A study of soil heat flux

Abstract —It is common that surface energy balance is not closure for many land surface types. The reasons to affect energy balance include several aspects. This paper uses three methods to correct soil heat flux based on the data from Xiaotangshan experiment, Beijing, 2004. It also compares energy balance closure ratio between every method. The results show that: the general method does not improve energy balance closure ratio, while thermal conduction method and water-heat exchange method enhance closure ratio obviously, and the correction are 0.0655, 0.0619 respectively. Keywords- Energy balance; Soil heat flux; closure ratio I. I NTRODUCTION In soil-plant-atmosphere system, the energy balance equation R n =H+LE+G is one of the most important equations. Most of experiments have showed that: the surface energy balance is not closure most of the time, that is, R n >H+LE+G . The soil heat flux G in the energy balance equation, about 20% of net radiation, is measured by soil heat flux plate. Many papers have discussed the problems of soil heat flux measurement. Erik Kellner[1] pointed out that the most difference between the calculated and the measured was the former larger than the latter. Kun YANG[2] calculated the soil heat flux at Anduo site, Tibet plateau. The calculated and the measured have the same phase, but the amplitude was larger compared with the measured. He thought that the measured needed to be corrected because of the difference of thermal conductivity between the plate and the soil. Kustas et al[3] found that there should be at least 3 plates to determine soil heat flux for sparse clumped vegetation with one out in the open or interspace area, one underneath the vegetation and one in a partial cover condition. At the same time, the soil heat flux plate can not be set at the surface directly since the influence of solar radiation[4], instead, it is at about 2-10cm depth generally. So the determined is not the soil surface heat flux, because of ignoring the heat storage in the soil layer above the plate. B.G. Heusinkveld et al[5] set a soil heat flux plate just below the surface and another one at a depth of 46mm. They found that the measured at the surface had a good agreement with the calculated using Calorimetric method or Harmonic analysis. C.L.Mayocchi et al[6] have showed in their study that the largest error may reach 80W/m