Long Period Fading of hf & lf Signals during Meteorological Activities in Relation to Internal Atmospheric Gravity Waves

Abstract

Long period fading with quasi-periods of the order of 1 hr, was observed at Calcutta (lat., 22ᵒ33 N; long., 88ᵒ24E) simultaneously in the field strength of hf signals, during local meteorological activities. The fading usually starts suddenly and the effects observed at hf and if are closely associated. The results obtained from an analysis of the observations in 1972 during the period June-December; when meteorological disturbances were prevalent in and around Calcutta, are presented. It is suggested that the fading might be due to internal atmospheric gravity waves of meteorological origin affecting the ionosphere. It appears that the closely associated hf and if fading effects are produced by the gravity waves bringing about disturbances in a common region of the ionosphere responsible for the absorption of the signal and the reflection of the if signal, respectively.