Space weather influences on atmospheric electricity

Atmospheric electricity is a venerable topic of geophysical science, dating back to the 1750s when Franklin and Dalibard established the presence of electricity in thunderstorms. Subsequently even fine conditions were observed to be electrified, and a downward vertical atmospheric electric field of magnitude ~100V/m observed near the surface during fair weather conditions. The origin of the “fair weather field” remained unknown the pioneering electrical measurements of the geophysical survey ship Carnegie in the 1920s, which demonstrated a diurnal variation in the electric field aligned with universal time rather than local time. This characteristic variation remains known as the “Carnegie Curve” and was subsequently demonstrated as similar to the diurnal variation in global thunderstorm area. This supported the idea of a “Global atmospheric Electric Circuit” (GEC), postulated by CTR Wilson (Wilson 1929; Harrison, 2011), through which charge separation in thunderstorms sustains large scale current flow around the world and the fair weather field, now confirmed by Blakeslee et al (2014). Figure 1 represents the GEC. The Earth’s surface and the lower ionosphere (at approximately 60km altitude) are represented as two oppositely charged “electrodes) of a spherical capacitor, within which air provides a leaky dielectric. Charge transfer from thunderclouds, rain and lightning continuously electrify the ionosphere to a potential 250kV more positive than Earth’s surface, known as the ionospheric potential, Vi.