Download Chapter 6 Cloud Development and Forms • Creating clouds needs

Chapter 6
Cloud Development and Forms
• Creating clouds needs air to rise and cool
• 4 Mechanisms that lift air
– ________________ – lifting caused by a mountain
• Air hits a a mountain and is forced upwards
• Windward side – upwind side of the mountain rising air causes cooling
– Abundant precipitation
• Leeward side –
– Lack of precipitation (________________)
– Frontal lifting
• Boundaries between different air masses
• Warm/moist air is forced to rise and form clouds
• Cold (a) and warm (b) fronts occur
–
• Air converges into low pressure regions
• Convergence causes air to rise and cool
– Localized convection
• Air heated at the surface becomes warmer and less dense and rises freely into
updrafts
• Creates small localized summer thunderstorms
• Stability of the air
– Static stability – determines if air rise, falls, or remains at a certain level
• Related to temperature and controlled by buoyancy
– Positive and negative buoyancy
– Types
• Statically unstable
• Statically stable
• Statically neutral
• Conditionally unstable
•
– If air is forced to rise and it continues rising freely
– Positive buoyancy
– Parcel of air cools slower than that of surrounding air
• Parcel of rising air is always warmer than surrounding air
• DAR and WAR less than ELR
–
– Associated with low pressure
• Absolutely stable air
– If air is forced to rise and it sinks back to its original position
–
– Parcel of air cools faster than surrounding air
• Parcel of air is always warmer than surrounding air
•
–
– Associated with high pressure
• Absolutely Neutral air
– If air is forced to rise and parcel remains in the location where lifting ceased
– Parcel of air temperature equal to surrounding air
• Conditionally unstable air
– Parcel of air forced to rise is initially stable but eventually becomes unstable after
saturation is reached
– ELR is between the DAR and the WAR
–
•
Factors Influencing the ELR
– Heating/cooling the lower atmosphere
– Advection of Cold/Warm Air at Different Levels
– Advection of an Air Mass with a Different ELR
• Limitations on the Lifting of Unstable Air
– Stability
• Eventually a rising stable parcel runs into stable air, especially at the
stratosphere
• Strong thunderstorm updrafts can penetrate the stratosphere
– Entrainment
• Rising air pulls in dryer air near its edges causing evaporation and cooling
• Extremely Stable Air
–
•
– Creates radiation fog and traps pollutants
• Frontal interactions
– Fronts moving through cause inversions
• Subsidence
–
– Established stable polluted skies especially over Los Angeles
• Cloud Classifications
– Based on appearance and height
– High clouds (______________)
• Bases above 6000m (19,000 ft)
•
• _________________ – thin white wispy clouds
• Cirrostratus (Cs) – more extensive often produces a halo around Sun or Moon
• Cirrocumulus (Cc) – layered clouds with billows or rolls. Often look like fish
scales.
– Middle clouds (prefix = alto)
• Bases between 2000 and 6000m (6-19,000 ft)
• Composed of liquid drops and ice crystals
• Altostratus (As) – more extensive than cirrostratus. Sun and Moon are slightly
visible.
• Altocumulus (Ac) – a series of puffy clouds arranged in rows. Allows less light
through than cirrocumulus and the scales are larger in size.
– Low clouds (________________)
• Bases below 2000m (6,000 ft)
•
• Stratus (St) – uniform layer of low clouds often a darker gray in color. Covers a
wide region.
• ____________________ – low layered clouds that produce light precipitation
• Stratocumulus (Sc) – low layered clouds with some vertical development
– Clouds with vertical development
•
• Cumulus humulus (Cu) - local updrafts create individual clouds. “Fair weather”
clouds
• Cumulus congestus - contains numerous updrafts and form towering cumulus
• __________________ – towering cumulus clouds otherwise known as
“thunderheads”.
–
– Characteristic anvil shape made of ice
– Extreme updrafts and downdrafts
– Unusual clouds
• Lenticular - form from mountains disturbing the wind flow. Flying saucer
shape.
• Mammatus –
• Shelf clouds – large horizontal roll clouds leading a strong downdraft from
thunderstorms
• Observations of cloud coverage
– Surface-Based Observations
• _____________ – lasers used to measure cloud coverage at different heights
– Cloud Observation by Satellite
• Visible images
• Infrared images
• Enhanced IR images
End of Chapter 6