As I'm studying for the PPL knowledge exam, I had the following note:
Pressure levels are raised on warm days and the indicated altitude is lower than true altitude.
But I don't quite understand why.
From my understanding, on warm days the air density is lower. If the air density is lower then the plane will think it's at a high elevation than it really is.
Secondly, if you have warm air and it can expand (since the atmosphere isn't a closed container), the pressure levels should decrease.
Hence, the entire statement that pressure levels increase on warm days and indicated altitude is lower seems false. But apparently it is true. Can someone reconcile this?