Organized collections of thunderstorms, known as mesoscale convective systems (MCS), are the major source of rainfall and severe weather in the Spring and Summer time in the continental United States. A field observational program (Oklahoma.Kansas Preliminary Regional Experiment for STORM.Central; STORM stands for Stormscale Operational and Research Meteorology) was conducted in the Spring of 1985 to study various aspects of MCSs. The Principal Investigator was one of the planners and participants in this investigation. Previous work by the Principal Investigator has utilized data from a variety of instruments (e.g. Doppler radar, aircraft, ground stroke lightning location devices) to study what has been termed the trailing stratiform region of MCSs. While most rain produced by MCSs is deposited by convective storm cells, the precipitation that falls from the stratiform region is almost equally important. In his previous work the Principal Investigator has discovered that most precipitation in the stratiform region is produced by growth upon small ice particles that are advected from the convective region into the stratiform cloud. He found that approximately 20% of the rainfall from the stratiform region is due to the original particles advected from the convective region and the remaining 80% from subsequent growth of these particles. The particles produced in the convective region, therefore, act as "seed" particles; thus, providing a mechanism for condensate generated by the mesoscale updraft to be converted efficiently into precipitation. The Principal Investigator also discovered that positively charged cloud.to.ground flashes are most concentrated in the stratiform region. He concludes that the positive ground flashes are due to positive charges carried on small ice particles advected from the convective cells. The Principal Investigator will continue to exploit this rich data set by expanding the number of analyzed cases. He also will enhance his research by adding a more complex modeling component to assist in physical interpretation of the structure of MCSs.
