Frise
Bandeau Lafoudre 
 
The influence of structures underneath a cumulonimbus cloud formation
The influence of  structures
The influence of structures
The earth's electric field is measured at ground level. Anything which is closer to the base of the cloud, such as chimneys, electricity pylons, trees and even large plants, show a higher concentration of positive charges. This can develop into a corona,  generating positive ions which move towards the base of the cloud, which  is negatively charged. As these ions move upwards they form a cushion of positive charges which partially mask the influence of the cloud's charges. The electric field increases the further it gets away from ground level.

 
Development of electric field between the cloud base and ground level
Illustration of the vertical electric field relative to height.
Illustration of the vertical
electric field relative to height.
Numerous experiments have measured the electric field at ground level to be a maximum of around 10 kilovolts or kV.  A field of 65 kV/m has been measured at 603m above ground level.  In general, the electric field is much greater above water than above ground. This shows that atmospheric discharges from the ground have an effect on the electric field between the cloud base and ground level.

A tall, ground connected object, which has a stronger electric field at its summit as it is closer to the cloud base, is , therefore, a prime target for a lightning discharge. This analysis enables protective measures to be taken for such structures.