Whistlers

Whistlers have a relationship to tweeks similar to the one tweeks have with sferics. Whistlers travel a long enough distance to have relatively large dispersions. Therefore, we hear the distinctive falling pitch as the slower lower frequencies arrive. To get this greater distance, the signal interacts with the earth's magnetic field and the ionosphere.

The whistlers we hear are probably generated by lightening strikes in the northern hemisphere. The signals follow the magnetic field lines into the southern hemisphere and then are reflected back to us. The amount of dispersion indicates the waves are traveling above the ionosphere.

A fairly detailed and mathematical description of propagation is available here.

Listen!

Here is a graph of the whistler you are listening to above:


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