A regional lightning climatology of the UK and Ireland and sensitivity to alternative detection networks

A total lightning (cloud-ground and cloud-cloud) climatology of the UK and Ireland is presented combining 3 different ground-based lightning location systems over a 12-year period (2008-2019). The study area is divided into seven geographical regions using k-means clustering to identify areas with distinctive seasonal distributions of lightning flashes per km2/yr (referred to as flash density or FD). Different regions exhibit contrasting summer thunderstorm seasons (for example from April to August in the South-east of England and May to July in Southern England coastal regions). Summer FD peaks in July in the English Channel and south-east and midland areas of England range from 0.1-0.3 FD whilst the southern England coastal region sees FDs in the range 0.03-0.06 FD. Regions more prone to winter thunderstorms are identified as having Northwest facing coastlines (<0.02 FD in Northwest Scotland). Diurnal lightning distributions are also shown to have regional dependence with stronger afternoon peaks over-land (0.05-0.1 FD in the South of England), while in the South coastal and English Channel regions early morning or overnight peaks (0.03-0.09 FD) are more pronounced relative to afternoon FDs (0.015-0.03). This study has demonstrated the benefit of using multiple lightning detection networks to mitigate the effects of inhomogeneities within any one data source. It is also shown that significant additional insight comes from taking a regional approach to analysing temporal distributions of lightning.