UCAR Communications

staff notes monthly

May 2003

In the midnight hour: BAMEX takes aim at dangerous night storms

Researchers are taking to the field this month to peer into giant clusters of thunderstorms, called mesoscale convective systems, that can strike at night with devastating impacts. Their goal: improve predictions of these mesoscale monsters.

As the director of the Atmospheric Technology Division, Dave Carlson has worked on his share of demanding field projects. But the assignment this spring and summer to help track powerful storms that form in the middle of the night and span hundreds of miles is enough to give him pause.

This menacing arcus cloud was part of a mesoscale convective system studied in a 1981 field project near Miles City, Montana. Such systems, dominated by strong, outflowing winds and heavy rain, are the focus of the Bow Echo and MCV Experiment, slated for this May through July across the Midwest.

“This one is very challenging,” says Dave. “You take a big system that’s moving through four states in the night and you have to coordinate the ground systems and the aircraft in the right locations— man, it’s going to be tough.” BAMEX, or the Bow Echo and MCV (Mesoscale Convective Vortex) Experiment, is the most ambitious attempt yet mounted to peer into giant clusters of thunderstorms, called mesoscale convective systems, that batter the eastern two-thirds of the country. The storms typically form by evening, rage through the night, and die the next morning. Some regenerate the following night or even the next. They can dump as much rain as a landfalling hurricane and plaster huge areas with hurricane-force winds.

Morris Weisman and Chris Davis flank a bow echo.

Chris Davis and Morris Weisman of the Mesoscale and Microscale Meteorology Division are overseeing the experiment, which will run from 20 May to 6 July. Collaborating institutions include NOAA’s National Severe Storms Laboratory, the Naval Research Laboratory, and over a dozen universities. ATD and the Joint Office for Science Support (JOSS) will be handling much of the logistics.

“Ultimately, what we’re trying to do is get enough knowledge so these storms can be predicted,” Morris says.

The stakes are high for protecting lives and property. Chris talks about a storm that formed in South Dakota in July 1977, dumped torrents of rain as it moved east, and ultimately caused a devastating flood in Johnstown, Pennsylvania, that killed 78 people.

And just three years ago, a storm barreled through Kansas City, packing winds that were clocked at 74 mph (119 kmph), ripping off roofs, downing trees, and cutting electric power to about 100,000 homes and businesses. Such storms can be terrifying, especially late at night—the most likely time for the Midwest to get summertime thunderstorms.

“I saw water coming through the ceiling,” 13-year-old Reginald Smith told the Kansas City Star. “The water started getting heavier, so I panicked and started packing my clothes and put the rest of my stuff in my closet.” His family fled to safety in the darkness when the roof of their townhouse blew off.

A pair of silos in western Kansas was half-flattened on 27 May 2001 by a
derecho—a long, intense swath of destructive wind produced by a mesoscale convective system. This derecho extended from northwest Kansas into north Texas, producing more than 170 reports of high wind over 12 hours. Derechoes typically produce a bow echo on radar. (Photo by Bob Henson.)

The alarming bow

While lines of storms are informally called squall lines, some of them are classified by meteorologists as “bow echoes.” The name comes about because strong upper-level winds that descend through the core of rain-cooled air cause the leading edge of the system to bow outward. The characteristic radar echo that results can serve as a good indicator of potential severe weather.

Bow echoes are dangerous because the outflowing winds of their rapidly moving thunderstorms produce gusts that can approach 100 mph (161 kmph)—and they can also spin off tornadoes. Such tornadoes can be difficult to predict because often there are no clear precursors, such as a storm-scale rotation at upper levels, that can signal potential tornado formation.

While a typical tornadic thunderstorm might span 20 kilometers (12 miles), the agglomerations to be studied in BAMEX can stretch more than 140 kilometers (87 miles) in width and carve paths that span several states.

