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The β-effect in tropical cyclones: impact on intensity and sensitivity to temperature

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Title: The β-effect in tropical cyclones: impact on intensity and sensitivity to temperature
Authors: Corsaro, Carlo Maria
Item Type: Thesis or dissertation
Abstract: Tropical cyclones are large weather systems whose development is characterised by complex physical processes that are not yet fully understood. A better understanding of how cyclones work is vital to help forecasters make more accurate predictions. The objective of this study is to contribute to the understanding of the track and intensity evolution in relation to the β-effect. While the β-effect has been widely studied, its response to changes in environmental conditions has been investigated only marginally. To this end a series of idealised experiments using the Weather Research and Forecasting model is performed. The sensitivity of the β-drift is investigated with no background flow by changing uniformly sea surface and atmospheric temperature. With increasing temperature tropical cyclones become more intense, larger and move faster with a stronger westward deflection. In particular, there is a linear relationship between the β-drift speed and size above a gale-force wind radius of 250 km. Another aspect investigated is the impact of the β-effect on cyclone intensity. A comparison between an experiment with variable Coriolis parameter f and one on an f -plane shows that after the initial intensification the former has a lower intensity and undergoes a weakening not present in the latter. The main reason behind this weakening is the dry intrusion of a mid-upper tropospheric westerly flow. Back-trajectories show that the intrusion originates from the anticyclonic recirculation of the air expelled from the cyclone deep convection at earlier times, eventually causing a self-weakening of the cyclone. A real-case simulation of Hurricane Katrina (2005) and two sensitivity experiments are performed to investigate the results of the idealised simulations. The occurrence of both the β-drift sensitivity to temperature and the dry intrusion further demonstrates that the results presented here might contribute to the general understanding of the intensity and track evolution of tropical cyclones.
Content Version: Open Access
Issue Date: Jan-2017
Date Awarded: Jul-2017
URI: http://hdl.handle.net/10044/1/49420
DOI: https://doi.org/10.25560/49420
Supervisor: Toumi, Ralf
Sponsor/Funder: European Union
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses



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