Multiscale Analysis of Lightning Strike Maps

Electric power utilities face increasing demand for service reliability. Since cloud-toground lightning strikes are among the most frequent yet least understood causes of service interruption, predicting the geographical and temporal distribution of the lightning strikes can help power system planners and designers improve the protection of new and existing transmission lines. Lightning is the transfer of significant charge between two charged objects. Lightning discharges can occur as cloud-tocloud, (C-C, intercloud and intracloud), cloudto-air, and cloud-to-ground (C-G). A C-G flash is typically composed of a sequence of individual C-G return strikes which transfer significant charge from the cloud to the ground, each strike exhibiting peak current in the range of a few kiloamperes (kA) to 300 kA (Global Atmospherics 1999). These flashes have a nominal duration of 20 to 50 microseconds (μs), and are usually comprised of 2 to 3 strikes, but may vary between one and twenty. For most flashes, the strike which occur after the first strike of a flash contacts the earth at the same strike point as the first strike, because they travel through the channel established by the first strike. However, approximately one third of all flashes can contain strikes with different ground strike points. For practical purposes, researchers have defined a typical flash as a set of all C-G discharges which occur within 10 km of one another within a one second interval. The Canadian Lightning Detection Network (CLDN) is a network consisting of lightning detection sensors strategically located throughout Canada. The network provides both real-time data and archived lightning information. The network collects all the lightning strikes over time, and it has the best achievable location accuracy of 500 m, and time error less than 1.5 (μs). In each data file, 14 different data specifications of lightning strikes are stored: date and time, latitude, longitude, peak current, chi-square value of the strike, ellipse semi-major and minor axis length value of the flash, ellipse angle (azimuth from the north) value, degrees of freedom, multiplicity, and number of sensors used in locating the strike (Global Atmospherics, 1999). Since the number of lightning strikes which hit the Earth is very large, visualization and study of individual lightning strikes are very difficult. Instead, one can focus on ensembles of the lightning strikes as their densities (number of strikes/area/time) and study their spatiotemporal distribution maps. Such maps are known as lightning strikes maps (LSMs). Figure 1 illustrates the LSM in Manitoba for the year 2002. The color intensity of the map represents the density of the strikes (number of strikes/km/year). The red and white