ExtraTropical Weather

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Extra-Tropical Weather

• Lynn Gribble
• 6/2/08

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Eco Tip 5 Reduce Energy Usage at Home

• Compact Fluorescent Light bulbs If each family
  switched out one bulb, it would be the equivalent
  of taking one million cars off the road.
• Unplug unused appliances about 75 of the energy
  usage of each appliance actually occurs while the
  item is not in use.
• When and where possible air dry clothes from the
  dryer.
• According to the US department of Energy
  Efficiency and renewable energy 90 of energy
  used during washing goes to heating water, so use
  warm or cold water when possible.

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Review Pressure Balances

• Isobars lines of constant pressure
• Vectors (arrows) indicate wind direction.
• Hydrostatic Balance gravity and VPGF
• Geostrophic Balance HPGF and Coriolis
• Gradient Balance HPGF, Coriolis, and Cent.
• Guldberg Mohn HPGF, Coriolis, Friction
• Hadley Cells and Jet streams

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Air Masses

• Defined according to the temperature and moisture
  content where they develop
• Polar cold
• Tropical warm
• Arctic very cold
• Continental dry
• Maritime moist
• Combinations there of Maritime Tropical (moist,
  warm), Continental Polar (Dry, cold)
• Characteristics of a good source region builds
  over a long period of time low or no winds at
  surface, uniform surface (deserts, oceans)

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Air Masses
Figure 9-4
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Air Mass Modification

• Changes can be made to the temperature, moisture
  content, and/or stability of an air mass through
  exchanges with the surface or mechanical lifting.
• Lake Effect (exchanges)
• Box 9-2
• Rain Shadow (lift)

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A Low Pressure System

• Surface Cyclone (winds flow cyclonically/counter
  clockwise into the center)
• Upper level structure of jet (trough is
  associates with surface low pressure)
• See Board for Diagram

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A High Pressure System

• Surface Anticyclone (winds flow
  anticyclonically/clockwise out of the center)
• Upper level structure of jet (ridge is associated
  with surface high)
• See Board for Diagram

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Norwegian Cyclone Model

• Cyclogenesis the growth of a cyclone (Low
  pressure system)
• Surface temperature gradients
• Barotropic isotherms are parallel to isobars
• Baroclinic isotherms are perpendicular to
  isobars
• Strong jet stream pulls more air up through the
  center of the low into the upper atmosphere
• Surface boundaries

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Norwegian Cyclone Model
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Norwegian Cyclone Model
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Fronts

• Defn The transition zone between two air masses.
  
• Only exist on cyclones or low pressure systems
• Cold Front
• Warm Front
• Occluded Front

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Cold Fronts

• Cold air advancing , blue triangles
• Strongest Frontal Action vertical transition
  from cold to warm is sharp
• Cumulus at the front

Figure 9-15
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Cold Fronts
9-14
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Warm Fronts

• Warm air advancing, red half circles
• Various stratus and cirrus cloud types ahead of
  frontal passage.

Figure 9-18
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Warm Fronts
9-17
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Cold and Warm Fronts

• Basically, the clouds occur within the cold air
  in both occasions.
• Cold front clouds behind or at the front
  (usually cumulus) highest risk for severe
  weather and t-stroms
• Warm front clouds ahead of the front
  (progression from high to low clouds)

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Occluded Fronts

• Cold front has caught up to warm front. Purple,
  alternating triangles and half circles.
• Warm air forced above cold and cool air.
• Signature of mature low pressure system

Figure 9-20
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Dry Lines

• Change in moisture content of air masses but not
  temperature. Brown closely drawn half circles
• Associated with severe weather

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Final Notes

• HW 1 returned tomorrow
• Exam 1 review tomorrow (6/3)
• Exam 1 on Thursday (6/4)