• consider light getting refracted by a prism, the red light with the least frequency gets refracted the least. and the violet with the highest frequency gets refracted the most. now consider skywave propagation. the waves with higher frequencies escape without being refracted and lost into atmosphere. and those with lower frequencies get refracted enough to return to earth which contradicts what we saw in prism. The reason i cud thin of was that the refractive index of ionosphere maybe less than 1 or even negative and the principles of refraction gets reversed or somethng... but this is not a solid thought. can you help me ?

The ionosphere is is not going to respond the same way as a dielectric. The behavior in the ionosphere is a combination of reflection and refraction, further complicated by the penetration distance of the wave, which is frequency-dependent. Polarization is also going to play a role.

Thanks a lot Swansont, I understand what you said.

 

But can u explain a bit more in regards with why exactly is the process completely reversed in the ionosphere (even though it is not expected to respond exactly like a dielectric).

Thanks a lot Swansont, I understand what you said.

 

But can u explain a bit more in regards with why exactly is the process completely reversed in the ionosphere (even though it is not expected to respond exactly like a dielectric).

I don't have enough depth of understanding; the response of the ionosphere is much more complicated than the relatively simple modeling of a dielectric.

http://en.wikipedia.org/wiki/Ionosphere#Radio_application

except that calling this "refraction" is misleading!

In the case of our ionosphere, it's reflection against a conductive plasma.

 

You're perfectly right, the index of air is nearly 1, which would not allow a total refraction with an interestnig angle against any medium with index >1.

 

Meta-materials can have an index <1 but only over a very limited frequency range, near some kind of resonance. Similar to a waveguide that propagates the phase significantly faster than c slightly above its cutoff frequency.