Long-term measurements of the global atmospheric electric circuit at Eskdalemuir, Scotland, 1911–1981

A long series of surface potential gradient (PG) measurements made at a remote site at Eskdalemuir, Scotland (55°19′N, 3°12′W) has been recovered from archives. The data span 1911–1981, but measurements between 1950 and 1970 were affected by surface radioactive deposition from nuclear weapons tests. A long-term decline in the monthly mean values is apparent in all months. Close agreement is demonstrated between hourly PG changes observed on the research ship Carnegie and those at Eskdalemuir during selected days in 1928/1929, supporting the global circuit concept. In December, a month in which the correlation between the average hourly PG and the Carnegie curve is high, similar variations are seen between the observations at Eskdalemuir and the annual averages of the ionospheric potential 1970–1976, a global circuit parameter. Changes in the shape of the Carnegie curve are apparent between spring and autumn, using data averaged between 1970 and 1981. The Eskdalemuir data offers long-baseline measurements from which, with careful analysis, changes in the global atmospheric electric circuit may be inferred.