Investigating boundary layer processes in tropical cyclones in the Met Office operational forecasting model

每年，热带气旋由于其破坏性的风、强降水及其对海洋的影响，例如风暴潮，造成巨大的破坏。2017年大西洋热带气旋季节是一个特别具有破坏性的季节。飓风艾尔玛的风速达到每小时285公里，在加勒比海的几个岛屿和佛罗里达造成了约647.6亿美元的损失，直接死亡44人，间接死亡85人。飓风玛丽亚的最高风速达到每小时280公里，造成112人死亡，经济损失达916.1亿美元。飓风玛丽亚直接从波多黎各上空掠过，造成严重破坏。准确预报这些影响力大的天气系统的路径和强度，对市民及时采取适当行动，以减少对民生、财产和经济的损害，至为重要。边界层是大气中直接受地表影响的部分，影响范围约在一小时或以内。这些地表影响包括摩擦阻力、蒸发和蒸腾，热传递和污染排放。边界层的深度从几百米到几公里不等，并且随时间和空间而变化。边界层中的湍流在调节我们在地面经历的天气方面起着至关重要的作用，因此迫切需要了解这部分大气的过程和特征。与本项目特别相关的是，边界层在热带气旋加强期间也起着重要作用。正确捕捉这种增强是热带气旋研究的主要挑战之一，而准确表示热带气旋中的边界层是其中的一个关键方面。该博士项目的科学目标是：（i）对热带气旋模拟中边界层结构和过程的表现进行详细调查;（ii）了解模型的局限性，并研究改进方法。

Each year tropical cyclones cause enormous amounts of damage due to their destructive winds, heavy precipitation and their effects on the sea, e.g. storm surges. The 2017 tropical cyclones season in the Atlantic was a particularly destructive one. Hurricane Irma reached wind speeds of 180 mph (285 km/h), and caused damage of around US$ 64.76 billion as well a 44 deaths directly and 85 indirectly in several Caribbean Islands and Florida. Hurricane Maria reached a maximum wind speed of 175 mph (280 km/h) and caused 112 fatalities and US $91.61 billion in damages. Hurricane Maria moved directly over Puerto Rico and left considerable destruction in its wake. Being able to accurately forecast the track and intensity of these high impact weather systems is crucial to enable people to take appropriate action in time to minimise the damage to livelihood, property and economy.The boundary layer is the part of the atmosphere directly influenced by the earth's surface within about an hour or less. These surface influences include frictional drag, evaporation and transpiration, heat transfer and pollution emission. The depth of the boundary layer ranges from a few hundred meters to kilometres, and is variable in time and space. Turbulence in the boundary layer plays a crucial role in modulating the weather we experience at the surface and so there is a strong need to understand the processes and characteristics of this part of the atmosphere. Of particular relevance to this project, the boundary layer also plays an important role during the intensification of tropical cyclones. Correctly capturing this intensification is one of the main challenges of tropical cyclone research, and accurate representation of the boundary layer in tropical cyclones is a key aspects of this. The scientific objectives of the PhD project are: (i) conduct a detailed investigation into the representation of the boundary-layer structure and processes in simulations of tropical cyclones; (ii) develop an understanding of the model's limitations and investigate ways to improve it.