Chapter 5: Cloud development and precipitation

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Chapter 5 Cloud development and precipitation

• Atmospheric Stability
• Determining stability
• Cloud development and stability
• Precipitation processes
• Precipitation types
• Measuring precipitation

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Atmospheric stability
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Atmospheric stability

• stable and unstable equilibria
• air parcels
• adiabatic process
• adiabatic lapse rates

• Stability does not control whether air will rise
  or sink.Rather, it controls whether rising air
  will continue to riseor whether sinking air will
  continue to sink

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Determining stability
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A stable atmosphere

• environmental lapse rate
• absolute stability
• stabilizing processes
• subsidence inversions

• stable air provides excellent conditions for
  high pollutionlevels

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An unstable atmosphere

• absolute instability
• warming of surface air
• destabilizing processes
• superadiabatic lapse rates

• unstable air tends to be well-mixed

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Conditionally unstable air

• conditional instability
• dry and moist adiabatic lapse rates

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Cloud development and stability
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Cloud development and stability

• surface heating and free convection
• uplift along topography
• widespread ascent
• lifting along weather fronts

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Convection and clouds

• thermals
• fair weather cumulus

• fair weather cumulus provide a visual marker of
  thermals
• bases of fair-weather cumulus clouds marks the
  lifting condensation level, the level at which
  rising airfirst becomes saturated

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Topography and clouds

• orographic uplift
• rain shadow

• The rain shadow works for snow too. Due to
  frequentwesterly winds, the western slope of the
  Rocky Mountainsreceives much more precipitation
  than the eastern slope.

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Precipitation processes
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Collision and coalescence process

• terminal velocity
• coalescence
• warm clouds

• A typical cloud droplet falls at a rate of 1
  centimeter per second.At this rate it would take
  46 hours to fall one mile.

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Ice crystal process

• cold clouds
• supercooled water droplets
• saturation vapor pressures over liquid water and
  ice
• accretion

• The upper portions of summer thunderstorms are
  cold clouds!

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Cloud seeding and precipitation

• cloud seeding
• silver iodide

• It is very difficult to determine whether a
  cloud seedingattempt is successful. How would
  you know whetherthe cloud would have resulted in
  precipitation if it hadntbeen seeded?

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Precipitation in clouds

• accretion
• ice crystal process

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Precipitation types
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Rain

• rain
• drizzle
• virga
• shower

• Virga is much more commonly observed in the
  westernUS, because the humid climate of the
  eastern US reduces the visibility.

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Snow

• snow
• fallstreaks
• dendrite
• blizzard

• Snowflake shape depends on both temperature
  andrelative humidity

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Sleet and freezing rain

• sleet
• freezing rain
• rime

• Sleet makes a tap tap sound when falling on
  glass

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Snow grains and snow pellets

• snow grains
• snow pellets
• graupel

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Hail

• updraft cycles
• accretion

• a hailstone can be sliced open to reveal
  accretion rings,one for each updraft cycle

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Measuring precipitation
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Instruments

• standard rain gauge
• tipping bucket rain gauge

• It is difficult to capture rain in a bucket when
  thewind is blowing strongly

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Doppler radar and precipitation

• radar
• Doppler radar