Cyclones - Understanding Storm Systems
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Transcript of Cyclones - Understanding Storm Systems
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Storms Systems
What is a Cyclone? Types? Paths?
How do we recognize a cyclone?
What are Mid-latitude Cyclonic Systems?
What are their stages, from birth to dissipation?
What is the weather associated with the passage of a wave cyclone?
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What is a cyclone?
Cyclones
• Enclosed area of low pressure (mb)• Air circulation is into centre and up• Rotation = CCW-NH and CW-SH
Types of cyclones:
• Wave Cyclone: mid & high latitudes• Tropical Cyclone: low latitudes• Tornado (small & very intense vortex)
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How do we recognize a cyclone?
Map of surface observationsWind Barbs (speed & direction)
Very Windy Calm
http://ww2010.atmos.uiuc.edu/(Gh)/wwhlpr/cyclone_wnd.rxml?hret=/guides/mtr/cyc/def.rxml
Satellite ImagesComma-shaped cloud mass
Midlatitude Cyclone
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Mobile Storm Systems
What do you call the Cyclones shown as: Green arrows? Black arrows?
www.physicalgeography.net/fundamentals/7s.htmln arrows
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Daily World Weather Map
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Mid-Latitude (Wave) Cyclone
• Typically accompanied by fronts• They are leading edges of air masses• Wrapping around a centre of low pressure
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/def.rxml
Pulling
Pushing
Transporting warm, moist air NDragging colder, drier air S
Why is it called a wave?What steers it?What generates its cyclonic motion?
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Understanding the entire system… Mid-Latitude Cyclone.
(3-10 days)
(1000-1500 km wide)
(50-60 km/h or 1200 km in a day)
(generally eastward)
(Cold = 30-40 km/h and 1:50 or steeper)
(Warm = 10-20 km/hr and 1:200)
What is a typical lifespan?
Horizontal extent?
Direction of travel?
Speed and Slope of the fronts?
Speed of Travel (entire system)?
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Life Cycle of a Mid-latitude Cyclone
What is Cyclogenesis?Atmospheric process in which low pressure wave cyclones develop and strengthen
Initial Stage
Open stage
Occluded stage
Dissolving stage
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Life Cycle of a Mid-latitude Cyclone
Initial StageStationary front b/t warm & cold air masses (at the polar front)
Divergence aloft (at jet stream) causes air to rise
Causes low pressure along front
http://www.on.ec.gc.ca/skywatchers/swtc_docs/frontal_poster/
front_weather_e.html
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Life Cycle of a Mid-latitude Cyclone
Open StageMaturing depression
Fronts develop
• Cold, denser air pushing south• Undercuts warm, lighter air• = Lift
• CCW funnels warm air towards centre• Pressure drops• Storm intensifies Cold air: advancing, retreating
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Development of a Mid-latitude Cyclone
Occluded StageCold front overtakes Warm front (forced aloft)
Mixes
Gradually cools = Stop rising
Influx of warm air ↓’edPressure stops falling
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Development of a Mid-latitude Cyclone
Dissolving StageSystem dissipates
Lifting mechanisms is cutoff
No source of energy and moisture
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Midlatitude Cyclone
Christopherson and Byrne 2009
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http://science.jrank.org/pages/47861/middle-latitude-tropospheric-circulations.html
Life Cycle of a Mid-latitude Cyclone
Can you identify the stages? Can you differentiate the symbols? Can you visualize it in cross-sectional view?
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Last Wednesday
Today
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Two Fronts (boundaries)• Warm & Cold Front
Three Sectors of a wave cyclone:a) cool sector ahead of the warm front
b) warm sector between the cold and warm fronts
c) cold sector located behind the cold front
What is the weather associated with the passage of a wave cyclone?
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/weather_systems/
weather_and_wave_cyclones.html
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Pressure distribution (isobars)
Where is the lowest pressure?
Gradient and V-shape
Wind Direction
Differ in the 3 sectors?
Precipitation
Where and Extent?
From the south
From the north
From the east
To Interpret Weather, You need to think about…
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a) Cool Sector Air Mass (cP) Pressure Tendency (falling) Wind Direction (E – SE) Clouds (Cirrus–Nimbostratus) Precipitation
At warm front• low intensity• long duration
Weather, as the Wave Cyclone Passes…
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b) Warm Sector Air Mass (mT) Pressure Tendency (rising-falling) Wind Direction (SE–S-SW) Clouds (Clring–Cumulonimbus) Precipitation
At cold front• high intensity• long duration
Weather, as the Wave Cyclone Passes…
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c) Cold Sector Air Mass (cP) Pressure Tendency (rising) Wind Direction (W-NW) Clouds (Cumulonimus-Clring)
Weather, as the Wave Cyclone Passes…
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Can you identify Initial, Open, Occluded, Dissolving Stages?
Life Cycle of a Mid-latitude Cyclone
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