AM radio waves can travel up to 20 times farther at night. Electromagnetic waves naturally curve upward over distance, but nighttime conditions reduce that upward bend.
After sunset the air near the ground becomes colder and more humid, creating a lower atmospheric layer with greater radio refractivity. As a result, radio waves curve upward LESS and cling closer to the surface, allowing them to cover more distance.
The same principle explains why radio waves can travel farther over the ocean. Cold water cools the air directly above the surface, increasing its radio refractivity and reducing the sharpness of the wave's upward curve. As a result, the signal remains closer to the surface and can cover a greater distance.
At night, thunder, trains, and other distant sounds can often be heard from much farther away. The same general principle applies: sound waves normally curve upward as they travel, but nighttime atmospheric conditions reduce that upward bend. This keeps the sound closer to the ground, allowing it to carry farther than it typically would during the daytime.
There is no skywave propagation. They simply made it up to explain radio transmissions unexpectedly traveling thousands of milesaway. They had to. There's no other explanation on a convex planet.
A station transmits its call sign, location and frequency. Receivers at known distances report where it is heard and where it disappears. When nearby receivers lose the signal but receivers hundreds or thousands of miles away receive it, a skip pattern can be mapped. It has everything to do with the objects like mountains that get in the way. The temperature dictates the ultimate path of the EMF.
The radio waves are not traveling hundreds of miles high and then bouncing back to Earth off the ionosphere, that's just the explanation they had to come up with on a convex ball planet. T
This is a much more reasonable explanation and it's backed up by physics. EMF craves the more optically dense medium. [(Snell's law)]() And the determinant factor for the path is temperature. Cold air attracts the wave/sound/frequency/light.