Naked Science Forum
Life Sciences => The Environment => Topic started by: chris on 25/04/2008 23:13:46
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What causes the formation of different cloud types (stratus, cumulus, cirrus and so on), and how can they exist together at the same time?
Chris
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Is it because we have little pockets of different air temperatures wind conditions and such.. like changes in evaporation from one place to another? humidity etc..
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A quick reply.
Well, most books or websites will tell you that there are between two and four different ways. I think there are six!
The most obvious way is through convection. This is the rapid rising of locally heated air, otherwise known as 'thermals'. The most obvious cloud that this produces, is the short lived cumulus cloud. If this cloud was to remain stationary, and you were a keen observer then you would be able to see the thermals in action. The 'fluffy' tops of the cloud would look like a fountain, rising and falling, always changing shape. They are however, soon moved on by the slightest of winds
Then you have Orographic lifting, which is the formation of clouds by forcing air over a mountain, hill or high ground. A common cloud associated with this is the altocumilus lenticularis, strangely enough i see these around my local area which is quite flat!
Then there is the 'interaction' of fronts. These basically force warm air to rise above cold air (warm and cold fronts).
And then you have terbulent air which is caused by friction.
But you also have clouds that are manmade, the burning of large grassed areas, bush fires etc. these produce 'pyrocumulus' clouds
And the clouds you see above the chimneys of powerstations, these are 'fumulus' clouds.
Different types of cloud can exist in your field of vision because they may be at different altituteds. The part of the atmosphere where clouds form id the troposphere, and this is divided in to three sections. Low, mid and high, different clouds are found in different sections, although some clouds such as cumulonimbus grow tall enough to occupy more than one layer.
Then again, the cumulonimbus really isn't a single cloud...is it?
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The parcels, layers and packets of air above you are unique, differing in the air pressure, moisture content and it's stability or lack of. If you are looking up and seeing cumulus then you 'know' that there are thermals at work.
To visualise this, imagine the weather last weekend. It was dry, warm and (for me) the sky was relatively cloud free. If we say the temperature was 20 degrees C and the dew point was 10C, we then say that a bubble of cloud free air leaves the heated ground as a thermal. We know the air is unsaturated and that this air will decrease in temperature at a rate of 9.8C per Km.
After the bubble of air has ascended 100m, the temperature is now 19C, and so on until it reaches it's dewpoint temperature of 10C. Should the bubble continue to rise, the water vapour will condense. This condensation marks the beginning of the cloud, not only that but it is also the reason why some cloud bases are flat, they are flat because this is their dewpoint level, a sort of invisable shelf.
This invisable shelf is similar to why cumilunimbus have a flat anvil top, instead of sitting on a shelf, they are hitting an invisable ceiling which is either an inversion or the top of the troposphere.
Should these cumulus continue to develop, they may turn in to (cumulus) fractus, congestus, mediocris and even cumulonimbus.
In turn cumulus clouds may spread out and form stratocumulus, so in one skyscape you may have more than one form of cumulus plus stratocumulus.
Stratocumulus can also form when low level stratus ascends on thermals and breaking up during the process. So you see, clouds become other clouds.
Another reason why you may notice the skyscape changing is a warm or cold front moving in, stormy weather approaching, a trough......You can even see the jetstream with the aid of cirrus cloud.