The Earth has a natural potential gradient between the ground and the ionosphere which is created and sustained by cosmic ray ionisation and global thunderstorm activity. The strength of the field, as measured from the ground, is approximately 100 V m-1 in fair weather (a cloudless sky with no precipitation). High voltage power lines can create corona ions which can escape the line and are carried away by the wind, modifying this potential gradient.
There are two ways in which the weather can affect the fluctuations in potential gradient. Firstly, the direct effect on the production and escape rates of ions at the conductor surface, secondly, by modifying the atmospheric transport of ions through meteorological effects.
Fews et al. 2002, measured the potential gradient on either side of a power line using an array of electric field mill meters. They discovered a larger fluctuation in gradient when a wind blew across the line, carrying corona ions towards the field meters. Corona was detected in many of the sites investigated, however measurements were restricted to fair weather days. Continuous 24/7 monitoring is required to allow a better understanding of how corona can affect the Earth’s electrical environment.