Which type of fog forms during the night under clear skies with negligible wind?

Radiation fog forms during the night under clear skies with negligible wind because it is created when the ground loses heat rapidly through radiation, causing the air near the surface to cool and reach its dew point. On clear nights, this process is enhanced as there are no clouds to trap heat, resulting in a rapid decrease in temperature. As the temperature drops, moisture in the air condenses into tiny water droplets, forming fog close to the ground.

In contrast, advection fog typically occurs when warm, moist air moves over a cooler surface, often seen near coasts or over bodies of water. Upslope fog forms when air is lifted over a terrain, cooling as it rises and condensing to form fog. Steam fog occurs when cold air covers warm water, causing the warmer water to evaporate and create fog. Each of these types of fog involves different processes and conditions, making radiation fog distinct to clear, calm nights.