Why high frequency waves cannot be used in sky waves?

[jd12345]

Sky waves transmission is done using the total internal reflection phenomena. The waves reflect as we go to a rarer medium from a denser medium.
My book states that high frequency waves cannot be used for sky waves. IT says it will penetrate the atmosphere. I don't get it

refractive index for high frequency waves is greater so they will be refracted and hence their total internal reflection will be easier

Any help? Thank you

 

[Jano L.]

I think the answer lies in that the phenomenon cannot be understood as simple internal reflection of visible light on the boundary glass-air. There indeed the violet light should reflect even better than red light.

The difference with ionosphere is that if the frequency gets high enough (near its plasma frequency), the electrons are not able to function as effective refelctors and the wave penetrates the layer and is damped down there instead. The same thing happens in optics, when we use ultraviolet light - this gets absorbed in glass as well.

There is also short explanation on Wikipedia (middle of the page)
https://en.wikipedia.org/wiki/Ionosphere