Cloud-to-ground lightning activity in the Iberian Peninsula: 1992-1994

For the first time, the temporal and spatial distribution of cloud-to-groun d lightning activity in the Iberian Peninsula are being studied. The databa se covers the years 1992-1994, and it was recorded over 2.2 x 10(6) cloud-t o-ground lightning flashes. The monthly variation shows a single peak in th e warmer months (May to September) with a strong year-to-year variability. The diurnal cycle of lightning activity peaks at 1700 LT with a subsequent slow decrease toward the minimum in the morning hours. The percentage of po sitive flashes is 8%, although this percentage is higher in the winter than in the summer. The lightning flash polarity is found to be very similar th roughout the day. The average multiplicity is found to be 2.0 for the negat ive flashes and 1.1 for the positive flashes and is very similar in the win ter and summer seasons, while the percentage of single-stroke flashes tends to increase in the winter. The median (mean) intensity is found to be 22.5 kA (32.4 kA) for the negative flashes and 52.3 kA (69.3 kA) for the positi ve flashes. The excessively high intensity for the positive flashes could b e due to the detection system has low efficiency in detectiong weak amplitu de flashes. The distribution of amplitudes is very similar in the winter an d summer seasons. The decay at large amplitudes is slower for the positive flashes. The median and mean amplitudes are higher in the winter for both p olarities. The spatial cloud-to-ground lightning distribution confirms the well-known preference for certain areas in the development of thunderstorms . The average maximum negative, positive, and combined flash densities are 3.1, 0.2, and 3.3 flashes km yr,respectively. The comparison between indivi dual years shows a considerable year-to-year variability. The average perce ntage of positive flashes ranges from 0% to 41%. The grid block median peak current amplitudes vary from 12.5 to 47.4 kA for the negative flashes and from 17.6 to 107.5 kA for the positive flashes. The results are discussed i n the context of other measurements taken at different parts of the world.