Analysis of the Surface Energy Budget at a Site of GAME/Tibet using a Single-Source Model

Abstract

In the GAME/Tibet project, the Anduo site is a typical plateau prairie area that is covered by short and sparse vegetation. From May to September 1998, we measured all the surface energy fluxes at this site to quantitatively describe the surface energy budget, but it was still questionable because of low energy closure ratios in most days of the rainy season.To clarify the surface energy budget at this site, this study proposes a single-source energy partition model, to simplify the processes of heat and water vapor transfer from the surface. The model does not distinguish the contribution of turbulent fluxes from the vegetation, and the one from the ground, and thus has fewer parameters to be calibrated comparing to a dual-source model. The main model parameters are: the soil surface evaporation resistance, the parameter kB À1 (the logarithm of the ratio of the aerodynamic roughness length to the thermal roughness length), and the surface emissivity. Their values are calibrated by minimizing the discrepancy between measured and model-predicted values of soil temperatures.This tuned single-source model is then validated by the agreement between the measured and simulated net radiation flux, surface soil heat flux, sensible heat flux, and latent heat flux on the days with high energy closure ratios. This model also reproduces these measured fluxes, except latent heat flux on the days with low closure ratios. The simulated latent heat flux is much higher than the measured one. We further show that the measured latent heat flux is untrustable due to an instrumental limitation, while the model provides a reasonable surrogate. Therefore, the single-source concept is applicable to the heat and water vapor transfer on the Tibetan plateau sparse-vegetation surface, and would contribute to a further research on the land-atmosphere interactions over the plateau.

Some practical notes on the land surface modeling in the Tibetan Plateau

“…In Fig. 3d, observed flux at Anduo is not shown, because three independent studies that used different analysis methods (Tanaka et al, 2003;Yang et al, 2004;Su et al, 2006) have demonstrated that the observation is prone to severe errors. Nevertheless, we can figure out the importance of a soil surface resistance for evaporation (Sun et al, 1982).…”

Determination of land surface heat fluxes over heterogeneous landscape of the Tibetan Plateau by using the MODIS and in situ data

“…Figure 1 shows the geographic location and topographic characteristics of the TP. Because of its topographic character, the plateau surface absorbs a large amount of solar radiation energy, and undergoes dramatic seasonal changes of surface heat and water fluxes (e.g., Ye and Gao, 1979;Ye, 1981;Yanai et al, 1992;Ye and Wu, 1998;Ma et al, 2002a;Ma and Tsukamoto, 2002;Hsu and Liu, 2003;Yang et al, 2004;Ma et al, 2006;Sato and Kimura, 2007;Ma et al, 2008;Cui and Graf, 2009;Zhong et al, 2010). In order to understand the effect of the Tibetan Plateau on the climatic change over China, east Asia and even the global, one has to get the regional distribution of surface heat fluxes over whole Tibetan Plateau.…”

Using MODIS and AVHRR data to determine regional surface heating field and heat flux distributions over the heterogeneous landscape of the Tibetan Plateau

“…1). Because of its topographic character, the plateau surface absorbs large quantities of solar radiation energy and undergoes dramatic seasonal changes in its surface heat and water fluxes (e.g., Ye and Gao 1979;Ye 1981;Yanai et al 1992;Ye and Wu 1998;Ma and Tsukamoto 2002;Hsu and Liu 2003;Yang et al 2004;Ma et al 2005;Sato and Kimura 2007;Ma et al 2008;Xu et al 2008;Cui and Graf 2009;Zhong et al 2010). Many studies have found that the east Asian monsoonal climate and the middle Asian dry climate in summer are intensified by TP mechanical and thermal forcing (e.g., Liu et al 2007).…”