1. Tornados and Climate Change
Michael Pateman
And
Drew Vankat

2. What is a tornado?
An intense, rotating column of air extending from the base of a thunderstorm cloud to the ground.

3. Ingredients for tornado formation:
Polar jet stream
Low pressure trough
Inversion layer
Layer of warm humid air near surface
Triggering mechanism
Conditionally unstable is essential.
Polar jet stream: provides area of divergence that initiates surface convergence and lift
Low pressure trough: cold, dry air—ready for moisture
Inversion layer: of warm, dry air in the middle levels of the atmosphere
Low relative humidity
acts as a lid
Surface layer: Middle layer prevents it from rising
Builds up an enormous amount of energy
Triggering mechanism: cold front or dryline
Weakens convective cap, allowing warm, humid air to burst through, initiate extremely violent convection
Supercells often form as a result of this violent convection
Ahrens, C. Donald. Meteorology Today, pp407-8

4. How are they formed? Supercell Thunderstorms Mesocyclones 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
up to 20km high and 20-50km in diameter
they can persist for many hours
Wind being lifted in the updraft may start off from the south, but then shift to the west at a higher elevation, causing a rotation to form.

5. Tornado Structure Extremely low pressures Steep pressure gradient
Estimated 10 percent less than the immediate surrounding area
Steep pressure gradient
Wind speeds of up to 300 miles an hour

6. Weaker tornadoes: one vortex
Larger, stronger tornadoes: several smaller 'suction vortexes’
very concentrated
often no larger than 10 meters in diameter

7. Where are they found? United States All over the world
Great Plains during spring and summer
“Tornado Alley”
All over the world
Mike will talk about frequency and distribution.
US averages over 900 annually
Tornado Alley: central TX to NE

8. Tornado Magnitude Fujita Tornado Damage Scale
Measures strength and intensity
Ratings from F0 (weakest) to F5(most powerful)

9. 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 ( mph); Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off road.
Category F2: Considerable Damage ( mph); Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.

10. Category F3: Severe Damage ( 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 ( mph); Well-constructed houses leveled; structure with weak foundations blown off some distance; cars thrown and large missiles generated.
Category F5: Incredible Damage ( 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.

11. 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.

12. 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

13. 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.

14. What is La Nina?
Characterized by unusually cold ocean temperatures in the Equatorial Pacific
US warmer southwest winters, colder Northwest

15. How do they affect Tornados?
Mideastern US April 3 - 4, Massive Tornado outbreak - “Classic La Nina Year”
In Ohio 16 Tornados
All within 6 hrs of each other
5 - F F2 2 - F F F5
Coincidence?

16. 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

17. Tornado Data (US)

18. Tornado Data (Texas) # Tornados 1950’s 647 1960’s 1195 1970’s 1484

19. Tornado Data (Nebraska)
# Tornados
1950’s 319
1960’s 302
1970’s 405
1980’s 377
1990’s 701

20. Tornado Data (Ohio) # Tornados 1950’s 71 1960’s 148 1970’s 202

21. Data http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms
All Tornado Data downloaded from this site.
Any questions?