Characteristics of Surface Sensible Heat Flux Calculated from Satellite Remote Sensing and Field Observations in the Tibetan Plateau

Based on normalized difference vegetation index(NDVI) data for the period of July 1981 to December 2012 from National Aeronautics and Space Administration(NASA) and observations collected at 70 meteorological stations in the Tibetan Plateau,, the C_H-I_NDV parametric relational expressions which giving the relationship between NDVI and surface heat transfer coefficient (C_H) are used to calculate monthly mean surface heat transfer coefficient (C_H) over the entire plateau. Characteristics of spatial distribution and temporal variability of the C_H are discussed, and monthly mean surface sensible heat fluxes (SSHF) at the 70 meteorological stations have been calculated using a bulk transfer method. Results are compared with available observations. Climatic features of SSHF and the relationship between SSHF and climatic factors are then analyzed. Results show that the C_H value has significant spatial and seasonal differences with high values in eastern Plateau and in the summer and low values in western Plateau and in the winter. The interannual variation of SSHF is mainly affected by changes in surface wind (v) in the summer, while in the winter it is largely affected by changes in the difference between surface temperature and air temperature (T_s-T_a). Since the decreasing trend of v slowed down in 2003 while T_s-T_a increased at the same time, interannual changes in SSHF switched from decreasing to increasing at around 2003. Note that such a switch first occurred in the autumn of 2001 over the entire plateau.