Final answer:
During storms, electric fields cause the ground to become positively charged as the storm clouds induce an opposite charge on the Earth's surface, creating conditions similar to a giant capacitor.
Step-by-step explanation:
The ground can become positively charged during storms due to the separation of charge within the storm clouds. This charge separation creates localized electric fields that can be larger and even reversed in direction compared to the fair weather conditions. The exact charge distributions are influenced by local conditions and can vary, which is why there are several potential configurations such as mentioned in Figures 18.20(b), 18.22(b), and 18.30(b).
When a storm cloud with a negative charge base moves over the ground, it induces a positive charge on the Earth's surface. This happens because negative charges in the cloud repel the free electrons in the Earth, causing an area of positive charge to build up below the cloud. This positive charge on the ground can increase to the point where a negative lightning strike occurs, transferring the charge from the cloud to the ground, neutralizing the difference between them.
Moreover, conductors with sharp points like lightning rods can collect more charge. A lightning rod can help dissipate the positive charge accumulated on the ground by directing it back into the air, reducing the likelihood of a lightning strike in the immediate area of the rod. Overall, this phenomenon can be likened to a giant capacitor, with the storm cloud and ground acting as plates having opposite charges separated by an insulating medium, which is the air.