Frost develops under conditions similar to dew, except the temperatures of the Earth's surface and earthbound objects fall below 32. Frost usually occurs under conditions of radiational cooling, so it is most common when the temperature is in the mid-30s. When a metal rod is warmed, the transfer of heat is by conduction. Convection transfers heat by the movement of heated liquid or gas. Radiation transfers heat without a physical connection.
Radiation brings the sun's energy to Earth and crops lose heat at night through radiant transfer.
During the day, the sun's radiant energy warms the soil and other solid objects, such as crops. When these objects become warmer than the air, they pass heat to the air by conduction. This air becomes less dense, rises and is replaced by cooler air from above. The convective mixing of these currents of warmer and cooler air warms thousands of feet of the lower atmosphere. The soil and crops may also radiate heat energy into space.