For years Morris and his colleagues, have simulated various modes of thunderstorm growth and decay in computer models, while Chris Davis and his colleagues have studied and simulated mesoscale convective vortices. Davis and NCAR colleague Stanley Trier were the first to reproduce the vortices in a cloud- resolving computer model. They found that when a vortex outlives its parent thunderstorms, it can help trigger more storms the following day—making it a potentially useful forecast tool.

The scientists decided to move from modeling to fieldwork because, as Morris puts it, “We came to realize that we’d gone about as far as we could with the idealized simulations. We needed to get good data.” They joined forces with Roger Wakimoto (University of California, Los Angeles) and Dave Jorgenson (National Severe Storms Laboratory), who had extensive experience making aircraft observations of convective systems—and BAMEX was born.

The BAMEX study area extends from the central plains to the Ohio Valley, an expanse that should keep the odometers of both aircraft and ground vehicles churning. On the ground, researchers will line up three vehicles on a north-south axis, with two ATD sounding units flanking the University of Alabama in Huntsville’s Mobile Integrated Profiling System (an atmospheric research system that includes Doppler radar, lidar, and other instruments). In addition, a mobile weather station will double as scout car, seeking out clearings large enough for the balloon launchers and profilers to operate safely.

Three aircraft will probe the storms, including P-3s from NOAA and the Naval Research Laboratory with onboard Doppler radars. A chartered Learjet will deploy NCAR dropsondes, key to analyzing the convective vortices. All three planes will be based at MidAmerica Airport, a little-used facility located about 25 miles east of St. Louis. BAMEX will virtually have the place to itself, which simplifies the aircraft operations enormously. “At least on paper, it’s probably the ideal setup for this kind of experiment,” Morris says.

A daunting task

Still, the logistics are formidable. To begin with, researchers are confined to areas that are built up enough to have good networks of paved roads, but not so densely populated as to have regular traffic jams and obstructions such as power lines that could snarl weather balloons. Much of the Midwest is made to order but, as Morris points out, “the farther west you go, you just run out of road.”

A second challenge is the sheer size of the region. Traveling as a unit between deployments, the ground crews will zigzag from one storm to the next, working without a home base for the entire seven-week project.

And then there’s the matter of the timing of the storms. Most bow echoes blow through at night, meaning crews will often work past midnight.

“It’s going to be unique in that we’ll be all over the place and never know where we’ll be the next night,” says ATD’s Ned Chamberlain, who is overseeing the balloon launches. “We’ll be driving hundreds of miles in a day. We’ll head out about 10, and then at noon we’ll get a further definition of the forecast area. Early to mid afternoon is when they [the scientists in Mid America Airport] do a final sighting of the system. Then we’ll set up and start working. We’ll start making balloon launches at 4 p.m., and we may be out there until 2 in the morning.” The goal is to work no more than 42 hours during each three-day period, and then take the fourth day off, Ned explains.

At ATD, dozens of staffers are working on the project. Brigitte Baeuerle is the division’s BAMEX project manager, and she is working with Mike Daniels, Allen Schanot, Peggy Taylor, and Melinda Tignor on project logistics. Terry Hock is overseeing dropsonde operations; Mike Spowart is taking care of outfitting the Naval Research Laboratory P-3; and Eric Loew, Kurt Zrubek, and a team of technicians are assisting with aircraft operations.

JOSS will help oversee the airport-based operations center. The office also created the online BAMEX catalog, which has a substantial real-time component. “It’s a living, breathing thing on the Web,” says JOSS’s James Moore. The catalog will ingest vast amounts of data from the BAMEX fleet as well as the standard National Weather Service observing network.

If the storm season comes through, this $4 million experiment—funded primarily by NSF—may compile as many as 15 case studies. With any luck, that will include two or three detailed cases. It’s about time, says Morris. The last major study of mesoscale convective systems was in 1985, when the emphasis was on fixed sensors. This time, the behemoths are being chased instead of watched.

•Bob Henson and David Hosansky

Also in this issue:

The long riders: How some staffers cope with epic commutes

Study finds lower atmosphere warming

An information divide

Building bridges for Latina students

Short takes

Delphi Question: Publications on the Web


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