GREYBLS: modelling GREY-zone Boundary LayerS

社会从气象局提供的数值天气预报中受益匪浅。最近，PA咨询公司对英国气象局的公共气象服务的估值超过了6亿GB/a。气象局的高分辨率(小网格框)数值天气预报提供了例如：地面温度、低层云和雾以及雷暴开始的信息。这使公众和广泛的行业受益，包括：农业、航空、建筑、风能、零售和运输。该项目旨在改进用于进行这些预报的高分辨率数值天气预报(NWP)模式。大气边界层是指与地面相邻的区域，在该区域内有显著的湍流热量、水汽和动量通量。在太阳加热的强迫下，边界层在陆地上有一个重要的日循环。它还与大气中的其他重要过程密切相关，例如大范围天气系统和对流风暴。因此，边界层的日循环在许多高影响天气方面起着关键作用，例如：地表温度、污染物和化学物质的扩散、低层云和雾以及雷暴的开始。边界层的日循环在区域气候和气候变化中也很重要，例如，温室气体排放增加的陆地上的极端温度。然而，在我们对高分辨率边界层的日循环预报的理解和能力方面仍有很大的局限性。这个项目的目的是发展新的技术，在一个被称为“灰色地带”的区域内模拟高分辨率的边界层。灰色区域描述了数值预报模式的网格框的大小与边界层深度相当的情况。随着超级计算机能力的增强，NWP模式的网格箱现在不到5公里，因此灰色地带正成为一个紧迫的问题。然而，目前人们对如何对其进行建模知之甚少。可能需要新的建模技术，例如应用随机强迫。该项目旨在通过对灰色地带建模的可能方法进行系统比较来提高我们的理解。在此基础上，我们将为灰色区域设计一种新的边界层参数化(表示法)，用于英国气象局数值预报模式。灰色地带模型的改进将导致气象局高分辨率预报的改进。

Society benefits significantly from the numerical weather forecasts provided by the Met Office. Recently, PA consulting valued the Met Office's public weather service in excess of £600 million pa. The high-resolution (small grid box) numerical weather forecasts of the Met Office provide information on, for example: surface temperature, low-level cloud and fog, and the onset of thunderstorms. This benefits the public and a wide range of industries including: agriculture, aviation, construction, wind energy, retail and transport. This project aims to deliver improvements to the high-resolution numerical weather prediction (NWP) models used to make these forecasts.The atmospheric boundary layer is the region adjacent to the surface in which there are significant turbulent fluxes of heat, moisture and momentum. The boundary layer has a significant diurnal cycle over land forced by solar heating. It is also strongly coupled to other important processes in the atmosphere such as large-scale weather systems and convective storms. The boundary layer diurnal cycle thus plays a key role in many high-impact aspects of weather such as: surface temperature, the dispersion of pollutants and chemical species, low level cloud and fog, and the onset of thunderstorms. The diurnal cycle of the boundary layer is also important in regional climate and climate change, for example, extreme temperatures over land with increased greenhouse gas emissions. Nevertheless, there are important limitations in our understanding and ability to forecast the diurnal cycle of the boundary layer at high resolution.The aim of this project is to develop new techniques for modelling the boundary layer at high resolution in a regime called the "grey zone". The grey zone describes the situation where the grid box of a NWP model is of comparable size to the boundary layer depth. With increasing supercomputer power, the grid boxes of NWP models are now below 5 km, so the grey zone is becoming a pressing issue. However, there is currently little understanding about how to model it. New modelling techniques will likely be required such as applying stochastic forcing. This project aims to improve our understanding by performing a systematic comparison of the possible methods for modelling the grey zone. From this understanding, we will then design a new parametrization (representation) of the boundary layer for the grey zone for use in the Met Office NWP model. Improved modelling of the grey zone will then lead to improved high resolution forecasts at the Met Office.