10/3/2011
Forms of
Condensation
and
Precipitation
Chapter 5
Cloud Formation
v Clouds
v Visible aggregate of minute droplets of water (ice)
v Form as a result of adiabatic cooling
v Lifted condensation level
v Cooled to dew point
v Air is saturated
v Needs surface to condense to
v Condensation nuclei
v Dust, smoke, salt
Growth of Clouds
v Condensation nuclei
v Hygroscopic
v Effective particles for condensation
v Salt, dust, ash, pollen
v Hydrophobic
v Not effective particles for condensation
v Examples?
Cloud Classification
v Cirrus
v High, white, thin
v Wispy, feathery, curly
v Cumulus
v Flat base, rising domes, towers
v Stratus
v Sheets, layers
v A billion cloud droplets equal one rain drop
Cloud Classification
Cloud Classification
v High
v High
v Above 6000m
v Middle
v 2000 – 6000m
v Low
v Below 2000m
v Vertical development
v 2000-6000m
v Above 6000m
v Composed of ice crystals
v Indicate stormy weather coming
v Cirrus
v Form hooks (mares tails)
v Cirrostratus
v Transparent
v Cover much of the sky
v Cirrocumulus
v Patches
v Mackerel sky
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Cloud Classification
Cloud Classification
v Low
v Middle
v Below 2000m
v 2000 - 6000m
v Stratus
v Prefix - alto
v Uniform
v Altocumulus
v Covers sky
v Larger patches
v Light precip
v Altostratus
v Stratocumulus
v Formless
v Combo of
v Grayish
v stratus and cumulus
v May produce
v Nimbostratus
v Rain or snow
v Nimbus = Rain or snow
v Stable Air
Cloud Classification
Cloud Classification
v Vertical Development
v 2000 - 6000m
v Associated with unstable air
v Cumulus
v White, puffy
v Clear days
v Fair weather clouds
v Cumulonimbus
v Huge towers
v Dark, dense
v Top = anvil
v Thunderstorms
Mammatus
Types of Fog
Types of Fog
v Fog from cooling
v Fog
v A cloud with its base or very near the ground
v
Form from
v Cooling
v Radiation Fog
v Advection Fog
v Upslope Fog
v Evaporation
v Addition of water vapor
v
Radiation Fog
v Ground radiates heat
v Ground and air cool rapidly
v Clear skies and high rel. hum.
v How thick depends on wind
v Little to no wind
v Thin and low to ground
v Slightly more wind
v Thicker and higher up
v Thicker in valleys
v Cold and dense
v Lifting (Not really)
v Steam Fog
v Ground warms up
v Frontal (precip) Fog
v Fog dissipates
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Types of Fog
v Fog from cooling
v Advection Fog
Types of Fog
v Fog from cooling
v Upslope Fog
v Air moving horizontally
v Humid air moves over slope
v Warm moist air
v Air expands and cools (adiabatically)
v Blown over cool surface
v Heat loss to surface
v Air cools to dew point
v Dense
v 300 - 600m deep
Types of Fog
v Fog from evaporation
v Steam Fog
v Cool air moves over warm water
v Warm water evaporating
v Saturates cool air
Types of Fog
v Fog from evaporation
v Frontal Fog
v Frontal wedge
v Warm air get lifted over cold
v Rain
v Rain evaporates
v Cool air becomes saturated
Dew and Frost
Dew and Frost
v White frost
v Dew
v Condensation of water vapor on objects
v Not frozen dew
v Cooler objects
v Dew point below freezing
v Grass is common because of transpiration increasing the
v Deposition
relative humidity of the air
v Water vapor directly to solid
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How Precipitation Forms
v Cloud droplets
v Very tiny (.02 mm)
How Precipitation Forms
v Cloud droplets
v Don’t freeze at 0oC
v Supercooled water
v Raindrop
v Freeze on contact
v 2 mm
v Freezing nuclei
v -10 to -20oC
v Mix ice and water
v
-20oC
v All ice
How Precipitation Forms
v Bergeron Process
v Ice crystals have lower vapor pressure than liquid droplets
