UPLIGHTS Upward Lightning Triggering Study

The Upward Lightning Triggering Study (UPLIGHTS) is a three-year National Science Foundation-funded field project that is taking place in Rapid City, South Dakota, from April 2012 to September 2014. Three upward flashes that occurred within a 20-min period were all triggered by a preceding +CG (cloud-to-ground) flash. In each case, in-cloud brightening following the +CG propagated toward the towers prior to upward leader initiation. Supporting electric-field data suggested that the approaching in-cloud brightening was horizontally propagating negative-leader development occurring during the +CG continuing current, and that the electric-field change created by the approaching negative leaders caused the initiation of upward positive leaders from the towers. Although none of the 10 towers had current sensing instrumentation, it is likely that a large majority of the upward flashes were upward negative lightning. The research may result in improved detection of upward lightning by lightning location systems.