An investigation of short-term solar wind modulation of atmospheric electricity at Mauna Loa Observatory

Abstract

A search has been made for short-term signatures in the global electric circuit of solar wind modulated inputs into the atmosphere, using atmospheric electricity observations made at Mauna Loa, Hawaii, in 1976–1984. The short-term events were Forbush decreases of the galactic cosmic ray flux (characterized by decreases in neutron monitor count rates); geomagnetic disturbances (characterized by the Ap index); and ring current changes (characterized by the Dst index). Each set of events was designated by a set of key days, which were used in superposed epoch analyses of the time-series of daily averages of the atmospheric electricity parameters. The observations consisted of measurements of air-earth current density, potential gradient, positive conductivity, and negative conductivity. The Mauna Loa observatory is at an altitude of 3.4 km in a relatively clean and dust free oceanic environment. The meteorologically-induced electrical noise there is less than at most other atmospheric electricity observatories, with the exception of high altitude sites on the polar ice caps. Nevertheless the noise level was still a problem even after making superposed epoch analyses using several tens of events. We find responses similar to those expected from solar wind inputs but of marginal statistical significance. Diurnal and annual variations were found to be well defined, and consistent with those found by others.