Atmospherics are heard as a quasi-steady background of crackling noise
) on certain radio frequencies, such as those used to broadcast AM radio signals. Since any acceleration
of electric charge
leads to emission
of electromagnetic radiation
, and since the several processes involved in propagation of lightning
lead to very large charge accelerations, the lightning channel
acts like a huge transmitter
, sending out radiation
with frequencies of the order of 10 kHz. Atmospherics may occasionally be detected at distances in excess of 3500 km (2000 mi) from their source. Advantage has been taken of this characteristic by using radio direction-finding equipment to plot cloud-to-ground lightning
locations, and to locate active thunderstorm
areas in remote regions and in-between weather reporting stations.
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