Cloud-to-ground lightning characteristics in the Spanish Basque Country area during the period 1992-1996

This paper summarises the results corresponding to the first study of lightning phenomenology in the Spanish Basque Country area where a maximum value for lightning density in Spain was observed. Data used in this study comes from the DF network deployed by the Spanish Meteorological Set-L ice, integrating 14 observation points in Spain. Results regarding lightning density confirms the existence of a relative maximum in cloud-to-ground (CG) counts located over Bilbao, the largest city in the area. This maximum represents an annual average of 3 flashes/km(2). However, for the rest of the area, a random pattern in CG counts discharge is observed. A high variability in the annual counts can be seen, this number is reaching a factor of 2 if we compare two different years. This variability also affects the number of counts observed in 1 month in different years and for example, counts can change from 0 to more than 10.000 in a single month in different years. We can also report that positive lightning flashes that present an intensity double than that of negatives strokes follow a seasonal variation in their relative percentage that evolve from 39% in winter to 5% in summer, similar to what has been observed by other researchers. Finally, we found that the lightning activity observed in summer and spring relates to the solar heating cycle and consequently electrical storms occur mainly in the afternoon. (C) 2001 Elsevier Science Ltd. All rights reserved.