[Efrem]

Efrem  asked the Naked Scientists:
   
Dear Chris!
 
When in an aeroplane one can see the clouds lined up at the same level/altitude. Basically they seem as a flat carpet  below you. When it is cloudy on the ground it is not above the clouds.
 
So my question is what is the science behind the condensation of water at that level? Or is it different depending on which part of the world you are?
 
By the way I enjoy the show and you are always in my i pod and you live in my ears. Keep up the good work and I hope your funding goes on forever. Will you run out of questions to discuss?
 
Efrem

What do you think?

[lyner]

Hi Efrem

Imagine a cloud starting off as a volume of warm air at ground level. The energy that was used to warm up the air can be used to raise it up in the same way as lifting a piece of metal. The air will stop rising at a particular height - when it has reached the same density as the air it's floating in; all the added energy has been used up in the gained Gravitational Potential Energy. As it rises, its temperature will drop and water droplets (may) form - making a cloud. If all the air in a given area starts off at the same temperature, all the clouds will end up at the same height.
Hope that helps.

[dnwx]

The easiest way to answer your question is: "For a cloud to form, a part of the atmosphere must be cooled below it's dew point"

We see this in the type of cloud that is forming. Stratiform clouds develop when the atmosphere is stable. The presence of stratiform clouds tells us that there is widespread atmospheric coling, this is usually the result of adiabatic expansion. Although it can be because of contact with the ground which is at a lower temperature, the apperance of fog for example.
This link easily explains the adiabatic process with nice pictures:
http://www.srh.noaa.gov/jetstream/synoptic/clouds.htm

There will be people that disagree with the material in that link, they will state that "air is not a sponge"; whilst this is true, it's nice to keep things simple and easily understood. You can always look at this link as to why "air is not a sponge" http://www.ems.psu.edu/~fraser/Bad/BadClouds.html

On the other hand Cumiliform clouds are the result of instability. They are a "visual evidence of convection". .
A good resource is provided by The Met Office: http://metoffice.gov.uk

This link to a pdf file should provide you more than enough information and is presented in an easy to understand way. http://www.metoffice.gov.uk/corporate/library/factsheets/factsheet01.pdf

Another way that clouds form that is not mentioned in the file is through the recondensation of evaporated moisture from raindrops, these types of cloud are called scuds. You will have seen these on an overcast rainy day when the sky was full of dark unorganised layered nimbus clouds. they are small black raggy looking clouds that move very fast below the main cloud.