Extended Abstract (388K)P12.1
Early Results from Observations with Radar, a Lightning Mapping Array, and Balloon Soundings of Severe Thunderstorms during STEPS 2000
W. David Rust, NOAA/NSSL, Norman, OK; and D. R. MacGorman, P. R. Krehbiel, A. R. Bansemer, and S. A. Rutledge
A major objective of the Severe Thunderstorm Electrification and Precipitation Study (STEPS) was to obtain simultaneous observations of radar-derived storm structure and other parameters along with total lightning mapping and the electrical structure of the storms from balloons carrying a radiosonde and electric field meter. The goal was to use mobile ballooning within the coverage area of the radars and lightning mapping array to intercept and move with severe storms to obtain one or more soundings in key regions. From this endeavor has come a data base of about 25 complete and partial flights along with the accompanying data from the remote sensors. The combined data allow us to determine where in the storm lightning and intense electric fields occur. One intriguing early finding is evidence that the entire electrical structure of a storm--as depicted by its electric field profile--can be inverted from the generally recognized conceptual model. The suggestion that thunderstorm electrical structures such as the electric field polarity or the vertical stacking of charge regions can be inverted has been around awhile, mostly as part of some proposed explanations for positive ground flashes. More recently the finding that inverted-polarity cloud flashes not only exist in deep convection, but may occur frequently in certain regions or types of storms, has raised the issue of whether such lightning is produced by storms whose electrical structure is inverted, either totally or in a part of the storm. Looking for inverted structure must be done in the context of typical, noninverted thunderstorm structures. These are compared with the balloon-borne electric field soundings obtained during STEPS in the tristate region around northwest Kansas. We have soundings in nonsevere thunderstorms, severe nontornadic thunderstorms, and supercell/tornadic thunderstorms. Difficulties in deciding if there is an inversion of electrical structure include uncertainties in determining cloud top and base. At least a few of the electric field profiles reveal a structures that seem to be of inverted polarity. The key is to decide if inverted-polarity storms are merely noninverted thunderstorms with ‘extra' regions of charge in the vertical. Presently, the interpretation of electric field profiles is ambiguous, but evidence from the soundings indicates that thunderstorms can have fully inverted electrical structure in terms of inferred charge regions and order of occurrence of peaks in the electric field profile.
Poster Session 12, Lightning
Monday, 23 July 2001, 2:00 PM-3:30 PM
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