A 15-year climatology of Potential Gradient at a rural site in Southern Balkans

Potential gradient (PG) is measured continuously at Xanthi, NE Greece, since 2011, along meteorological variables and, in the last years, also particulate matter (PM). We present here a 15-yr climatology of PG at the measurement site. 1-min values up to +/- 34 kV/m were measured. 1-hr and mean daily maximum (minimum) values were 10 kV/m (-12 kV/m) and 6 kV/m (-2 kV/m), respectively. The highest mean values were encountered during the winter months. PG was influenced by the local meteorology, specific humidity having the largest impact on PG values. Additionally, PG was influenced by lightning activity within 50-km from the site, as well as aerosol levels. PG was exhibiting some anticorrelation with PMK2.5, especially during the cloud-free summer months. This probably means that one or more of the following apply for Xanthi: PM has low hygroscopicity, the size of PM is small, the presence of PM is correlated with high ion concentrations, as there is a relatively high radon flux at the site. An increase of 20 μg/m³ in PM2.5 leads to a decrease of 100 V/m in PG. Regarding global events, it was observed that during two Sudden Stratospheric Warming (SSW) events, mean daily values of PG were consistently higher by what would be expected by the influence of local meteorology alone.