Editing Cloud base (section)

==Weather and climate relevance==
Rain clouds and snow clouds are clouds that have their bases below 2,000 meters above the ground.<ref name="Education 2022 k673">{{cite web | title=Cloud | website=National Geography | date=2022-08-09 | url=https://education.nationalgeographic.org/resource/cloud/ | access-date=2023-09-06|quote=The prefix "nimbo-" or the suffix "-nimbus" are low-level clouds that have their bases below 2,000 meters (6,500 feet) above the Earth. Clouds that produce rain and snow fall into this category. }}</ref>

In well-defined [[air mass]]es, many (or even most) clouds may have a similar cloud base because this variable is largely controlled by the thermodynamic properties of that air mass, which are relatively homogeneous on a large spatial scale. This is not the case for the [[cloud top]]s, which can vary widely from cloud to cloud, as the depth of the cloud is determined by the strength of local [[atmospheric convection|convection]].

Clouds greatly affect the transfer of [[radiation]] in the atmosphere. In the thermal spectral domain, water is a strong absorber (and thus emitter, according to [[Kirchhoff's law of thermal radiation]]); hence clouds exchange thermal radiation between their bases and the underlying planetary surface (land or ocean) by absorbing and re-emitting this infrared radiation at the prevailing temperature – the lower the cloud base, the warmer the cloud particles and the higher the rate of emission. For a synthetic discussion of the impact of clouds (and in particular the role of cloud bases) on climate systems, see the [http://www.grida.no/climate/ipcc_tar/wg1/index.htm IPCC Third Assessment Report], in particular chapter 7.2.

Cloud base is an important meteorological variable for aviation safety, as it determines whether pilots may use [[visual flight rules]] (VFR) or [[instrument flight rules]] for take-off and landing.