Y.V. Ramanamurty

Electron density reference profile in the lower ionosphere

Abstract The new IRI formula, as accepted at the 1983 Stara Zagora Workshop, prescribes the use of Epstein functions for reproducing logarithmic electron density profiles. In this paper we discuss solutions which might be applicable to the lower ionosphere. The experimental data base is briefly reviewed. It appears that the stratification near 80 km must be accepted as a regular feature of the daytime lower ionosphere. The C-layer problem is left open. In order to reproduce such profiles, one needs three LAY-functions. Examples show that the weighted sum of these does very well represent experimental profiles, the amplitudes being determined by a least square fit. For profile synthesis (as in IRI) a least square determination of the three amplitudes, admitting four linear conditions, is proposed.

Modelling of the lower ionosphere according to the IRI guidelines

Abstract Different data sets containing experimental lower ionosphere profiles were considered and fitted with LAY-functions. Since the individual reported profiles show large differences, it is concluded that median profiles should be used for the purpose of the IRI. For the day-time profile, an inflection point near 80 km, as assumed in the present IRI, should continue to be taken as a typical feature which must be represented. At twilight and night, a description with only one or two LAY-functions should be sufficient until consistent data are produced for the levels below 80 km.

Input from station-oriented observations and its assimilation into the new formula for the International Reference Lower Ionosphere (IRLI)

Abstract In order to compare the station-oriented observations from a variety of experimental techniques, it is necessary to use standard and state-of-the art procedures for the methods of evaluation. While discussing the formulae used in the past for the calculation of mf/hf radio wave absorption and vlf/lf reflection coefficients, the use of the Sen-Wyller formula for the computation of A1 absorption at mf/hf and the use of generalised full wave theory for the calculation of vlf/lf reflection coefficients are recommended. For oblique incidence mf/hf (A3) absorption calculations, use of the generalised Booker quartic is recommended. The need to use a consistent and standard collision frequency model linked with the CIRA pressure model is recommended. While discussing the normalisation procedures used in the past for the global mapping of the D- and lower-E-region A1 absorption, the need to calculate the absorption (without normalisation) and then make a comparison with the IRI description is stressed. The use of the currently available rocket data, to model the peak parameters of the E-region, is discussed. More rocket observations to probe the E-region together with incoherent scatter data are needed to model the E-region peak parameters needed for incorporation into the new formula for the International Reference Lower Ionosphere (IRLI).

A note on the use of absorption measurements for improving the IRI electron density distribution in the lower ionosphere

Abstract Advantages and disadvantages of radio measurements by ground based techniques are discussed with a view to improve the IRI. In particular, these techniques allow the diurnal, seasonal and solar cycle variations of the D-region to be continuously followed. Also, the spatial variations might be established with a network of stations measuring radio wave absorption on several frequencies. In case of strong events, it is important to follow their development in space and time. It seems that absorption measurements alone do not allow the determination of the electron density profile unambiguously. It is, however, suggested that the addition of vertical soundings (with profile computation) potentially combined with rocket and balloon borne pressure determinations might produce some indications about how a certain part, at least, of such data might be used to check/improve the description of D-region variations in time and space.

D-region IRI profiles in relation to radio observations

Abstract The D-region IRI profiles are compared with the direct rocket measurements as well as with ground-based radio observations by a variety of techniques. The characteristics of D-region IRI profiles and the dependence of electron density on solar zenith angle, sunspot number, latitude and season are discussed. The sensitivity of certain reflection coefficients on the height distribution of electron density below 70 km is illustrated with a typical example. For D-region modelling, the results show the importance of simultaneous measurement of reflection and conversion coefficients together with polarization phase over a wide frequency range.

A new method of standardising Langmuir-probe data

Abstract While briefly describing available in-situ and ground-based data sources, a critical discussion of Langmuir probe measurements in the D-region is presented. A new method of validating the long term data sets via the solar cycle dependence is proposed. This method is applied to available rocket measurements in U.S.A and India and to ground based measurements in Europe. The shortcomings and limitations of existing data are recognised and recommendations are made for future in situ measurements and for the interpretation of ground based measurements.

Ionospheric informatics with special reference to the IRI modelling effort

Abstract When compared with the CCIR predictions, the observed values of NmF2 and hmF2 over Delhi and Ahmedabad show considerable differences. Comparison of the shape of the bottomside electron density profile obtained by true height analysis and the shape predicted by the interim 1985–1986 version of IRI shows that the observed values are typically lower (by day) than those given by the model in the sub-peak region, but higher below about 200km. The use of a sum of LAY functions to describe the middle ionosphere electron density profile is illustrated with a typical example.

Highlights of the 1975 URSI/COSPAR workshop on the IRI

Abstract Some of the presentations made at the IRI Workshop held at Louvain in 1985 have not appeared in the Proceedings. Some discussions which took place during the workshop could be of interest in future work. This article tries to highlight the IRI modelling aspects in the four principal height regions of the ionosphere.

Comparison of IRI profile with low latitude A1 absorption measurements — A summary

Abstract Comparison of the IRI-90 profiles for the lower ionosphere with those derived from A1 absorption measurements indicate that the IRI-90 values of electron density are consistently higher in the lower E-region. It is suggested that LAY function representation of electron density in the lower ionosphere be provided as an option in the IRI description.

Refinement in the diurnal variation of IRI-79 electron density distribution

Abstract While briefly touching the interpolation technique, used in the IRI-79 description and those used in other ionospheric (prediction) models, the use of solar zenith angle (χ) rather than solar time is recommended in the empirical modelling of the peak parameters of the F1 and F2 regions for incorporation into the contemplated new version of the IRI for the middle ionosphere.