Integrating canopy and large-scale effects in the convective boundary-layer dynamics during the CHATS experiment
Integrating canopy and large-scale effects in the convective boundary-layer dynamics during the CHATS experiment
复制标题
CHATS 实验期间对流边界层动力学中的冠层和大尺度效应进行整合
DOI：
10.5194/acp-17-1623-2017
复制
发表时间：
2017
影响因子：
6.3
通讯作者：
Jordi Vilà
中科院分区：
文献类型：
--
作者：
M. Shapkalijevski;H. Ouwersloot;A. Moene;Jordi Vilà
抽象的。通过描述一个相对稀疏和均匀的果园树冠上方的对流边界层的动态，我们研究了粗糙度子层（RSL）表示对预测的地表通量和状态变量的日变化的影响。我们的方法结合数值实验，使用大气混合层模型，包括陆地表面植被表示，和测量的冠层水平阵列湍流研究（CHATS）的现场实验附近的狄克逊，加州。RSL的参数化使用一个额外的因素在标准的莫宁-奥布霍夫相似理论通量剖面关系，考虑到冠层对大气流动的影响。我们选择了一个具有代表性的情况下，其特点是南风条件，以确保良好发展的RSL在果园树冠。然后，我们研究了边界层动态的日变化对RSL关键尺度、林冠调整长度尺度Lc和β = u*/|U|由于它们的稳定性和对冠层结构的依赖性，我们发现，包括RSL参数化导致改进的近地面平均量（例如，高达50%的风速）和传输（阻力）系数的日演变的预测。我们发现相对不显著的影响，对模拟的表面通量（例如，高达5%的摩擦速度，而3%的显热和潜热），这是由于平均梯度和阻力系数之间的补偿效应，这两者都在很大程度上受到RSL参数化。当Lc（从10到20 m）和β（从0.25到0.4 m）变化时，根据观测证据，发现预测的摩擦速度变化高达25%，模拟的表面能量通量（感热和蒸发潜热）变化高达2%和9%。因此，边界层高度变化高达6%。此外，我们的分析表明，解释CHATS测量冠层上方，非本地的影响，如夹带，沉降和对流的热量和水分在CHATS网站的贡献需要考虑。
Abstract. By characterizing the dynamics of a convective boundary layer above a relatively sparse and uniform orchard canopy, we investigated the impact of the roughness-sublayer (RSL) representation on the predicted diurnal variability of surface fluxes and state variables. Our approach combined numerical experiments, using an atmospheric mixed-layer model including a land-surface-vegetation representation, and measurements from the Canopy Horizontal Array Turbulence Study (CHATS) field experiment near Dixon, California. The RSL is parameterized using an additional factor in the standard Monin–Obukhov similarity theory flux-profile relationships that takes into account the canopy influence on the atmospheric flow. We selected a representative case characterized by southerly wind conditions to ensure well-developed RSL over the orchard canopy. We then investigated the sensitivity of the diurnal variability of the boundary-layer dynamics to the changes in the RSL key scales, the canopy adjustment length scale, Lc, and the β = u*/|U| ratio at the top of the canopy due to their stability and dependence on canopy structure. We found that the inclusion of the RSL parameterization resulted in improved prediction of the diurnal evolution of the near-surface mean quantities (e.g. up to 50 % for the wind velocity) and transfer (drag) coefficients. We found relatively insignificant effects on the modelled surface fluxes (e.g. up to 5 % for the friction velocity, while 3 % for the sensible and latent heat), which is due to the compensating effect between the mean gradients and the drag coefficients, both of which are largely affected by the RSL parameterization. When varying Lc (from 10 to 20 m) and β (from 0.25 to 0.4 m), based on observational evidence, the predicted friction velocity is found to vary by up to 25 % and the modelled surface-energy fluxes (sensible heat, SH, and latent heat of evaporation, LE) vary up to 2 and 9 %. Consequently, the boundary-layer height varies up to 6 %. Furthermore, our analysis indicated that to interpret the CHATS measurements above the canopy, the contributions of non-local effects such as entrainment, subsidence and the advection of heat and moisture over the CHATS site need to be taken into account.