Matt Beckwith wrote:
The clarity of local AM radio stations is less at night.

This is because all of the other stations everywhere else in the world
are coming in through skip at night, and interfering with local stations.

Is there
some sort of law that radio stations have to cut their output when it
gets dark? I've noticed that it's the amount of light outside, not
the time of day.

Many smaller stations are forced to reduce power at night, or go off the
air altogether, to protect stations on the same frequency in other parts
of the country.

That is, the lack of clarity occurs whenever it gets
dark, not at a certain time each day. I always presumed the stations
were cutting power to save money, but then why would it be based on
light vs dark, rather than on time of day?

Because the ionosphere is denser and closer to the earth at night, which
is why you can get transatlantic AM stations at night and not in the daytime.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."