What phenomenon primarily contributes to the formation of nighttime inversions?

The phenomenon that primarily contributes to the formation of nighttime inversions is radiational cooling of the earth's surface. At night, the earth's surface loses heat through radiation, causing the temperature of the ground and the air closest to it to drop. This cooling effect is pronounced during clear and calm nights, where there is little cloud cover to retain heat. As the ground cools, the air directly above it can also cool, leading to a temperature inversion where the air temperature increases with altitude, creating a stable layer that can trap cooler air below.

In contrast, heavy rain can influence temperature and humidity but is not a direct cause of nighttime inversions. Windstorms can mix the atmosphere, preventing the formation of inversions by disrupting this cooling process. Increased sunlight has the opposite effect; it heats the surface during the day, which can suppress the formation of inversions as warm air rises, disrupting the layering of cooler air below.