cyclones - understanding storm systems

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?

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)

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

Mobile Storm Systems

What do you call the Cyclones shown as: Green arrows? Black arrows?

www.physicalgeography.net/fundamentals/7s.htmln arrows

Daily World Weather Map

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?

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)?

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

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

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

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

Development of a Mid-latitude Cyclone 

Dissolving StageSystem dissipates

Lifting mechanisms is cutoff

No source of energy and moisture

Midlatitude Cyclone

Christopherson and Byrne 2009

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?

Last Wednesday

Today

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

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…

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…

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…

c) Cold Sector Air Mass (cP) Pressure Tendency (rising) Wind Direction (W-NW) Clouds (Cumulonimus-Clring)

Weather, as the Wave Cyclone Passes…

Can you identify Initial, Open, Occluded, Dissolving Stages?

Life Cycle of a Mid-latitude Cyclone