How and why humidity and vapour pressure change as a parcel of air with an unchanging amount of water vapor rises, expands, and cools I know that a parcel of air can rise, cool and create clouds and rain but I'm struggling to understand how:


absolute humidity
relative humidity
actual vapour pressure
saturation vapour pressure


change as a parcel of air with an unchanging amount of water vapour rises, expands and cools.

I think that absolute humidity and relative humidity increase, but is there a difference how absolute and relative humidity behave and how actual vapour pressure and saturation vapour pressure behave?
The imortant point is that absolute humidity is defined as

mass of water per volume of air

So if the parcel of air expands, and still has the same water content, there is less mass of water per volume, hence the absolute humidity decreases.

Maybe most if not all of the question depends on this and is much more clear now?