Largest effort yet to study lightning and 'dry storms' brings high tech to the high plains of Colorado and Kansas
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BOULDER--Scientists are scanning the skies for lightning and supercell storms from a host of high-tech platforms in the High Plains near Goodland, Kansas, from May 22 to July 15. Their tools include storm-chasing vehicles, radars, and an armored research aircraft. The Severe Thunderstorm Electrification and Precipitation Study (STEPS-2000) is the largest effort to date to study lightning and low-precipitation storms. The National Center for Atmospheric Research (NCAR) is one of the project's leaders, with funding from the National Science Foundation, NCAR's primary sponsor.
Besides NCAR, participating institutions include the National Weather Service (NWS), NOAA's National Severe Storms Laboratory (NSSL), Colorado State University (CSU), Los Alamos National Laboratory, the New Mexico Institute of Mining and Technology (NMIMT), the South Dakota School of Mines and Technology (SDSMT), Stanford University, and the University of Oklahoma. NCAR researchers Morris Weisman and Jay Miller and CSU's Steve Rutledge will direct field operations.
Low-precipitation storms have many of the earmarks of other intense supercells-- including hail, strong updrafts, and rotation--but they produce little rain. "We can't now differentiate between low-precipitation and other storms," explains Weisman. "With the newer technology we're focusing on these storms, we expect to observe features we've only theorized about until now."
STEPS-2000 is based at the NWS office in Goodland, Kansas, and at an operations center near Burlington, Colorado. The study area-- along the semipermanent dry line that marks the west edge of Tornado Alley--has one of the nation's highest frequencies of positive cloud-to-ground lightning, a primary research focus during STEPS.
Clues to storm behavior in precipitation and lightning
Researchers know little about low-precipitation supercells, except that they seldom produce tornadoes or flooding. Sorting out the microphysics of downdraft generation and precipitation in these "dry storms" could improve forecasters' ability to predict what happens to supercells as they evolve.
"We want to know how and why low-precipitation storms don't produce much rain, even when they contain as much water vapor as classic storms," says Weisman. Miller, Weisman, and colleagues will replicate STEPS data in computer models. They will look for differences between low- and high-precipitation storms and track the growth and movement of precipitation in three dimensions. According to Miller, the modeling will help to unravel how storms transport electrical charge and "grow" precipitation, especially hail.
Can lightning help tornado forecasters?
STEPS-2000 will be the largest research effort to date focused on lightning, and tornado forecasters may benefit from the effort. Low-precipitation storms produce more than their share of positive cloud-to-ground strikes. Recent studies at NSSL have found several cases in which a storm's predominant cloud-to-ground strikes suddenly shifted from positive to negative within minutes of tornado formation. A shift may be a good indicator of when a violent tornado might appear in some storms. If scientists can follow a storm as it produces a tornado, the link between a storm's electrical behavior and microphysics should become clearer, and that knowledge could translate in the future into better tornado forecasting.
A battery of research technology
Three radar systems
A combination of radar systems will be used to determine the
internal flow and precipitation structure of target storms. An NWS
Doppler radar based at Goodland will be joined by two special
research radars, both multiparameter Dopplers, brought in just for
STEPS-2000. NWS, NCAR, CSU.
Storm-chasing vehicles
Chase vehicles will collect hail and observe meteorological
conditions and precipitation directly beneath storms. CSU, NSSL,
University of Oklahoma (OU).
T-28 armored aircraft
The T-28, which can survive golf-ball size hailstones, will probe
storms at altitudes up to 20,000 feet. SDSMT.
Two weather-balloon vans
Two vans will launch weather balloons carrying disposable devices
that will radio data to the operations center about environmental
conditions on either side of the dry line. NCAR.
3-D lightning mapping system
The lightning mapping system will detect up to 10,000 energy
pulses per second to plot the three-dimensional distribution of
lightning. NMIMT.
Balloon-borne electric field measurements
Special instruments will measure electric fields inside the
storms. NMIMT, NSSL, OU.
Lightning detection networks
Scientists will use the National Lightning Detection Network to
track the location and polarity of cloud-to-ground strikes and the
CSU flat plate antenna network to quantify intracloud discharges.
Global Atmospherics.
Low-light optics
The Yucca Ridge Field Station near Fort Collins, Colorado, will
provide low-light optical recording at night of storm-top
electrical phenomena, such as jets and sprites. FMA Research.
World Wide Web
STEPS organizers plan to update lightning data on a real-time
weather Web site every minute to help researchers track the storms
on radar and in the aircraft. They'll also use the site to post
STEPS weather-balloon data which, along with satellite images and
other observations from the national operational systems, will be
used to "nowcast"weather conditions in the study area. NMIMT,
NCAR.
NCAR is managed by the University Corporation for Atmospheric Research, a consortium of more than 60 universities offering Ph.D.s in atmospheric and related sciences.
Writers: Bob Henson, Zhenya Gallon, and Anatta