An interesting tidbit from the Australian Antarctic Division (h/t to Trevor Gunter)
Scientists have long searched for linkages between solar variability and weather. The sun varies on a wide-range of time scales, most dramatically on an ~11 year cycle which is strongly associated with the number and extent of sunspots on the sun and the occurrence of aurora at high latitudes. While correlations of weather and solar variability have been reported, often-times to disappear when further measurements become available, no viable mechanism for the strongest associations has been confirmed. One difficulty is that the variable solar energy, despite sunspots and aurora being spectacular, is but a small fraction of 1% of the total solar energy. Any mechanism for changing weather and climate by solar variability must involve influencing the distribution of the energy within the weather system. One possible mechanism is via the Earth’s geoelectric field.
Thunderclouds separate electric charge with positive charges accumulating in the upper reaches of the cloud and negative charges near its base. The lightning generated drags current from the Earth and, perhaps counter-intuitively, it is easier for this current to return to the Earth in a less dramatic fashion via the 99% of the Earth not covered by thunderstorms at any particular time. Currents preferentially travel along lines of least resistance. At altitudes above ~90 km, the Earth’s atmosphere contains a sufficient density of free electrons for a global equipotential to be largely maintained. The Earth’s surface is another global equipotential. Conductivity in the region of the atmosphere between these boundaries generally increases with altitude, and is dominantly maintained by ionising radiation from cosmic rays. The variation in conductivity in the atmosphere is such that the path of least resistance at an altitude greater than ~5 km is via the ionosphere, where it may spread globally and return to ground via the global ‘fair-weather’ field.
Global thunderstorms maintain the lowest reaches of the ionosphere at a potential of ~250 kV with respect to the ground. This results in a very weak atmospheric current (3 pico-amps per meter squared) toward the Earth in the fair-weather regions of the globe, and near the ground maintains a substantive vertical electric field of some 100 volts per meter. Cosmic ray ionisation, the magnitude of which can be controlled by solar activity via the solar wind, modulates the resistance of this global electric circuit in which thunderstorms are the generators. By controlling the ease with thunderstorms can dissipate current it is feasible that solar activity may modulate the intensity of thunderstorm development, thus modulating the distribution of energy within the meteorological system.
High, dry regions with no thunderstorms, such as the Antarctic plateau, are ideal for monitoring the global geoelectric circuit. Additional solar influences on the geoelectric field occur at high latitudes, via the same processes that generate the aurora. In conjunction with Russian and American colleagues, we presently measure the geoelectric field at the Russian station, Vostok, on the Antarctic plateau. We have shown that solar variability can influence the geoelectric field measured at ground level in polar regions, and are continuing to develop research instrumentation and methods of testing the viability of a solar variability influence on weather and climate through modulation of the geoelectric circuit.
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