Feb 29, 2016

Tornado outbreak variability follows Taylor's power law of fluctuation scaling and increases dramatically with severity

Michael K. Tippett, Joel E. Cohen
Nature Communications
  • States the largest tornado impacts come from ‘outbreaks’ consisting of multiple tornadoes closely spaced in time
  • Finds an upward trend in the annual mean number of tornadoes per US tornado outbreak for the period 1954–2014
  • Finds the variance of this quantity is increasing more than four times as fast as the mean
  • States the mean and variance of the number of tornadoes per outbreak vary according to Taylor’s power law of fluctuation scaling (TL), with parameters that are consistent with multiplicative growth
  • Finds tornado-related atmospheric proxies show similar power-law scaling and multiplicative growth
  • States path-length-integrated tornado outbreak intensity also follows TL, but with parameters consistent with sampling variability
  • Results show observed TL power-law scaling of outbreak severity means that extreme outbreaks are more frequent than would be expected if mean and variance were independent or linearly related