ionospheric absorption of hf radio wave in vertical propagation

in this study, absorption of high frequency radio waves in the ionospheric plasma have beeninvestigated. the wave equation was obtained in terms of ionospheric parameters. the numerical values ofthe absorption have been calculated for 4 mhz, 4.5 mhz and 5 mhz waves. the necessary parameters forcalculation have been obtained using an international reference ionosphere (iri) model. the altitudinal,diurnal, seasonal and the variations of absorption with frequency have been examined. the calculations showthat the highest absorption occurs in the d-region. the absorption is higher in summer than in other seasonsand is maximum at daylight. in addition, absorption decreases with the increase of frequency.