#TIL Tropospheric Ducting Propagation (facilitated by temperature inversion weather) is not limited to RF, but also works for sound waves.
I got rudely awoken by really loud jet engine sounds around 05:30 local. That's really unusual as there are no civil aviation routes are close by. We do get the occasional interceptor F-18 flying by every few months since that war got started.
This wasn't a mil jet, this was big jet airliner sound.
HEL airport is 70 km from here.
contd. 1/x
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Then it struck me, could it be tropo ducting, but with sound? I'm quite familiar with the eerie sudden long distance propagation from #hamradio and you can receive e.g. VHF or UHF signals from hundreds of km away. It occurs when there is a thermal inversion due to weather.
As a treat, those who read it all get the actual audio.
fin 3/3
I kept hearing those big engine noises for 1-2 minutes at a time and they were *loud* and I could hear them inside with the windows closed.
ADSBexchange didn't show any flights near our location, only HEL was slowly waking up and the regional feeders from all over Finland were arriving.
Once I woke up, listened to the audio from the outdoor camera, it was clear those were civil airliners, maybe even a turbo prop sound in one of them?
contd. 2/x