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.Gene Naden said: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.)Tech2025 said: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.ZapperZ said:Wait, isn't "the night" is also when the "sun is out"?
sophiecentaur said:With no cosmic rays, there would be no ionisation.
DrClaude said: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!davenn said: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
. . . . . . .
When I leave a room, I turn on the Dark Switch.davenn said:I suspect Zz was having a play with words …. maybe?
sophiecentaur said: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.
The sun's activity, specifically its solar flares and coronal mass ejections, can cause disturbances in the Earth's ionosphere. This can affect the way radio waves travel through the atmosphere, resulting in changes in signal strength and propagation paths.
The sun's magnetic field can also impact radio wave propagation. This is because the Earth's magnetic field interacts with the sun's magnetic field, creating disturbances in the ionosphere. These disturbances can cause changes in the way radio waves travel, leading to fluctuations in signal strength and propagation paths.
During the daytime, the sun's radiation ionizes the Earth's ionosphere, making it more reflective to radio waves. This results in shorter propagation paths and stronger signals. At night, when the sun's radiation is not present, the ionosphere becomes less reflective, leading to longer propagation paths and weaker signals.
Solar flares, which are sudden bursts of energy from the sun, can cause strong bursts of radio waves. These bursts can interfere with radio communication and disrupt propagation paths. Additionally, solar flares can also cause changes in the Earth's ionosphere, which can impact radio wave propagation in various ways.
Yes, the sun's activity can affect all types of radio waves, including AM, FM, and shortwave. However, higher frequency radio waves, such as those used in satellite communication, are less affected by changes in the ionosphere caused by the sun's activity.