Review:
What is the difference between the Adiabatic rate and environmental lapse rate
ELR vs adiabatic rate
Environmental lapse rate says how the surrounding air/atmosphere is
changing due to heating from earth
Adiabatic rate says how a particular air mass is changing temperature due to
pressure changes.
Adiabatic rate is usually 10oC/1000m (dry) or 9o to 5oC/1000 m (wet)
ELR can vary to any rate
Stability of an air mass
Combine ELR and adiabatic rate to determine if an air mass is stable.
Stability means they no longer rise or fall.
Stable air masses
occur when temperature of surrounding/atmosphere air is greater than air
mass
Absolute unstable air masses
occur when temperature of surrounding/atmospheric air is less than air
mass
Conditional unstable air masses
dry air is stable, saturated is not
General rule
Stable air masses occur when ELR is less than the dry adiabatic rate
Unstable air masses occur when the ELR is more than the dry adiabatic rate
Clouds, Fog and Dew
All form by changing the temperature of an air mass
Do we need to heat the air mass to cause condensation or cool the air mass?
Fog is created by:
Radiant cooling (cooling of an air mass due to a cool surface
Adding H2O to air mass
Dew is created by radiant cooling
Clouds are created by adiabatic cooling
Clouds form at high altitudes and often in afternoon. Why?
Clouds form when dew point is reached
Often require something to condense on.
Millions of small drops of water and ice
Vertically developed clouds
range of low to high
Air moves upward quickly
creates thunderstorms
How does rain form?
Cloud drops--> <10 microns (< 0.01mm)
Rain drops--> million times more water than cloud drop
Create rain through
Bergeron Process
Collision/coalescence
Bergeron Process
Clouds must be supercooled and supersaturated to create ice
once ice begins to form water vapor is used to grow ice crystals
When Ice reaches a certain size they fall
as ice falls it can warm and is convert to liquid
Collision Coalescence
Primarily occurs in tropics
Aerosols remove water from air and grow droplets
When they exceed 0.02mm water drops fall
Collide with other drops as they fall growing larger
Drag on falling drop eventually pulls it apart creating many smaller drops
Thunderstorms
Most occur in lower latitudes
lifting mechanism
moisture
instability
Stages of Development:
Warm moist air: migrates up and releases latent heat
Swirling updrafts up to 60 mph
Downdrafts are created as rain begins--event ends
Lightning
Charge difference in cloud due to particle interaction
Cloud bottom (-) charge
Cloud top (+) charge
Earth surface (+) charge
As potential of cloud overcomes air resistance lightning bolt is created
Thunder?
END OF LECTURE. Below this line you do not need to know for the final.
Tornadoes
Pressure differences at different levels in the cloud
Inside tornado--> very low
Air rushes into the low pressure region
Pushes upwards quickly and creates vortex
Associated with severe t-storms
Where do severe thunderstorms
and tornadoes develop commonly in
Hurricanes
Originates over warm waters
Development:
tropical depression, tropical storm, hurricane
Minimum wind speed of 74 mph
~6 Atlantic hurricanes develop in a season
Season from May to October
Differences in pressure is extreme
Lowest pressure in middle
Warm moist air rises and creates latent heat
Upward air is forced outward--spiral
Center becomes calm