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Concept
Cloud albedo
Résumé
Cloud albedo is a measure of the albedo or reflectivity of a cloud. Clouds regulate the amount of solar radiation absorbed by a planet and its solar surface irradiance. Generally, increased cloud cover correlates to a higher albedo and a lower absorption of solar energy. Cloud albedo strongly influences the Earth's energy budget, accounting for approximately half of Earth's albedo. Cloud albedo depends on the total mass of water, the size and shape of the droplets or particles and their distribution in space. Thick clouds (such as stratocumulus) reflect a large amount of incoming solar radiation, translating to a high albedo. Thin clouds (such as cirrus) tend to transmit more solar radiation and, therefore, have a low albedo. Changes in cloud albedo caused by variations in cloud properties have a significant effect on global climate.
On a microscopic scale, clouds are formed through the condensation of water on cloud condensation nuclei, such as pollution and aerosol particles. The size, concentration, structure, and chemical composition of these particles influence cloud albedo. For example, black carbon aerosol particles absorb more solar radiation and sulfate aerosol reflects more solar radiation. Smaller particles form smaller cloud droplets, which tend to decrease precipitation efficiency of a cloud, increasing cloud albedo. Additionally, more cloud condensation nuclei increases the size of a cloud and the amount of reflected solar radiation.
Cloud albedo on a planet varies from less than 10% to more than 90% and depends on drop sizes, liquid water or ice content, thickness of the cloud, solar zenith angle, etc.
A cloud's liquid water path varies with changing cloud droplet size, which may alter the behavior of clouds and their albedo. The variations of the albedo of typical clouds in the atmosphere are dominated by the column amount of liquid water and ice in the cloud. The smaller the drops and the greater the liquid water content, the greater the cloud albedo, if all other factors are constant.
Source officielle
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