Surface Layer Turbulent Characteristics over the Complex Terrain of the Loess Plateau Semiarid Region

Surface layer turbulence has an important influence on land-air interactions and pollutant dispersion, and studying the characteristics of surface layer turbulence in complex terrain can contribute to understanding land-air interactions, improving model surface layer parameterization, and enhancing pollution prediction capabilities. The surface layer turbulence observations from the Semi-Arid Climate and Environment Observatory (SACOL) of Lanzhou University in 2008 were processed in this study. High-quality turbulence parameters were calculated, the statistical and transfer characteristics of turbulence were analyzed, and the formation of turbulence was assessed in terms of dynamics and thermodynamics. The atmospheric stability in the semiarid region of the Loess Plateau is basically dominated by neutral/near-neutral and weakly unstable/weakly stable conditions; this pattern is significantly different from the preponderance of unstable and stable layers at other sites. The turbulence intensity differs significantly in both the horizontal and vertical directions and basically shows the relationship I-u approximate to I-v>I-w. The mean values of I-u and I-v are 0.42 and 0.40, respectively, and the mean value of I-w is 0.14, which is different from the general pattern of I-u>I-v>I-w, indicating that the turbulence intensity at SACOL is characterized by a large lateral wind contribution. The dimensionless standard deviations of the nonneutral wind velocity components satisfy the "1/3rd law," and the dimensionless standard deviations of u, v, and w components are 3.35, 2.98, and 1.26, respectively, in the semiarid Loess Plateau. These values are larger than those over flat terrain. The contribution of the shear term to the formation of turbulence is greater than that of the buoyancy term, and the mean annual values of the shear term and the buoyancy in the kinetic energy budget equation in SACOL are 47.94 x 10(-4) m(2).s(-3) and 11.32 x 10(-4) m(2).s(-3), respectively. The annual mean values of the momentum transfer coefficient C-D and the heat transfer coefficient C-H under near-neutral conditions are 8.54 x 10(-3) and 2.52 x 10(-3), respectively.