Monday, 7 January 2013
Exhibit Hall 3 (Austin Convention Center)
Despite the large number of sprite observations, there have not been detailed three-dimensional observations of the parent lightning discharges. This is because sprites are observed from large distances, and none have been within the detailed range of three-dimensional lightning mapping systems. To provide support for the Deep Convective Clouds and Chemistry (DC3) project, New Mexico Tech installed a Lightning Mapping Array in northern Colorado, the COLMA. During the summer of 2012, there were two periods (8 June and 25 June) when numerous sprites were observed over or very close to the COLMA. In addition to video observations of the sprites and LMA observations of the parent lightning discharges, we have electric field change observations from two New Mexico Tech slow antennas located near the center of the COLMA, charge moment change measurements from the National Charge Moment Change Network (CMCN) operated by Duke University, return stroke peak current from the National Lightning Detection Network (NLDN) and detailed dual-polarization multi-parameter radar observations from the Colorado State CHILL radar.
All of the sprites were produced by positive cloud-to-ground lightning discharge. The discharges were from anomalously electrified storms, with mid-level positive charge at about 8 to 10 km altitude, an upper negative charge at about 10 to 12 km, and a small lower negative charge at about 4 to 6 km altitude. The LMA showed an upward negative leader propagating from the lower negative into the midlevel positive charge, with an inferred downward positive leader propagating into and through to lower negative charge to ground. After reaching the midlevel positive charge, negative leaders propagated horizontally through the positive charge layer, covering areas of several hundred square kilometers. The positive return stroke and subsequent continuing current occurred several tens of milliseconds after the initial upward negative leader. Detailed data on several discharges will be presented.
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