Cloudiness of the atmosphere

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Cloudiness in the atmosphere are common phenomena that first become noticeable in a reduction in visibility , often also through reduced solar radiation . They are primarily a research topic in meteorology , but also other sciences such as climatology , observational astronomy or volcanology .

The air is clouded either by small water droplets or by suspended solid particles ( aerosols ). The following can contribute to haze and other cloudiness:

Types of air cloudiness

A distinction is made with regard to the type and intensity of air cloudiness

  • Hazy weather: only weak cloudiness with visibility of several kilometers
  • Haze : turbidity with visibility> 1 km, water vapor still below the saturation limit
  • Haze over cities (due to air pollution), occasionally also over basins , the strongest in the so-called
  • light to heavy fog ( air saturated with water vapor , different degrees of condensation of the water droplets on small suspended particles, fog and haze - in contrast to clouds - always have contact with the ground )
  • Altitude smoke : air cloudiness through smoke, the finest ash and similar aerosols at high altitudes, e.g. B. from bog or clearing fires and volcanic eruptions
  • Dust storm : Visibility is obscured by particles with grain sizes from 0.002 mm to 0.06 mm ( silt ), can reach up to great heights
  • Sandstorm : Particles with grain sizes of 0.06 to 2 mm ( sand particles ), mostly only a few meters above the ground
  • Ash cloud from a violent volcanic eruption . In the event of a strong eruption, it can spread over the whole earth ( volcanic winter ) and be visible for months, see also year without summer
  • Several times in the history of the earth, large meteorite impacts caused rock debris to be thrown up into strong twilight for months to years and to the mass extinction of many species due to a lack of light and food.

Water vapor and aerosols

In the case of haze and fog, the influence of the water droplets outweighs that of the suspended particles. The hygroscopic nature of the aerosol particles causes condensation below vapor saturation. However, the droplets only grow as long as the particles can bind moisture and the influence of the surface forces remains low. The maximum droplet size is therefore limited to around 1 μm.

Haze and fog often arise in inversion weather conditions , where no vertical air exchange can take place. In conurbations and industrial zones with high levels of air pollution, one speaks of smog , in which the aerosols consist of a mixture of soot (e.g. from diesel engines), sulfur dioxide (SO 2 ), dust and smoke particles (wood heating).

In dust and sand storms as well as volcanic ash clouds, the (here larger) aerosols themselves are responsible for the clouding of the air, because they can be up to a millimeter in size.

See also

Literature and web links