It seems that recent research has come up with information that may be surprising to many, particularly those in the non-scientific community, but not me. That came from a December 17th article in physics.org titled “New research finds tornadoes form from the ground up, contrary to popular thought.” written by Lauren Lipuma, from the American Geophysical Union. Here’s how the article began. “Historically, scientists assumed tornado rotation began in storm clouds, creating a funnel that travels downwards. This theory matches what storm chasers observe visually in the field. Viewers often report seeing funnel clouds gradually descending until they make contact with the ground.” Now we get to the point of the article. “But new research combining a new type of Doppler radar with photos and videos of tornadoes formed by supercell thunderstorms shows the opposite is true: Tornadoes materialize from the ground up.”
The way it has been since I got into the weather business in the early 70s is that tornadoes or their rotation were spotted up in the sky and often found on radar or when they started chewing up the ground causing destruction and then warnings were issued. What follows is a definition and tornado formation information.
Here is how the National Weather Service defines the term tornado. “A tornado is a violently rotating column of air, usually pendant to a cumulonimbus, with circulation reaching the ground. It nearly always starts out as a funnel cloud and may be accompanied by a loud roaring noise. On a local scale, it is the most destructive of all atmospheric phenomena.”
They need certain elements to form including warm moist airflow from the south, cooler drier air from the north and a rotation that begins when a mesocyclone is formed. A mesocyclone is defined as a “storm-scale region of rotation, typically 2-6 miles in diameter and often found in the right rear flank of a supercell.” The mesocyclone’s circulation is much larger than the tornado circulation that can develop within it. Research I have seen over the years has shown the tornado funnel itself can build in various stages sometimes starting high in the sky and dropping down to the ground or building from the ground level upward, ore even from mid-levels expanding both upward and downward. Remember the difference between a funnel cloud and a tornado? The funnel cloud has the vortex rotation but is not touching the ground. In order for a funnel cloud to be called a tornado it must reach the ground.
The way the wind speeds rotating around a tornado vortex are calculated was originally devised by the late Dr. Tetsuya Theodore Fujita who worked out of the University of Chicago in Illinois. The scale went from F-0 to F-5 with F-0 being the weakest causing minor damage and F-5 being the strongest causing total destruction.
The scale has been updated (February 2007) and improved and is now called the Enhanced Fujita-Pearson Scale. According to Pearson the reasons for the updating of the scale are “that tornado wind speeds required to inflict the described damage were actually much lower than the F-Scale indicated, particularly for the upper categories. Also, though the scale gave general descriptions of the type of damage a tornado could cause, it gave little leeway for strength of construction and other factors that might cause a building to receive higher damage at lower wind speeds.”
Now back to the latest research. The El Reno tornado, which occurred on May 31, 2013 in central Oklahoma, was a record breaker. It’s winds were clocked at 300 miles per hour, the second highest wind speeds recorded on Earth, and at 2.6 miles in diameter it was the widest tornado ever recorded. As luck would have it a research team was at the site of the outbreak with all of their equipment. Meteorologist Jana Houser, from Ohio University at Athens led the team.
“Houser and a team of researchers from the University of Oklahoma happened to be monitoring the storm with a new type of mobile Doppler radar system that collected tornado wind speeds every 30 seconds.
Afterwards, Anton Seimon, a geographer at Appalachian State University in Boone, North Carolina who had chased the El Reno storm, collected hundreds of still photos videos of the epic twister from citizens and fellow storm chasers.” Comparing the the pictures with her low-level radar data Houser found the photos showed the tornado funnel at ground level several minutes before it was seen on the radar. She studied four data sets and all indicated the development from the ground up.
Jana Houser presented her findings at the American Geophysical Union’s Fall meeting. She feels her research indicates that the forecasters need to chance the current priority of paying attention to the upper rotation and be more concerned with the ground-level rotation in order to make better tornado predictions.
It will be very interesting to see how the meteorological community reacts to the latest data and what steps might be taken to improve tornado forecasting and detection methods.
Let me know what you would like me to talk about or explain. You can email me at: [email protected].