Seasonal Anomaly in Ionospheric Radio Wave Absorption

Abstract

The temporal variation of the ionospheric absorption of radio waves in the 1.5 to 6 MHz range with the solar zenith angle (χ) is usually written in the form cos n χ. Theoretically n = 1.5 for absorption occurring in a Chapman layer, although such a theory cannot strictly be applied to the D region. On a diurnal basis, this variation is largely obeyed with values of n ranging from 0.5 to 1.0 and possessing a certain latitude dependence1. There is, however, a delay in maximum absorption of approximately twenty minutes on local noon, due to the relaxation time of the D region2.