K. Rawer

International reference ionosphere — past, present, and future: I. Electron density

The most important investigations leading to the International Reference Ionosphere 1990 (IRI-90) are overviewed, and the latest version of the model is described. The shortcomings and limitations of the IRI-90 are pointed out, together with the ways of overcoming them. The list of studies that the IRI group has yet to carry out includes the investigations of magnetic storm effects as the highest priority. This paper discusses determinations of and the available data on the electron density, plasma temperatures, ion composition, and ion drift in the ionosphere, together with future improvements needed on these parameters.

Replacement of the present sub-peak plasma density profile by a unique expression

Abstract It is proposed to apply Bookers ‘skeleton’ description which is actually used in IRI fu¨r the topside only, in future for the bottomside too. However, in order to overcome some drawbacks a slightly more involved descriptive function must be applied the time- and place-dependent parameters of which may be determined once for ever by fitting methods (as was earlier done for the topside). In order to avoid interference between different height ranges, in particular between the ranges lower, middle and topside ionosphere, it is proposed to use independent descriptions in these ranges and connect them smoothly by suitable ‘filter functions’. So, finally, a unique analytical expression covering all heights might be obtained.

New formulas for the IRI electron density profile in the topside and middle ionosphere

Abstract Following the guidelines established at the Stara Zagora Workshop profile description by a sum of LAY-functions is tried out with typical examples. In the middle ionosphere at least 3 members are needed, and, preferably, 4, if F1 is to be reproduced. In the topside the present description needs improvement in particular in the equatorial zone.

International reference ionosphere — past, present, and future: II. Plasma temperatures, ion composition and ion drift

In December 1990 a new IRI handbook was published by NASAs National Space Science Data Center (NSSDC) describing in detail the International Reference Ionosphere 1990. Shortly thereafter, the IRI-90 software was released on tape, diskette, and computer networks. This paper is intended as an inventory of the most important IRI activities up to 1990 and as a starting point for the next improvement cycle. It summarizes the work and studies that led to IRI-90 and provides an overview over this latest version of the model. Shortcomings and limitations are pointed out and ways of overcoming them are discussed. Priorities are suggested for the list of work items that the IRI group has to tackle in the future. High on the wish-list are (i) major improvements at high latitudes and (ii) inclusion of magnetic storm effects. This paper deals with plasma temperatures, ion composition, and ion drift; the preceding companion paper discusses the electron density.

Variability of F2 parameters depending on MODIP

Using hourly daily data of 15 stations the average quiet-time variability of f0F2 was determined hour by hour and month by month. An approximation of the resulting 24×12 tables by double Fourier analysis up to second order, first by hour and then by month, gave one 5×5 coefficient matrix per station. At low and middle latitudes the model amplitudes (averaged over all months) are found comparable, except for stations near the equatorial crest or at high latitudes where they are greater. With the modified dip coordinate (used by CCIR), they increase from midlatitude toward the auroral zone.

New options for IRI electron density in the middle ionosphere

Abstract This paper reviews the present International Reference Ionosphere (IRI) model of electron density in the middle ionosphere and explores two new options for future editions of IRI. The first of these options is a better description of the bottomside thickness parameters, and the second is an analytical representation from E- to F2-peak using LAY-functions. For this analytical representation we have established a table of standard parameters and constraints for the four LAY-functions recommended for IRI.

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.

Determining electron density profiles for the middle ionosphere

Abstract Using daytime numerical ionospheric profiles from W. Beckers mid-latitude collection, the geometric parameters of 3 or 4 LAY-functions were determined by best fit while all amplitudes were redetermined step by step with a least squares criterion. It appeared that the transition height and scale of the main function are interrelated while all other geometric parameters are independent. Median values for a spring and a summer period are found, and relations with the peak altitude and half-density thickness of the input profile are established.

Ionospheric mapping in the polar and equatorial zones

Abstract Ionospheric mapping, traditionally based on station data suffers from the inadequateness of the network of stations, particularly in the equatorial and the polar zones, and from involved structures in certain geographical regions, as in the equatorial belt and, in particular the polar caps. Distinct aeronomic conditions require additional information and separate mapping. Involved aeronomic computations alone were unsuccessful in the polar caps so that empirical information had to be introduced additionally, e.g. patterns of corpuscular influx and electric fields. The resulting maps depend primarily on these rapidly changing features. As long as these cannot be predicted high latitude mapping will remain unsatisfactory.

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.