Swedish Institute of Space Physics, IRF
The Ionosphere
Snell's law!
Refraction and reflection; drag the balls
The sun is "lifted" over the horizon at sunset and sunrize; Snell's law.
The sun looks slighly as an elips at sunset and at sunrize; "Derivative" of Snell's law.
Think about a glasphere with a spherical whole inside filled with plain air.
The ball inside will be used as the earth later.
According to Snell's law ; all light rays from the inside will go out but refrakted.
Normally one consider radiowaves as lightwaves or the other way around; the only difference is the frequency.
But if we transmitt radiowaves up in the sky sometimes they will come back.
A reflecting or refracting layer has to be optically thinner than air aoocording to Snell's law.
Can there be such a medium. The glas above as medium consist of electrons, but they are
bound to atoms. A lightwave will act as a fast vibrating electric field and the small
translation of the electrons will be in antiphase to this field if the frequency is not too large. The effect of the translation
would be felt by the wave, which will go slower through the medium.
A layer out in space, which reflect radiowaves consists of free electrons together with free heavier ions. The electrons will
be accelerated by the electric field in the radiowave, but their translations will be in phase and the positive ions in antiphase;
quite the contrary to the glas above. The radio wave will go faster than it normally do, but not realy only so the
refraction and reflection will be explained. We call the layer the ionosphere and it shows up as an optically thinner medium than vacume.
Free and bounded electrons forced by an alternating electric field
We have seen a similarity between the refraction of the sunlight and the bending and reflexion af radiowaves in the ionosphere.
But what about the blue light in the sky; that's towards the Eiscat way.
jan 1997
christer juren