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I noticed HF radio waves travel farther and easier when the sun is out rather then during the night. Why?
I noticed HF radio waves travel farther and easier when the sun is out rather then during the night. Why?
..., or any other discontinuity, density/temperature/compostition/whatever.ionosphere
Several factors at work here. With no cosmic rays, there would be no ionisation. At low intensity level, the ionisation is just at the high layers and, because the gas is low pressure, the ions spend a long time before recombining and the free electrons behave a bit like the electrons in a metal. They reflect radio waves. As the intensity of cosmic rays goes up (daytime) the lower levels become ionised and the electrons which the radio waves set in motion, collide with air molecules (more of them ) and lose the energy from the wave. (Poor propagation) The high ionisation layers take longer to recombine so the higher levels hang around longer after dark (and the sun 'sets' later up there too.)I noticed HF radio waves travel farther and easier when the sun is out rather then during the night. Why?
I take "the sun is out" to mean it is shining, so not at night.Wait, isn't "the night" is also when the "sun is out"?
With no cosmic rays, there would be no ionisation.
I take "the sun is out" to mean it is shining, so not at night.
That's right of course - I forgot the details of ionisation causes. I should have used the term "ionising radiation" and kept on the safe side!No, that isn't correct.
Ultraviolet radiation from the sun is the main cause of the ionisation of the Earth's ionosphere …
hence the difference in propagation seen between day and night
. . . . . . .
Dave
When I leave a room, I turn on the Dark Switch.I suspect Zz was having a play with words …. maybe?
That's right of course - I forgot the details of ionisation causes. I should have used the term "ionising radiation" and kept on the safe side!
It makes good sense about cosmic rays. There are relatively few and their effect can only be significant where there is a dense atmosphere. If there really were enough to have the same effects as UV from the Sun (which must have an energy density of many W/m2), we would surely all be frazzled.