| Stratus cloud |
|
Stratus cloud
|
| Abbreviation |
St |
| Symbol |
|
| Genus |
Stratus (layered) |
| Altitude |
Below 2,000 m
(Below 6,000 ft) |
| Classification |
Family C (Low-level) |
| Appearance |
horizontal layers |
| Precipitation cloud? |
Drizzle, freezing drizzle or snow grains |
Stratus clouds are a genus of low-level cloud characterized by horizontal layering with a uniform base, as opposed to convective or cumuliform clouds that are formed by rising thermals. More specifically, the term stratus is used to describe flat, hazy, featureless clouds of low altitude varying in color from dark gray to nearly white. The word "stratus" comes from the Latin prefix "strato-", meaning "layer".[1] Stratus clouds may produce a light drizzle or a small amount of snow. These clouds are essentially above-ground fog formed either through the lifting of morning fog or through cold air moving at low altitudes over a region. Some call these clouds "high fog" for the fog-like cloud. While light rain may fall, this cloud does not indicate much meteorological activity.
Contents
- 1 Formation
- 2 Description
- 3 Forecast
- 4 Relation to other clouds
- 4.1 Cirrostratus clouds
- 4.2 Altostratus clouds
- 4.3 Nimbostratus clouds
- 4.4 Stratocumulus clouds
- 5 Sources
Formation
Stratus clouds form when a sheet of warm, moist air lifts off the ground and depressurizes, following the lapse rate. This causes the relative humidity to increase due to the adiabatic cooling.[2]
Status clouds are usually formed in an occluded or cold front.
Stratus clouds can also form in a similar manner to fog when the ambient air temperature decreases, increasing the relative humidity. Once the temperature drops below the dew point, a stratus cloud can form.[2]
Description
Stratus clouds look like featureless gray to white sheets of cloud.[2] They can be composed of water droplets, supercooled water droplets, or ice crystals depending upon the ambient temperature.[1]
Subforms
Stratus clouds come in two species: stratus nebulosus and stratus fractus. The nebulosus species has a uniform veil-like appearance, whereas the fractus species are torn and shredded (fractured). Stratus clouds have three varieties: stratus opacus, stratus translucidus, and stratus undulatus. The opacus variety is opaque, the translucidus variety is translucent, and the undulatus variety has undulating layers. Stratus praecipitatio is the only supplementary feature of stratus clouds, and it implies that precipitation is falling from the cloud.[3]
Forecast
A stratus cloud can form from stratocumulus spreading out under an inversion, indicating a continuation of prolonged cloudy weather with drizzle for several hours and then an improvement as it breaks into stratocumulus. Stratus clouds can persist for days in anticyclone conditions. It is common for a stratus to form on a weak warm front, rather than the usual nimbostratus.
Effects on climate
According to Sednev, Menon, and McFarquhar, Arctic stratus and other low-level clouds form roughly 50% of the annual cloud cover in Arctic regions, causing a large effect on the energy emissions and absorptions through radiation.[4]
Relation to other clouds
Cirrostratus clouds
Main article: Cirrostratus cloud
Cirrostratus clouds, a very high ice-crystal form of stratiform clouds, can appear as a milky sheen in the sky[5] or as a striated sheet.[6] They are sometimes similar to altostratus and are distinguishable from the latter because the sun or moon is always clearly visible through transparent cirrostratus, in contrast to altostratus which tends to be opaque or translucent.[7] Cirrostratus come in two species, fibratus and nebulosus.[5] The ice crystals in these clouds vary depending upon the height in the cloud. Towards the bottom, at temperatures of around −35 °C (−31 °F) to −45 °C (−49 °F), the crystals tend to be long, solid, hexagonal columns. Towards the top of the cloud, at temperatures of around −47 °C (−53 °F) to −52 °C (−62 °F), the predominant crystal types are thick, hexagonal plates and short, solid, hexagonal columns.[8][9] These clouds commonly produce halos, and sometimes the halo is the only indication that such clouds are present.[10] They are formed by warm, moist air being lifted slowly to a very high altitude.[11] When a warm front approaches, cirrostratus clouds become thicker and descend forming altostratus clouds,[1] and rain usually begins 12 to 24 hours later.[10]
Altostratus clouds
Main article: Altostratus cloud
Nimbostratus clouds
Main article: Nimbostratus cloud
Stratocumulus clouds
Main article: Stratocumulus cloud
A stratocumulus cloud is another type of a cumuliform or stratiform cloud. Like stratus clouds, they form at low levels;[1] but like cumulus clouds, they form via convection. Unlike cumulus clouds, their growth is almost completely retarded by a strong inversion, causing them to flatten out like stratus clouds and giving them a layered appearance. These clouds are extremely common, covering on average around twenty-three percent of the earth's oceans and twelve percent of the earth's continents. They are less common in tropical areas and commonly form after cold fronts. Additionally, stratocumulus clouds reflect a large amount of the incoming sunlight, producing a net cooling effect.[12] Stratocumulus clouds can produce drizzle, which stabilizes the cloud by warming it and reducing turbulent mixing.[13]
Sources
- Footnotes
- ^ a b c d "Cloud Classification". National Weather Service. Retrieved 2 January 2014.
