Forcing factors of cloud-to-ground lightning over Iberia: regional-scale assessments

Abstract. Cloud-to-ground lightning in a sector covering the Iberian Peninsula, the Balearic Islands and nearby seas (36–44° N, 10° W–5° E) is analysed in the period from 2003 to 2009 (7 yr). Two Iberian lightning detection networks, composed of 18 sensors over Portugal and Spain, are combined for the first time in the present study. The selected characteristics are cloud-to-ground flashes (CGFs), first stroke peak current, polarity and multiplicity (number of strokes in a given flash). This study examines the temporal (on hourly, monthly and seasonal timescales) and spatial variability of CGFs. The influence of five forcing factors on lightning (elevation, lifted index, convective available potential energy and daily minimum and maximum near-surface air temperatures) over the Iberian sector is also assessed. For regional-scale assessments, six subsectors with different climatic conditions were analysed separately. Despite important regional differences, the strongest lightning activity occurs from late spring to early autumn, and mostly in the afternoon. Furthermore, CGFs are mainly located over high-elevation areas in late spring to summer, while they tend to occur over the sea in autumn. The results suggest that (1) orographically forced thunderstorms over mountainous areas, mostly from May to September, (2) tropospheric buoyancy forcing over western-central and northern regions in summer and over the Mediterranean regions in autumn, and (3) near-surface thermal contrasts from October to February largely control the location of lightning in Iberia. There is no evidence of different forcings by polarity. A clear correspondence between summertime precipitation patterns and CGFs is also found.