This award supports continuing analysis of observations from the STEPS project (Severe Thunderstorm Electrification and Precipitation Study) conducted in western Kansas in the early summer of 2000. Data from polarimetric radar, aircraft, sounding balloons, and a lightning-mapping network are employed to investigate the relation between thunderstorm electrification and the microphysical and kinematic properties of clouds. Special attention is directed to storms that exhibit anomalous behavior such as the absence of lightning, predominantly positive cloud-to-ground lightning, or much intracloud lightning. Motivating the work are questions about the source region for the positive charge in clouds that produce positive lightning, the kinematic and microphysical differences that distinguish these clouds from the more typical ones, the role of intracloud lightning in the creation and maintenance of anomalous charge structures, and the extent to which the occurrence of lightning and its polarity can be predicted once convection develops. The work is done in collaboration with STEPS investigators from other institutions, and involves analysis and synthesis of data from two S-band polarimetric radars (the CHILL radar of Colorado State University and S-Pol of NCAR), 3-D maps of lightning flashes from the New Mexico Tech lightning-mapping array, microphysical and electrical measurements obtained by the storm-penetrating T-28 aircraft of South Dakota School of Mines and Technology, and vertical soundings of the thunderstorm electric field measured by special balloons of the National Severe Storms Laboratory. The project will lead to a better understanding of storm electrification and to new ways of monitoring and predicting storm intensity.
