I’m caught between sessions but wanted to post this. From a presentation at AGU that I couldn’t attend. This from SciAm:
James Elsner at Florida State University has a killer curve, and lots of caveats. The curve indicates that tornadoes in the U.S. may be getting stronger. The caveats indicate they may not be.
“If I were a betting man I’d say tornadoes are getting stronger,” he noted on Tuesday during a lecture at the annual American Geophysical Union fall meeting in San Francisco.
But when asked directly at a press conference whether that is the case, he would not commit. “I’m not doing this [work] to establish the future intensity of tornadoes,” he explained, but to establish a method that someday could indeed determine if the storms are becoming more powerful.
Because the lecture was titled “Are tornadoes getting stronger?” the audience expected an answer. And their consternation rose when Elsner showed his final graph, adding up the kinetic energy of tornadoes each year from 1994 to 2012.
More here: http://blogs.scientificamerican.com/observations/2013/12/11/tornadoes-may-be-getting-stronger-or-not/
This reminds me of Dr. Ryan Maue’s ACE (accumulated cyclone energy) for hurricanes.
Since measuring tornado wind speed is a hit/miss proposition, even with doppler radar I have many reasons to suspect the data in this graph.
Elsner has 18[years of data]. His data begin in 1994 because that’s when Doppler radar, the best at tracking tornadoes, began covering the entire U.S.
The point of the curve, however, is to show that measuring the length and width of a tornado’s damage path gives an accurate indication of its strength, which is driven by the storm’s peak wind speed. It is difficult if not impossible to measure that speed directly, as is done for hurricanes by ground instruments and planes that fly into the storms.
So, like Mann’s hockey stick, it is a proxy, not the actual measurement.