EL NIÑO-SOUTHERN OSCILLATION’S
EFFECT ON AMERICAN TORNADOS
Jake Mittelman
April 24 2012
Overview
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ENSO
Tornados
Data
Hypothesis
Periodogram
Correlations
Bootstrap
Jacknife
Title Source: http://en.wikipedia.org/wiki/Tornado
Image Source: http://dailypicksandflicks.com/wp-content/uploads/2012/04/Dallas-Tornado-Throwing-Semi-Trucks-and-Trailers.jpg
El Niño-Southern Oscillation
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Quasiperiodic
Tropical Pacific Ocean
Variations in SST
El Nino – Warm Phase
La Nina – Cool Phase
Image Source: http://en.wikipedia.org/wiki/El_Ni%C3%B1o-Southern_Oscillation
ENSO
El Nino
La Nina
Image Source: http://en.wikipedia.org/wiki/El_Ni%C3%B1o-Southern_Oscillation
Tornados

Severe Weather
 Instability
 Wind
Shear
 Lifting
 Moisture
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Moisture
 Tornados
more likely with low LCL
 Can increase instability
Image Source: http://en.wikipedia.org/wiki/File:Binger_Oklahoma_Tornado.jpg
Hypothesis
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Whole U.S.
 Little

to no correlation
Southeast
 Positive
Correlation with El
Nino
 Negative Correlation with
La Nina (Winter)

Midwest
 Positive
Correlation with
La Nina
Image Source: http://en.wikipedia.org/wiki/File:Dimmit_Sequence.jpg
Nino 3.4 Index
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1950-2007
Middle Ocean
NCAR CGD’s Climate Analysis Section
Compute area averaged total SST from Niño 3.4
region.
 Compute monthly climatology (1950-1979) for area
averaged total SST from Niño 3.4 region, and
subtract climatology from area averaged total SST
time series to obtain anomalies.
 Smooth the anomalies with a 5-month running mean.
 Normalize the smoothed N3.4 by its standard
deviation over the climatological period 19501979.

Image Source: http://en.wikipedia.org/wiki/File:Enso-index-map.png
Nino 3.4 Index
Tornado Data Initial Problem
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Severe Weather Database from SPC
1950-2007
EF0-EF5
LSQR On Tornado
Pearson Correlation Coefficients
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Strength of Linear Dependence
Nino 3.4 & Tornado (all)
r
= .0411
Correlation By Year
States
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No Correlation
Southeast (MS, AR, LA, GA, SC, FL, TN,
MS, AR, LA, SC, GA, FL, TN)
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No Correlation
El Nino and La Nina Correlations
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Southeast
 La
Nina r = 0
 El Nino r = 0
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Midwest (IL, IN, IA, KS, MI, MO, NE, ND, OH, SD, WI)
 La
Nina r = .11
 El Nino r = -.06
 Total r = .02
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Total
 La
Nina r = .13
 El Nino r = 0
Periodograms
Bootstrap
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Tends to be overly optimistic
Seasons
 Still
Working On
 Summer r = .15
Bootstrap
Jackknife
Other Research
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Cook, A. R., Schaefer, J.T. 2007
Used Tornado Days
 Problem: Not a lot of Data – Total ~220 Days
 Found Jet Stream Movement Had Effect
 Used Trends
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Bove, Mark 1999
Boostrap Method to Increase Data
 Most Places Show No Change
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Knowles, J., Pielke, R. 1993
Used 7 El Nino and 5 La Nina Events
 Found Little Difference in Number
 But Found El Nino to have Weaker Tornado Outbreaks
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More I can Do
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Take out More
Neutral ENSO
Months
Create Smaller
Areas
Look at Numbers
not Linear
Correlations
Image Source: http://en.wikipedia.org/wiki/Tornado
Conclusion
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No Correlation
Overall
 Number
of Tornados
and ENSO Phase
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Go More Into Year
ENSO still can have
an effect
 Tornado
Strength
 Number per
Outbreak
 Location
Image Source: http://uncyclopedia.wikia.com/wiki/File:Animated_tornado.gif
Any Questions?
Image Source: http://www.google.com/imgres?imgurl=http://a.abcnews.com/images/US/Severe_Weather_110427_wg.jpg