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

Dr Andrew Ross (SEE), Dr Juliane Schwendike (SEE), Dr Adrian Lock (Met Office), Dr John Edwards (Met Office), Dr Jeff Kepert (Bureau of Meteorology)

Project partner(s): UK Met Office (CASE); Bureau of Meteorology, Australia

Contact email: A.N.Ross@leeds.ac.uk

Summary

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. 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 strongest winds in tropical cyclones are typically found within the atmospheric boundary layer. Since it is these boundary layer winds that directly impact on people and buildings, there is a strong need to understand the processes and characteristics of this part of the atmosphere. The boundary layer also plays an important role during the intensification of tropical cyclones by mediating exchange of heat and moisture between the ocean and the atmosphere. Boundary layer structures can also influence the organisation of convection above the boundary layer. Accurately modelling the intensification of tropical cyclones remains one of the main challenges of tropical cyclone research. 

Despite the importance of the boundary layer in tropical cyclones, the extreme environment means there are few direct observations within the boundary layer. Boundary layer parametrisation schemes in global models are not developed with such extreme conditions in mind and are not well tested against the observations. Much of what is known about the role the boundary layer in tropical cyclones comes from idealised simulations. The extent to which these ideas still apply in real tropical cyclones is less well understood. 

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 real tropical cyclones; 

ii. Develop an understanding of the model’s sensitivity to the representation of boundary layer processes in tropical cyclones, and investigate ways of improving this to more accurately forecast cyclone development.

In particular, according to your particular research interests, the studentship could involve the following:

(1) Investigate the representation of the boundary layer structure of selected tropical cyclones in Met Office Unified Model (MetUM) simulations at different horizontal resolutions. 

(2) Compare the modelled boundary-layer structure with flight-level (e.g. wind, temperature, radar), and dropsonde (wind, temperature, moisture) observations from the U.S. Hurricane Research Division aircraft reconnaissance program to identify potential model biases. 

(3) Investigate the three-dimensional thermal and wind structure in the boundary layer for selected storms and compare them to existing simplified models in the literature.

(4) Investigate the representation of the height of the boundary layer in the model simulation. Is the height represented correctly? If not, how can we improve the representation of the height of the boundary layer in the MetUM?

(5) Develop ways to improve the representation of the boundary layer in the model and to minimise the identified model biases.

(6) Investigate the coupling between the boundary-layer and the free-troposphere in tropical cyclones, in particular how the boundary layer may control the initiation and structure of convection in the cyclone.

(7) Compare the MetUM set up at the Met Office to the tropical cyclones system at the Bureau of Meteorology for the same Atlantic tropical cyclone. Both systems use the MetUM, but will different data assimilation systems and slightly different model configurations and parametrisations. Do different data assimilation systems have an impact of the representation of boundary-layer processes and hence on tropical cyclone development?

In this project we will focus on tropical cyclones in the Atlantic, as there are generally better observations available for these cyclones from the US Hurricane Research Division. Inner-core tropical cyclones dynamics are the same in different ocean basins and so the results of the project will be useful in other regions too. Close collaboration with the Met Office and the Bureau of Meteorology will ensure the results of this study will feed into model development. The project will involve regular meetings between all partners and regular visits to the Met Office in Exeter. You may also have the opportunity to visit the Bureau of Meteorology in Melbourne, Australia. 

Click here for a full project description.

Related undergraduate subjects:

  • Applied mathematics
  • Atmospheric science
  • Engineering
  • Environmental science
  • Mathematics
  • Meteorology
  • Natural sciences
  • Oceanography