What phenomenon causes air radiativity to cool near the surface on clear, calm nights?

The phenomenon that causes air radiatively to cool near the surface on clear, calm nights is radiation inversion. During these nights, the surface loses heat through radiation, particularly in the absence of clouds, which otherwise would trap heat. As the ground cools, the air right above the surface also loses heat and becomes cooler than the air higher up. This creates a temperature inversion, where typically cooler air is situated beneath warmer air.

Under clear conditions, the lack of clouds allows for a more significant loss of infrared radiation, enhancing the cooling effect. Calm winds also play a significant role by minimizing the mixing of air layers, which helps maintain the cooler air close to the ground. This leads to the development of a stable layer of air, preventing vertical mixing and trapping the cooler air near the surface until the sun rises and heating begins again.