What atmospheric condition is associated with calm clear nights leading to rapid cooling of the ground?

Radiation fog occurs during calm and clear nights, which allows for significant heat loss from the Earth's surface due to radiation. On such nights, the ground cools quickly as it radiates heat away into the atmosphere. This rapid cooling leads to the condensation of moisture in the air near the ground, resulting in the formation of fog.

The conditions that are favorable for radiation fog include high humidity and low wind, which contribute to the cooling and help retain moisture in the air. It typically forms in the early morning in valleys and low-lying areas, where cooler air tends to settle. This process is different from other types of fog, such as advection fog, which is formed by warmer, moist air moving over a cooler surface, or ice fog, which occurs at very low temperatures when water vapor turns directly into ice crystals.