IN SITU MEASUREMENTS OF THE CHARGE STRUCTURE OF TWO SEVERE STORMS IN OKLAHOMA (ELECTRIC FIELDS, CORONA PROBE, THUNDERSTORM, BALLOON)
BYRNE, GREGORY JOHN
Doctor of Philosophy
Electric field measurements inside two severe thunderstorms in Oklahoma were acquired with instrumented free balloons in order to investigate the properties of the storm electrical charge regions. These measurements are analyzed in conjunction with the balloon meteorological measurements and standard weather and Doppler radar data sets to relate the charge regions with the storm environmental features. The first known electric field measurements to be made within the core of a severe storm are presented. The storm exhibited a bipolar charge structure with diffuse net positive charge in the upper portion of the cloud and concentrated negative charge in the lower cloud. The average charge concentrations of the two regions were 0.15 nC/m('3) and -1.2 nC/m('3) respectively. The lower negative region was less than a kilometer in vertical extent, located at the -9 C atmospheric temperature level, and coincident with downdraft air in heavy precipitation. Highly concentrated charge of up to -16.7 nC/m('3) was observed in a thin region less than 100 meters in vertical extent. Electric fields in the anvil region of a severe storm were measured in two widely separated locations. The similar features of both measurements indicate that large amounts of layered charges extended horizontally for several tens of kilometers within the severe storm anvil. A 2 km thick layer of positive charge was measured in the lower portion of the anvil. A layer of negative charge, previously unobserved in thunderstorm anvils, was measured above the positive layer. Three measurements of charge screening layers at cloud boundaries were acquired. The layers were observed to extend approximately 300 meters or more into the cloud with evidence that their depth was largely influenced by turbulence at the cloud boundary. Measured charge concentrations were comparable to those of the main charge regions in thunderstorms. The unique calibration of the electric field measuring instrument, a corona probe, is presented. The effects of the various atmospheric parameters on the electric field measurements are evaluated so that for the first time, thunderstorm electric fields can be accurately determined with a corona probe.