The Role of Shear in the Morning Transition Boundary Layer
The Role of Shear in the Morning Transition Boundary Layer
复制标题
剪切力在早晨过渡边界层中的作用
DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
R. Beare
中科院分区：
文献类型：
--
作者：
R. Beare
我们使用大涡模拟（LES）来更好地定义早晨过渡边界层的早期阶段。先前有关早晨过渡边界层的 LES 研究重点是夹带对流边界层 (CBL) 的作用。通过使用不同域大小和网格长度的组合，这里对从稳定边界层 (SBL) 到 CBL 的完整演化进行了建模。在早晨过渡的早期阶段，边界层显示为浅混合层的组合，其上覆盖着显着剪切驱动的稳定边界层（所谓的混合 CBL-SBL 状态）。混合 CBL-SBL 状态是理解剪切敏感性的关键。湍流动能收支也表明它是剪切驱动的。来自混合 CBL-SBL 状态的负通量比当天晚些时候 CBL 中通常发现的负通量远高于最小值，渗透深度为 wm/Ni，其中 wm 是摩擦和对流速度组合尺度，Ni 是逆温层顶部的静态稳定性。
We use large-eddy simulation (LES) to better define the early stages of the morning transition boundary layer. Previous LES studies relating to the morning transition boundary layer focus on the role of the entraining convective boundary layer (CBL). By using a combination of different domain sizes and grid lengths, the full evolution from the stable boundary layer (SBL) to the CBL is modelled here. In the early stages of the morning transition the boundary layer is shown to be a combination of a shallow mixed layer capped by a significant shear driven stable boundary layer (the so-called mixed CBL–SBL state). The mixed CBL–SBL state is the key to understanding the sensitivity to shear. Turbulent kinetic energy budgets also indicate that it is shear driven. The negative flux from the mixed CBL–SBL state extends much further above the minimum than is typically found for the CBL later in the day, and the depth of penetration scales as wm/Ni, where wm is the combined friction and convective velocity scale and Ni the static stability at the inversion top.