1!Lecture Ch. 8a!• Cloud Classification!• Precipitation Processes!Curry and Webster, Ch. 8!Please complete online evaluations!!Cloud Classification!2!10 main cloud types!1. Cirrus (Ci)!2. Cirrocumulus (Cc)!3. Cirrostratus (Cs)!4. Altocumulus (Ac)!5. Altostratus (As)!6. Nimbostratus (Ns)!7. Stratocumulus (Sc)!8. Stratus (St)!9. Cumulus (Cu)!10. Cumulonimbus (Cb)!All high clouds!Middle clouds!Grayish, block the sun, sometimes patchy!Sharp outlines, rising mounds, bright white!Cumulus Clouds!Swelling Cumulus Active heaped-up cloud with flat bottom and growing cauliflower top. [http://www.fox8wghp.com/spacious.htm]!10.2 Cumuliform Clouds!Types of cumulus!• Fair weather cumulus!– Horizontal/vertical scale = 1 km!– No precipitation!• Towering cumulus!– Horizontal/vertical scale = several km!– Frequently precipitate!• Cumulonimbus!– Vertical extension to tropopause with anvil tops!– Width = 10s of km!– Heavy precip, lightning, thunder, hail!• Mesoscale convective complex!– Aggregation of cumulonimbus (100s of km)!– Large amount of rain!– Can develop circulation pattern!Southeast Pacific!Cumulonimbus Clouds!Cumulonimbus Massive cloud system producing heavy showers, sometimes with hail. Most active clouds may have lightning and thunder. A few spawn tornadoes. [http://www.fox8wghp.com/spacious.htm]!10.2 Stratus Clouds!Stratus Low lying layer of cloud (called fog if on the ground) with no structure. [http://www.fox8wghp.com/spacious.htm]!10.23!Cirrus Clouds!Cirrus! An ice crystal cloud, wispy in appearance. May produce ice crystal snow in winter or in mountains. [http://www.fox8wghp.com/spacious.htm]!Altostratus Clouds!Altostratus Thickly layered water droplet cloud. Sun seen as through ground glass. [http://www.fox8wghp.com/spacious.htm]!Nimbostratus Clouds!Nimbostratus Thick layered cloud - usually dark gray. Produces continuous rain or snow over large area. [http://www.fox8wghp.com/spacious.htm]!Fog!http://www.tqnyc.org/2009/00767/fog.jpg!Global Cloud Distribution"Zonally averaged climatology of cloud type"Cirrus!Cumulonimbus!Altitude (km)!Latitude!Altostratus!Nimbostratus!Stratus!Cumulus!Cloud Types and Drop Sizes!• Frequency distributions of the mean cloud droplet size for various cloud types!4!Decoupling of Stratocumulus-Topped Boundary Layer!Drizzle evaporates, net cooling!Drizzle forms, net warming!Observations: "Varying cloudy structure!R. Wood, 11/17/10!Precipitation Processes!• Collision/coalescence (accretional growth)!Small, spherical drop!Larger, spherical drop!Largest, spherical drop!Larger than 3 mm, drops break up due to aerodynamic forces!Ice crystals!5!Larger drops are faster so they collide with the smaller drops in their way.!Whether or not the two particles stick is determined by the collection efficiency!Collection Efficiency E is the probability that a collision AND coalescence event will occur.!r/R = 0.2!Flow field around large particle will move smaller particle, lower E !r/R = 1!Inertia of collected drop increases, higher E !Drop Growth and Size!• Bigger particles (~25 micron) grow faster !Drops above this size grow and precipitate!Precipitation and Drop Size!• Terminal velocity increases with drop size!• Precipitation occurs when !!– terminal velocity exceeds updraft velocity!Precipitation and Cloud Type!• Precipitation depends on!– Condensed water (water and temperature)!– Updraft velocity (dynamics)!– Temperature (cold or warm processes)!– Drop size (aerosol effects)!6!Stochastic collection model: based on probability!10% collide (w/ drops outside this population)!10% collide (w/ drops outside this population)!Diffusion of water onto ice in water-saturated environment!Slow growth by collision/coalescence!Aggregation is slower!Collision/coalescence is faster for larger droplets!Liquid Water Path!MODIS cloud LWP, and cloud temperature, used to determine adiabatic h!PBL Clouds are thin!!Adiabatic cloud thickness of stratiform boundary layer clouds!Precipitation Efficiency!Depth of precip!Adiabatic precipitation rate! Precip. Efficiency =
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