Thank you Navyfag. I found your write-up very interesting and noteworthy. In VHF radio there are atmospheric phenomena that similarly act as a waveguide when the temperature and humidity are just right, and during those rare openings VHF signals, normally limited to line-of-sight, are sometimes conducted hundreds of miles further. So the analogy to the underwater acoustic ducting made a lot of sense to me.
The article you linked was very informative too; thanks!