v More evaporation from liquid droplets
v Raises rel. humid. (already 100%)
v Supersaturated
v Ice crystals collect more water
v Ice crystals grow larger
v Rapid growth
How Precipitation Forms
v The Collision-Coalescence
v Liquid droplets fall through cloud
v Collect other cloud droplets
v Droplet gets bigger (a)
v Bottom flattens out (b)
v Depression (c)
v At 5 mm raindrop breaks apart
v Numerous small drops (d)
v Repeats process
v Large snowflakes
v 10 - 30 ice crystals
Forms of Precipitation
v Rain
v Snow
v Sleet
v Glaze
v Hail
v Rime
v Graupel
Forms of Precipitation
v Rain
v .5 - 5 mm
v Drizzle
v .05 to .5 mm
v Mist
v .005 to .05 mm
v Most precip. starts as snow and melts on the way
v Precip can evap. before reaching the ground
v Produces virga
v Rain streaks don’t reach the surface
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Forms of Precipitation
v Snow
Forms of Precipitation
v Sleet
v Aggregate of ice crystals
v Particles of ice
v Low temp.
v Light fluffy snow
v High temp.
v Heavy wet snow
v Snowballs
Forms of Precipitation
v Glaze
Forms of Precipitation
v Hail
v Freezing rain
v Hard round pellets
v Lumps of ice
v Layers inside
v Form in
cumulonimbus
clouds
v Updrafts and
downdrafts
v Carry hail up and
down
v Become larger in
size
Forms of Precipitation
Precipitation Measurement
v Standard rain gauge
v Rime
v Formed from
v Freezing of supercooled fog or
cloud droplets
v Freezes on contact with object
v
Funnel water
Channel 1/10 of funnel
v Trace of precipitation
v
v Unmeasurable
v Tipping-bucket gauge
v
Each bucket holds .025 cm
v
Bucket fills and dumps
Records measurement on graph
v
v Weighing gauge
v
Weighs the fallen rain
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Precipitation Measurement
v Snow
Precipitation Measurement
v Errors
v Measure
v Rain fall varies drastically
v Depth
v Place to place
v Multiple spots
v Gauges
v Water equivalent
v Should be far away from objects
v Melt
v Open fields
v Measure as rain
v Wind
v Gauges should have windscreens
v 10 inches of snow equals 1 inch of rain?????
Not exactly
v 30 cm of light fluffy snow ≈1 cm of rain
v 4 cm of heavy wet snow ≈ 1 cm of rain
Precipitation Measurement
Weather Modification
v Intentional Weather Modification
v Radar
v Sends out radio waves
v Radio waves reflect off of precip.
v Reflected signal called - echo
v Deliberate human intervention to influence atmospheric
processes
v 3 categories
v Energy (heat or air mixing)
v Helicopter disperses fog
v Changing land and water surfaces
v Covering with dark substance
v Absorbs solar energy
v Increase in temp.
v Triggering, intensifying, or redirecting
v Cloud seeding
v Uses dry ice
Weather Modification
v Triggering, intensifying, or redirecting
v Cloud seeding
v With
v Dry ice
v Cools air
v Silver iodide
v Freezing nuclei
v Increases precip.
v Must have clouds
v Clouds below 0oC
Weather Modification
v Fog and Cloud Dispersal
v Dry Ice
v Water à Ice
v Light snow shower
v Clouds disperse
v Helicopters
v Strong downdrafts
v Dry air mixes with saturated
v Heat
v Turboclair
v Jet engines heat the air
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Weather Modification
v Hail Suppression
v HailStop
v Uses sound waves
v Intent to disrupt hail cycle
v Does it work?????
Weather Modification
v Frost Prevention
v 2 methods
v Conserve heat
v Cover plants
v Add heat
v Water sprinklers
v Warms ice
v Latent heat released when freezes
v Air mixers
v Mixes warm air above with cold air
below
v Heaters
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