Mystery of Large Cloud Bottoms: Why Are They Flat?

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Discussion Overview

The discussion revolves around the phenomenon of flat bottoms in large clouds, exploring the reasons behind this characteristic. It includes theoretical explanations related to atmospheric conditions and cloud formation processes.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant suggests that a layer of air with different temperature or pressure prevents cloud formation, leading to flat bottoms, similar to the anvil-shaped tops of tall clouds.
  • Another participant questions why this layer is abrupt rather than exhibiting a gradual transition.
  • A further contribution explains that in convective cloud formation, warm humid air rises until it cools enough for condensation, defining the cloud base, which can appear flat if temperature and humidity are uniform at that height.

Areas of Agreement / Disagreement

Participants present various explanations for the flat bottoms of clouds, but no consensus is reached regarding the nature of the layer that influences this characteristic or the reasons for its abruptness.

Contextual Notes

There are assumptions regarding the uniformity of temperature and humidity that are not fully explored, and the discussion does not address potential variations in atmospheric conditions that could affect cloud formation.

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Why are the bottoms of large clouds flat?
 
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Because there's a layer of air there with a different temperature or pressure (depending) that's not conducive to cloud formation. It's the same reason that very tall clouds, thunderheads for instance, have flat "anvil-shaped" tops.
 
Why is this layer so abrupt instead of being like a transitional gradient?
 
in convective cloud formation, warm humid air rises until the point that it is cooled sufficiently for water to condense (i.e. reaches its dew point). This point is called the cloud base, and significant condensation will not occur below it. As long as the air has a fairly uniform temperature at a given height, and the rising air is of fairly uniform humidity, this should give a pretty flat cloud base.
 

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