde data recorded at Korhogo, Ce Longitude - 5.4, Dip -0.67) during a year of low solar activity (1995) were used to investigate ways of improving the representation of equatorial F2 peak height (hmF2) in the International Reference Ionosphere (IRI). For this purpose we have studied the correlation between hmF2 and the equatorial F region vertical drift as given by the model of Scherliess and Fejer (1999). The positive correlation found during nighttime could be helpful in representing the post-sunset peak of hmF2 that is currently not represented by IRI. We have also investigated the reliability of the CCIR model for the propagation factor M(3OOO)F2 model since the IRI hmF2 model is based on the strong anti-correlation between hmF2 and M(3OOO)F2. Overall the CCIR model represents the diurnal variation of M(3OOO)F2 quite well but does not represent small-scale features. With the M(3OOO)F2 values deduced from the Korhogo ionograms as input, the IRI hmF2 model provides an excellent representation of the observed diurnal structure including the post-sunset peak.

Diurnal variation of ionospheric profile parameters B0 and B1 for an equatorial station at low solar activity

Abstract Parameters B 0 and B 1 are compared with those of the International Reference Ionosphere (IRI), using the Gulyaeva option. The data used are those of Ouagadougou, Burkina Faso, (latitude 12.4°N, longitude 1.5°W, dip 5.9°N) for 1994, a year of low solar activity. Night-time and early daytime B 0 values agree well with those of the IRI. The average value of B 0 for night-time is 73. Major differences occur during the daytime (09:00–18:00 LT) and these are dependent on season. Daytime B 0 shows a diurnal variation which depends on the solar zenith angle χ. The cos(χ) exponents were found to be 0.45, 0.67, 0.56, and 0.75 for winter (January), spring (April), summer (July), and autumn (October), respectively. For B 1 , IRI assumes a constant value of 3 most of the time and this appears to overestimate the experimental B 1 values. The experimental values of B 1 are fairly constant during daytime hours (08:00–15:00 LT), with an average value of 1.7. They are between 2.6 to 3.8 during the evening and night-time period up to 07:00 h.

Total electron content in the Martian atmosphere: A critical assessment of the Mars Express MARSIS data sets

The total electron content (TEC) is one of the most useful parameters to evaluate the behavior of the Martian ionosphere because it contains information on the total amount of free electrons, the m ...

Variation of bottomside profile parameters B0 and B1 at high solar activity for an equatorial station

Abstract Diurnal and seasonal variations in experimental profile parameters B0 and B1 are examined, at high solar activity, for Ouagadougou, Burkina Faso, an equatorial station in Africa (latitude 12.4°N, longitude 1.5°W, dip 5.9°N). The diurnal variations for B0 indicate a solar zenith angle dependence that can be described as B0 = A cosn (χ) with n = 0.40, 0.51, 0.46, and 0.71 for Winter, Spring, Summer and Autumn, respectively. The seasonal effect is most pronounced from 10:00–18:00 LT. Within this period, B0 is highest in Spring and lowest in Winter. A comparison of experimental B0 with the IRI B0 shows that the greatest discrepancy occur from about 11:00 to about 18:00 LT. Both are closer during most of the night time hours and in the early hours of the daytime. There is no obvious solar zenith angle dependence in B1. The range of variation for all seasons, during the day time (10:00–18:00 LT) is 0.8. For the remaining part of the 24 h period, the range is about 1.8. Generally, there is an overestimation of B1 by the IRI model.