Cloud formation

Cloud formation requires significant amounts of water vapour, adequate condensation nuclei and a cooling mechanism to bring air to saturation.

The most efficient way to cool air is by lifting it to higher altitudes. Ascent may be initiated when:

  • air warmer than its environment becomes buoyant and rises (convection);
  • air is forced to flow up and over higher terrain (orographic);
  • air is forced to rise over frontal surfaces (widespread ascent);
  • winds converge at low levels (sometimes widespread but can be local).

If the rising air is warmer than the surrounding atmosphere and condensation occurs, a cumuliform type of cloud is produced. If the rising air remains cooler than the surrounding atmosphere and condensation occurs, cloud formation is stratiform. Two other important mechanisms for cooling air are:

  • the mixing of warmer air with cooler air (turbulent mixing);
  • air contacting cooler surfaces (conduction).

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