|A Texas Panhandle tornado from 2 June 1995. Photo copyright Harald Richter.|
The project, called VORTEX (Verification of the Origins of Rotation in Tornadoes Experiment), found the twisters it sought. The results will be analyzed up to the turn of the century and beyond. Already, though, the people behind VORTEX have uncovered some surprising results and a set of baffling new questions.
VORTEX was managed by Erik Rasmussen, a scientist with the National Severe Storms Laboratory (NSSL) and a long-time tornado chaser. Rasmussen cut his teeth as a youngster riding his bike to the outskirts of Hutchinson, Kansas, to watch storms approach. For VORTEX, Rasmussen carried out a much more sophisticated strategy: deploy 10 to 20 instrument-studded vehicles around a single storm to capture its full life cycle. Only then can you collect the dense observations needed to learn why some of the long-lived severe storms called supercells bear tornadoes while many other supercells do not.
What?Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX)
Who?A host of researchers, scientists, programmers, technicians, and pilots from the National Severe Storms Laboratory, National Oceanic and Atmospheric Administration, the University of Oklahoma and its Center for Analysis and Prediction of Storms, several other universities, NCAR's Atmospheric Technology Division and Mesoscale and Microscale Meteorology Division, and UOP's Office of Field Project Support (now merged into the Joint Office for Science Support)
Why?To learn more about how and why some severe thunderstorms produce tornadoes and others do not
How?By deploying a net of instrumentation--aircraft, instrument-studded vehicles, mobile Doppler radars--to intercept severe storms
Where?The southern Great Plains from Kansas to Texas
When?Field program in the spring of 1994 and 1995; data analysis ongoing
Why not the others? VORTEX set out to study the nonproducers just as closely as the tornadic storms. Thus, a day without tornadoes would not necessarily be a failure for the experiment. That turned out to be fortunate during 1994, when the skies were sparing with twisters. Less than a dozen were caught by the experiment's observing network in Kansas, Oklahoma, and Texas.
Still, the 18-vehicle VORTEX armada had its hands full. Each vehicle was topped by a customized instrument package that sent weather observations to a front-seat laptop and a mobile operations center every six seconds. The instrument package was designed by Jerry Straka, an assistant professor at the University of Oklahoma (OU). Its readings were so sensitive and frequent that a single VORTEX vehicle could drive only a few blocks and document both sides of the dry line, a perennial moisture boundary in the southern Plains that often serves as a trigger for storms.
Each vehicle had a specific mission for a given storm type and a specific place to go relative to each storm--for instance, near tornadic development, in the rain core, or well ahead of the action. However, even the best-laid plans went awry at times. On one May day, a fast-moving supercell in Oklahoma made a sharp right turn and trapped the mobile operations center in torrential rain, hail, and winds of over 120 kilometers an hour (75 mph).
The VORTEX network expanded in 1995 with two major additions, both with NCAR involvement. The first was the Electra Doppler radar (ELDORA), a dual-transmitter unit mounted on the National Science Foundation/NCAR Electra turboprop aircraft. ELDORA uses a rapid-scan technology to take slices through the atmosphere on the fly at resolutions as low as several hundred meters (or yards). Its multimillion-dollar development during the early 1990s, in collaboration with the French government, was NCAR's largest instrumentation effort to date.
Although some form of ELDORA was taken on field programs over the preceding two years, the 1995 VORTEX field effort was the maiden voyage for the radar in its complete incarnation. It proved its mettle that May, capturing almost two hours in the life cycle of a Kansas tornado. "With a fixed Doppler radar, you can only collect about 30 minutes of good data at best," says Roger Wakimoto (University of California, Los Angeles), a prime ELDORA user. "We were able to follow this storm across a good fraction of the state with ELDORA."
