Precipitation. Precipitation Formation Requires Requires –condensation nuclei (solid particles) –saturation (air at dew point) Result is temperature dependent
Precipitation Formation Requires Requires condensation nuclei
(solid particles) saturation (air at dew point) Result is
temperature dependent Result varies geographically Result is
temperature dependent Result varies geographically
Collision-Coalescence Process = Raindrop Bergeron Ice-Crystal
Process = Snowflake
Slide 3
How Precipitation Forms Important Facts: -cloud droplets are
tiny (20 micrometers). -many condensation nuclei are present. -tiny
particles fall more slowly than large ones. -a cloud droplets
diameter must grow ~200 times to reach a raindrops diameter. -to
attain the volume of a rain droplet, the cloud droplet increases a
million times in volume.
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Where do nuclei come from? Ocean salt Ocean salt Pollution
Pollution Wind born dust Wind born dust Cloud seeding Cloud seeding
Microbes Microbes
Slide 6
Relative sizes of raindrops, cloud droplets, & condensation
nuclei
Slide 7
Mist drizzle rain/sleet 0.005-0.05 mm less than 0.5mm 0.5 5 mm
Approximate size of types of Precipitation
Slide 8
As droplets fall they collide with smaller droplets and
coalesce. after collecting ~1 million cloud droplets the particle
is large enough to fall without evaporating. Because there are a
large number of collisions needed, clouds with great vertical
extent are typically produce precipitation by this process. The
Process from Warm Clouds: The Collision-Coalescence Process
Slide 9
Collision & Coalescence: a) warm cloud composed only of
small cloud droplets of uniform size; b) different size
droplets
Slide 10
Cloud droplet rising & then falling through a warm cumulus
cloud by growth and coalescence
Slide 11
Distribution of ice and water in a cumulonimbus cloud
Slide 12
Water droplets and ice crystal are in equilibrium; water vapor
molecules > liquid is saturation vapor pressure over water is
greater than it is over ice
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Types of Precipitation: Rain Rain Freezing rain or Glaze (ice
crystals freeze onto a frozen surface) Freezing rain or Glaze (ice
crystals freeze onto a frozen surface) Snow (ice crystals have not
melted) Snow (ice crystals have not melted) Sleet (ice crystals
melt as they fall) Sleet (ice crystals melt as they fall)
Slide 17
Precipitation Types / Properties
Slide 18
Temperature Profile for Rain
Slide 19
Temperature Profile for Snow
Slide 20
Snowflakes and Temperature Snow crystal images from an electron
microscope
Slide 21
Sleet and Freezing Rain sleet sleet freezing rain freezing rain
Sleet makes a tap tap sound when falling on glass.Sleet makes a tap
tap sound when falling on glass.
Slide 22
Sleet Sleet is a wintertime phenomenon that refers to the fall
of small particles of ice that are clear to translucent. Sleet
forms when rain passes through a cold layer of air and freezes into
ice pellets. This occurs most often in the winter when warm air is
forced over a layer of cold air.
Slide 23
Sleet partially snowflake (cold droplet) freezes into a pellet
of ice before reaching the ground
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Temperature Profile for Sleet and Glaze
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Blizzards & Ice Storms
Slide 26
hail Hail: Pieces of ice either transparent or partially
opaque, ranging in size from that of small peas to that of golf
balls or larger; biggest size in US 757 g & 14 cm diam.; Hail:
Pieces of ice either transparent or partially opaque, ranging in
size from that of small peas to that of golf balls or larger;
biggest size in US 757 g & 14 cm diam.; Single hailstorm can
damage in minutes; annual loss hundreds of millions of $ in US;
Single hailstorm can damage in minutes; annual loss hundreds of
millions of $ in US; Hail is produced in a cumulonimbus cloud when
large frozen raindrops that grow by accumulating supercooled liquid
droplets Hail is produced in a cumulonimbus cloud when large frozen
raindrops that grow by accumulating supercooled liquid
droplets
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Hail contd. For a hail to grow to the size of golf ball, it
must remain for 5-10 minutes in the cloud For a hail to grow to the
size of golf ball, it must remain for 5-10 minutes in the cloud Ice
crystals of appreciable size that cant be supported by rising air,
begin to fall Hail Ice crystals of appreciable size that cant be
supported by rising air, begin to fall Hail Largest form of
precipitation occurs during the warmest time of the year (due to
strong updraft that keeps the crystal to become bigger) Largest
form of precipitation occurs during the warmest time of the year
(due to strong updraft that keeps the crystal to become
bigger)
Slide 28
Accumulation of small hail after a thunderstorm
Slide 29
What about hail? updraft cycles updraft cycles accretion
accretion A hailstone can be sliced open to reveal accretion rings,
one for each updraft cycle.A hailstone can be sliced open to reveal
accretion rings, one for each updraft cycle.
