Stability & Cloud development

							Chapter 9
Small-scale winds interacting
with the environment
   Scales of motion
     Micro, meso, synoptic
   Friction and Turbulence in Boundary
    Layer
     Laminar flow
     Irregular turbulent motion
     Planetary boundary layer (PBL)
     Depth of PBL
Small-scale winds interacting
with the environment
   Observations: Eddies & Air Pockets
     Eddies on leeward side of solid object
     Roll eddies, mountain wave eddy (clear air
      turbulence)
     Increase wind speed/shear deforms layer
      into wave and air pocket.
   Force of the Wind
     Bridges and hills or rises can modify wind,
     increasing the force at specific locations.
Determining wind speed and
direction
 Wind characterized by direction, speed,
  and gustiness
 Wind direction describes the direction
  from which it is blowing
 Topic: Pedaling in the Wind
     As wind blows against an object it exerts
     force (V2 or P x A)
Determining wind speed and
direction
   Influence of Prevailing Winds
     Prevailing most frequently observed
      direction during a given time period
     Impact human and natural landscape
     Wind rose
   Topic: Wind Power
     Turbines need moderate, steady winds
     Only a few percent of nation’s total energy
     needs generated by wind power in the first
     half of the century
Local Winds
   Thermal circulation
     Heating and cooling of the atmosphere
      above the ground create cold, core high and
      warm, core low pressure cells.
     Wind travels from high to low and rises until
      it cools and begins to sink.
Local Winds
   Sea and Land Breeze
     Uneven heating of land and water
     Day: land hot, water cold = sea breeze
     Night: water hot, land cold = land breeze
     Sea breeze front, sea breeze convergence
   Local Winds and Water
     Local winds will change speed and direction
     as they cross a large body of water due to
     less friction, greater speed and greater
     Coriolis effect
Local Winds
   Seasonally Changing Winds: The
    Monsoon
     Arabic for seasonal
     Winds change direction seasonably causing
      extreme dry and wet season
     Eastern and southern Asia, North America
Local Winds
   Mountain and Valley Breeze
     On mountain slopes, warm air rises during
      the day creating a valley breeze; during
      night nocturnal drainage of cool air creating
      a mountain breeze
     Associated with cumulus clouds in the
      afternoon
   Katabatic winds
     Cold wind rushes down elevated slopes,
     usually 10 kts or less but can reach
     hurricane strength
Local Winds
   Chinook/Foehn Winds
     Dry warm descending on the leeward side of
      a orographic barrier
     Eastern slope of Rockies (chinook), Europe
      (foehn), Argentina (zonda)
   Focus: Snow Eaters
     Thirsty wind on east side of Rockies that eat
     or melt snow due to rapid change in
     temperature
Local Winds
   Santa Anna Winds
     Warm dry that blows from east or northeast
      don canyons into S. California
     Very fast, desiccates vegetation, providing
      fuel for fires
   Desert winds
     Dust storms, sand storms, dust devil,
     haboob