Forest Ecosystem Turbulent Analysis For Improving Calculation Accuracy Of Sensible Flux With Scintillometers Method

The exchange of hydrothermal from land to atmosphere interactions is the most direct andsignificant physical processes, which has been considered to be the important and difficultresearch in the Meteorology, climatology, hydrology, ecology and other related disciplines. Thesensible heat flux （H） is the the driving factors of surface turbulent motion and energyexchange, therefore, it is particularly important to accurately measure regional scale sensibleheat flux. However, due to vegetation above the underlying surface, the flatness of the surface,hydrothermal regime, and weather conditions, it is difficult to solve the problem of technologyof flux measurement and space representation of the data in the kilometer scale.Thelarge-aperture scintillometer （LAS） has greater prospect in measuring a region of severalkilometers and heterogeneous surface-sensible heat fluxes. The parameter that directlyobtained by LAS is the structure parameter of the refractive index of air （C_n²） based on changesin light intensity fluctuation. The structure parameter of temperature （C_T²） is calculated firstly,and then we must select the appropriate universal function for the temperature structureparameter （f_T） according to Monin-Obukhov Similarity Theory （MOST）. The data of C_T²,, f_T of C_T²and zero-plane displacement （z0）, surface roughness （d）, wind velocity （v）, air temperature（T） and any other meteorological data have been used to calculate sensible heat flux withiterative method. MOST could be applied only on homogeneous flat underlying surfaces. Theturbulent motion characteristics of the observed area should be researched to understand firstlywhen we would be ready to calculate sensible heat flux, because that MOST could be appliedonly on homogeneous flat underlying surfaces. But so far, there is no detailed studies reportedin literature.The cork oak, cedar-black and locust was the object in the Hilly North of China. Thequality control theoretical system of the km scale sensible heat flux data was established to verify data quality control and to improve the sensible heat flux estimates of the need foraccuracy. The main conclusions are as follows:（1） There is a strong correlation between turbulence intensity and wind velocity. Theturbulence intensity is the biggest when wind velocity is not more than3m/s.The turbulentintensity of the three wind directions are: I_u=0.326, I_v=0.306, I_w=0.189andI_u=0.324, I_v=0.296, I_w=0.173respectively in two typical time at growing season.（2） The dimensionless standard deviations of turbulent velocity components anddimensionless turbulent kinetic energy （TKE） can be well described by "1/3" power lawrelationships under stable, neutral, and unstable conditions. Land use and land cover changesmainly impact dimensionless standard deviations of horizontal componentuctuations, but theyhave very little effect on those of the vertical component. The dimensionless standarddeviations of wind components and dimensionless; the trend of the vertical wind component isthe opposite. Dimensionless standard deviation of temperature declined with increasing z/Lwith an approximate "-1/3" slope in unstable stratication and "-2/3" slope in stable stratication.Results show that the meteorological elementsMountain in the plantation ecosystem complexsurface conditions obey the Monin-Obukhov similarity theory.The turbulence spectra followed the–5/3power law, and turbulence above the forestcanopy was locally non-isotropic.（3） The best MOST universal function were given byf T_JiYuan=4.91（16.51ζ）^2/3（ζ≡z/L） under unstable conditions andf T_JiYuan=6.43(1+2.20ζ^2/3)under stableconditions.Under unstable conditions and the heat factor （k w’T ’g/T,TT）is less than0.0008, Themeasured value of the degree of dispersion is big; under unstable conditions and TT is greaterthan0.0012, the degree of dispersion is small. The heat factor had significant effect on theapplication of MOST. The heat factor had significant effect on the application of MOST, The values obtainedfrom eddy covariance fluxes by using f T_JiYuanagreed with the values obtained from rawtime series data by using independent methods. MOST can be applied during the interactionbetween heat turbulence and momentum turbulence.TheC2T calculated using the LAS method had a high aggrement with the results given bythe turbulence spectral method, indicating that it was feasible to use the LAS method tomeasure turbulence fluxes over the heterogeneous surface. The accuracy of the selectedappropriate universal function for the temperature structure parameter was high.（4） The source area was relatively larger under stable stratification conditions as a resultof weaker turbulant activity, and was smaller under unstable stratification conditions withstronger turbulant activity. Even the smallest source area under stable stratification conditionwas14.7%bigger than the largest source area under unstable stratification condition. Therefore,spatial representation analysis of measured information should be emphasized under stablestratification condition. Flux information measured by scintiloscope is the most comprehensiveand intact when wind direction almostly perpendicular to optical pathway.（5） The iterative method was determined to caculate sensible heat flux with LAS underthis complex underlying suiface. Considering overlapping area imprint weight and each winddirection source area, the formulation that is suitale for this area to measure flux based on ECflux was expanded to LAS scale,H_ec={0.77f₁/（0.77f₁+0.57f₂）}H_ec1+{0.572f₂/（0.77f₁+0.57f₂）}H_ec2;Correlation analysis was carried out between the sensible heat data caculated by the screenedappropriate universal function and by EC. The result showed that they correlated significantlyand the correlation coefficient between HfECand HLaswas0.9. It proved that the appropriateuniversal function screened for temperature structure parameter has higher accuracy.