Atmospheric Circulation and
Weather Systems
The Seasons
Heat Lag
Heat Lag
Atmospheric Circulation
Asymmetric Earth
Asymmetric Earth
Atmospheric Circulation
Zonal and Meridional Flow
Semi-Permanent Features, January
Semi-Permanent Features, July
Rotation Effects
The Coriolis Effect
• Due to moving on a
rotating earth
• Things on equator are
moving faster than
points near poles
• Affects:
– Winds
– Ocean Currents
– Tides
The Coriolis Effect
• Things moving
toward the equator are
deflected west
• Things moving
poleward are
deflected east
• Deflected Right in
Northern Hemisphere
• Deflected Left in
Southern Hemisphere
“Centrifugal” Force ?
Or No Force?
“Centrifugal” Force Does Not Exist
• When anything turns, the only forces that
act are in the direction of the turn
• These forces are called centripetal (centerseeking) force
• “Centrifugal” force is an illusion
• “Centrifugal” force is due to inertia and
centripetal force opposing each other
High Pressure Systems
High Pressure Systems
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Air flows out from center
Spin clockwise in Northern Hemisphere
No air mixing
Stable, fair weather
Sinking Air, few clouds
Long duration can result in inversions,
pollution
• Winter: often extreme cold
– Cold Air is Dense
– Clear Skies and Radiational Cooling
Low Pressure Systems
Why Counterclockwise?
Low Pressure Systems
• Air flows in toward center
• Spin counter-clockwise in Northern
Hemisphere
• Mixes air of different properties
• Associated with fronts
• Stormy, sometimes violent weather
• Passage often results in sharp change in
weather conditions
Isobars and Air Flow
Fronts and Low Pressure Systems
Fronts
Warm Fronts
Warm Fronts
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Gradual Onset
Warm Air over Cool Air
Little Turbulence
Weather Rarely Violent
Cold Fronts
Cold Fronts
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Abrupt Onset
Cold Air Lifting Warm Air
Considerable Turbulence
Weather Sometimes Violent
Thunderstorms Common
Can Spawn Tornadoes
Old Low Pressure Systems
Occluded Fronts
Occluded Fronts
• Two fronts merge
• Any two types of front can occlude
• Most common: Cold Front overtakes Warm
Front
• Starts off like a warm front, finishes like a
cold front
Weather Prediction
Weather Prediction
Weather Prediction
Chaos Theory
Does Not Mean:
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Cloned Dinosaurs will run amok
Systems do not follow physical laws
Systems behave with wild unpredictability
Systems do not have limits
Phenomena cannot be predicted
Chaos Theory
Does Mean:
• Small differences compound
over time
• There are limits to how
accurately phenomena can be
predicted
• Examples:
– Weather
– The Planets