Oct 6, 2014

Changing volatility of U.S. annual tornado reports

Tippett, Michael K.
Geophysical Research Letters
  • States that a simple measure of the US tornado climatology is the average number of tornadoes per year; however, even this statistic is elusive because of nonstationary behavior due in large part to changes in reporting practices
  • States that differencing of the annual report data results in a quantity without mean trends, the standard deviation of which is denoted as volatility, since it is an indication of the likely year-to-year variation in the number of tornadoes reported
  • Finds that while volatility changes detected prior to 2000 can be associated with known reporting practice changes, an increase in volatility in the 2000s across intensity levels cannot
  • Finds a volatility increase in a tornado environment index which measures the favorability of atmospheric conditions to tornado activity, providing evidence that the recent increase in tornado report volatility is related to the physical environment