Download or read book Convectively generated Potential Vorticity in Rainbands and Secondary Eyewall Formation in Hurricanes written by Falko Judt and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Concentric eyewall formation and eyewall replacement cycles are intrinsic processes that determine the intensity of a tropical cyclone, as opposed to purely environmental factors such as wind shear or the ocean heat content. Although extensive research has been done in this area, there is not a single widely accepted theory on the formation of secondary eyewall structures. Many previous studies focused on dynamic processes in the inner core of a tropical cyclone that would precede and ultimately lead to the formation of a secondary eyewall. Hurricanes Katrina and Rita in 2005 were frequently sampled by research aircraft which gathered a copious amount of data. During this time, Rita developed a secondary eyewall which eventually replaced the original eyewall. This thesis will investigate the formation of a secondary eyewall with particular emphasis on the rainband region, as observations show that an outer principal rainband transformed into the secondary ring. A high resolution, full physics model (MM5) initialized with global model forecast fields correctly predicted the secondary eyewall formation in Rita. The model output will be used to investigate both Katrina and Rita in terms of their PV generation characteristics since PV and vorticity maxima correlate well with wind maxima that accompany the eyewall and rainbands. Furthermore, dynamical processes such as vortex Rossby wave (VRW) activity in the inner core region will be analyzed. Comparison of the differences in the two storms might shed some light on dynamics that can lead to structure changes. Comparison of the model data with aircraft observation is used to validate the results. Doppler radar derived wind fields will be used to calculate the vertical vorticity. The vorticity field is closely related to PV and thus a manifestation of the PV generation process in the rainband. The investigation has shown that Rita2s principal rainband features higher PV generation rates at radii beyond 80 km. Both the azimuthal component and the projection of asymmetric PV generated by convection onto the azimuthal mean connected with the principal band are hypothesized to be of importance for the formation of the secondary eyewall. VRW were found not to be important for the initial formation of the ring but might enhance convective activity once the outer eyewall contracts.

Download or read book The Role of Asymmetric Rainband Processes in Secondary Eyewall Formation in Tropical Cyclones written by Chau Lam Yu and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Secondary eyewall formation (SEF) in tropical cyclones (TCs) can cause significant changes in both the intensity and storm structure. Through a systematic analysis of model simulations, this study examined the dynamical relationships between a sequence of important asymmetric rainband processes that contribute to the onset of SEF. In an idealized simulation where artificial rainband diabatic forcing is imposed, wind field broadening is observed, together with a newly found low-level spiral updraft that resembles the updraft structure observed in Hurricanes Rita (2005) and Earl (2010). These features are also embodied clearly in a full-physics simulation of Hurricane Matthew (2016). Prior to the onset of the SEF, the simulated TC experiences a storm-scale wind field broadening accompanying with an intensifying spiral rainband. The associated wind acceleration is nearly 100 km in radial extent and covers the left-of-shear half of the storm with a slantwise descending structure. Quadrant tangential wind budget shows that this inward descending structure is due to the presence of a mid-level convergence zone associated with stratiform diabatic forcing, which draws angular momentum inward and accelerates the wind field. Collocated with stratiform cooling, the accelerated mid-level inflow turns into downdraft, forming a mesoscale descending inflow (MDI) that shapes the inward descending pattern of the acceleration field. At the upshear-left quadrant where this MDI reaches the surface, low-[theta]_E air is flushed into the boundary layer, forming a near surface cold pool. At the inner edge where this cold pool interacts with high [theta]_E moist envelope of the TC inner core, a tight thermodynamic gradient is established, with intense convective updrafts being reinvigorated and maintained. An equivalent potential temperature budget shows that the inward intruding cold pool destabilizes the atmospheric column by forming differential azimuthal warm advection, sustaining the intense convections at the vicinity of strong thermodynamic gradient. To investigate whether the identified asymmetric rainband processes generally occur in other SEF cases, a nonlinear boundary layer model is used in conjunction with airborne observations of tangential wind in TCs before, after, and without undergoing SEF. The model simulation results show that among all quadrants, the downshear-left and left-of-shear quadrants exhibit the strongest secondary updraft signals that resembles an early signal of an incipient secondary eyewall. This finding aligns well with the asymmetric rainband processes identified in our full-physics simulation, and suggests that the dynamical processes in the left-of-shear quadrants, where the stratiform portion of the rainband typically lies, are of particular importance to the onset of SEF.

