Approaches to assessing the daily average ground surface soil heat flux on a regional scale over the Qinghai-Tibet Plateau

The daily average ground surface soil heat flux (G0_daily) has been widely applied in land surface models. The accuracy of modeling G0_daily greatly impacts the estimation of the evapotranspiration and heat and moisture exchanges between the atmosphere and ground surface in frozen ground regions. We propose two methods for estimating G0_daily over the Qinghai-Tibet Plateau (QTP): the combination method (CM) and the sine method (SM). The instantaneous surface soil heat flux (G0_ins) is estimated at multiple times per day using the CM, and then, G0_daily is obtained. The SM simulates G0_daily by estimating G0_ins during the satellite transit based on the diurnal variation in the sinusoidal curves of G0_ins under clear-sky conditions. For G0_ins, the root mean square error (RMSE) and coefficient of determination (R2) of the CM are more than 10 W/m2 lower and 0.12 higher than those of the surface energy balance system (SEBS), respectively. For G0_daily, at the four sites (TGLMS, Naqu, Biru, and Nierong), the RMSE and the correlation coefficient (R) values of the CM are better than those of the SM by -0.86 W/m2, 9.04 W/m2, 4.33 W/m2, and 2.55 W/m2 and 0.19, 0.12, 0.10, and 0.08, respectively. The CM is applicable under all weather conditions and multi-period and multi-parameter observations throughout a day. Due to the principle of the SM, it can only simulate G0_daily when the satellite observes at least once each in the daytime and nighttime under clear-sky conditions. The SM overcomes the shortcomings of the CM, i.e., the requirements of complex input parameters and a large data volume. The advantage of the high spatial resolution of polar-orbiting satellite remotely sensed data (such as Moderate Resolution Imaging Spectroradiometer (MODIS) data) is given full play by the SM.

Automated summary

This study proposes two methods, the combination method (CM) and the sine method (SM), for estimating the daily average ground surface soil heat flux (G0_daily) over the Qinghai-Tibet Plateau (QTP). The CM estimates the instantaneous surface soil heat flux (G0_ins) at multiple times per day and then calculates G0_daily. The SM simulates G0_daily by estimating G0_ins during satellite transit based on diurnal variations in sinusoidal curves under clear-sky conditions. The CM shows better performance than the SM in terms of accuracy and applicability.