What holds clouds together?

[Xerxes]

I was taking a flight back to the UK the other day, looking out of the window and got to wondering; what holds clouds together? On a sunny day over here you can get single (large) clouds (can't remember the name... cumulo-nimbus? Something like that) scudding across the sky. Given that there's probably a fair amount of wind up there, they seem to hold their shape pretty well. I guess what I'm asking is that if they're a collection of water droplets, why don't they behave a bit more like a gas and disperse?

Over to you _{and I'm really hoping the answer isn't something that an average 5 year knows}

[Enola Straight]

There is no bonding action between the water droplets in a cloud.

Condensation of vapor occurs due to any one of three factors:

A drop in temperature,
A drop in pressure,
Or a rise in humidity.

Clouds have just a slight difference in atmospheric conditions than the surrounding non-cloudy areas.

Actual precipitation occurs when the difference becomes significant enough to reach a certain significant point.

[Xerxes]

Thanks enolan, that answers most of it. I guess that I'm still surprised that the strength of the wind doesn't tend to homogenise the very local atmospheric conditions..... sometimes some of these clouds can be going at quite a pace.

[Demo]

Xerxes, I always thought that was strange too.

But, you actually can see the clouds getting "mixed in" and homogenizing with the rest of the surrounding air, especially when then are small eddies or the cloud(or fog)bank is being channeled through a narrow space. You can also see the cloud being "torn apart" where two different weather fronts meet each other and a cold front is pushed under a warm front.

Generally, if it is a stable blow, though, the whole pattern of weather can move pretty much intact. This is when you see clouds flying across the sky.

Funny, I actually asked this same question in a metereorology class a few years ago. I wish I could remember the teacher's explanation better.

[barbitu8]

The single, large clouds ae cumulus. They are fair weather clouds. Cumulo-nimbus are rain clouds. They are the clouds from which thunderstorms occur. Nimbus clouds are similar, but do not have as much elevation. Stratus clouds are the steady rain clouds, and they can form from cirrus (wispy tails) and are then called cirro-stratus, analagous to cumulo-nimbus.

Now, what's the question again? Oh. Well I heard that clouds are continuing dispersing, but also continuing reforming. So my take on this is that if the moisture is there, the dew level has been reached, or there is sufficient instability, altho they may be dispersed by winds, they are also continuing to be reformed. IANAM and this, as I said, is just my guess.

[casdave]

I always wondered what held them apart, I mean there's nothing in between them right ?

Clouds are made of stuff ?

Stuff pulls itself together in the long run so what keeps them apart? Why isn't there just one very large cloud?

What? there is ? and it's always over Northern England no wonder the bloody Londoners always looks so smug, pushing all their clouds oop north, southern jessies!!

[Demo]

Well, the way I've always thought of it was by looking at it in 3D. Imagine columns or pillars of hot, moist air rising from certain terrain features. When they get high enough, and cool enough, they release the moisture in the form of clouds or precipitation. That can cause a blanket of cloud cover or individual clouds, depending on how it is rising. At the same time, if there is a wind blowing, it can move that whole pattern of weather one way or another. If it is turbulent enough, it can knock it apart. Weather is so anomalous so often and so little understood that it's hard to conceptualize though.

I'll let you in on a little secret though, casdave. We Californians decided a few years ago to secretly export all our clouds and fog to England using surplus B52s enhanced with sky hooks. Don't tell anyone.

[reprise]

Duct tape.

[GargoyleWB]

It's important not to think of clouds as fixed static objects. They are dynamic, constantly forming and dispersing and strecthing and roiling and perturambulating and...you get the idea.

Just as often, clouds are smeared into a great mass. Overcast layers and stratus clouds are far more common than the picturesque puffy popcorn cumulus.

Clouds tend to intiate their formation in "lumps" however because of the optical/reflective properties of water vary vastly between its vapour state (individual molecules suspended in the air) and liquid state (large accumulated droplets of clouds). As soon as a pocket of air reaches a temperature that forces water to condense into droplets, a cloud starts to form. A "chain reaction" starts as the cloud blocks out the sunlight from the air below, lowering the surrounding air temperature, forcing that air to subsequently condense into cloud, and so on and so on...combine this with the air turbulence associated with the cooling of the air and suddenly all sorts of cloud shapes and growth paths become possible.

This all takes time and is a slow process, so we tend to think of clouds as fixed pockets of moisture that happily wander their way across the world. Watching time-lapse movies is probably the best way to get to understand the critters.

[Xerxes]

Yes, of course. I'd forgotten I've seen time-lapse of clouds a good few years ago. Thanks to you and all for the input....