mainly by cosmic rays in the free troposphere and above, and by radioactivity in the lowest 1km or so). The ions make the air weakly conductive; different locations, and meteorological conditions have different electrical conductivity. Fair weather describes the atmosphere away from thunderstorms where this weak electrical current between the ionosphere and the earth flows. Measurement The voltages involved in the Earth's circuit are significant. At sea level, the typical potential gradient in fair weather is 120 V/m. Nonetheless, since the conductivity of air is limited, the associated currents are also limited. A typical value is 1800 A over the entire planet. When it is not rainy or stormy, the amount of electricity within the atmosphere is typically between 1000 and 1800 amps. In fair weather, there are about 3.5 microamps per square kilometer (9 microamps per square mile). This can produce a 200+ volt difference between the head and feet of a regular person. Carnegie curve The Earth's electrical current varies according to a daily pattern called the Carnegie curve, caused by the regular daily variations in atmospheric electrification associated with the earth's stormy regions. The pattern also shows seasonal variation, linked to the earth's solstices and equinoxes. It was named after the Carnegie Institution for Science. See also Atmospheric electricity Geophysics Earth's magnetic field Sprites and lightning Space charge Telluric currents External sources Publications Le Monnier, L.-G.: "Observations sur l'Electricité de l'Air", Histoire de l'Académie royale des sciences (1752), pp. 233ff. 1752. Sven Israelsson, On the Conception Fair Weather Condition in Atmospheric Electricity. 1977. Ogawa, T., "Fair-weather electricity". J. Geophys. Res., 90, 5951–5960, 1985. Wåhlin, L., "Elements of fair weather electricity". J. Geophys. Res., 99, 10767-10772, 1994 RB Bent, WCA Hutchinson, Electric space charge measurements and the electrode effect within the height of a 21 m mast. J. Atmos. Terr. Phys, 196. Bespalov P.A., Chugunov Yu. V. and Davydenko S.S., Planetary electric generator under fair-weather condition with altitude-dependent atmospheric conductivity, Journal of Atmospheric and Terrestrial Physics, v.58, #5,pp. 605–611,1996 DG Yerg, KR Johnson, Short-period fluctuations in the fair weather electric field. J. Geophys. Res., 1974. T Ogawa, Diurnal variation in atmospheric electricity. J. Geomag. Geoelect, 1960. R Reiter, Relationships Between Atmospheric Electric Phenomena and Simultaneous Meteorological Conditions. 1960 J. Law, The ionisation of the atmosphere near the ground in fair weather. Quarterly Journal of the Royal Meteorological Society, 1963 T. Marshall, W.D. Rust, M. Stolzenburg, W. Roeder, P.