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Lecture Ch. 8a Cloud Classification

VIEWS: 15 PAGES: 6

									                      Lecture Ch. 8a

     •  Cloud Classification

     •  Precipitation Processes





Curry and Webster, Ch. 8

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                                        Cloud Classification





                                                               1

                                                                                                                                                           10.2




                                   

                 10 main cloud types                                                                   Cumulus Clouds

1.  Cirrus (Ci)
                                                                Swelling Cumulus
2.  Cirrocumulus (Cc)
       All high clouds
                                     Active heaped-up cloud
3.  Cirrostratus (Cs)
                                                            with flat bottom and
                                                                                  growing cauliflower top.
4.    Altocumulus (Ac)
                                                           [http://
                                  Middle clouds

5.    Altostratus (As)
                                                           www.fox8wghp.com/
6.    Nimbostratus (Ns)
                                                          spacious.htm]

                            Grayish, block the sun, sometimes patchy

7.    Stratocumulus (Sc)

8.    Stratus (St)


9.  Cumulus (Cu)

10.  Cumulonimbus (Cb)
     Sharp outlines, rising mounds, bright white





                                                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
                                           Southeast Pacific

                                                                                –  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





                                                                     10.2                                                                                  10.2




              Cumulonimbus Clouds
                                                                        Stratus Clouds

  Cumulonimbus                                                                  Stratus
    Massive cloud system                                                           Low lying layer of cloud
    producing heavy showers,
    sometimes with hail. Most                                                      (called fog if on the
    active clouds may have                                                         ground) with no structure.
    lightning and thunder. A                                                       [http://
    few spawn tornadoes.                                                           www.fox8wghp.com/
    [http://www.fox8wghp.com/                                                      spacious.htm]

    spacious.htm]





                                                                                                                                                                  2

                                   Cirrus Clouds
                                            Altostratus Clouds

  Cirrus
                                                                       Altostratus
         An ice crystal cloud, wispy                                              Thickly layered water
         in appearance. May                                                       droplet cloud. Sun seen as
         produce ice crystal snow in                                              through ground glass.
         winter or in mountains.
                                                                                  [http://
         [http://
         www.fox8wghp.com/                                                        www.fox8wghp.com/
         spacious.htm]
                                                           spacious.htm]





                           Nimbostratus Clouds
                                                           Fog

Nimbostratus
  Thick layered cloud -
  usually dark gray.
  Produces continuous rain
  or snow over large area.
  [http://
  www.fox8wghp.com/
  spacious.htm]





                                                                                                                 http://www.tqnyc.org/2009/00767/fog.jpg





                      Global Cloud Distribution
               Zonally averaged climatology of cloud type                          Cloud Types and Drop Sizes

                                                                           •  Frequency
                                                      Cirrus
                 distributions of the
                                                                              mean cloud droplet
   Altitude (km)





                                                                              size for various
                                                                              cloud types

                                                          Cumulonimbus

                               Altostratus
                     Cumulus

                    Stratus


                                    Nimbostratus

                                              Latitude





                                                                                                                                                            3

       Decoupling of Stratocumulus-Topped Boundary Layer


                                                                        Precipitation Processes

 Drizzle forms, net warming


Drizzle evaporates, net cooling





                                                               •  Collision/coalescence (accretional growth)





        Small, spherical drop





                                                                                           Larger than 3 mm, drops break up
                                                                                           due to aerodynamic forces

        Larger, spherical drop




       Largest, spherical drop





   Ice crystals

                                                            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.





                                                                                                                                   4

  r/R = 0.2
                                    r/R = 1
                           Drop Growth and Size

                                                                       •  Bigger particles (~25 micron) grow faster 




Flow field around
large particle will
                                             Inertia of collected
move smaller
                                             drop increases,
particle, lower E 

                                             higher E 





                            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





                                                                                              Stochastic collection model:
                                                                    10% collide
                                                                    (w/ drops                 based on probability

         Precipitation and Cloud Type
                              outside this
                                                                    population)

    •  Precipitation depends on
                                    10% collide
        –  Condensed water (water and temperature)
                 (w/ drops
        –  Updraft velocity (dynamics)
                             outside this
                                                                    population)

        –  Temperature (cold or warm processes)

        –  Drop size (aerosol effects)





                                                                                                                             5

                       Diffusion of water onto ice in water-
                       saturated environment
      Collision/             Liquid Water Path

                                                  coalescence is faster
                                                  for larger droplets




                      Slow growth              Aggregation is slower

                      by collision/
                      coalescence





             Precipitation Efficiency



           Depth of precip




Adiabatic precipitation rate
              Precip. Efficiency = P/Pad





                                                                                               6


								
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