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

Abstract

For the first time, the temporal and spatial distribution of cloud-to-ground lightning activity in the Iberian Peninsula are being studied. The database covers the years 1992-1994, and it was recorded over 2.2 × 106 cloud-to-ground lightning flashes. The monthly variation shows a single peak in the 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 positive 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 throughout the day. The average multiplicity is found to be 2.0 for the negative flashes and 1.1 for the positive flashes and is very similar in the winter 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 positive flashes. The excessively high intensity for the positive flashes could be due to the detection system has low efficiency in detectiong weak amplitude flashes. The distribution of amplitudes is very similar in the winter and 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 polarities. 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-2 yr-1, respectively. The comparison between individual years shows a considerable year-to-year variability. The average percentage 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 in the context of other measurements taken at different parts of the world. Copyright 2001 by the American Geophysical Union.