Atmospherics are electromagnetic wave-pulses with a maximum of energy near 10 kHz, adequate to a wavelength of 30 km (Kimpara, 1963). Sources of atmospherics are mainly lightning flashes. Ten years of registration of atmospherics at Berlin-Dahlem 1960 to 1970, permitted us to discover both annual and daily cycles in atmospherics. EQUIPMENT: The atmospherics were measured undirected by a VLF-broadband-receiver of a medium frequency at 10 kHz (-3 dB: 3 to 40 kHz). The pulses were registered at two amplitude-thresholds: A1 > 0.02 V/m and A2 > 0.4 V/m. The results of registrations show an exponential amplitude distribution with relatively high (low) puls-rate at low (high) amplitudes of atmospherics. 10-year -means: A1-stage: 2.2 Hz; A2-stage: 3.4.10-2 Hz. ANNUAL CYCLES: The annual cycles in atmospherics in general follow sun's altitude, partly with phase shift. Maximum of pulse-rate was reached at June (10-years monthly means: fA1 =4.7 Hz; fA2 =8.8.10-2 Hz), minimum at February/March (fA1=0.65Hz; fA2 =0.88.10-2Hz). The mean max./min.-ratio of pulse-rates characterizing mean annual variations amounts to 7.2 (A1 -stage) and 10 (A2-stage). DAILY CYCLES: In the winter-time daily cycles in atmospherics show maximum-values of pulserate at night and minimum-values at day, caused by different ionospheric VLF-propagation conditions night and day. Therefore the decrease of pulse-rate from night-level to day-level is synchronized with sunrise, the increase from day- to night-level with sunset. In the summer-time to the simple day-night-cycle of winter-time an additional afternoon-maximum is superimposed with maximum-time at 15 to 16 hours LMT. This afternoon-maximum is caused by thunderstorm-activity on the European continent during this season. The mean max./min.-ratio of pulse-rates characterizing mean daily variations amounts to 6 for summer-time and 3.3 for winter-time. In spring and autumn daily cycle show transition forms between winter- and summer-type. The pulse-rate-quotient of both the amplitude-stages qA2/Al=fA2:fA1 gives a criterion for the rate-pulse amplitude-distribution of atmospherics, he 10-year monthly mean values of this quotient show no important annual cycle. The 10-year-mean amounts to qA1/A2= 1-67.10-2. Daily cycles in this pulse-rate-quotient are existent. One interesting fact of these daily cycles is the morning minimum short after sunrise which exists during the whole year. Together with the morning decrease of pulse-rate this minimum of the quotient should be discussed as a possible “triggering pulse”; for the 24-hour-cycles in living organisms (Lotmar, et al., 1969; Wever, 1968).
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