The second newcomer to the scene in 1995 was Doppler on Wheels (DOW). It sprang from the synergy between associate OU professor Joshua Wurman and NCAR engineer Mitchell Randall. Wurman wanted to create a portable Doppler radar durable and responsive enough to be taken near tornadoes for quick data collection. Meanwhile, Randall had just created a piece of hardware that allowed a closet's worth of radar processing technology to be compressed into a shoebox-sized space. See "What Else?" for more on Randall's creation, called PIRAQ.) With help from NCAR radar engineers, Randall's hardware, and a few parts cannibalized from older NCAR radars, Wurman and colleagues built DOW on a shoestring in a scant three months. (NSSL's Paul Griffin and Dennis Nealson later won a Department of Commerce Bronze Medal for their work in constructing DOW and other VORTEX platforms.)
By the end of May 1995, despite a few clear successes, the participants in VORTEX were exhausted and discouraged. The experiment's end was only a few days off, and they had yet to bring the complete instrument network within range of a classic, supercell-based tornado.
|Peter Hildebrand with a hail shaft (upper left). Photo of Peter by Carlye Calvin; photo of hail shaft courtesy Peter.|
Later that evening, another intense tornado struck near Dimmitt, with the VORTEX ground teams in place to document the process. DOW collected data from within 3 kilometers (1.8 miles) of the tornado. The resulting images caused jaws to drop. Inflow bands similar to those in hurricanes were evident, along with a nearly circular eyewall, a debris cloud, and a center virtually free of debris.
If 2 June was the day that made VORTEX a success, another tornado outbreak in Texas six days later confirmed it. Power loss incapacitated many gas stations and stranded some of the VORTEX fleet, but other vehicles were still mobile and able to add to the treasure trove of data that was being amassed.
UOP's Office of Field Project Support was a key player in the experiment's data analysis stage, with its own online retrieval system giving researchers quick access to data through the World Wide Web. What the investigators already have found is that tornado formation seems to be much more idiosyncratic and variable than previously thought. Many rotating supercells failed to spawn twisters, and one strong tornado occurred more than ten kilometers (six miles) away from the parent storm's center of rotation. Small-scale gust fronts and other boundaries appear to play an important role in causing updrafts to rotate. As for the twister itself, a powerful downrush of air that sometimes descends from just behind a storm is being studied as a possible trigger.
The Texas twisters at the end of VORTEX provided a climax worthy of Steven Spielberg, but the experiment's final scenes--painstaking data analysis and, ultimately, a better understanding of tornadoes--are still being written.
Sampling a tropical atmospheric brew
The dirtiness of clean air
Africa exerts a powerful influence on global air chemistry. Vast sections of grassland and forest are burned each year, pumping hydrocarbons and oxides of nitrogen into the air. These react in the presence of sunlight to produce ozone and other smoglike products. Humans have been burning the African savanna for centuries, but the atmospheric effects--when combined with those of modern industrial processes--could have changed over time. Because of the vast extent of the tropics, any understanding of global air chemistry has to come to grips with the chemical fluxes in and above this region.|
Late in the fall of 1995, dozens of researchers traveled to Tasmania, attracted not by the island's rugged beauty and wildlife but by its distance from Northern Hemisphere pollution. ACE-1, the first of the Aerosol Characterization Experiments, was designed to help scientists understand the chemical, physical, and optical properties of natural atmospheric aerosols (particles) and their effect on radiation and climate. ACE-1 involved over 100 investigators from 57 institutions in ten countries. Major platforms included the National Science Foundation/NCAR C-130 aircraft, which took air samples all the way from Alaska to Tasmania, and two research ships, the National Oceanic and Atmospheric Administration's Discoverer and Australia's Southern Surveyor. Support came from UOP's Joint International Climate Project/Planning Office and Office of Field Project Support (now merged as the Joint Office for Science Support). "It was the largest and most comprehensive experiment on natural background aerosols that we have ever done," says principal investigator Barry Huebert (University of Hawaii). Among the first results was verification of aerosol nuclei forming in the outflow from cumulus clouds.|