[Atomic-S (OP)]

If the sky is overcast, is the quantity of water (grams per meter³) up in the clouds more than, less than, or equal to that at ground level?  What about the quantity of water in relative terms, as a percentage of atmospheric matter?

[evan_au]

This week I had the opportunity to visit a tropical cloud forest. Apparently, it does not rain much, but the clouds that frequently gather around this extinct volcano provide enough moisture to support vigorous growth. It was certainly a very damp and green location inside the forest!

[Atomic-S (OP)]

I wonder how damp and green it was at elevations below the cloud levels, assuming they exist. Dampness in this case might manifest itself more as mugginess.  The question would be, then, whether the actual amount of moisture at the lower level were the same or perhaps more than in the cloud level, but not visible dud to temperature.

[alancalverd]

The water content of saturated air at ground level is generally around 10%. The only difference between a cloud and clear air is that the water in the cloud has condensed into droplets or ice. So given the density of air at -5 deg C is about 1.3 kg/m^3 the water content of a cloud is about 100 - 200 gram per cubic meter.

Parts of some clouds may be a lot denser - the active hail-forming bit of a cumulonimbus could be well above saturation and I would guess contains anything up to 500g/cu m. But wispy cirrus clouds are very widely dispersed ice crystals at -50 deg C or lower, where the saturation concentration is much less - possibly less than 1%.

[evan_au]

I wonder how damp and green it was at elevations below the cloud levels

The landscape was quite hot and dry at sea level, in the rain shadow of the volcano.
This was at Kona, on the big island of Hawaii.

[alancalverd]

Small "dry" islands are often greener than the inhabitants of rainy places (like the UK) can imagine. The mechanism is condensation from warm sea air, which is saturated with water, passing over land which has cooled by radiation at night. Since the nucleation and condensation occurs on "sharp" edges (hairy leaves, tips of grass, "air roots"  etc) precipitation takes place very close to the ground and isn't noticed as rain.

Canary island tomatoes were traditionally grown on volcanic soil with almost no actual rain but a constant westerly sea fog at night.