Atmosphere-canopy interaction over complex terrain

陆面动量通量、热量通量、水汽通量和成分通量是数值天气预报和气候模式中至关重要的因素。它们都特别受到植被和森林的强烈影响，其中冠层内的流动和交换决定了来源和汇。对这些冠层流动的了解现在已经在广泛的平坦地区得到了很好的发展，但许多丘陵和山区要么是部分森林，要么是完全森林。迄今为止，地形流模型通常忽略了森林内部的过程，并使用粗糙度长度来参数化山丘表面。最近，理论和计算的发展已经开始建立一个框架来理解这些森林冠层内的平均流量。这些结果表明，正确模拟树冠和大气之间的相互作用可以在山区和更大的尺度上产生重要的影响。迫切需要利用现场测量来验证最新的模型开发，但迄今为止还没有。该项目将提供这样一个验证数据集，通过收集覆盖一个小而陡峭的山丘的森林内部和上方几个月的测量数据。目前还没有什么理论框架来理解山冠层内的湍流结构，但这对风力破坏和扩散应用至关重要。冠层内部和上方的高分辨率湍流测量将为冠层内部的湍流结构提供新的见解，这将导致改进冠层流动的湍流关闭方案。结合这些方案的进一步数值模拟将把预测范围扩展到更复杂的地形。

Land surface fluxes of momentum, heat, moisture and constituents are factors of crucial importance in numerical weather prediction and climate models. They are all strongly influenced by vegetation and forests in particular, where flows and exchanges within the canopy determine the sources and sinks. The understanding of these canopy flows is now quite well developed for extensive areas of flat ground, but many hilly and mountainous areas are either partially or fully forested. To date, models for orographic flow have generally ignored the processes within the forest and parametrize the hill surface using a roughness length. Very recently, theoretical and computational developments have begun to set out a framework for understanding the mean flow within these forest canopies. These suggest that correctly modelling the interaction between the canopy and the atmosphere can have important consequences on mountain and larger scales. There is an urgent need to validate the latest model developments using field measurements, but to date none are available. This project will provide such a validation dataset by collecting several months of measurements within and above a forest covering a small but steep hill. There is as yet little theoretical framework for understanding the turbulence structure within canopies on hills and yet this is crucial for wind damage and dispersal applications. High resolution turbulence measurements within and above the canopy will provide new insight into the structure of turbulence within the canopy and this will lead to improved turbulence closure schemes for canopy flows. Further numerical modelling incorporating these schemes will extend the range of the predictions to more complex terrain.