Tornado energy in real time

In light of the tornado outbreak that caused widespread destruction across parts of Indiana and Ohio the other day, I thought I would explain how estimates of tornado energy are made in real time and why they are important. 

 

Using the timeline below, you will see how tornado reports are validated at the National Weather Service (NWS). The process of recording a tornado begins through initial accounts from the general public, storm chasers, and/or law enforcement alike. These initial accounts typically involve either pictures or videos of the event and set the process of confirming a tornado in motion. Next, comes a post-storm survey typically performed by the closest NWS office. This involves getting an estimate of the magnitude of the storm, as well as start and end points and start and end times. This rough estimate is then noted and a formal process of recording the tornado begins. The formal process of recording a tornado can involve looking at doppler radar, piecing together footage of the tornado, and using remote sensing techniques to outline the path of the storm. 

 

Where does tornado energy come into play, then? Well, estimates of tornado energy can initially begin after the NWS post-storm survey is performed (see flow-chart below). For example, using the EF category, path length, and path width noted by the NWS Indianapolis for the Kokomo, Indiana tornado, I found that the event had 1.54 terajoules (TJ) of energy. To put this into perspective, the atomic bomb dropped on Hiroshima ("Little Boy") had 63 TJ of energy. 

 

Why is tornado energy important? Tornado energy is important, because it allows us to think about the intensity or strength of a storm based on physical theory. Currently, the NWS uses the EF-scale to rate tornadoes. This measure can be misleading, though, as it represents the maximum damage found within the storm's path. This means that even though most of a tornado's path may be EF1 damage (winds around 100 mph), if there is a building or area that has EF3 damage (winds around 165 mph), it is given the EF3 distinction.

Estimates of tornado energy take away this confusion, using a model of average damage area by EF category within a storm's path. It also expresses tornado intensity or strength in units of energy (joules) that can be compared to other energetic phenomena (including other tornadoes). The ability to estimate tornado energy in real time (as the data become available by the NWS) allows for a faster and better understanding of the strength of the storm. For example, if there is a tornado outbreak and there are multiple EF3 tornadoes, how will you know which one is the strongest? While some may look to the severity of the damage or the number of casualties, others may look at the size of the damage path. Interestingly, tornado energy accounts for almost all of these things. 

Getting estimates of tornado energy allows us to rank tornadoes beyond a dimensionless categorization. Back to the Kokomo, Indiana tornado. While the 1.54 TJ of energy would make it the strongest August tornado in Indiana history, it would only rank 61st out of all Indiana tornadoes dating back to 1994. Being able to frame tornadoes in this way is important for both historic and scientific perspective. It allows us to understand the behavior of tornadoes in a deeper manner.