Observations of simultaneous multiple upward leaders from tall structures

We present high-speed video observations (up to 54,000 images per second) and correlated electric field measurements of upward leaders initiated simultaneously from several towers. Four towers spanning a distance of 2.9 km, ranging in height from 121 to 191 m, developed upward leaders following a nearby positive cloud-to-ground (+CG) flash on 7/16/09 UT in Rapid City, South Dakota, USA. The optical and electromagnetic observations suggest that all four leaders were positive polarity.