Atmospheric Circulation and Weather Systems
Take-Away Points Weather is driven by unequal solar heating and cooling Air motions are affected by the Coriolis Effect and “centrifugal” force High and Low Pressure Systems Air flows parallel to pressure contours (Geostrophic winds) Air masses meet along sharp boundaries or fronts Weather is inherently chaotic and that limits our ability to forecast it
The Seasons
1. Weather is driven by unequal solar heating and cooling Heat Lag 1. Weather is driven by unequal solar heating and cooling
Heat Lag
Atmospheric Circulation 1. Weather is driven by unequal solar heating and cooling
Atmospheric Circulation 1. Weather is driven by unequal solar heating and cooling
1. Weather is driven by unequal solar heating and cooling Asymmetric Earth 1. Weather is driven by unequal solar heating and cooling
1. Weather is driven by unequal solar heating and cooling Asymmetric Earth 1. Weather is driven by unequal solar heating and cooling
Atmospheric Circulation 1. Weather is driven by unequal solar heating and cooling
Zonal and Meridional Flow 1. Weather is driven by unequal solar heating and cooling
Semi-Permanent Features, January 1. Weather is driven by unequal solar heating and cooling
Semi-Permanent Features, July 1. Weather is driven by unequal solar heating and cooling
Rotation Effects 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
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 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
The Coriolis Effect Things moving toward the equator are deflected west Things moving poleward are deflected east Deflected to Right in Northern Hemisphere Deflected to Left in Southern Hemisphere 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
The Coriolis Effect 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
The Coriolis Effect 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
The Coriolis Effect 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
Inertial Circles 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
“Centrifugal” Force ? 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
Or No Force? 2. Air motions are affected by the Coriolis Effect and “centrifugal” 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 (center-seeking) force “Centrifugal” force is an illusion “Centrifugal” force is due to inertia and centripetal force opposing each other 2. Air motions are affected by the Coriolis Effect and “centrifugal” force
3. High and Low Pressure Systems High Pressure Systems 3. High and Low Pressure Systems
3. High and Low Pressure Systems High Pressure Systems 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 3. High and Low Pressure Systems
3. High and Low Pressure Systems
3. High and Low Pressure Systems Why Counterclockwise? 3. High and Low Pressure Systems
3. High and 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 3. High and Low Pressure Systems
4. Air flows parallel to pressure contours (Geostrophic winds) As air flows in or out of pressure cells, Coriolis Effect deflects it At surface, friction limits the deflection. Winds blow about 45 degree angles to isobars Aloft, friction not a factor Deflection continues until limited by pressure gradient (winds can’t go against pressure) Winds blow parallel to contours This is called geostrophic flow 4. Air flows parallel to pressure contours (Geostrophic winds)
Geostrophic Flow
Geostrophic Flow
4. Air flows parallel to pressure contours (Geostrophic winds) Geostrophic Flow 4. Air flows parallel to pressure contours (Geostrophic winds)
1905 Weather Map of US
First U.S. Weather Map With Fronts
Fronts and Low Pressure Systems 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Warm Fronts 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Warm Fronts Gradual Onset Warm Air over Cool Air Little Turbulence Weather Rarely Violent 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Cold Fronts 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Cold Fronts Abrupt Onset Cold Air Lifting Warm Air Considerable Turbulence Weather Sometimes Violent Thunderstorms Common Can Spawn Tornadoes 5. Air masses meet along sharp boundaries or fronts
Old Low Pressure Systems 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Occluded Fronts 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or 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 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Weather Prediction 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Weather Prediction 5. Air masses meet along sharp boundaries or fronts
5. Air masses meet along sharp boundaries or fronts Weather Prediction 5. Air masses meet along sharp boundaries or fronts
Chaos x
Does Not Mean: Chaos Theory 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 6. Weather is inherently chaotic and that limits our ability to forecast it
Does Mean: Chaos Theory Small differences compound over time There are limits to how accurately phenomena can be predicted Examples: Weather The Planets Traffic 6. Weather is inherently chaotic and that limits our ability to forecast it