Fading Patterns on on the Sonagram of Atmospherics
It is known that whistler traces on a sonagram have a pattern consisted of some deep minima in intensity. Fading patterns made by this kind of intensity minima are found on almost all traces of normal sferics. In this report the fading patterns on the sonagram of atmospherics; normal sferics, tweeks, and whistlers has been investigated. It was suggested that there are two possible mechanisms making the fading patterns. The first is that caused by the time lag between two or more waves generated from impulsive sources. The second is that caused by the pulse width of a source current waveform. The fading patterns caused by two mechanisms are similar when the time lag of double impulses equals to the pulse width of single unipolar pulse. The theoretical patterns of the spectrum obtained by FFT of the waves which are numerically calculated specifying the time lag or the pulse width bear a close resemblance to the measured fading patterns.
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