The Absorption of Radio Waves in the Upper Atmosphere

Abstract

Recent measurements have shown that radio waves below 150 meters fall off in intensity faster than required by an inverse square law for distances up to 1000 miles. This points to absorption of the wave by the medium, in this case the upper atmosphere. The absorption of the waves variously polarized is calculated on the assumption that it results from collisions between the electrons and molecules of the atmosphere. With reasonable average values of the electronic and molecular densities the amplitude $A$ of the wave $\lambda$ cms at a distance $x$ cms is $A=a{x}^{-1\mathrm{}}exp(-11.8\mathrm{}\times {10}^{-16\mathrm{}}{\lambda }^{2}x)$, theoretically valid for waves from 16 to 160 meters to distances of 1000 miles. This agrees well enough with the scant range and intensity data, and it is pointed out that an extension of these data may lead to more exact knowledge of the overhead electronic and molecular pressures. From the absorption curves interesting possibilities appear of polarization of waves in the broadcast band 200-600 meters.