What causes frost to form under certain atmospheric conditions?

Frost formation under certain atmospheric conditions primarily occurs due to the deposition of water vapor directly onto surfaces as ice crystals. This process, known as sublimation, happens when the temperature and dew point are both below freezing. In these conditions, water vapor in the air transitions directly from a gas to a solid state, resulting in the formation of frost without becoming liquid water first.

When the air reaches saturation and the temperature drops, the vapor condenses, but since it is below freezing, the immediate reaction is to form ice crystals. This process is distinct from condensation, where water vapor turns into liquid; instead, frost results from the direct transition of vapor to solid. Understanding this mechanism illustrates why specific temperature and dew point conditions are crucial for frost development.

In contrast, condensation, high humidity, and rapid temperature changes alone do not specifically describe the phase transition necessary for frost formation. Hence, the emphasis on conditions conducive to sublimation directly leads to the formation of frost.