Download or read book Interaction Between Two Concentric Potential Vorticity Rings written by Jia Hu and published by . This book was released on 2008 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Analysis of the Structure and Dynamics of Inner Core Precipitation Features in a Tropical Cyclone written by Anthony Carl Didlake (Jr.) and published by . This book was released on 2012 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Airborne Doppler radar observations of the stationary rainband complex and secondary eyewall in Hurricane Rita (2005) were analyzed to better understand the inner-core dynamics of tropical cyclones. In the upwind end of the rainband complex, convective cells displayed kinematic structures that varied with radius. Cells at smaller radii contained a low-level tangential jet constrained in altitude largely by tangential acceleration due to angular momentum conservation, while cells at larger radii contained a low-level and/or midlevel jet determined jointly by angular momentum conservation and vertical advection. These variations are attributable to vortex-scale dynamics in which convective buoyancy (associated with vertical advection) and vertical shear of the radial wind (associated with angular momentum conservation) change with radius. With jets constrained to low altitudes, inner cells are more likely to increase low-level convergence and amplify convection, possibly influencing the formation of a secondary eyewall. In the downwind end of the rainband complex, collapsing convective cells formed a mesoscale stratiform rainband that contained rising radial outflow within the stratiform cloud layer. Below the cloud layer, descending radial inflow was driven by horizontal buoyancy gradients, and thus horizontal vorticity generation, introduced by regions of sublimational and melting cooling. This inflow advected higher angular momentum inward, which resulted in the development of a midlevel tangential jet and broadening of the tangential wind field. This circulation may have also contributed to ventilation of the eyewall as inflow of low-entropy air continued past the rainband in both the boundary layer and midlevels. The stationary rainband complex soon evolved into a secondary eyewall, consisting of a ring of heavy precipitation outside the pre-existing eyewall. Enhanced radial outflow was located just above the boundary layer which modified the deeper overturning circulation of the secondary eyewall. This outflow was associated with a low-level tangential wind maximum which was strongly supergradient, mimicking the low-level circulation of the primary eyewall. Axisymmetric and asymmetric processes contributed comparably to strengthening the secondary eyewall tangential wind maximum. The evolution of these inner-core features likely played an important role in modifying the structure and intensity of the total vortex.

Download or read book Secondary Eyewall Formation and Sheared Convection in Mature Hurricanes written by Wesley D. Terwey and published by . This book was released on 2007 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Potential Vorticity Component based Study of the Extratropical Transitions of Hurricanes Danielle and Earl 1998 written by R. McTaggart-Cowan and published by . This book was released on 2003 with total page 398 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Potential Vorticity Perspective on the Extratropical Transition of Tropical Cyclones written by Anna Agust©Ư-Panareda and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Extratropical transitions (ET) of tropical cyclones are common in all ocean basins where tropical cyclones recurve polewards. They can result in the development of large and deep extratropical cyclones. Two detailed case studies are presented: hurricane Irene and hurricane Lili which resulted in a reintensification with different deepening rates - two potential vorticity-based conceptual models have been devised from these results - abstract.

Download or read book Impacts of Asymmetric Dynamics on Tropical Cyclone Eyewall Replacement Cycles written by Tsz Kin Lai and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "In mature tropical cyclones (TCs), secondary eyewall formation (SEF) is a frequently observed feature associated with the formation of an outer (secondary) eyewall outside the existing (primary) eyewall. The two eyewalls are separated by a moat region of convective minimum and vorticity minimum. An SEF is often followed by an eyewall replacement cycle (ERC) during which the contracting outer eyewall gradually intensifies while the inner eyewall dissipates. Throughout this period, significant changes in the size and the intensity of the TC usually occur. Therefore, a better understanding of ERC is desired for better TC forecasts. Nevertheless, the mechanisms underlying inner eyewall decay (IED) and outer eyewall intensification (OEI) are not well-understood. It is widely accepted that the cutoff effect associated with the OE makes the main contribution to the IED. However, radar imagery of some double-eyewall TCs showed that the TC vortices became elliptic prior to and during the IED. This kind of elliptic development could result from the dynamic (barotropic) instability across the moat, which is a region of sign reverse of vorticity gradient and satisfies the Rayleigh necessary condition for barotropic instability. Hence, the instability across the moat (known as the type-2 instability) may also make contributions to IED. As the first part of the thesis (Chapter 2), a study of the simulated Hurricane Wilma (2005) is conducted by using a three-dimensional (3D) cloud-resolving full-physics numerical model. It is found that the timing of the onset of the type-2 instability is coincident with the start of the rapid decrease of the low-level IE circulation, indicating that the circulation of the IE is likely weakened by the vorticity mixing associated with the type-2 instability. In the second part of the thesis (Chapter 3), two 3D numerical experiments are performed to further explore the underlying dynamics. The detailed budget analyses of azimuthally averaged absolute angular momentum (AAM) in the moist full-physics experiment clearly show that the eddy radial flux of vorticity associated with the type-2 instability makes significant contributions to the decrease in AAM of the IE and the increase in AAM of the OE. It is also found that the type-2 instability can work with the cutoff effect to accelerate the IED process. Similar patterns of the AAM budget analyses are also obtained from the dry experiment in which all physics parameterisation schemes are switched off. It is thus suggested that the type-2 instability is a fundamental process responsible for the IED and OEI in these two experiments. In the third part of the thesis (Chapter 4), unforced shallow water (SW) experiments further reveal that the intensity changes in the eyewalls through the eddy radial flux of vorticity are intrinsic nonlinear features of the type-2 instability. In addition, a detailed analysis of the most unstable eigenmode of a double-eyewall TC-like vortex shows evidence of substantial divergence of angular momentum flux over the IE and significant convergence of angular momentum flux over the OE. This further demonstrates that the origin of the intensity changes of the eyewalls is the angular momentum transport from the IE to the OE by the eddy processes associated with the type-2 instability. The last part of the thesis (Chapter 5) discusses the long-term effect of the type-2 instability on the eyewall intensity changes during ERCs. A series of forced and unforced SW experiments, which are initialised with different parameters of the vortex and convective heating, show repeated cycles of decay-intensification after the type-2 instability has been excited for a longer time. It is found that the oscillation results from the periodic elongation and contraction of the vortices associated with the long-term nonlinear evolution of the type-2 instability. These results suggest that predicting the eyewall intensity changes during ERCs may be a challenge"--

