Atmos. Chem. Phys. Discuss., 12, 6957-6988, 2012
www.atmos-chem-phys-discuss.net/12/6957/2012/
doi:10.5194/acpd-12-6957-2012
© Author(s) 2012. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Statistics of severe tornadoes and severe tornado outbreaks
B. D. Malamud1 and D. L. Turcotte2
1Department of Geography, King's College London, Strand, London, WC2R 2LS, UK
2Department of Geology, University of California, Davis, CA 95616, USA

Abstract. The standard measures of the intensity of a tornado in the USA and many other countries are the Fujita and Enhanced Fujita scales. These scales are based on the damage that a tornado causes. Another measure of the strength of a tornado is its path length of touchdown, L. In this study we consider 4061 severe tornadoes (defined as L≥10 km) in the continental USA for the time period 1981–2010 (USA Storm Prediction Center Severe Weather Database). We find for individual severe tornadoes: (i) The noncumulative frequency-length statistics of severe tornado touchdown path lengths, 20 < L < 200 km, is well approximated by an inverse power-law relationship with exponent near 3. (ii) There is a strong linear scaling between the number of severe tornadoes in a year and their total path lengths in that year. We then take the total path length of severe tornadoes in a day, LD, as a measure of the strength of a 24-hour USA tornado outbreak. We find that: (i) On average, the number of days per year with at least one continental USA severe tornado (path length L≥10 km) has increased 16% in the 30-year period 1981–2010. (ii) The daily numbers of severe tornadoes in a USA outbreak have a strong power-law relationship (exponent 0.87) on their daily total path lengths, LD, over the range 20 < LD < 1000 km dy−1. (iii) The noncumulative frequency-length statistics of tornado outbreaks, 10 < LD < 1000 km dy−1, is well approximated by an inverse power-law relationship with exponent near 1.7. We believe that our robust scaling results provide evidence that touchdown path lengths can be used as quantitative measures of the systematic properties of severe tornadoes and severe tornado outbreaks.

Citation: Malamud, B. D. and Turcotte, D. L.: Statistics of severe tornadoes and severe tornado outbreaks, Atmos. Chem. Phys. Discuss., 12, 6957-6988, doi:10.5194/acpd-12-6957-2012, 2012.
 
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