A study on turbulent characteristics of the surface layer in Ejina oasis of the lower reach of Heihe

The turbulent data observed in the Tamarisk scrub over Ejina oasis in the lower reaches of Heihe River from September 5 to 27, 2003 are used to investigate the relation between dimensionless turbulent speed variances and stability parameter Z/L. The results show that under the unstable stratified condition the stability parameter (Z/L) dependence of , , and can be fit to a power law with a power law index of 1/3, in accordance with the Monin-Obkuhov similarity theory. Under the near neutral condition, , / are slightly smaller/larger than their counterparts over the flat underlying surface. Under the convective condition, the stability parameter (Z/L) dependence of variances of dimensionless temperature and specific humidity fluctuations can be fitted to a power law with an index of -1/3, and under both the stable and unstable stratification the variance increases with the reduction of | Z/ L|. The sensible heat flux dominates the surface heat fluxes, with a peak value of about 250 W.m-2 for sensible heat and 170 W.m-2 for latent heat; and in night-time the latent heat flux is smaller, the sensible heat flux becomes negative. In day-time, the momentum flux ranges from 0.2 to 0.3 N.m-2 with a peak value of 0.31 N.m-2. The aerodynamic roughness length in the Ejina Tamarisk scrub is larger than those over the Gobi and other oasis underlying surfaces in the HEIFE, with =0.47551m under the neutral stratification. The bulk momentum transfer coefficient under the neutral, unstable, and stable stratification are 22.2×10-3, 10.3×10-3, and 7.2×10-3 and the corresponding values of the bulk heat transfer coefficient are 3.2×10-3, 3.3×10 -3,and 2.7×10 -3, respectively.