Transcript Tornados and Climate Change

Tornados and Climate Change
Michael Pateman
And
Drew Vankat
What is a tornado?
• An intense, rotating column of air extending from the base
of a thunderstorm cloud to the ground.
www.spc.noaa.gov
Ingredients for tornado formation:
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Polar jet stream
Low pressure trough
Inversion layer
Layer of warm humid air near surface
Triggering mechanism
Ahrens, C. Donald. Meteorology Today, pp407-8
How are they formed?
• Supercell Thunderstorms
– Large
– Long-lasting
– Complex
• Mesocyclones
– Area of rotating air in a severe thunderstorm
– May be stretched vertically, increasing rate of rotation
– Can protrude downward, through base of storm
• Funnel cloud
• Becomes a tornado when contact is made with ground
Tornado Structure
• Extremely low pressures
– Estimated 10 percent less than the immediate
surrounding area
• Steep pressure gradient
– Wind speeds of up to 300 miles an hour
• Weaker tornadoes: one vortex
• Larger, stronger tornadoes: several smaller 'suction
vortexes’
very concentrated
– often no larger than 10 meters in diameter
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Where are they found?
• United States
– Great Plains during spring and summer
– “Tornado Alley”
• All over the world
Tornado Magnitude
• Fujita Tornado Damage Scale
– Measures strength and intensity
– Ratings from F0 (weakest) to F5(most powerful)
Fujita Scale
• Category F0: Light Damage (<73 mph); Some damage to chimneys;
branches broken off trees; shallow-rooted trees pushed over; sign
boards damaged.
• Category F1: Moderate Damage (73-112 mph); Peels surface off
roofs; mobile homes pushed off foundations or overturned; moving
autos blown off road.
• Category F2: Considerable Damage (113-157 mph); Roofs torn off
frame houses; mobile homes demolished; boxcars overturned; large
trees snapped or uprooted; light-object missiles generated; cars lifted
off ground.
www.noaa.gov/tornadofacts.html
• Category F3: Severe Damage (158- 206 mph); Roofs and some walls
torn off well-constructed houses, trains overturned; most trees in forest
uprooted; heavy cars lifted off ground and thrown.
• Category F4: Devastating Damage (207- 260 mph); Well-constructed
houses leveled; structure with weak foundations blown off some
distance; cars thrown and large missiles generated.
• Category F5: Incredible Damage (261- 318 mph); Strong frame
houses lifted off foundations and swept away; automobile sized
missiles fly through the air in excess of 100 meters; trees debarked;
incredible phenomena will occur.
www.noaa.gov/tornadofacts.html
ENSO
• The ENSO (El Nino/
Southern Oscillation)
cycle refers to the
coherent, large-scale
fluctuation of ocean
temperatures, rainfall,
atmospheric circulation,
vertical motion and air
pressure across the
tropical Pacific.
http://www.cpc.ncep.noaa.gov/
When has it happened?
El Nino
• 1958
• 1964
• 1966
• 1969
• 1973
• 1983
• 1987
• 1988
• 1992
• 1995
La Nina
•1951
•1952
•1956
•1965
•1971
•1974
•1989
What is El Nino?
• a disruption of the ocean-atmosphere system in the
Tropical Pacific
• development of abnormally warm sea surface
temperatures across the eastern tropical Pacific
• having important consequences for weather and
climate around the globe.
• These consequences can include increased rainfall
in some areas (which can lead to flooding)
• extreme drought in others.
What is La Nina?
• Characterized by unusually cold ocean
temperatures in the Equatorial Pacific
• US warmer southwest winters, colder Northwest
How do they affect Tornados?
• Mideastern US April 3 - 4, 1974 - Massive
Tornado outbreak - “Classic La Nina Year”
• In Ohio 16 Tornados
• All within 6 hrs of each other
• 5 - F1 4 - F2 2 - F3 2 - F4 3 - F5
• Coincidence?
Tornado Data (US)
1950’s
1960’s
1970’s
1980’s
1990’s
Total
4796
6813
8579
8141
10696
Yearly
Average
533
757
953
905
1188
Monthly
Average
44
63
79
75
99
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Tornado Data (US)
Tornado Data (Texas)
# Tornados
• 1950’s 647
• 1960’s 1195
• 1970’s 1484
• 1980’s 1492
• 1990’s 1836
Tornado Data (Nebraska)
# Tornados
• 1950’s 319
• 1960’s 302
• 1970’s 405
• 1980’s 377
• 1990’s 701
Tornado Data (Ohio)
# Tornados
• 1950’s 71
• 1960’s 148
• 1970’s 202
• 1980’s 165
• 1990’s 251
Data
• http://www4.ncdc.noaa.gov/cgiwin/wwcgi.dll?wwEvent~Storms
• All Tornado Data downloaded from this
site.
• Any questions?