Colorado State University Moves Radar to Join National Thunderstorm Study

The big CHILL has descended on Burlington, Colo., as part of Colorado State University’s contribution to the Severe Thunderstorm Electrification and Precipitation Study 2000 (STEPS 2000).

CHILL is a Colorado State-operated, highly sophisticated weather radar that can track severe storms, hail and other weather phenomena. Based near Greeley, Colo., under major support from the National Science Foundation, CHILL has been moved to Kit Carson Airport at Burlington May 22-July 16 to join a multi-organizational effort bent on tracing a particular kind of storm in hopes of learning more about lightning, hail and rain.

So-called low precipitation supercell storms feature bell-shaped clouds, seldom produce tornadoes or significant rain and are most commonly found over the High Plains. They’ve largely avoided close scientific scrutiny until now.

Steven Rutledge, professor and head of atmospheric sciences at Colorado State and one of three co-directors of field operations, says that disinterest has disappeared as a result of several unusual characteristics of low-precipitation supercells. While resembling storms that produce lots of rainfall and cause flooding, low-precipitation storms tend to drop little rain or hail. They produce lots of lightning, and researchers suspect there may be links between the lightning and occasional tornadoes. Just finding out more about electrical discharges and microphysical phenomena (e.g., rain and hail) will be of scientific interest, Rutledge said.

Colorado State will field several teams of scientists and graduate students, each focused on a particular aspect of storm study:

• The Colorado State CHILL radar will join other radar systems in locating storms and helping identify their internal dynamics. (The abbreviation represents the universities of Chicago and Illinois at Urbana-Champaign, which jointly developed the CHILL device more than 20 years ago.) The radar determines distance and contents of storms by bouncing microwave electromagnetic pulses off ice particles and raindrops. The radar also measures storm winds by its Doppler capability. In addition to collecting data about the size, movement and structure of storms, the CHILL system will assist in guiding an armored plane from the South Dakota School of Mines and Technology into storm cells and in guiding a hail-collecting van and other observational vehicles on the ground.
• Rutledge will lead a team including research associates Walter Petersen and Lawrence Carey and several graduate students to study the relationship between storm kinematics (wind flow) and microphysics (rain, hail, etc.) in producing lightning in severe storms. They’re particularly interested in understanding why some severe storms produce an anomalously high percentage of positive polarity cloud-to-ground flashes (most are negative polarity in typical storms).
• V. Bringi, professor of electrical and computer engineering, and research associate John Hubbert will study the growth of hail in low-precipitation storms. Bringi and Hubbert are interested in how hailstones form and grow and how the CHILL radar can be used to identify hail. Bringi and associates will collect hailstones and compare them to the storm structure as revealed by radar. The collection effort will fall to graduate students who will drive a storm-chase van equipped with a hail collection net on top and a raingauge.
• A project under the auspices of the Colorado Climate Center at Colorado State, the Colorado Collaborative Rain and Hail Study, organizes volunteers from the general public to map the time, location, and nature of rain and hail in northeastern Colorado. The study is now expanding into the STEPS experimental region. It provides detailed measurements for very specific areas and has been useful in building a climatological database for Colorado’s northeastern counties.

Researchers from Colorado State, the National Center for Atmospheric Research, the New Mexico Institute of Mining and Technology, South Dakota School of Mines and Technology, National Weather Service, University of Oklahoma and FMA Research are participating in the project, headquartered in Goodland, Kan. Field operations are based in Burlington. The National Science Foundation and National Oceanic and Atmospheric Administration are funding the project.