The clouds
Alessandro Pezzoli, Ph.D.
Sen. Lecturer in Meteo-Hydrology & Weather Risk Management – Politecnico di Torino & Università di Torino (Italy) Meteorologist (Swedish Sailing Federation, SSF)
6th ÷ 7th February 2016 Understanding Clouds and fog
Clouds are usually the most obvious feature of the sky. They both reflect weather patterns and play a role in what the weather does. The links below take you to a great deal of information about clouds.
Locations of clouds
- Low-level clouds: (generally found below 6,500 feet, or 2,000 meters) Low-level clouds are usually composed of liquid water droplets, but they can have snow and ice crystals in cold weather - Mid-level clouds: (generally found between 6,500 and 23,000 feet, or 2,000 and 7,000 meters) Most mid-level clouds are composed of liquid water droplets during summer and a liquid droplet-ice crystal mix during winter. Mid-level cloud names are preceded by an "alto" prefix. - High-level clouds (cirro clouds): (generally found above 20,000 feet, or 6,000 meters) High-level clouds are composed of ice crystals and tend to be very thin - Multi-level clouds: Cumulonimbus are the clouds that can produce lightning, thunder, heavy rains, hail, strong winds, and tornadoes. They are the tallest of all clouds that can span all cloud layers and extend above 60,000 feet.
1000 m=3281 ft 1 ft=0.305 m 1 m=3.28 ft 12 ÷ 18 km Cumulus of Fair Weather: Widely separated heaps with flat bottoms and rounded tops. Small vertical development Ground Fog: Layer of stratus lying on the ground. Forms at night and burns off by morning Stratocumulus: A layer of clumps of cloud with thick and thin areas, often mixed with cumulus Nimbostratus: Widespread thick layer of dark gray cloud producing steady rain Lightning: Electrical discharge between cloud and ground, or cloud to cloud, that occurs in stormy weather cumulonimbus Virga: Precipitation of ice or water that evaporates in warmer, drier lower regions Crepuscular Rays: Open spaces between clouds allow sun to scatter light in 'dirty' air. This comes to eye as illusory diverging rays Stratus: Poorly defined low cloud, usually with ragged edges High (Alto) Stratocumulus: Higher layer of clumpy cloud, sometimes mixed with Cumulus Cumulonimbus Shower: Widely separated showers or squalls of rain, and sometimes hail, developing in tall cloud Cumulonimbus (Base and Top): A massive cloud system with flattish base and top sometimes flattened at base of the stratosphere. The source of lightning and thunder, hail, tornados, heavy localized rain showers Sun Pillar: A beam, or pillar, of sunlight reflected upward from horizontal surfaces of hexagonal ice crystals Cap Cloud: Lenticular cloud that sits on a mountain peak. Caused by ascending air on windward side and descending on the lee side Billow Altocumulus: Unusual long rolls of cloud occurring in alto or cirrocumulus due to shearing motion. Clouds in regions of ascending air; spaces in regions of descending air Swelling cumulus: Separated actively growing heap clouds with flattish bottoms and rounded, hard-edged tops Altostratus: Layer of cloudy air, sometimes thick and preceding rain. Sun seen as if shining through ground glass Altocumulus: Mid-level layered-heap cloud with many convective cells. Thin regions, descending air; thick regions, ascending air Nimbostratus: Widespread thick layer of gray cloud producing steady snow Cumulonimbus: Most active member of cumulus family; flattish base, tops sometimes extending 5 miles Corona: Colored ring about moon and sun due to diffraction of light passing through a water crystal cloud Mamma: Layer of cloud with pouch-like downward extensions, associated with cumulonimbus in latter stages of development "Flying Saucer": Lenticular altocumulus with remarkable symmetry. Wind blows through stationary cloud Cumulus Congestus: An active form of cumulus with many convective cells yielding cauliflower appearances to the top. Base is flattish representing the condensation level. Can produce showers Cirro stratus: Widespread layer of thin veil- like ice crystal cloud. Though it appears thin it can be deceptively thick Cirro cumulus: Layered cloud permeated with small cumuliform lumpiness Cirrus: Ice crystal clouds in wide variety of feathery shapes, evaporating as they precipitate. (A type of virga) Cumulonimbus (top): Top often resembles a flattened anvil which sometimes spreads ahead of main cloud mass. Ice crystal structure indicated by striations; stringiness Halo, 22-1/2 degrees: Colored ring about sun or moon formed as light shines through cirrostratus ice crystals and experiences refraction. Interior, red; exterior, violet Aurora Borealis (Northern Lights): Multi colored light comes from ionized atoms at top of the atmosphere in polar regions Contrail: Cloud formed in wake of jet aircraft, indicative of upper level humidity and wind drift. Note vortex twisting motion Pileus: Fibrous "lid" over cumulus congestus due to cooling uplift in upper air currents Thanks for your attention!!!
The clouds
Alessandro Pezzoli, Ph.D.
Sen. Lecturer in Meteo-Hydrology & Weather Risk Management – Politecnico di Torino & Università di Torino (Italy) Meteorologist (Swedish Sailing Federation, SSF)
6th ÷ 7th February 2016