Download Tropical cyclone

Chapter 6
Weather Systems
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Air Masses
Air Mass: large body of air with fairly uniform temperature and
moisture characteristics
• Source region: region where an air mass acquires its characteristics
• Air masses move in response to pressure gradients and upper-level wind
patterns
Air Masses
North American Air
Masses:
cA—very cold, dry
cP—cold, dry
mP—cool, moist
mT—warm, moist
cT—hot, dry
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Air Masses
Front: surface of contact between two unlike air masses
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Air Masses
Cold, Warm, and Occluded Fronts
Cold front: moving weather front along which a
cold air mass moves underneath a warm air
mass, lifting the warm air mass
•Cumulus and cumulonimbus clouds
•Thunderstorms
Warm front: moving weather front along which a
warm air mass slides over a cold air mass,
producing stratiform clouds and precipitation
•Stratus, nimbostratus clouds
•Steady precipitation, sometimes
thunderstorms
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Air Masses
Cold, Warm, and Occluded Fronts
Occluded front: weather front along which a moving
cold front overtakes a warm front, forcing the warm air
mass aloft
Stationary Front: two air masses
are in contact, but there is little
or no relative motion
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Traveling Cyclones and Anticyclones
Cyclonic storm: intense weather disturbance within a moving
cyclone generating strong winds, cloudiness, and
precipitation
Three types of cyclones:
1.Wave cyclone
• midlatitudes, Arctic, Antarctic zones
2.Tropical cyclone
• tropical and subtropical zones
3.Tornado
An anticyclone is a fair-weather system.
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Traveling Cyclones and Anticyclones
The Tornado
Tornado: small, very intense wind vortex with
extremely low air pressure in the center,
formed below a dense cumulonimbus cloud
in proximity to a cold front
• Favorable conditions: cold front
of mP air lifts mT air
• Tornados most frequent in U.S
• Wind speeds up to 100 m/s
(225 mph).
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tropical and Equatorial Weather Systems
Tropical Cyclones
• Hurricane in western
hemisphere
• Typhoon in western Pacific
• Cyclone in Indian Ocean
• Develops over warm oceans
• High sea-surface
temperatures--27º C (81º F)
• Develops between 8º to 15º N
and S, not on equator
Tropical cyclone: intense
traveling cyclone of tropical and
subtropical latitudes,
accompanied by high winds
and heavy rainfall
Hurricane Katrina, 2005
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tropical and Equatorial Weather Systems
Tropical Cyclones
•
•
•
•
•
•
•
Circular storm center
Extremely low pressure (950 mb)
Intense convergence and uplift
Heavy rainfall
Gains energy through release of latent heat
Eye has clear skies and calm winds
Wind speeds highest in eyewall
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tropical and Equatorial Weather Systems
Tropical Cyclones
• Always form over warm oceans; temperatures >26.5ºC
• Move towards west through trade-wind belt
• Usually occur late summer or early autumn; water temperatures are
highest
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tropical and Equatorial Weather Systems
The intensity of storms increases when
sea surface temperatures increase
Hurricanes in
2005—most
active year on
record for
Atlantic
hurricanes
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Tropical and Equatorial Weather Systems
Impacts of Tropical Cyclones
Destruction from hurricanes:
•
•
•
•
High winds
Wave action
Storm surge
High rains and freshwater
flooding
Storm surge: rapid rise of coastal water level
accompanying the onshore arrival of a tropical
cyclone
Hurricane Mitch,
Honduras
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Hurricane
Andrew, Florida
Tropical and Equatorial Weather Systems
Impacts of Tropical Cyclones
Hurricane Katrina, 2005
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.
Cloud Cover, Precipitation, and Global Warming
How global climate may be influenced by clouds and precipitation:
Visualizing Physical Geography
Copyright © 2008 John Wiley and Sons Publishers Inc.