The Naked Scientists

The Naked Scientists Forum

Author Topic: Flat Cloud Bottoms - Temperature or Air Pressure?  (Read 10273 times)

Offline jysk

  • Jr. Member
  • **
  • Posts: 41
    • View Profile
I've just discovered the general consensus says that the flat bottoms of clouds are governed by the air's temperature.

Now, the trouble is I've seen eagles soaring on warm thermals even on overcast days. Days overcast with flat-bottomed clouds. Having observed this, I suspect that temperatures are not constant enough over large areas and that they are in fact, quite variable. Temperature fluctuations like these would make for lumpy and boiling looking cloud bottoms.

The only constant with respect to the flat bottom seems to be the altitude. (More curious since the "flattnessness" always appears level too.)

Now I've never read this anywhere, but it seems to me the drop in pressure with increasing altitude (not air temperature) is why clouds have flat bottoms. The air pressure at the cloud's base marks the level where water vapor finally saturates and condenses back to it's liquid state. A visible cloud with a well defined lower boundary at a uniform altitude.

Is this right or have I had it backwards all these years?

Mike


 

Offline daveshorts

  • Neilep Level Member
  • ******
  • Posts: 2583
  • Physics, Experiments
    • View Profile
    • http://www.chaosscience.org.uk
Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #1 on: 09/01/2007 08:19:48 »
I would have to think about the thermodynamics more closely, but if you drop the pressure on some air it will cool down, so both are closely related.
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #2 on: 09/01/2007 17:38:36 »
Its neither really, because clouds form when the water vapour in the air condenses out to form droplets now the sunlight warms the ground much more effectively than it does the air so the ground warms up and the air expands and tends to rise and cool down  if it continues to rise for long enough it will cool down enough to cause the water vapour in it to condense out.  This level is known as the cloud base and it can be calculated by knowing the relative humidity of the air at ground level.  OK it is the expansion and cooling of the air as it rises that causes the water vapour to condense but the critical thing is the amount if the air is very wet the cloud base is low if it is dry it can be very high.
 

Offline JimBob

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 6564
  • Thanked: 7 times
  • Moderator
    • View Profile
Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #3 on: 10/01/2007 01:19:07 »
Air currents also play a role, many times a critical role. Often, the passage of a cooler layer of air over a warmer layer will produce clouds.
 

Offline Atomic-S

  • Hero Member
  • *****
  • Posts: 928
  • Thanked: 18 times
    • View Profile
Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #4 on: 17/01/2007 04:59:24 »
So then, I gather, when air rises at differing rates in differing locations, if the humidity is the same, then the cloud base will be the same, because condensation occurs as soon as the air reaches the requisite temperature, which is determined by decompression with altitude?
 

Offline AlphBravo

  • Full Member
  • ***
  • Posts: 65
    • View Profile
Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #5 on: 01/02/2007 22:27:01 »
H'mm certainly a phenomena I have observed, but think it has more to do with air pressure, as why would the whole section of cloud appear flat in the first place so it must have some resistance to make it appear as if grounding, or is it that more condensation has occurred in the lower part as a result of gravity effect?
 

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • Posts: 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #6 on: 01/02/2007 23:55:23 »
I thought that we had cleared this up with the last topic.

It is the combination of temperature pressure and humidity that causes vapour to start condensing out of rising air at a reasonably precise altitude creating what is known as the cloud base
 

The Naked Scientists Forum

Flat Cloud Bottoms - Temperature or Air Pressure?
« Reply #6 on: 01/02/2007 23:55:23 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums