Evaluating the role of latent heating in extratropical cyclone development using a new cyclone climatology

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In the mid-latitudes cyclones are observed to form in the north Atlantic. These cyclones can develop explosively causing flooding and severe wind damage in the UK and Western Europe. Cyclones that form in the east Atlantic can be particularly hard to forecast owing to their small scales and rapid development. Studies have shown that a wide range of processes may be important for their development. However, the dominant mechanism responsible for their development remains unclear. One such process is the release of latent heat into the cyclone. As air rises, it cools and, if water vapour condenses, this energy is released into the atmosphere as latent heat of condensation. A large amount of heat is thus released into the atmosphere causing air to rise. The increase in vertical velocity is accompanied by an increase in low-level convergence and upper-level divergence which leads to an increase in cyclonic circulation and hence cyclone intensification. Observational case studies have shown that latent heating by itself cannot form a cyclone but it can play an important role in their development. Theoretical studies have shown that the smaller the cyclone, the greater the potential impact of latent heating. Thus it is hypothesised that east Atlantic cyclones, which generally occur on smaller scales, will be strongly influenced by the release of latent heat. Furthermore, there is evidence to suggest that the number and intensity of east Atlantic cyclones may increase in the future and that the role of latent heating may play a more important role. Thus it is vital for both improvement of the current cyclone forecasts and for climate change predictions that we understand the factors controlling the development of east Atlantic cyclones. In this project the processes responsible for the development of mid-latitude cyclones will be determined; in particular an evaluation of the role of latent heating in east Atlantic storms will be investigated. The project has three main aims; to calculate the structural evolution of a newly available dataset of cyclones; to classify these cyclones according to the evolution of their structure; and to determine the relative contribution of latent heating in their development. The research findings will be of relevance to the regional climate predication community who will be able to use the resulting dataset to verify climate model simulated cyclones. This is an essential step towards understanding current model performance and allowing model cyclones to be used in future impacts studies. Understanding cyclone structures and their related impacts is also of benefit to the insurance industry and catastrophe modellers.