Tornadoes are the most violent of atmospheric storms with wind speeds exceeding 120 m/s. A tornado consists of a rotating column of air reaching from a thunderstorm cloud all the way to the ground. When a tornado develops a condensation funnel of water droplets and debris it becomes visible to the human eye like in the photo below. As opposed to hurricanes, tornadoes are occurring on a much smaller scale with shorter lifetimes and travel distances. Yet, they can be very destructive.
Prof. Elsner and colleagues from Florida State University (USA) recently published an article in the journal Geophysical Research Letters examining tornado power over the past few decades. Studies before had shown that the number of strong and violent tornadoes occurring every year remained relatively constant. However, they also found that the timing of occurrence has been changing. There are more days in the year now, where many tornadoes form on the same day. The authors also call those “big tornado days”.
So far it had not been possible to quantify the magnitude of increase in tornado power, which refers to the energy dissipated near the ground. It takes into account path area, wind speed and air density. The study applied a statistical model controlling for influencing factors like time of day and year, natural variability and the change to a new system of rating tornadoes. It showed that there is an increasing trend of tornado power between 1994 and 2016, of 5.5 % per year.
The authors explain some of this trend with changing convective storm environments in the long term but also highlight the knowledge gaps that exist with regard to fully understanding tornado processes. Future research will address the reasons behind that increase in tornado power, including the potential effect of climate change.
- MetLink: Make a tornado in a jar (http://www.metlink.org/experimentsdemonstrations/tornadojar/)
- Elsner, J. B., Fricker, T., & Schroder, Z.(2019). Increasingly powerfultornadoes in the United States.Geophysical ResearchLetters,46, 392–398.https://doi.org/10.1029/2018GL080819Received 8
- The National Severe Storms Laboratory (NSSL)/ Severe Weather 101 Tornado Basics. https://www.nssl.noaa.gov/education/svrwx101/tornadoes/