Download or read book A Numerical and Observational Study of the Genesis of Concentric Eyewall Hurricanes written by Shangyao Nong and published by . This book was released on 1999 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Introduction to Boundary Layer Meteorology written by Roland B. Stull and published by Springer Science & Business Media. This book was released on 1988-07-31 with total page 688 pages. Available in PDF, EPUB and Kindle. Book excerpt: Part of the excitement in boundary-layer meteorology is the challenge associated with turbulent flow - one of the unsolved problems in classical physics. An additional attraction of the filed is the rich diversity of topics and research methods that are collected under the umbrella-term of boundary-layer meteorology. The flavor of the challenges and the excitement associated with the study of the atmospheric boundary layer are captured in this textbook. Fundamental concepts and mathematics are presented prior to their use, physical interpretations of the terms in equations are given, sample data are shown, examples are solved, and exercises are included. The work should also be considered as a major reference and as a review of the literature, since it includes tables of parameterizatlons, procedures, filed experiments, useful constants, and graphs of various phenomena under a variety of conditions. It is assumed that the work will be used at the beginning graduate level for students with an undergraduate background in meteorology, but the author envisions, and has catered for, a heterogeneity in the background and experience of his readers.

Download or read book Dynamics and Predictability of Large Scale High Impact Weather and Climate Events written by Jianping Li and published by Cambridge University Press. This book was released on 2016-03-24 with total page 371 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book examines the dynamical processes between high-impact weather and climate events, and between atmospheric and ocean phenomena.

Download or read book Intense Atmospheric Vortices written by L. Bengtsson and published by Springer. This book was released on 1982-08 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: The concept of vorticity is of central importance in fluid mechanics and the change and variability of atmospheric flow is dominated by transient vortices of different time­ and space scales. Of particular importance are the most in­ tense vortices such as hurricanes, typhoons and tornadoes which are associated with extreme and hazardous weather events of great concern to society. In recent years the un­ derstanding of these phenomena has grown due to increased and improved surveillance by satellites and aircraft as well as by numerical modelling and simulation, theoretical studies and laboratory experiments. The symposium on "Intense Atmospheric Vortices" was held at the European Centre for Medium Range Weather Forecasts (ECMWF), Reading, England, July 14-17, 1981. The subject area of the Symposium was concerned with observational work, experimental models, theoretical and numerical studies in­ volving hurricanes, typhoons, tornadoes and related pheno­ mena. The aim was to bring together experts on these meteo­ rological processes and on the fundamental fluid-dynamic mechanisms for vorticity intensification from all parts of the world. Thirtyfour scientists participated in the Sympo­ sium, including more than half of those leading world ex­ perts in the field whom the organizers had invited.

