YES-27-A-24: The impact of air-sea interaction on Borneo vortices and Cold Surges
Borneo vortices are synoptic-scale cyclonic disturbances with distinct structure and behaviour and unique to the Maritime Continent during boreal winter (e.g. Hardy et al., 2021). They can often be found north or west of Borneo. They are associated with major impacts including heavy rainfall, landslides and rough seas in Malaysia, Vietnam, and Thailand, which makes it essential for forecasters in Southeast Asia to be able to understand and forecast them. Borneo vortices often occur in conjunction with cold surges, which are characterised by relatively cold air and strong surface winds that move in a mainly northeasterly direction through the South Chin Sea (e.g. Crock et al., 2025). Cold surges themselves are also associated with high impact weather during boreal winter.
Understanding the dynamics of the interaction between Borneo vortices, cold surges and the South China Sea as well as forecasting their track and impact is a key challenge for numerical weather prediction models. This project aims to investigate the air-sea interaction between Borneo vortices and Cold Surges and the South China Sea and how this interaction impacts the occurrence of high impact weather. We will evaluate how certain dynamical processes are represented in the atmosphere-ocean coupled Met Office Unified Model (MetUM) model. In addition, we will investigate how Borneo vortices and cold surges and their interaction with the underlying ocean is represented in seasonal to sub-seasonal (S2S) model simulations with Global Seasonal Forecasting System (GloSea6). We will investigate if the improved understanding the air-sea interactions has a positive impact on forecast skill at medium range and S2S timescales. The overarching aim is to improve our ability to forecast these weather systems more accurately at synoptic (1-5 days) and S2S time scales, ultimately benefiting people at risk.
The scientific objectives of the project are:
- Investigate the impact of air-sea interaction on Borneo Vortices and cold surges;
- Investigate the impact of air-sea interaction on high-impact weather in relation to both Borneo Vortices and cold surges;
- Investigate how well Borneo Vortices and cold surges are represented in S2S models simulations and how good S2S models are at forecasting both weather systems.
The project will start by investigating a high impact weather case study of an intense Borneo vortex that occurred in conjunction with a strong cold surge and caused high impact weather such as heavy rain and strong winds. We will analyse this case study in atmosphere only MetUM simulations and coupled atmosphere-ocean simulations to assess the impact of the coupling. We want to understand how the coupling affects the Borneo vortex and the cold surge (strength and track) and how the interaction impacts the formation of deep convection and why.
After the in-depth analysis of the case study, we will investigate a larger number of cases to be able to generalise the results. We will then test how well the Met Office S2S model is able to represent the key characteristics identified and what the skill of the model is in predicting cold surges and Borneo vortices.
The Met Office CASE award will allow the student access to a suite of state-of-the-art model products and computing facilities as well as staff expertise in remote sensing and in-situ observations, modelling and understanding of atmospheric processes such as convection. The CASE award will also provide additional funding. The student will be based and registered at the University of Leeds. Through the collaboration with Met Malysia and the University of Melbourne there might be the possibility to visit the project partners in Malaysia and Australia.
References:
Crook, J., Hardy, S., Methven, J., Schwendike, J., Yik D.J., Yang, G.Y., (2025). The structure of Borneo vortices and their relationship with cold surges, the Madden–Julian oscillation and equatorial waves. Quarterly Journal of the Royal Meteorological Society: doi/10.1002/qj.4905.
Hardy, S., Methven, J., Schwendike, J., Harvey, B., and Cullen, M. (2023). Examining the dynamics of a Borneo vortex using a balance approximation tool. Weather and Climate Dynamics Discussions: https://wcd.copernicus.org/articles/4/1019/2023/.
Aslam, A.A., Schwendike, J., Peatman, S.C., Matthews, A.J., Birch, C.E., Bollasina, M.A., Barrett, P.A., Azaneu, M.V.C. (2025) Atmospheric Response to Mesoscale Ocean Eddies in the Maritime Continent. Journal of Geophysical Research Atmospheres, 130, doi.org/10.1029/2024JD042606Digital Object Identifier (DOI).