Thunderstorms are among the most impressive weather phenomena with their strong winds and sometimes heavy rain and hail. But what distinguishes them from other storms is the lightning and thunder that are their trademark.

It is well known that it is lightning that causes thunder. But the lightning itself is caused by charge separation in a cloud, a process called cloud electrification that is still not totally understood at present. In this chapter, we will first examine the electricity in air during fair weather, and then we will discuss the electrical phenomena occurring during a thunderstorm. Finally, we will discuss the mechanisms that may be responsible for the electrification of thunderclouds.

Fair-weather electricity

Electricity in the atmosphere is not limited to stormy weather. During a clear day, a downward-pointing static electric field of about 130Vm−1 (volts per meter) near the Earth’s surface can be measured and is called the fair-weather electric field (see Fig. 14.1). This is just a highly averaged condition, and large variations may occur for specific locations and specific times – the field may vary from less than 50Vm−1 to more than 300Vm−1. In general, this fair-weather field is usually larger over land than over the ocean surface.