Low-Frequency Components of Atmospheric Pulses and their Origin

Abstract

THE work of Appleton and Chapman¹ has shown that when the source of atmospheric disturbance is at a distance of about 200 km., an aperiodic or quasi-periodic pulse which represents the high-frqeuency component is usually followed by a slow component. In our recent experimental study of the wave-forms of atmospherics carried out at Dacca, we have been able to obtain oscillographic records showing (i) a slow component ahead of the aperiodic or quasi-periodic pulse, and (ii) slow components on either side of the high-frequency group in addition to the records showing a slow component following the high-frequency component. In a few oscillograms two or three half cycles of very slow components with a range of frequencies between 130 and 1,265 cycles/sec, have been observed. The object of the present note is to report these observations and to suggest interpretations as to their origin. These observations were made in addition to the usual aperiodic and quasi-periodic pulses, the aperiodic or quasi-periodic pulse followed by a slow component, 'precursors' and 'repeater pulses' due to multiple reflexion between the earth and the ionosphere.