Martin J. Murphy and Kenneth L. Cummins, Global Atmospherics, Inc., Tucson, Arizona
Lightning is a major cause of death or injury, principally due to misinformation and inappropriate behavior during thunderstorms. We quantify the use of total lightning (cloud-to-ground and cloud lightning) information, provided by lightning location networks, to produce point-specific advance warnings of the threat of cloud-to-ground lightning. We consider a cloud-to-ground lightning threat to exist when the first cloud-to-ground flash occurs within 5 km of the point of interest. This is because the strokes of a cloud-to-ground flash can sometimes contact ground in different locations that are several kilometers apart, and because the typical spatial separation of sequential flashes is several km. To quantify the advance warning of the threat, we examine cloud-to-ground lightning flashes outside the threat area and cloud lightning information in and around (nearby) the threat area. Cloud lightning within the threat area can provide advance warning when storms develop overhead because of the tendency for cloud lightning to precede cloud-to-ground lightning by a few minutes in developing storms. At the center of a four-sensor network in Hong Kong, the combination of nearby cloud flash information and cloud-to-ground flash information outside the threat area provided at least 5 minutes of advance warning (lead time) in about 75% of the 72 cases studied. When there was lead time, nearby cloud flashes and more-distant cloud-to-ground flashes usually provided comparable lead times, but in 14% of cases, the cloud flashes provided at least 10 minutes more lead time than the cloud-to-ground flashes. A similar study using LDAR at Kennedy Space Center (KSC) showed that cloud flashes gave 10 or more minutes of additional advance warning in about 35% of the cases. This appears to approach an upper limit, which occurs when the majority of storms develop overhead rather than moving into the area and when the lightning detection system has a high detection efficiency for both cloud and cloud-to-ground flashes. The upper limit is the fraction of all developing storms in which cloud flashes precede cloud-to-ground lightning by 10 minutes or more.