On the influence of lightning distance on the atmospheric electric field

The influence of lightning on the atmospheric electric field (potential gradient, PG) is examined at Xanthi, NE Greece. The data span one year, 01/06/2011 - 31/05/2012. The influence of lightning distance on PG is large, and is evident up to distances of 50 km. At distances shorter than 1 km, the 1-min absolute PG values mean increase is 10 kV/m, while 1-sec values may increase above 20 kV/m for lightning distances below 10 km. It appears that PG increases linearly with decreasing lightning distance. Lightning can cause both positive and negative PG values. It is found that negative PG values increase faster than positive ones as the lightning distance decreases, and mean negative values are at any distance up to 50 km 20% higher than the mean positive ones. It is also examined how synoptic weather types influence lightning frequency and PG values. Circulation Weather Types (CWT) that produce more lightning near Xanthi are ones associated with high 500 hPa geopotential heights over the area and high thickness of the 850-500 hPa isobaric surfaces. Thgey are encountered predominantly during summer, and to a lower extend during spring and autumn. During such systems, when lightning was detected at distances shorter than 100 km from the site, the mean absolute values of PG were 1-1.2 kV/m.