Day-to-day variability of the IRI electron density height profile

Much uncertainty currently exists in the use by different workers of the term 'variability' in describing the results of statistical analyses applied to ionospheric measurement data sets and in their relationships with various existing or new ionospheric models. Often it is not clear whether data for different time periods or different geographical areas, and if so which, are being used to formulate results. Terms are presented in the Annex which it is suggested should be used, at least once in every publication addressing this topic, to describe unambiguously what is talked about. The background to the proposed terminology is discussed. Options for variability parameters are also addressed.

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Proposed terminology for the classification and parameters for the quantification of variability in ionosphere morphology

Simple empirical equations are presented which give circuit availability in terms of the upper-decile, median and lower-decile values of the maximum usable frequency. The equations are based on approximations to halves of two normal distributions.

Prediction of h.f. circuit availability

Factors which govern the circuit reliability of a long-range hf sky-wave link are discussed with particular reference to the relationship between circuit reliability, median received signal-to-noise ratio and operating frequency Representative cases are analysed and quantitative relationships are obtained for these parameters Consideration is given to the implications of the findings on the design and operation of hf air-ground links

Assessing the circuit reliability of an h.f. sky-wave air-ground link

A method is presented for fitting chi-square (or gamma) distributions to observed distributions, either positively or negatively skewed, of telecommunication variables such as critical frequencies and maximum usable frequencies. These observed distributions have been recorded for years only in terms of the 10, 50, and 90% points, but in applications it is necessary to estimate the entire distribution. It is assumed in the present study that the observed variable can be approximated by a linear function of a chi-square variable with unknown degrees of freedom. The three unknown constants are determined from the three per cent points and a convenient table. Several examples of complete observed distributions are compared graphically with normal, chi-square, Gram-Charlier, and Edgeworth fitted distributions.

Edwin L. Crow

Papers

Fitting Distributions of Telecommunication Variables with Chi‐Square Distributions