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I know auroras are a propagation mode, but I was wondering with the recent outburst of noctilucent clouds (as reported on www.space.com) brings with it any interesting propagation modes, either on HF or VHF/UHF?

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NLCs may propagate radio waves, according to a 21 May 2019 article on Polar Mesospheric Summer Echoes:

The underlying physics of these echoes is still uncertain. A leading theory holds that the ice particles in noctilucent clouds are electrically charged, and this makes them good reflectors of radio waves. However, NLCs are not always visible when the radar echoes are observed and vice versa.

According to Rob Stammes of the Polarlightcenter in Lofoten, Norway:

“I detected these [56.25MHz] VHF signals coming from transmitters in Eastern Europe. Before they reached my receiver in Norway, they bounced off something in the mesosphere. The patterns were recognizable and very strong.”

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Noctilucent clouds are just clouds at a very high altitude. The temperature is low so they are formed by ice crystals. They are visible only when the sun is below the horizon but still shining on the clouds that are at very high altitudes. I can not imagine any effect on radio propagation. Maybe with visible light from a laser one could get reflections(??)

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