chapter 4. HEAT BALANCE OF BARE GROUND
4.1 introduction
The basic component in the system we are considering is bare ground. In the daytime, its surface is heated by solar radiation when the weather is fine. The surface also loses heat to the cold sky by long-wave radiation. It can be visualized that heat is transferred by conduction to the lower soil layer. neglecting water movement in the soil. At the surface, not only sensible but also latent heat transfer occurs. These heat flows from the surface to the ambient air are by convection. Therefore, three types of heat transfer are at work in a soil-air system, as shown in Fig. 4.1.
Heat conduction is heat flow due to molecule movement and is predominant in solid bodies, in which the other two types of heat transfer do not occur. The amount of heat per unit time per unit area is proportional to the product of the thermal conductivity of the material and the temperature difference, and inversely proportional to the distance Where the temperature difference occurs:
where Q is heat flow (W/ma), KS is thermal conductivity (W/m/°C), DT is temperature difference (°C), and DZ is a distance (m) short enough that we can neglect heat stored in this thin layer. The sign (-) indicates that the direction of heat flow which is shown by the arrow in Fig. 4.1 is opposite to the temperature gradient. Heat transfer due to convection is given by