No, this is not natural, this signal is a type of ionosonde called a chirp sounder. And yes, they are propagation monitoring tools. They start from some defined frequency and transmit continuously (sometimes except for specific skipped frequencies, which vary per installation) to another defined frequency. For example, it might start at 5000 kHz and chirp up to say 28000 kHz, at 100 or 150 kHz per second. In one example, 5000 kHz to 28000 kHz at 100 kHz / sec, it would take about 230 seconds, just under 4 minutes, to make the entire sweep. Since the target set is the ionosphere, and that is pretty slow to change, it does not have to do this very often, a few times an hour is enough to keep up with changes.
It absolutely can be thought of as a radar for tracking what is going on in the ionosphere. And there are dozens of these scattered around the World, so you often can hear two or three zipping by a given frequency in just a few minutes.
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