Here is a more detailed explanation of what happens:
* During the day, the Earth's atmosphere is heated by the sun, which causes the air to become less dense. This makes it difficult for AM radio waves to travel through the atmosphere, and they are mostly absorbed by the Earth's surface. This is why you can only hear AM stations that are relatively close by during the day.
* At night, the Earth's atmosphere cools down and the air becomes more dense. This makes it easier for AM radio waves to travel through the atmosphere, and they are reflected back to Earth by the ionosphere. The ionosphere is a layer of the Earth's atmosphere that is located about 60-300 miles above the surface. It is made up of charged particles that reflect radio waves.
* The reflection of AM radio waves by the ionosphere allows you to hear AM stations from much greater distances at night. In fact, you can sometimes hear AM stations from hundreds or even thousands of miles away at night.
Here are some additional factors that can affect AM radio reception:
* The power of the radio station. The more powerful the radio station, the farther its signal will travel.
* The frequency of the radio station. AM radio stations broadcast on frequencies between 535 and 1705 kHz. The lower the frequency, the farther the signal will travel.
* The location of the radio station. Radio stations that are located near the coast or in a mountainous area will have a stronger signal than stations that are located inland or in a valley.
* The time of day. AM radio reception is usually best at night, when the ionosphere is most active.
By understanding the factors that affect AM radio reception, you can improve your chances of hearing the stations you want to hear.