Atmospheric diffraction

This effect dramatically disappeared when the Sun rose high enough until the pattern was no longer visible on the Earth's surface.

The Moon is seen through thin vaporous clouds, which glow with a bright disk surrounded by an illuminated red ring.

When radio waves travel into this zone, which commences about 80 kilometers above the earth, they experience diffraction in a manner similar to the visible light phenomenon described above.

[1] In this case some of the electromagnetic energy is bent in a large arc, such that it can return to the Earth's surface at a very distant point (on the order of hundreds of kilometers from the broadcast source.

And, at times of favorable atmospheric conditions good "skip" occurs, then even a low power transmitter can be heard halfway around the world.

This phenomenon is also inherent in calculating the sound levels from aircraft noise, so that an accurate determination of topographic features may be understood.

In that way one can produce sound level isopleths, or contour maps, which faithfully depict outcomes over variable terrain.