Thunderstorm electrical structures observed by lightning mapping arrays

Lightning mapping arrays (LMA) use Global Positioning System time of arrival to locate very high frequency radiation sources emitted by lightning discharges. For a given lightning flash, an LMA may locate thousands of such sources which provides detailed maps of the total lightning activity and allows for diagnosis of the time-evolving three-dimensional charge structure of thunderstorms. This talk will first describe LMA-based charge structure methodologies. A variety of case studies from New Mexico and the STEPS field program will then be presented. The diagnosed charge structures of these storms evolved with time and ranged from normal tripole to inverted dipole to far more complex charge structures. Where possible, the LMA observations will be compared to snap-shots of the vertical electric field provided by balloon-borne soundings. Based on the limited number of storms analyzed thus far using the LMA charge structure methodology, it appears that the parent charge structure of a given storm determines the dominant polarity of cloud-to-ground (CG) flashes the storm produces. Normal tripole storms produce mostly negative CG flashes, while ``inverted'' storms produce mostly positive CG flashes. In both cases, the CG flashes require the presence of a lower charge region: lower positive charge in the case of normal tripole storms, and lower negative charge in the case of ``inverted'' storms.