Revised Planner

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Revised Planner

• Chapter 8 Critical Thinking Due ASAP
• Ignore everything else for now
• Bring your textbooks Tomorrow
• Bring your lab manuals on Tuesday

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Air Masses and Fronts andThe Mid-Latitude
Cyclone

• Chapters 9 and 10

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Air Masses and Fronts

• Chapter 9

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Air Masses

• Large masses of air with uniform temperatures and
  humidity
• Named for their source region
• The source region will impart properties on the
  air mass

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Source regions

• (c) Continental dry
• (m) Maritime - moist

• (T) Tropical warm
• (P) Polar cold
• (A) Arctic really cold

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Possible types of air masses

• mP maritime polar
• mT maritime tropical
• cP continental polar
• A arctic
• cT continental tropical

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Continental Air Masses

• cP cold and dry

• A even colder and dry

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Continental Air Masses

• cT hot and dry

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Maritime Air Masses

• mP more moderate temperature and humidity
• Responsible for the noreasters

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Maritime Air Masses

• mT warm, moist, and unstable

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Fronts

• Front boundary between two air masses

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Cold front

• Cold air mass over taking a warm air mass
• Uplift of air along the front leads to cumuliform
  clouds

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Cold vs. warm front

• Warm front have less slope, thus greater distance

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Warm front

• Warm air over runs the cold air and leads to
  extensive cloud formation and precipitation

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Stationary Front

• A boundary where neither air mass is moving

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Occluded front

• A cold front overtakes a warm front, lifts the
  warm air, produces clouds and precipitation along
  the front

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Cause of occlusion

• Mid latitude cyclone
• Warm front from the south and a cold from the
  north rotate around a low

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Cause of occlusion

• The low becomes elongated in a trough, this
  forces the two fronts together

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Mid-latitude Cyclone

• Chapter 10

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Mid-latitude cyclone

• Large systems
• Persist for about a week
• Travel across the US
• Associated weather conditions

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Cyclogenesis

• Formation of a cyclone
• A disruption in the boundary between the cold
  easterlies and the warm westerlies
• Sets up a counterclockwise rotation
• Low pressure system

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Cyclogenesis

• Boundary between cold easterlies and warm
  westerlies

• Slight disturbance sets up counterclockwise
  rotation

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Cyclogenesis

• Low pressure deepens and distinct fronts emerge

• Occlusion marks the end of the cyclones life
  cycle

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Typical mature cyclone

• Note probability of precipitation along the
  fronts
• Note the temperatures associated with each front

Cold
Warm
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Formation of cyclones

• Associated with Rossby waves and
• Vorticity rotation of a fluid, such as air

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Vorticity

• 1,2,3 air is rotating counterclockwise in a
  trough
• 3,4,5 air is rotating clockwise in a ridge

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Vorticity
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• Counterclockwise rotation positive vorticity

• Clockwise rotation negative vorticity

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Vorticity

• As air moves through a trough it develops
  positive vorticity
• Begins the formation of a low pressure cyclone

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Divergence and convergence

• Upper air divergence, caused by decreasing
  vorticity causes uplift and surface low pressure

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Divergence and convergence

• Upper air convergence, caused by increasing
  vorticity causes sinking and surface high
  pressure

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Divergence and convergence

• Low pressure tends to follow troughs
• High pressure tends to follow ridges

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Mid-latitude cyclone

• Lows develop coming out of a trough
• Develop
• Occlude
• Dissipate as they reach the ridge

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Which is more likely to favor cyclone development?

• Meridoional
• Significant changes in vorticity associated with
  troughs and ridges

• Zonal
• minor changes in vorticity

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Steering currents

• The movement of mid-latitude cyclones and
  associated weather can be predicted from a 500 mb
  map
• Surface systems tend to follow the 500mb at about
  ½ the speed
• 500mb map surface map

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The conveyer belt model of cyclone movement

• The circulation of the mid-latitude cyclone is
  driven by three wind currents
• Warm conveyer belt
• Cold conveyer belt
• Dry conveyer belt

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Conveyer belts
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Conveyer belts
Cold
Dry
Warm
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Have a fantastic Day!