Tornado watchers from the sky
Last November, a new weather satellite (GOES-R*), was launched from the Kennedy Space Center in Florida (Fig. 1). This new space dweller is equipped with modern and powerful instruments, opening numerous possibilities for improved weather analysis and forecasting.
Today, I would like to focus on a brand-new instrument – The Geostationary Lightning Mapper (GLM). Scientists believe that this could be the key to improved tornado forecasting. Studies have shown that there is a positive relationship between changes in the lightning pattern inside a storm and the formation of a tornado. But, before we get into that, let’s talk about thunderstorm formation, particularly that of tornadic thunderstorms.
In areas with vertical differences in wind direction and speed (what meteorologists call wind shear), there is a potential for the formation of horizontal rolls (Fig. 2).
When a powerful thunderstorm develops, the lifting air associated with it tilts these rolls, turning them into more vertical positions (one with rising air and one with sinking air) as shown in Fig. 3.
Under some circumstances, the upward rotation can extend to the ground generating a violent column of rotating air, known as a tornado. Unfortunately, there are still limitations to pin-pointing the onset or potential onset of tornado formation (i.e., the warning process). Severe weather forecasters typically recognize the larger-scale conditions and general geographic areas in which tornadoes can possibly form (watch process).
Once a watch is issued (or localized conditions suggest possible tornado or severe weather development), storm spotters and Doppler radar become the key tools available to local National Weather Service forecasters. Trained spotters can recognize cloud features that suggest possible severe weather. Radar, however, can probe the interior of the thunderstorms. Determining the presence of certain echoes (radar patterns based on the size and distribution of water droplets) can indicate the presence of a rotating core that is often linked to the occurrence of tornadoes. Doppler radars are also capable of detecting areas of rotation (based on the wind movement toward/away from the radar). Still, radars have limitations regarding vertical and horizontal coverage and resolution. At large distances, the radar may even “overshoot” the tornadic circulation, passing high above it. So, depending on the distance from the storm to the radar and other factors, forecasters may not be able to detect a tornadic signature.
Recent research indicates there is a close relationship between lightning and tornado formation. A considerable and sudden increase in lightning flash rates (lightning frequency), known as a “jump,” has been observed to take place just before tornado formation. These jumps have been registered 20-25 minutes before the tornado occurs (i.e., about 10 minutes more than the current average tornado warning lead-time). Until now, the only possible way to measure the lightning activity inside the storms, was to use the National Lightning Detection Network, which was the most accurate way to record time, strength and number of strokes of cloud to ground lightning flashes. But, the more intense and severe the storm is, the more important the intra-cloud lightning (cloud to cloud strokes) may be.
That is why the meteorological world is celebrating the launch of GOES 16. This satellite is opening new ways to make huge advancements in weather observing, analysis and forecasting. With the arrival of the GLM, the satellite is capable of detecting intra-cloud, cloud-to-ground and cloud-to-air lightning.
With the 2017 tornado season well underway, scientists have already been looking at GLM’s capabilities and reliability in detecting tornadoes.
*The name of the satellite was changed from GOES R to GOES 16, once the spacecraft reached its stationary orbit on November 29th.
© 2017 Mayguen Ojeda
Originally posted 6/14/17