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Selsley fog layer (picture G. Harrison)

The global atmospheric electric circuit and the effects of current flow through layer clouds

Prof Giles Harrison  |  Department of Meteorology  |  University of Reading, UK

The existence of an electric field in the atmosphere, even in fair weather conditions, has been known since the mid-eighteenth century, soon after the defining work of Benjamin Franklin. Understanding its origin provoked the experimental ingenuity of well-known physicists such as Lord Kelvin and the Nobel Prize winner C.T.R. Wilson. Notably, Wilson devised the concept of a global electrical circuit. One important aspect of the earth’s atmospheric electrical system is that it provides a route to couple solar variations into the lower regions of the atmosphere, right down to the surface. This is because of solar influences on high energy particles such as galactic cosmic rays, which are responsible for the ionisation permitting current flow between the upper and lower atmosphere. The vertical “global circuit” current also passes through layer clouds, and electrical responses in such clouds have now been directly observed with balloon-carried instrumentation. This talk will provide an introduction to atmospheric electricity, and report some of the recent work at Reading conducting electrical measurements in stratiform clouds.