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Vogl, Stefanie (2009): Tropical Cyclone Boundary-Layer Models. Dissertation, LMU München: Faculty of Physics
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Abstract

Hurricanes are some of the most spectacular yet deadly natural disasters. Especially in times of the widely discussed anthropogenic climate change, public interest focusses on such extreme weather events. Nowadays, highly sophisticated numerical models are used for example for track prediction, but still there are many fundamental open questions. Among these, the question how intense a tropical cyclone may become is of major interest. In this work a study of the two most common types of models for the hurricane boundary layer is carried out. This study reveals major deficiencies of boundary layer models and finally leads to a reassessment of the established theory of potential intensity of hurricanes. In chapter (2), a linear model for the hurricane boundary layer is derived from a detailed scale analysis of the full equations of motions. It is shown how analytic solutions for the model may be calculated and how these solutions may be used to appraise the integrity of the linear approximation. Some of the results of this chapter are published in Vogl and Smith (2009). In chapter (3), a slab model is examined, which yields results for the main thermodynamic quantities. Depending on the chosen boundary layer depth and the imposed wind profile, two different types of solution behaviour found and interpreted. Other aspects of the dynamics and thermodynamics of the boundary layer are studied as for example the influence of shallow convection. The limitations and strengths of the slab model are discussed at the end of chapter (3). The results are published in Smith and Vogl (2008). The results of the detailed investigation of the linear and the slab model both point out an important deficiency of hurricane boundary layer models, namely the assumption of gradient wind balance. In chapter (4) it is shown that indeed the major deficiency of the established hurricane (P)otential (I)ntensity theory is the tacit assumption of gradient wind balance in the boundary layer. The results of chapter (4) show a fundamental problem of the established PI theory and then point to an improved conceptual model of the hurricane inner core region. Thus this work suggests a way forward to an urgently needed more consistent theory for the hurricane potential intensity. It is published in Smith, Montgomery and Vogl (2008).