- ^ a b c "Stratus Clouds". Weather. USA Today. 16 October 2005. Retrieved 2 January 2014.
- ^ "WMO classification of clouds" (PDF). World Meteorological Organization. Retrieved 2 January 2014.
- ^ Sednev, Menon & McFarquhar 2009, p. 4747
- ^ a b "Common Cloud Names, Shapes, and Altitudes" (PDF). Georgia Institute of Technology. pp. 2, 10–13. Retrieved 12 February 2011.
- ^ Hubbard & Hubbard 2000, p. 340
- ^ Day 2005, p. 56
- ^ Parungo 1995, p. 254
- ^ Parungo 1995, p. 256
- ^ a b Ahrens 2006, p. 120
- ^ Hamilton, p. 24
- ^ Wood 2012, p. 2374
- ^ Wood 2012, p. 2398
- Bibliography
- Ackerman, Steven A; Knox, John A (2003). Meteorology: Understanding the Atmosphere. Brooks Cole.
- Ahrens, C. Donald (February 2006). Meteorology Today: An Introduction to Weather, Climate, and the Environment (8 ed.). Brooks Cole. ISBN 978-0-495-01162-0. OCLC 693475796.
- Day, John A. (August 2005). The Book of Clouds. Sterling. ISBN 978-1-4027-2813-6. OCLC 61240837.
- Grenci, Lee M.; Nese, Jon M. (August 2001). A World of Weather: Fundamentals of Meteorology: A Text / Laboratory Manual (3 ed.). Kendall/Hunt Publishing Company. ISBN 978-0-7872-7716-1. OCLC 51160155.
- Hamilton, Gina. Blue Planet – Air (eBook). Milliken Publishing. ISBN 978-1-4291-1613-8.
- Parungo, F. (May 1995). "Ice Crystals in High Clouds and Contrails". Atmospheric Research 38: 249. doi:10.1016/0169-8095(94)00096-V. OCLC 90987092.
- Sednev, I; Menon, S; McFarquhar, G (July 2009). "Simulating Mixed-Phase Arctic Stratus Clouds: Sensitivity to Ice Initiation Mechanisms" (PDF). Atmospheric Chemistry and Physics (9): 4747–4773. Retrieved 2 January 2014.
- Wood, Robert (August 2012). Stratocumulus Clouds 140 (8). doi:10.1175/MWR-D-11-00121.1. ISSN 1520-0493. Retrieved 2 January 2014.
|
Cloud genera and selected species, supplementary features, and other airborne hydrometeors - WMO Latin terminology except where indicated
|
|
| Extreme-level |
- Polar mesospheric cirriform type
- Noctilucent
|
|
| Very high-level |
- Polar stratospheric cirriform type
- Nacreous
|
|
| High-level |
- Tropospheric cirriform, stratiform, and stratocumuliform genera
- Cirrus (Ci)
- Cirrostratus (Cs)
- Cirrocumulus (Cc)
- General type (non-WMO terminology)
- Aviaticus cloud (Contrail)
|
|
| Medium-level |
- Tropospheric stratiform and stratocumuliform genera
- Altostratus (As)
- Altocumulus (Ac)
- Stratocumuliform species
- Altocumulus castellanus (Ac cas)
|
|
| Low-level |
- Tropospheric stratiform, stratocumuliform and cumuliform genera
- Stratus (St)
- Stratocumulus (Sc)
- Cumulus (Cu)
- Stratiform and cumuliform species
- Fractus
- Cumulus humilis (Cu hum)
- Stratocumulus variants (non-WMO terminology)
- Actinoform cloud
- Undulatus asperatus
|
|
| Moderate vertical |
- Tropospheric stratiform and cumuliform genera
- Nimbostratus (Ns)
- Cumulus (Cu)
- Cumuliform species
- Cumulus mediocris (Cu med)
- Cumuliform supplementary features
- Cumulus Pileus
- Cumulus Arcus (Roll)
|
|
| Towering vertical |
- Tropospheric cumulonimbiform genus
- Cumulonimbus (Cb)
- Cumuliform species
- Cumulus congestus (ICAO term Towering cumulus [Tcu])
- Cumuliform and cumulonimbiform supplementary features
- mamma
- Tuba (Funnel cloud)
- Pileus
- Arcus (Shelf)
- Cumuliform and cumulonimbiform variants (non-WMO terminology)
- Wall cloud
- Pyrocumulus
- Pyrocumulonimbus
- Cumulonimbus Overshooting top
- Hot tower
|
|
| Surface based |
|
|
| Non-height specific |
- General types
- Accessory cloud
- Kelvin-Helmholtz cloud
|
|
