7.13
The Severe Thunderstorm Electrification and Precipitation Study
Steven A. Rutledge, Colorado State University, Ft. Collins, CO; and M. Weisman, L. J. Miller, L. Barker, V. N. Bringi, A. Detwiler, J. Helsdon, C. Knight, P. Krehbiel, D. MacGorman, and D. Rust
The Severe Thunderstorm and Precipitation Study (STEPS) field project was conducted from 22 May through 15 July 2000 in eastern Colorado and western Kansas along the climatological position of the dry line. The broad goal of STEPS was to achieve a better understanding of the interactions between kinematics, precipitation production, and electrification in severe thunderstorms on the High Plains. Several fundamental processes are still not well understood, but can now be investigated due to technological advances in instrumentation. STEPS focussed on supercell thunderstorms, including addressing why some supercells produce markedly little precipitation (LP supercells) while others produce large amounts of precipitation (HP supercells). STEPS was also interested in examining the lightning behavior across this spectrum of storms, and sought answers to why some severe storms produce anomalously large amounts of positive cloud-to-ground lightning. STEPS deployed the following observing systems to perform coordinated measurements of environmental wind and thermodynamic vertical profiles, storm windfields, hydrometeor contents, electric fields, particle charge and lightning. The deployment of this particular suite of instruments was unprecedented:
Two S-band polarimetric radars, CHILL from Colorado State University (CHILL also served as the Operations Center for the field campaign) and S-Pol from the National Center for Atmospheric Research
The South Dakota School of Mines and Technology armored T-28 aircraft
A 10 station lightning mapping system from the New Mexico Institute of Mining and Technology
Two mobile environmental sounding systems (MGLASS) from NCAR
Two mobile sounding systems from NOAA/NSSL to collect balloon-borne measurements of electric fields
Six mobile mesonet stations from OU and NSSL to observe the meteorological conditions and precipitation types beneath storms
The Yucca Ridge Field Station (YRFS) for monitoring sprite activity above the storms sampled in the STEPS domain
The STEPS observational platforms were deployed in the context of the National Lightning Detection Network, which provided data on CG lightning locations, polarity and peak currents, and the NWS NEXRAD network which provided larger scale context for the research radars. Additionally, a triple- Doppler network was formed by the CHILL, S-Pol and Goodland KS NEXRAD radars. STEPS worked closely on a daily basis with the Goodland KS NWS Weather Forecast Office. Three NWS personnel produced detailed forecasts for STEPS and worked closely with STEPS personnel in all aspects of the project. Their insights regarding the local climatology were particularly helpful to the project. In this paper we will present the network design and discuss preliminary results from multiple platform observations of selected case studies. One particular interesting aspect of the observations suggested that a good number of the cases sampled, whether severe or not, contained inverted charge structures with positive charge situated below negative charge. Many storms sampled produced large fractions of positive cloud-to-ground lightning, including the tornadic supercell sampled on the evening of 29 June 2000.
Session 7, Role of Observing Systems
Thursday, 18 January 2001, 1:30 PM-5:15 PM
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