Abstract
Using an XQC-300 electronic temperature recorder, a continuous automatic record of the in situ diurnal changes in soil temperature under different weather conditions over several years was collected in a valley of the Sichuan Basin in China. A vast amount of experiment data was obtained. Analysis of the measurements of diurnal fluctuation in soil temperature showed that the fluctuation could be described by a damping wave equation. A comparison was made between the damping wave equation and the sine wave equation to describe the diurnal fluctuation under different weather conditions and in different seasons. The results showed that the damping wave equation was more accurate. Using given boundary conditions, a damping wave equation describing the diurnal fluctuation at different depths of the soil body was derived from the heat flow equation. The calculated result and the measured data at different depths in an upland and a paddy soil were found to be in good agreement. These results show that the damping wave equation is much better than the sine wave equation in describing the diurnal changes of soil temperature and that the sine wave equation is a special case of the damping wave equation when the damping coefficient equals zero.
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