UMBRELLA - UM Boundary Layer Representation including land-atmosphere interactions

大气边界层是地球表面附近直接受地表影响的大气层。边界层在大气中起着关键作用——控制地表和自由对流层之间的热量、水分和其他大气成分（包括自然的和人为的）交换。边界层在对流的形成中也起着至关重要的作用，从而影响对流降雨的位置和时间。湍流是BL的一个关键特征，但通常尺度太小，无法在天气和气候模式中解决，因此需要参数化。随着计算资源的增加，现在可以在千米尺度上运行天气预报，对流可以明确地解决（尽管不一定解决得很好）。当我们向亚公里尺度移动时，模式也将开始解析大尺度的边界结构。我们在一定程度上解决这些关键过程的机制被称为灰色地带。对灰色地带的边界层进行建模需要重新评估和修改边界层参数化方案及其与对流的耦合（参数化或显式）。该项目将首先评估目前可用的边界层方案及其在灰色地带不同分辨率下与英国气象局统一模型（MetUM）中对流的耦合，并测试作为该计划一部分产生的任何新发展。其次，研究表面非均质性、边界层结构和对流之间的耦合，了解非均质性的关键作用。以前的研究主要集中在同质案例研究上，尽管事实上大多数土地实际上并不平坦，并且涵盖了各种土地利用和地表条件。包括表面异质性将允许对当前边界层方案进行更彻底的评估，并为更现实的参数化提供物理基础，这些参数化意识到表面特征的潜在可变性。该项目将利用即将到来的韦斯康野外活动的最新野外观测数据，以及英国和美国长期观测站点的数据。我们还将利用最新的第三代气象卫星观测来评估热带地区的模式。我们将把这些观测结果与理想的大涡模拟和更现实的MetUM模拟结合起来，研究均匀站点和非均匀区域（例如表面温度和湿度变化的区域，或平缓地形）的边界层在日循环中的行为。

The atmospheric boundary layer (BL) is the layer of the atmosphere near the Earth's surface which is directly influenced by the surface. The BL plays a key role in the atmosphere - controlling the exchange of heat, moisture and other atmospheric constituents (both natural and anthropogenic) between the surface and the free troposphere. The boundary layer is also crucial in the initiation of convection and so impacts on the location and timing of convective rainfall. Turbulence is a key characteristic of the BL but is generally too small scale to be resolved in weather and climate models and so needs to be parametrised. With increased computational resources it is now feasible to run operation weather forecasts at km scales where convection can be resolved explicitly (though not necessarily well resolved). As we move towards sub-km scale the models will also begin to resolve large scale boundary structures. This regime where we partly resolve these key processes is known as the grey zone. Modelling the boundary layer in the grey zone requires re-evaluation and modification of the boundary layer parametrisation schemes and their coupling to convection (parametrised or explicit). This project will firstly evaluate the currently available boundary layer schemes and their coupling to convection in the Met Office Unified Model (MetUM) at different resolutions across the grey zone as well as testing any new developments produced as part of this programme. Secondly it will study the coupling between surface heterogeneity, boundary layer structures and convection to understand the key role of heterogeneity. Previous studies largely focus on homogeneous case studies, despite the fact that most land is actually not flat and covers a variety of land use and surface conditions. Including surface heterogeneity will allow a more thorough evaluation of the current boundary layer schemes as well as providing a physical underpinning for more realistic parametrisations which are aware of the underlying variability in the surface characteristics. The project will make use of the latest field observations from the upcoming Wescon field campaign as well as data from long term observational sites in the UK and US. We will also utilise the latest Meteosat third generation satellite observations to evaluate the model in the tropics. We will combine these observations with idealised large eddy simulations and more realistic simulations with the MetUM to study the behaviour of the boundary layer over the diurnal cycle at homogeneous sites and for heterogeneous regions (e.g. regions with variable surface temperature and moisture, or gentle topography).