The Stratus

Stratus

In our review of the different types of clouds we begin to describe on this occasion the Stratus or Strata, which are one of the two genera classified as low clouds. They are described as a generally gray cloud layer, with a uniform base, from which drizzle, ice prisms or cinarra can fall. When the Sun is visible through the layer, its outline is clearly distinguishable. These clouds sometimes appear in the form of frayed shreds (fractus), under other clouds.

Stratus are normally found between 0 and 300 m above the ground and are composed of small water droplets although at very low temperatures they can consist of small ice particles. They are formed by the combined effect of cooling in the lower layers of the atmosphere and turbulence due to wind. Normally they are formed on the ground, for irradiation night or by advection of relatively warm air over colder ground while over the sea, cooling is usually by advection.

Stratus forming a "sea of ​​clouds"

Stratus forming a "sea of ​​clouds"

They produce fog if they are level with the surface. Stratus fractus form as accessory clouds (pannus) below the Altostratus, nimbostratus, Cumolonimbus and Precipitating Clusters. When they produce fogs they are usually associated with anticyclonic weather while when they appear below Altostratus or Nimbostratus they are associated with a Warm Front. They also appear torn under the Cumulonimbus, in full storm or downpour.

They should not be confused with the Altostratus or Nimbostratus, these have a "wet" appearance, while the Stratus have a "dry" appearance. Precipitation in the Stratus It is very weak and in the Nimbostratus it is moderate, therefore it is another discriminatory characteristic.

If they are photographed producing fog, look for reference objects such as trees, buildings or elevations of the terrain. They are interesting to photograph if they appear below the Nimbostratus, torn by rain or snow.

Two species (nebulosus and fractus) and three varieties (opacus, translucidus, undulatus) are recognized in the Stratus.

Source - AEMET

More information - The Nimbostratus, The Altostratus


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