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

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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.