中文摘要：

近地层观测的强风运动表明,叠加在平均流动之上的脉动通常有两种,一种是随机的湍流脉动,还有一种具有相干结构的阵风扰动。分析表明,上层强风的剪切运动产生阵风,并向下传递能量,对近地层的通量传输起到重要作用。本文利用北京325 m气象塔、位于海拔1257 m的妙峰山测风塔和位于海拔1688 m的灵山测风塔的资料,分析了强风天气下,边界层上层出现阵风并向下传递的过程,进一步证实无论在近地层还是边界层上层,强风期间,叠加在平均流动上除了高频湍流脉动之外,还有周期为1~10分钟的阵风,即相干结构。阵风峰期有下沉运动,阵风谷期有上升运动。这些相干结构在边界层上层产生,向下运动和传播过程中受到平均气流梯度的切变作用和地面摩擦,破碎为湍流结构。边界层上层的阵风和湍流产生的动量通量向下传递,使得强风期间,边界层中阵风和湍流对通量具有同样的输送能力,对边界层中沙尘、污染物等气溶胶的传输具有重要作用。本研究为模式中进行通量输送参数化方案的修正提供了观测和理论依据。

英文摘要：

Observation of surface-layer strong winds shows there are two kinds of velocity fluctuations superimposed on the average flow： random turbulent fluctuations, and coherent gusty wind disturbances. Studies on the boundary-layer structure under strong wind weather infer that the shear effect of strong wind in the upper layer produces gusty wind disturbances and transports energy downward. This is important for flux transportation in the surface layer. In this study, data were obtained from the Beijing 325 m meteorological tower, the wind tower at a height of 1257 m on Miaofengshan Mountain, and the tower at a height of 1688 m on Lingshan Mountain. Based on these data, the gusty wind disturbances in the upper layer and the downward transportation under strong wind weather were analyzed. Results showed that there were gusty wind disturbances in both the surface and upper layers（coherent structures whose periods were between one and ten minutes）, superimposed on the average flow, as well as high-frequency turbulent fluctuations during strong wind periods. The coherent structures showed that the vertical velocity was downward when the horizontal velocity was in its peak phase, and vice versa. Furthermore, they were produced in the upper part of the boundary layer, and affected by the shear of the average flow and friction of the ground during their downward movement and transport process, before being broken up to form turbulence. The momentum fluxes of windy gusts and turbulence in the upper layer transported downward. During strong wind periods, the downward fluxes of momentum by windy gusts and turbulence were the same, both being important for the transportation of sand, dust, pollution, and other aerosols. This study provides an observational and theoretical basis for the development of flux transportation parameterization in models.