A study of the relation between ionospheric absorption and predicted HF propagation parameters at high latitudes

Much of the attenuation of ionospheric HF radiowave signals is caused by non-deviative absorption in the D-region (60-95 km). The non-deviative absorption is proportional to the electron density and is also a function of the collision frequency between electrons and neutral atoms and molecules. If these quantities are known, the non-deviative absorption for a specific path can be calculated. Existing prediction programmes at HF do not include a complete model of the D-region, simply because adequate models of the D-region have not been available. Absorption losses have been introduced in a semi-empirical, ad-hoc manner. Particularly at high latitudes the understanding of the dynamic D-region is incomplete, but some rocket and ground-based data now exist. Friedrich and Torkar (1983) have measured electron densities as a function of height, and simultaneously recorded the riometer absorption. From these data they have developed statistical electron density profiles with the measured riometer absorption as the driving parameter. This paper is an attempt to improve the calculation of ionospheric absorption in the prediction programmes by including the statistical profiles (a D-region model) suggested by Friedrich and Torkar. These model calculations have been compared with the losses predicted by ICEPAC and also with measurements performed by NDRE (see Jodalen et al., 1991)