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: 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

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.

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

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

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

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  

Tornado Data (US)

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

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

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