What is the source of energy for Midlatitude cyclones

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What is the source of energy for Midlatitude
cyclones?

• Potential energy arising from the temperature
  differences found in the different air masses.
• Cold, dense air pushes warmer, less dense air up
  and out of the way.
• Up warm, down cold

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Development of surface cyclones is related to
upper air wind patterns

• Linked through the convergence /divergence
  patterns at the surface and aloft
• Convergence at the surface produces upward motion
  - divergence at the surface produces downward
  motion
• Convergence at upper levels produces downward
  motion - divergence produces upward motion

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Where do we find ascending air in a mid-latitude
cyclone?

• Fronts (why?)
• Convection (why?)
• Around the center of the Low Pressure(why?)

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Where do we find steady, wide spread
precipitation?

• Upwind of the warm front
• Wrapping around the Low Pressure Center

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Where do we find the strongest winds in a middle
latitude cyclone?

• Surface
• Where the pressure gradient is largest
• Near convective clouds
• Near the fronts (same thing?)
• Upper Air
• Where the pressure gradient is largest
• In pulses superimposed on the jet stream
• these pulses are sometimes called jet streaks

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Summary of Cyclone Weather
Roles of convergence and divergence
aloft Pattern of clouds, precipitation, and
temperatures on the ground
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Conveyor Belt Model
This model describes rising and sinking air along
three conveyor belts A warm conveyor belt
rises with water vapor above the cold conveyor
belt which also rises and turns. Finally the dry
conveyor belt descends bringing clearer weather
behind the storm.
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Rapid Cyclone Intensification

• An Example from November 9, 10 and 11, 1998

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700 mb Analysis 12 Z Nov 10 98
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The Big Picture

• Weve emphasized horizontal transport of energy
  to balance the planetary energy budget
• Hadley Cell
• Subtropical divergence
• Midlatitude cyclones and conveyor belts
• What about vertical motion?
• Up-warm, down cold
• Up moist, down-dry
• Severe weather is all about vertical motion, and
  represents local release of energy that
  contributes to planetary energy balance