The aim of this dissertation is to attain a better understanding of how tropical cyclones (TCs) respond to variations in the three-dimensional environmental wind field. Much attention has been given to the impact of environmental wind shear in the 850 -- 200 hPa layer on tropical cyclones. However, even with the same magnitude of shear, helicity in this layer can vary significantly. A new parameter is presented, the tropical cyclone-relative environmental helicity (TCREH). Positive TCREH leads to a tilted storm that enhances local storm scale helicity in regions of convection within the TC. Initially we proposed that this enhanced local scale helicity may allow for more robust and longer lasting convection which is more effective at generating latent heat and subsequent TC intensification. Further investigation shows that this is a secondary influence on TC intensity and that variations in the azimuthal and radial position of convection in the TC play a stronger role. Vertical tilt of the vortex is often attributed to wind shear. Different values of helicity modulate this tilt and certain tilt configurations are more favorable for development or intensification than others, suggesting that mean positive environmental helicity is more favorable for development and intensification than mean negative helicity. Idealized modeling simulations demonstrate the impact of environmental helicity on TC development and intensification. Results show that wind profiles with the same 850-200 hPa wind shear but different values of helicity lead to different rates of development. TCREH also is computed from Era-Interim reanalysis (1979 -- 2011) and GFS analyses (2004 -- 2011) to determine if a significant signal exists between TCREH and TC intensification. Mean annular helicity is averaged over various time periods and correlated with the TC intensity change during those periods. Results suggest a weak but statistically significant correlation between environmental helicity and TC intensity change with positive helicity being more favorable for intensification. Another goal of this dissertation is to identify the mechanisms that lead to the observed variations in intensification rate. Results suggest that the difference in intensification rate between TCs embedded in positive versus negative TCREH primarily results from the position of convection and associated latent heat fluxes relative to the wind shear vector. When TCREH is positive, convection is more readily advected upshear and air parcels that experience larger fluxes are more frequently ingested into the TC core. Trajectories computed from high resolution simulations demonstrate the recovery of equivalent potential temperature downwind of convection, latent heat flux near the TC core, and parcel routes through updrafts in convection. Trajectory characteristics show that low-level unstable air is lofted into deep convection near the radius of maximum winds more frequently when TCREH is positive. Contoured frequency-by-altitude diagrams (CFADs) show that convection is distributed differently around TCs embedded in environments characterized by positive versus negative TCREH. They also show that the nature of the most intense convection differs only slightly between cases of positive and negative TCREH. Finally, the implications of time-varying environments around TCs are examined. Until now, idealized numerical simulations of the tropical cyclone (TC) response to time-varying wind shear have applied instantaneous changes in the TC environment. A new modeling framework allows for smoothly transitioning environmental wind states: time-varying point-downscaling (TVPDS). TVPDS is an enhancement of the point-downscaling technique (Nolan 2011) developed for the Weather Research and Forecast (WRF) model. It uses analysis nudging to smoothly transition between different environmental vertical wind (and/or temperature and moisture) profiles while coordinating the point-downscaling method such that the environment remains in balance. Using this new framework, results from previous studies are reexamined to test whether the instantaneous 'shock' to the environment has implications for TC intensity evolution. Results suggest that instantaneous changes to the TC environment indeed do lead to an unrealistic response to an increase in shear. TVPDS simulations of quasi-steady state, moderately intense (~50 ms-1) TCs show that the response to increasing wind shear is a steady reduction in intensity without a recovery to the pre-shear intensity. TVPDS simulations also show that the rate at which the TC weakens depends on how rapidly the environment transitions from low to high shear. Analyses of surface fluxes and regions of convection are presented to determine how the time-varying shear affects the TC.

This book is a completely rewritten, updated and expanded new edition of the original Global Perspectives on Tropical Cyclones published in 1995. It presents a comprehensive review of the state of science and forecasting of tropical cyclones together with the application of this science to disaster mitigation, hence the tag: From Science to Mitigation.Since the previous volume, enormous progress in understanding tropical cyclones has been achieved. These advances range from the theoretical through to ever more sophisticated computer modeling, all underpinned by a vast and growing range of observations from airborne, space and ocean observation platforms. The growth in observational capability is reflected by the inclusion of three new chapters on this topic. The chapter on the effects of climate change on tropical cyclone activity is also new, and appropriate given the recent intense debate on this issue. The advances in the understanding of tropical cyclones which have led to significant improvements in forecasting track, intensity, rainfall and storm surge, are reviewed in detail over three chapters. For the first time, a chapter on seasonal prediction is included. The book concludes with an important chapter on disaster mitigation, which is timely given the enormous loss of life in recent tropical cyclone disasters.World Scientific Series on Asia-Pacific Weather and Climate is indexed in SCOPUS.

Tropical cyclones are topic that is not appropriately known to the public at large, but climate change has been on the public’s mind since the last decade and a concern that has peaked in the new millennium. Like the television programs of Jean Yves Cousteau the ‘plight of the oceans’, have recent documentaries nurtured a conscio- ness that major climatological changes are in the offing, even have started to develop. The retreat of glaciers on mountain tops and in Polar Regions is ‘being seen’ on ‘the small screen’ and has favored an environmental awareness in all populations that are enjoying an average well-being on Planet Earth. The vivid images on screen of storms, floods, and tsunamis share the fear provoking landscapes of deforestation, desertification and the like. Watching such as this one is seen are voices warning of what over is ‘in store’ if the causative problems are not remedied. Talking and d- cussing are useful, but action must follow. Understanding the full ramifications of climate change on tropical cyclones is a task that will takes several decades. In Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change (IPCC) a high probability of major changes in tropical cyclone activity across the various ocean basins is highlighted.

This highly illustrated book is a collection of 13 review papers focusing on convective storms and the weather they produce. It discusses severe convective storms, mesoscale processes, tornadoes and tornadic storms, severe local storms, flash flood forecast and the electrification of severe storms.

Tropical cyclones are a major threat to life and property, even in the formative stages of their development. They include a number of different hazards that individually can cause significant impacts, such as extreme winds, storm surge, flooding, tornadoes, and lightning. Tropical Cyclones: Observations and Basic Processes provides a modern overview of the theory and observations of tropical cyclone structure and behavior. The book begins by summarizing key observations of the structure, evolution, and formation of tropical cyclones. It goes on to develop a theoretical foundation for a basic understanding of tropical cyclone behavior during the storm’s life cycle. Horizontally two-dimensional dynamics of vortex motion and other non-axisymmetric features are considered first before tackling the axisymmetric balance dynamics involving the overturning circulation. Following a review of moist convective processes, later chapters focus mainly on a range of three-dimensional aspects of the tropical cyclone life cycle. Building from first principles, the book provides a state-of-the-art summary of the fundamentals of tropical cyclones aimed at advanced undergraduates, graduate students, tropical meteorologists, and researchers. Members of the Royal Meteorological Society are eligible for a 35% discount on all Developments in Weather and Climate Science series titles. See the RMetS member dashboard for the discount code. Develops a systematic foundation for understanding tropical cyclone dynamics and thermodynamics in two and three dimensions Provides a detailed appraisal of steady-state models and the widely accepted, but enigmatic, WISHE intensification theories Applies the new ideas developed in the book to a range of basic problems, including observational tests of the theory