The best chance of listening to whistlers is in summer, as local thunderstorms provide
plenty of lightnings, whose numerous and strong spherics make a lot of noise. They also can
be the sources for whistlers, which obviously are of the two hop variety: it takes
about 1.2 sec to fall from 5 to 2 kHz, and any strong spherics emission about 2.5 sec before
the whistler appears at 5 kHz would be the source (marked by the arrow) in this recording
from Aug. 24th, 2008:
listen to the sound file
Whistlers can also appear in winter: on March 3rd, 2009 many whistlers
were recorded like these three. They take only 0.6 sec to fall from 5 to 2 kHz, hence
they are one hop whistlers, greetings from southern Africa. In winter Europe doesn't
have thunderstorms. Thus the background noise is low, with only a few spherics, probably
from northern Africa or the Near East:
listen to the sound file
When we put the two data sets together, using the same time scaling, the difference
in the duration of the whistlers becomes more obvious:
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last update: Apr 2018 J.Köppen