Bolt-from-the-Blue Lightning Discharges

Bolt-from-the-blue (BFB) discharges are produced by normally electrified thunderstorms, and lower negative charge indirectly to ground from the storm mid-levels via the upper positive charge region of the storm. Because BFBs can strike well away from the storm they are a particularly dangerous type of lightning to humans. The discharges are also very interesting scientifically - for example concerning the relative magnitudes of the upper positive and mid-level negative charges in storms and the presence of positive screening charge around the lateral cloud boundary. In this paper we present photographic and VHF lightning mapping observations of BFB flashes, including some spectacular observations obtained at Langmuir Laboratory during the 2007 summer thunderstorm season.