The absorption of short radio waves in the ionosphere

Abstract

It is shown that the reflection coefficients (ρ) measured for radio waves on 2 and 4 Mc sec −1 reflected vertically from the ionosphere do not fit the expression −log ρ = A(ƒ + ƒ L) −2 (1) appropriate to “nondeviative” absorption. Since the two frequencies mentioned did not approach near to critical frequencies at the time of the measurements, this failure cannot be ascribed to excessive “deviative” absorption. If the measured values are inserted into the expression −log ρ = C + B(ƒ + ƒ L) −2 (2) it is found that 1. (a) C varies with the sun's zenith angle but not with solar epoch. 2. (b) B is a very variable quantity, it depends on the solar epoch and is greatest in winter. With values of B and C deduced from measurements on 2 and 4 Mc sec −1, equation (2) gives a reasonable approximation to the measured values of ρ on 2.4, 3.2, and 4.8 Mc sec −1. It is suggested that waves in the frequency range 2 to 4.8 Mc sec −1 are appreciably absorbed outside the nondeviating region, where equation (1) is appropriate.