Largest Effort Yet to Study Lightning and "Dry Storms"Brings High Tech to the High Plains of Colorado andKansas
BOULDER -- Scientists are scanning the skies for lightning andsupercell storms from a host of high-tech platforms in the HighPlains near Goodland, Kansas, from May 22 to July 15. Their toolsinclude storm-chasing vehicles, radars, and an armored researchaircraft. The Severe Thunderstorm Electrification andPrecipitation Study (STEPS-2000) is the largest effort to date tostudy lightning and low-precipitation storms. The National Centerfor Atmospheric Research (NCAR) is one of the project's leaders,with funding from the National Science Foundation, NCAR's primarysponsor.
Besides NCAR, participating institutions include the NationalWeather Service (NWS), NOAA's National Severe Storms Laboratory(NSSL), Colorado State University (CSU), Los Alamos NationalLaboratory, 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. NCARresearchers Morris Weisman and Jay Miller and CSU's Steve Rutledgewill direct field operations.
Low-precipitation storms have many of the earmarks of otherintense supercells-- including hail, strong updrafts, androtation--but they produce little rain. "We can't nowdifferentiate between low-precipitation and other storms,"explains Weisman. "With the newer technology we're focusing onthese storms, we expect to observe features we've only theorizedabout until now."
STEPS-2000 is based at the NWS office in Goodland, Kansas, and atan operations center near Burlington, Colorado. The study area--along the semipermanent dry line that marks the west edge ofTornado Alley--has one of the nation's highest frequencies ofpositive cloud-to-ground lightning, a primary research focusduring STEPS.
Clues to storm behavior in precipitation and lightning
Researchers know little about low-precipitation supercells, exceptthat they seldom produce tornadoes or flooding. Sorting out themicrophysics of downdraft generation and precipitation in these"dry storms" could improve forecasters' ability to predict whathappens to supercells as they evolve.
"We want to know how and why low-precipitation storms don'tproduce much rain, even when they contain as much water vapor asclassic storms," says Weisman. Miller, Weisman, and colleagueswill replicate STEPS data in computer models. They will look fordifferences between low- and high-precipitation storms and trackthe growth and movement of precipitation in three dimensions.According to Miller, the modeling will help to unravel how stormstransport electrical charge and "grow" precipitation, especiallyhail.
Can lightning help tornado forecasters?
STEPS-2000 will be the largest research effort to date focused onlightning, and tornado forecasters may benefit from the effort.Low-precipitation storms produce more than their share of positivecloud-to-ground strikes. Recent studies at NSSL have found severalcases in which a storm's predominant cloud-to-ground strikessuddenly shifted from positive to negative within minutes oftornado formation. A shift may be a good indicator of when aviolent tornado might appear in some storms. If scientists canfollow a storm as it produces a tornado, the link between astorm's electrical behavior and microphysics should becomeclearer, and that knowledge could translate in the future intobetter tornado forecasting.
A battery of research technology
* Three radar systems -- A combination of radar systems will be used to determine theinternal flow and precipitation structure of target storms. An NWSDoppler radar based at Goodland will be joined by two specialresearch radars, both multiparameter Dopplers, brought in just forSTEPS-2000. NWS, NCAR, CSU.
* Storm-chasing vehicles -- Chase vehicles will collect hail and observe meteorologicalconditions 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 probestorms at altitudes up to 20,000 feet. SDSMT.
* Two weather-balloon vans -- Two vans will launch weather balloons carrying disposable devicesthat will radio data to the operations center about environmentalconditions on either side of the dry line. NCAR.
* 3-D lightning mapping system -- The lightning mapping system will detect up to 10,000 energypulses per second to plot the three-dimensional distribution oflightning. NMIMT.
* Balloon-borne electric field measurements -- Special instruments will measure electric fields inside thestorms. NMIMT, NSSL, OU.
* Lightning detection networks -- Scientists will use the National Lightning Detection Network totrack the location and polarity of cloud-to-ground strikes and theCSU flat plate antenna network to quantify intracloud discharges.Global Atmospherics.
* Low-light optics -- The Yucca Ridge Field Station near Fort Collins, Colorado, willprovide low-light optical recording at night of storm-topelectrical phenomena, such as jets and sprites. FMA Research.
* World Wide Web -- STEPS organizers plan to update lightning data on a real-timeweather Web site every minute to help researchers track the stormson radar and in the aircraft. They'll also use the site to postSTEPS weather-balloon data which, along with satellite images andother observations from the national operational systems, will beused to "nowcast"weather conditions in the study area. NMIMT,NCAR.
NCAR is managed by the University Corporation for AtmosphericResearch, a consortium of more than 60 universities offeringPh.D.s in atmospheric and related sciences.
Writers: Bob Henson, Zhenya Gallon, and Anatta
Materials provided by National Center For Atmospheric Research (NCAR). Note: Content may be edited for style and length.
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