Analysis of the Factors Impacting Surface Sensible Heat Fluxes with Large Aperture Scintillometers

Large Aperture Scintillometers (LAS), Bowen ratio and eddy covariance measurements and other observed data were employed to study sensible heat flux over homogeneous bare soil surface from March 20th to April 20th, 2002, at XiaoTangshan area, Beijing. The diurnal variation of sensible heat flux from LAS is analyzed in this paper, and the relation between sensible heat flux and weather conditions is discussed. Moreover, the related coefficient between LAS based surface sensible heat fluxes and the influencing factors such as soil weight moisture content in various depths, soil surface temperature and wind speed were analyzed. The analysis could help us to improve the accurate of LAS based surface sensible heat flux. Further, the comparisons of the scintillometer flux measurements with the measurements of Bowen ratio and eddy correlation methods were done in order to make more research on scaling-up of surface sensible heat flux from point to region.This investigation showed that LAS measurements were ideal for long-term monitoring over spatial scales relevant to atmospheric models and remote sensing observations. The conclusion was to be obtained that (1) diurnal variation characteristic of sensible heat flux was similar to that of air temperature under different weather conditions, having a peak value. Generally the peak values were different for different weather conditions. The sensible heat flux in fine day was about twice than that in cloud shadow; (2) the relation between soil weight moisture content and LAS based surface sensible heat flux was negative, soil weight moisture content in 10cm had the largest impact on LAS based surface sensible heat flux and the correlation coefficients were over -0.87; (3) the relation between soil surface temperature and LAS based surface sensible heat flux was positive, and the correlation coefficients were over 0.9;(4) the impact of wind speed on LAS based surface sensible heat flux was small and the correlation coefficients were below 0.5; (5) The sensible heat flux obtained using the eddy correlation, Bowen ratio and scintillometer methods showed good agreement, and the correlation coefficients were normally over 0.8.