PRECIPITATION

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PRECIPITATION
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CURVATURE EFFECT
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Q. Why are cloud droplets larger over the ocean?
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COLLISION- COALESCENCE PROCESS
Most collide on forward edge Some collide on
backside
Terminal velocity Almost 10 m/s for largest
raindrops
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Q. Why can a cumuliform cloud produce heavier
precipitation than a stratiform cloud?
"Warm" Cloud
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Supercooled water droplets
"Cold" Cloud
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Deposition nuclei
Ice forms directly on ice nuclei
Freezing Nuclei
Promote freezing of supercooled droplets (contact
nuclei)
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Ice crystals grow at the expense of water droplets
Higher saturation vapour pressure
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• Riming causes
• snow pellets (graupel)
• supercooled droplets
• freeze on contact

Snowflakes form through aggregation
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Natural cloud seeding
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ARTIFICIAL CLOUD SEEDING
Source Desert Research Institute, Nevada, USA
Source North Dakota Cloud Modification Project,
USA
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Source North Dakota Cloud Modification Project,
USA
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VIRGA
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18cm diameter
World's Largest Hailstone
Aurora, Nebraska June 22, 2003
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I almost didn't make it here !
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AIR PRESSURE, FORCES AND WIND
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Remember the paper cup experiment
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WIND
SMALL-SCALE
LOCAL SYSTEMS
CHAPTER 10
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WIND VANE CUP ANEMOMETER
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SONIC
ANEMOMETER
SOUND WAVES DETERMINEWIND SPEED, DIRECTION
TEMPERATURE
Sonic transducers
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SNOWDRIFT
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SNOWDRIFT
http//www.wrds.uwyo.edu/wrds/rmfres/fendrift.html
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Effect of Surface Roughness and Instability on
Windspeed
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Depth of mixing depends on
Surface Heating
WIND SPEED
TOPOGRAPHY
SURFACE ELEMENTS
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Effect of Eddies on Wind Inclination
UNSTABLE
STABLE
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MOUNTAIN WAVES
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ROTOR CLOUDS
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Shelter Belts
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WIND SHEAR
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Reinforcement of Wave Structure
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SEA BREEZE
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LAND BREEZE
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Lake-induced convergence
Also SW Ontario
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CORIOLIS FRICTION EFFECTS
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MONSOON SEASONS
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CHINOOK !
Cooling At MALR 6C/km
Warming At DALR 10 C/km
Warming At DALR 10 C/km
Cooling At MALR 6C/km
Cooling At DALR 10 C/km
X
X
VANCOUVER
LETHBRIDGE
12C
8C
More sensible heat
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CHINOOK WALL CLOUD
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Santa Ana Winds
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KATABATIC WINDS
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HABOOB
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Ventifacts
Entrained Particle
Exposed section
Buried Portion
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DUST DEVIL
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