Why during the day the radio only receives AM stations from a nearby City while at night you're able to hear a distant City's stations?

Answer 1

Energy from the sun interacts with the particles in the ionosphere, causing them to absorb AM radio frequencies. At night without solar energy, AM radio transmissions reflect off the ionosphere, allowing radio transmissions to be received at greater distances.

Answer 2

There's a whole lot to it, actually, and real scientific. But basically, you can get AM radio from a distance at night, and only local during the day, because the straight waves of radio bounce from the ionosphere back to earth. The ionosphere is composed differently, depending on if it's day or night. When it's nighttime, the ionosphere reflects much better, thus you can hear stations from farther away.

Answer 3

During the day the sun's radiation forms an ionised layer in the atmosphere at a height of about 50 km that absorbs radio waves on the medium wave AM. So you only hear the ground-waves that the system was designed for you to hear. At night that layers disappears and the waves get reflected back down by another layer at a height of about 300 km - so you hear a lot more stations.

Answer 4

Two reasons:

1. at night a small number of AM stations are licensed to increase their broadcast power from their normal daytime level of 20 kilowatts to a nighttime level of 50 kilowatts, this allows their signal to reach much further. Any other stations operating on the same frequency as these high power stations must go off the air at night so as not to interfere with the high power stations.
2. on the night side of the planet the structure of the ionosphere is different and reflects AM and SW signals very effectively back down to the surface, this creates a "bounced" signal much farther from the transmitter far beyond the horizon where the signal would not normally be able to reach.

Answer 5

FM has a line of sight limitation, which means it can be obscured by structures, terrain, or the curvature of the earth. FM operates at very high frequencies, which tend to go through the ionosphere. AM stations operate at much lower frequencies - well below 30 mHZ. When those radio waves hit the ionosphere, they don't go through - rather, they are bounced back towards the earth. This gives AM radio a much broader transmission range.