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I heard there were powerful convective movements in clouds which were responsible for increasing the size of water droplets or ice crystals. My question is: do the same movements appear outside of clouds? Or in other words: what's so special about a cloud that makes it host these convective movements? Couldn't warm, dry air also create those movements?

If my question is not clear, don't hesitate in asking me for details.

Update: Another way to phrase the question would be: Are convective movements in clouds different than those not in clouds?

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The question title, but not the question body seems to ask if areas without convective activity exist. The answer to that is yes. Most obviously the stratosphere (whose name implies startification), but also whenever the temperature gradient with height is lower than the adiabatic lapse rate, convective activity will be damped because it is energetically unfavorable. –  Omega Centauri Jul 30 '11 at 22:29
    
Perhaps I didn't ask my question right. I meant to ask about the differences between convective movements in clouds and those not in clouds. So, for example, if we have 2 zones with temperature gradients higher than the adiabatic lapse rate, one of which has a big cloud in it, one which doesn't, will the convective movements in these 2 zones be different due to the presence-VS-absence of clouds? @user1631's answer seems to suggest the convective movement in the zone WITH clouds could be stronger due to the energy released when the water condenses. What do you think? –  Shawn Aug 1 '11 at 4:01
    
Just thought of another thing: Is it possible for a cloud to have no convective activity? –  Shawn Aug 1 '11 at 4:05

3 Answers 3

up vote 2 down vote accepted

Lets put it another way though @user1631 is correct :

There are convective movements in the atmosphere due to non uniform absorption of heat and release of energy through radiation due to ground formations ( ocean, land, mountain, desert), altitude, latitude, Coriolis forces, atmospheric tides etc. Generally air will move from hot to cold generating high pressure and low pressure areas which move slowly from west to east ( Coriolis).

If humidity and dew point are right, clouds form at high altitudes. Clouds change the density of air and general properties of emission and absorption of radiation and can create stronger convective currents up to cyclones in a feedback system.

So the answer is: there exist convective atmospheric motions, even strong ones ( sandstorms for example) without clouds, but clouds amplify by their properties convection effects also.

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Could you give me examples of properties that clouds have which could amplify convection? –  Shawn Aug 2 '11 at 13:55
    
Condensation into droplets release heat which increase upwards wind currents. See atmos-chem-phys-discuss.net/10/24015/2010/… for a model using this. –  anna v Aug 2 '11 at 17:00

In general, yes the updrafts also occur in warm dry air, as a result of heating on the ground which produces hyrdostatic instability in the atmosphere. As the updrafts go higher, they cool adiabatically and may, if they go high enough and if there is enough moisture in the air, cool enough to condense water vapor and form clouds. However there can also be very strong thermal updrafts on perfectly clear days. It is possible to predict if and at what altitude clouds will form fairly accurately based on temperature vs. altitude profiles obtained by weather balloon, together with dewpoint measurements and predicted high temperatures near the ground.

The condensation of water vapor, if it occurs, will release latent heat which can strengthen the updraft. In extreme cases this results in thunderstorms.

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Does that mean that where there is a cloud, there is forcibly convective movement? –  Shawn Aug 1 '11 at 4:07
    
I wouldn't say clouds are always associated with convective movement. Certain types of clouds, such as cumulus or cumulonimbus usually are though. –  user1631 Aug 1 '11 at 18:10

Water vapor inside clouds condenses into droplets that fall trough the cloud. If the cloud has sufficient up drafts then the droplet or crystal, if it's cold enough, will rise through the cloud gaining more mass before finally it becomes too heavy and the up draft is no longer neough to prevent it from falling out of the cloud. In extreme cases this can lead to hailstones the size of tennis balls. This sort of phenonmenom if usually associated with extreme weather.

In general you see up drafts that are more moderate. For example glider pilots use up drafts in the atmosphere to gain lift for their aircraft. Typically these are associated with geographical features, like cliffs and ridges, or differing land use patterns that cause the air near the ground to heat up due to differing colors etc.

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