EL NIÑO-SOUTHERN OSCILLATION’S EFFECT ON AMERICAN TORNADOS Jake Mittelman April

Overview  ENSO  Tornados  Data  Hypothesis  Periodogram  Correlations  Bootstrap  Jacknife Title Source: Image Source:

El Niño-Southern Oscillation  Quasiperiodic  Tropical Pacific Ocean  Variations in SST  El Nino – Warm Phase  La Nina – Cool Phase Image Source:

ENSO

Image Source: El Nino La Nina

Tornados  Severe Weather  Instability  Wind Shear  Lifting  Moisture  Moisture  Tornados more likely with low LCL  Can increase instability Image Source:

Hypothesis  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:

Nino 3.4 Index   Middle Ocean  NCAR CGD’s Climate Analysis Section  Compute area averaged total SST from Niño 3.4 region.  Compute monthly climatology ( ) 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 Image Source:

Nino 3.4 Index

Tornado Data Initial Problem  Severe Weather Database from SPC   EF0-EF5

LSQR On Tornado

Pearson Correlation Coefficients  Strength of Linear Dependence  Nino 3.4 & Tornado (all)  r =.0411

Correlation By Year

States  No Correlation

Southeast (MS, AR, LA, GA, SC, FL, TN, MS, AR, LA, SC, GA, FL, TN)  No Correlation

El Nino and La Nina Correlations  Southeast  La Nina r = 0  El Nino r = 0  Midwest (IL, IN, IA, KS, MI, MO, NE, ND, OH, SD, WI)  La Nina r =.11  El Nino r = -.06  Total r =.02  Total  La Nina r =.13  El Nino r = 0

Periodograms

CPSD

Coherence

Bootstrap  Tends to be overly optimistic  Seasons  Still Working On  Summer r =.15

Bootstrap

Jackknife

Other Research  Cook, A. R., Schaefer, J.T  Used Tornado Days  Problem: Not a lot of Data – Total ~220 Days  Found Jet Stream Movement Had Effect  Used Trends  Bove, Mark 1999  Boostrap Method to Increase Data  Most Places Show No Change  Knowles, J., Pielke, R  Used 7 El Nino and 5 La Nina Events  Found Little Difference in Number  But Found El Nino to have Weaker Tornado Outbreaks

More I can Do  Take out More Neutral ENSO Months  Create Smaller Areas  Look at Numbers not Linear Correlations Image Source:

Conclusion  No Correlation Overall  Number of Tornados and ENSO Phase  Go More Into Year  ENSO still can have an effect  Tornado Strength  Number per Outbreak  Location Image Source:

Any Questions? Image Source: