Cloud-to-ground Lightning and Urban Areas

The effect of small urban areas on cloud-to-ground (CG) lightning activity is analysed for Spain. The results shown that the CG-flash number is enhanced within and downwind the most of towns considered and that large population and higher SO2 concentration contribute to the increase of the number of CG-flashes. INTRODUCTION AND DATA Several studies have reported that large cities of the USA are associated to an enhancement of the storm activity (Changnon, 2001). This effect occurred in the urban area and/or downwind of the city (Wescott, 1995; Orville et al., 2001). Here it is analysed the urban effect on cloud-to ground (CG) lightning associated to small towns of Spain. Lightning data were obtained from the lightning detection network belonging to the Instituto Nacional de Meteorologia. We considered nine towns of the Regional Community of Castilla y Leon (Central Spain) (Table 1). The total number of CGlightning flashes were counted within blocks of 0.1o longitude x 0.1o latitude (~ 10 km) surrounding each town. Since the prevailing storm motion in the analysed zone has a westerly component, the upwind area is located to the west and the downwind area to the east. The upwind and downwind number of CG-flashes are the mean of the flash number counted within blocks of 0.1o longitude x 0.1o latitude located to the (NW, W, SW) and (NE, E, SE) of the town, respectively. Only CG-lightning data of three years (1992-1994) are considered. Table 1. Size and population of towns considered in this study Town Urban area (km) Urban population Valladolid (VA) Burgos (BU) Salamanca (SA) Leon (LE) Zamora (ZA) Ponferrada (PO) Avila (AV) Miranda de E.bro (MI) Velilla (VE) 24.9 12.3 10.1 16.5 10.8 5.0 6.1 4.7 0.5 33368