As part of the largest, most ambitious attempt ever launched to figure out how tornadoes form and how to predict them more accurately, engineers from the University of Massachusetts in Amherst this week are readying two special mobile Doppler radar systems for deployment to the Great Plains.
The national project known as Verification of the Origins of Rotation in Tornadoes Experiment 2, or VORTEX2, will enlist more than 50 scientists and 10 mobile radars to sample the wind, temperature and moisture environments in tornado-spawning storms in greater detail than before. One of the UMass Amherst units brings the highest spatial resolution of any mobile Doppler radar in the nation to address the study goals.
From early May to mid-June when these severe storms are most common, the $11.9 million project will look at events that have long been hidden behind rain and hail within supercell thunderstorms. With other specialists converging on one of the nation’s “tornado alleys,” the UMass Amherst group will use truck-mounted Doppler radars they’ve developed to “see” inside the violent storms at ground level, offering one of the most precise radars ever used for tornado detection, far more precise than those mounted on high towers or on satellites.
Electrical and computer engineering professor Stephen Frasier, director of the Microwave Remote Sensing Laboratory (MIRSL), leads the group of research engineer Pei-Sang Tsai and two graduate students taking part this spring. With any luck, they’ll capture data from a handful of actual tornadoes as they form, to help meteorologists understand tornado origin, structure and evolution. Another overall VORTEX2 goal is to build a complete observation network around and under a supercell storm.
It has been only in the past 15 years that results from the first VORTEX study in 1994-1995 allowed scientists to document the entire life-cycle of a tornado for the first time in history, according to the National Oceanic and Atmospheric Administration (NOAA). An important finding from that original experiment, according to an NSF program director, is that the factors responsible for causing tornadoes happen on smaller time and space scales than scientists had thought.
An exciting aspect of VORTEX2 is that to work most effectively some of the radars including one of the UMass Amherst rigs must be deployed quite close, within a mile or two, of tornadoes embedded in monster storms that can be 50 miles wide. Peril is reduced by approaching storms from the side, says Tsai, and overall “it’s not that dangerous because we know when to run. We keep the engine running in case the storm suddenly turns toward us,” she adds.
Tsai and Frasier explain that the two UMass Amherst Doppler radars send different signals into a storm, reflecting off water droplets or debris and returning data at either a fine or more coarse resolution. For example, the high-frequency 95 GHz W-band radar provides “the highest spatial resolution of all existing mobile Doppler radars,” Frasier notes. It can be very narrowly focused “because tornadoes are relatively small targets.” Also, W-band radar can better image internal tornado structures.
For best results, mobile W-band radar should be deployed quite close to a storm but not directly in its path, a mile or two to the side. Inside the truck, the engineer uses the radar to measure wind speed, density of raindrops, wind shear and other variables, Tsai adds. Frasier says this radar is critical to VORTEX2 because “it provides the best possible opportunity to map the wind field at the lowest levels of tornadoes. It also has the best chance to document the structure of multiple, sub-tornado-scale vortices, which are thought to cause much of the localized, extreme damage in some tornadoes.”
The other MIRSL truck, meanwhile, beams a 9.5 GHz signal known as X-band polarimetric radar at thunderheads from many miles away, to see the whole storm at once. This radar can better penetrate rain, providing information on the location and density of hail, rain and debris inside a storm, which is “essential to separate rain from debris,” says Frasier. Wind data from the X-band radar “will also be used in conjunction with data from the other X-band radars in the field to do multiple-Doppler analysis.”
For Venkatesh, VORTEX2 will be his second tornado study experience. He knows it means spending 15 hours a day driving hundreds of miles toward promising storm cells. “We usually pack two to three meals because it gets too intense to stop for a meal once the chase begins,” he says. “A team of radars leaves around noon and we drive until we reach our target region. We watch the weather events unfold, collect data with our radars, and are back around 2 or 3 a.m. to catch some sleep.” He adds, “On one hand, it is good for our research if we see a tornado. On the other hand, I was at Greensburg, Kansas, a year after the EF-5 storm wrecked their town. There was a severe storm watch in the area at the time, and you could see the concern on the faces of the local folks. It was natural for us to hope we didn’t see anything that day.”
VORTEX2 is supported by NOAA, the National Science Foundation, 10 universities and three nonprofits in 2009-2010, to provide forecasters with more tools to improve tornado warning times and short-term severe weather alerts.
Source: UMass Amherst