In other words, at 1 meter below the soil surface, it is hard to see any difference in daytime and nighttime temperature. Figure 1 shows a typical diurnal temperature wave. Temperature changes at different depths. Figure 2 shows the temperature change in winter at the Maricopa weather station. Note that the range of temperature variation in figure 1 at 2 in depth is approximately 20 o C, and the range of temperature variation in figure 2 at 2 in depth is approximately 12 o C. Figure 2.
Temperature changes at different depths.
The soil moisture content has a great effect to the diurnal range of soil temperature because with increased evaporation from the wet surface the increased heat capacity and thermal conductivity of the soil utilizes more energy instead of using the energy for increasing temperature. Thus, the soil temperature is moisture dependent. The net energy change at the surface is equal to the sum of sensible heat, latent heat, and soil heat flux. Water has a much higher heat capacity than soil. When most of the net radiation is used to evaporate water at the soil surface, then very little energy is added to the soil, and temperature change is minimal.