1 / 33

Clouds

Clouds. SOEE1400: Lecture 3. Cloud Classification. Four latin terms form the basis for the naming of clouds: Cirrus : fibrous or hair-like Cumulus : a heap or pile Stratus : a horizontal sheet or layer Nimbus : rain-bearing The prefix Alto is used to indicate medium altitude clouds.

latoyah
Download Presentation

Clouds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Clouds SOEE1400: Lecture 3

  2. Cloud Classification Four latin terms form the basis for the naming of clouds: • Cirrus : fibrous or hair-like • Cumulus : a heap or pile • Stratus : a horizontal sheet or layer • Nimbus : rain-bearing The prefix Altois used to indicate medium altitude clouds. Terms, and basic classifications first proposed by Luke Howard in 1803. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml - good online guide SOEE1400 : Meteorology and Forecasting

  3. Precipitation • Cloud droplets require a condensation nucleus (CCN) on which to form; growth then occurs by deposition of water molecules from vapour. CCN are abundant. • Cloud droplets are typically 10 to 30 m in diameter. Growth/evaporation can occur within a few 10s of seconds. • Rain drops are typically 0.5 to 5 mm in diameter, growth from the vapour would take several hours – longer than the lifetime of typical convective clouds. SOEE1400 : Meteorology and Forecasting

  4. Ice nuclei (IN) are not abundant – in many cases ice will not form spontaneously unless the temperature is down to about -40°C • The air is commonly supersaturated relative to ice • Commonly there are just a few ice crystals, which then grow very fast, “stealing” all the available water, and falling out of the cloud as they grow large. • Ice crystals provide a more efficient process of forming rain • Saturation vapour pressure over ice is less than that over water  ice crystals grow at expense of water droplets • If ice crystal touches a cold droplet, the droplet freezes • Once large enough, ice crystals – or clumps of crystals – fall past droplets and collect them. Rapid growth of soft hail pellet (graupel) by riming. • Graupel falls from cloud, melting before reaching the surface as rain SOEE1400 : Meteorology and Forecasting

  5. High Level: (cirro-) • Cloud base above 6000m • Are all forms of cirrus (ice clouds) Medium Level: (alto-) • Cloud base 2000-6000m Low level: • Cloud base below 2000m (within boundary layer) SOEE1400 : Meteorology and Forecasting

  6. High-Level Clouds Cirrus (Ci): White, delicate, fibrous in appearance. Forms in patches or narrow bands. May for comma-shaped streaks or “mare’s tails” (cirrus uncinus) Cirrus clouds are formed entirely of ice crystals. These grow and evaporate slowly, leading to soft edges to clouds. SOEE1400 : Meteorology and Forecasting

  7. Cirrostratus (Cs): Thin, transparent sheet or veil; sun clearly visible & casting shadows at surface. A halo may be seen around the sun (or moon). Sheets of cirrostratus may cover entire sky, and be up to several 1000m deep. SOEE1400 : Meteorology and Forecasting

  8. Cirrocumulus (Cc): Thin white patch or sheet of cloud; appears dappled or rippled. Dappling results from convective overturning within the cloud, ripples from gravity waves. Aircraft contrails: condensation from aircraft exhaust. May dissipate quickly, or be very long-lived depending on conditions. SOEE1400 : Meteorology and Forecasting

  9. Medium-Level Clouds Altostratus (As): A greyish sheet of cloud, may be fibrous or uniform in appearance. Thin enough in parts to make out the sun, but no halo. SOEE1400 : Meteorology and Forecasting

  10. Altocumulus (Ac): white or grey patches arranged in sheets. Shape and texture are variable. There are several distinct sub-classes of altocumulus SOEE1400 : Meteorology and Forecasting

  11. Altocumulus lenticularis (Ac len): white or grey lenticular (lens shaped) clouds formed by the lifting of air over a topographic barrier. SOEE1400 : Meteorology and Forecasting

  12. Altocumulus castellanus (Ac cas): white or grey, broken cumulus-like clouds; upper part appearing castle-like. Sometimes arranged in lines. SOEE1400 : Meteorology and Forecasting

  13. Altocumulus undulatus (Ac und): white or grey patches or sheets of cloud with an undulating or rippled appearance. SOEE1400 : Meteorology and Forecasting

  14. Low-Level Clouds Cumulus (Cu): Brilliant white to grey, dense detached clouds. Forms clumped or heaped (cauliflower-like) shapes, usually with sharp outlines and flat base. Field of Cu often have bases all at same (lifting condensation) level. SOEE1400 : Meteorology and Forecasting

  15. Cumulus humilis (Cu hum): small cumulus, of limited vertical extent, may have a flattened appearance. Also called fair-weather cumulus SOEE1400 : Meteorology and Forecasting

  16. Cumulus mediocris : cumulus, of moderate vertical extent. SOEE1400 : Meteorology and Forecasting

  17. Cumulus congestus: crowded (congested) field of cumulus or greater vertical extent. May produce rain. SOEE1400 : Meteorology and Forecasting

  18. Congestus over Benin, 17 August 2006 SOEE1400 : Meteorology and Forecasting

  19. Pileus : cap clouds that form above large cumulus as the upward motion of the convective cloud distorts the layer of air above (pileus is latin for skull-cap) SOEE1400 : Meteorology and Forecasting

  20. SOEE1400 : Meteorology and Forecasting

  21. Pileus over Benin, 17 Aug 2006 SOEE1400 : Meteorology and Forecasting

  22. Cumulonimbus (Cb) : huge towering cloud, dark base and white sides. Associated with heavy rain, thunderstorms, and hail. Frequently has an anvil shaped top. SOEE1400 : Meteorology and Forecasting

  23. More Cb SOEE1400 : Meteorology and Forecasting

  24. mammatus : smooth, rounded shapes sometimes formed on the underside of cumulonimbus; they result from downdrafts within the cloud. SOEE1400 : Meteorology and Forecasting

  25. Arcus cloud (over Lincolnshire). This cloud appears at the head of the “cold pool” of low level air which is produced by the rainfall in a cumulonimbus storm. It indicates the location of the “gust front”. SOEE1400 : Meteorology and Forecasting

  26. Arcus cloud (over Benin, August 2006). This cloud appears at the head of the “cold pool” of low level air which is produced by the rainfall in a cumulonimbus storm. It indicates the location of the “gust front”. Here we can see rainfall behind the gust front. SOEE1400 : Meteorology and Forecasting

  27. Stratocumulus (Sc) : white or grey sheet of cloud, usually formed in mounds or rolls. SOEE1400 : Meteorology and Forecasting

  28. SOEE1400 : Meteorology and Forecasting

  29. SOEE1400 : Meteorology and Forecasting

  30. Stratocumulus with virga – hair-like strands of falling rain, which evaporate below cloud before reaching the surface. SOEE1400 : Meteorology and Forecasting

  31. Stratus (St) : grey featureless layer of cloud with a uniform base. Often associated with drizzle or snow. SOEE1400 : Meteorology and Forecasting

  32. Nimbostratus (Ns) : Dark grey, featureless, thick layer of cloud. Associated with prolonged precipitation. Commonly forms in frontal systems SOEE1400 : Meteorology and Forecasting

  33. Homework, 30 January – 3 February 2012 • For the same time each day, make a note (and a photo, if possible) of the cloud types and nearest-in-time satellite image (from the Dundee site). • Put these into a word document, less than 2 Mb. • Email the document to me before 6 February. SOEE1400 : Meteorology and Forecasting

More Related