Further signatures of long-term changes in atmospheric electrical parameters observed in Europe

Abstract. Long-term decreases found recently in both the atmospheric electrical potential gradient (PG) and the air-Earth current density (J_z), using observation series from the UK and Hungary, have motivated studies of other European data. Two surface data series somewhat longer than a decade were available: PG data obtained at Serra do Pilar (Portugal), and PG, J_z and positive air conductivity measurements at Athens (Greece). Selecting data to minimise local effects, the 1960–1971 Serra do Pilar PG values decrease at dawn and in the evening. Dawn data obtained at Athens (1967–1977) indicate a reduction in J_z, while the simultaneous PG values there increase (coincident air conductivity values decrease) for the periods investigated. The Athens PG increase is attributed to local aerosol influences, typical of urban environments. Despite the urban influence, the Athens J_z shows similarities with soundings of the ionospheric potential. The decline in J_z at Athens occurs simultaneously with a decrease reported previously in J_z at Kew (UK), indicating that, at least, a regional decrease in the global atmospheric electrical circuit occurred during part of the twentieth century. Similar surface changes occur in European atmospheric electrical parameters, with a decrease of about 0.5% to 0.7% per year between 1920 and 1970 (possibly extending back to 1898), an annual decrease of between 2.7 and 3.4%, between 1959 and 1971 and a continued decrease of about ~1% per year between 1967 and 1984, possibly still continuing.

Keywords. Meteorology and atmospheric dynamics (Atmospheric electricity) – Geomagnetism and paleomagnetism (Time variations, secular and long term) – Atmospheric composition and structure (Aerosols and particles)