Large current lightning flashes in Canada

This study examines the characteristics of large current cloud-to-ground lightning flashes (LCLF) recorded by the Canadian Lightning Detection Network (CLDN) across Canada's landmass. We have defined LCLFs as flashes with peak currents > ±100 kA. The Canadian landscape is diverse and spans many eco-climatic regimes including the cordilleran zone of the Pacific, the grasslands zone of the Prairies, the boreal, sub-arctic, and the temperate zone of eastern Canada. Six years (1999-2004) of CLDN data were examined. Analysis of nearly 15 million cloud-to-ground flashes over this 6-year period indicates that LCLFs are rare occurrences, comprising approximately 0.5% of the annual cloud-to-ground flashes detected in Canada. About 52% of the LCLFs are positive CG flashes. Large current flashes are detected throughout the year, but distinct seasonal and geographic differences in their distributions are observed.

The majority of LCLFs in the winter months is detected along the Pacific coast of the cordilleran zone and temperate zone of eastern Canada. The timing of snowmelt on the land cover influences the distribution during spring as more flashes are initially detected over the grasslands and boreal zones in the early spring months and over the sub-arctic in the late spring. The greater part of annual LCLFs occurs during the summer. Some flashes have been detected as far as Southampton Island in northern Hudson Bay. The southward passage of the Arctic front in early fall diminishes LCLF occurrence over the arctic and boreal zones. Analyses of the diurnal distributions reveal two peaks of activity occurring in the early mornings (9-12 UTC) and late afternoons (20-01 UTC) during all seasons except winter. Analyses of the average stroke multiplicity also reveal seasonal and geographic differences. Most of the LCLFs with multiplicity ≥ 10 are associated with negative CG flashes and detected in all seasons except winter over several areas of the country. Positive flashes with multiplicity ≥ 10 have only been detected in the summer over the boreal zone of central Alberta and Saskatchewan.