Why do AM waves pick up better at night compared to the day?

Question

i know it has something to do with the ions in the ionosphere and that there is more reflection...I don't really understand the dteails.

Answer 1

there is less interference in the night because of the movement of our bodies and objects are generally not out and about as much at night as in the day.

Answer 2

You are correct in understanding that the ionosphere has a major role in radio reception.    Radio waves basically travel in a straight line and one would think that becaue of the curvature of the earth you should only be able to receive radio signal for a limited strainght line distance before the curvature of the earth blocks the line of sight between sending and receiving antennas.   However some frequencies, mainly in the lower frequency shortwave and AM bands have the ability to travel beyond a stright line of sight distance and in some cases can travel around the world.

This is done by what is known as skip. The radio wave bounces off of the ionosphere and is directed back down to earth.  Shortwave frequencies can bounce off the ionosphere and ground back and forth several times.   Each time a radio wave is reflected back to earth it can be received in the location where it is reflected to.  

During the day sunlight strikes the ionosphere and ionizes atoms which create a radio reflective surface.  Sunlight creates these ions so during the day the ionosphere becomes thicker and the base of the ionosphere gets lower to the ground.   At night there this solar ionization stops and reverses itself which causes the ionosphere layer to shrink in size. So at night the base of the ionosphere is at a higher altitude.

Since radio waves bounce off the ionosphere, during the day these waves are reflected back at a lower altitude than at night.  ecause radio waves get reflected back to earth at a higher altitude at night allows these waves to cover or skip across a larger area or distance than during the day.

You can visualize this effect by doing a quick experiment with a flashlight in a darkend room.   With the lights off turn on the flash light and shine the light towards the ceiling. The light will bounce back and light the room.   Bring the flashlight closer to the ceiling and less of the reflected light will make it to the edges of the darkened room.