Download or read book Diagnostic Study of Hurricane Asymmetries Using Empirical Normal Modes written by Yosvany H. Martinez and published by . This book was released on 2008 with total page 165 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book On the Origin of Asymmetric Dynamical Processes and Their Relation to the Structure and Intensity Change of Hurricanes a Diagnostic Study written by Konstantinos Menelaou and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "To a first approximation hurricanes can be considered as axisymmetric vor- tices. However, asymmetries often accompany the symmetric circulation. Spiral rainbands, elliptical eyewalls, polygonal eyewalls, secondary eyewalls, mesovortices, and deep rotating convective clouds are examples of such asym- metric structures. The contribution of these asymmetries to the intensity and structural changes of hurricanes are not well understood.In this thesis, a suite of numerical models (both two dimensional [2D] and three dimensional [3D]) along with a series of diagnostic tools (Empirical Normal Mode [ENM] method, linear eigenmode analysis, wave activities con- servations laws, Eliassen-Palm [EP] flux calculations, and eddy kinetic energy budget calculations), are used to study the underlying dynamics associated with: the lifetime of elliptical eyewalls (Chapter 2), the genesis of secondary eyewalls (Chapter 2,3), the origin of polygonal eyewalls and mesovortices and their contribution to the rapid intensification process (Chapter 4), and finally the role of asymmetric convective bursts to the intensification of developing hurricanes (Chapter 5). In Chapter 2, it is shown that the evolution and the lifetime of a 2D el- liptical eyewall may be controlled by the inviscid damping of sheared vortex Rossby waves (VRWs) or the decay of an excited quasimode. In the context of 2D vortex flows, it is also shown that secondary rings of enhanced vorticity (secondary eyewalls) can form by the radiation of VRWs that result from the release of barotropic instability, and the process of wave-mean flow in- teractions. In Chapter 3, the importance of VRWs to the secondary eyewall genesis is verified in a successful numerical simulation of hurricane Wilma (2005) that developed a secondary eyewall. In Chapter 4, an analysis of the simulated Wilma during the rapid intensification stage is performed to show that the observed polygonal eyewall in Wilma is the result of counterpropa- gating unstable VRWs. The analysis also indicates that the polygonal eyewall and mesovortices can assist in the rapid intensification process. Finally, in Chapter 5 it is shown that the response of a weak vortex to asymmetric con- vective bursts is dominated by the excitation of damped sheared VRWs that act to accelerate the symmetric flow through the radial transport of angular momentum." --

Download or read book Impact of Numerical Grid Spacing and Time Step Size on Vortex Rossby Waves in Secondary Eyewall Formation in a Simulation of Hurricane Wilma 2005 written by Jonathan Gadoury and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "To understand the impact of numerical grid spacing and time step size on vortex Rossby waves in hurricanes going through an eyewall replacement cycle, multiple simulations with identical parameterization but with different numerics were carried out using the WRF model on hurricane Wilma (2005). The method of Empirical Normal Modes was then applied on the dataset in order to find radially outward propagating vortex Rossby waves (VRWs). It was found that for varying grid lengths, using high resolution can resolve these VRWs while a mixture of gravity and vortex Rossby waves was propagating from the eyewall using coarse resolution. An examination of the divergence of the Eliassen-Palm flux showed that high resolution is required to form a secondary eyewall. In terms of varying the time step size, differences were noted in the eyewall replacement cycles as well as the final shape of the eyewall, implying that non-converging numerical errors can impact strongly the vortex Rossby waves and therefore the dynamics of the hurricane." --

Download or read book Encyclopedia of Atmospheric Sciences written by Gerald R. North and published by Elsevier. This book was released on 2014-09-14 with total page 2874 pages. Available in PDF, EPUB and Kindle. Book excerpt: Encyclopedia of Atmospheric Sciences, Second Edition, Six Volume Set is an authoritative resource covering all aspects of atmospheric sciences, including both theory and applications. With more than 320 articles and 1,600 figures and photographs, this revised version of the award-winning first edition offers comprehensive coverage of this important field. The six volumes in this set contain broad-ranging articles on topics such as atmospheric chemistry, biogeochemical cycles, boundary layers, clouds, general circulation, global change, mesoscale meteorology, ozone, radar, satellite remote sensing, and weather prediction. The Encyclopedia is an ideal resource for academia, government, and industry in the fields of atmospheric, ocean, and environmental sciences. It is written at a level that allows undergraduate students to understand the material, while providing active researchers with the latest information in the field. Covers all aspects of atmospheric sciences—including both theory and applications Presents more than 320 articles and more than 1,600 figures and photographs Broad-ranging articles include topics such as atmospheric chemistry, biogeochemical cycles, boundary layers, clouds, general circulation, global change, mesoscale meteorology, ozone, radar, satellite remote sensing, and weather prediction An ideal resource for academia, government, and industry in the fields of atmospheric, ocean, and environmental sciences

Download or read book Cloud Dynamics written by Robert A. Houze Jr. and published by Elsevier. This book was released on 1994-06-28 with total page 605 pages. Available in PDF, EPUB and Kindle. Book excerpt: Clouds play a critical role in the Earth's climate, general atmospheric circulation, and global water balance. Clouds are essential elements in mesoscale meteorology, atmospheric chemistry, air pollution, atmosphericradiation, and weather forecasting, and thus must be understood by any student or researcher in the atmospheric sciences. Cloud Dynamics provides a skillful and comprehensive examination of the nature of clouds--what they look like and why, how scientists observe them, and the basic dynamics and physics that underlie them. The book describes the mechanics governing each type of cloud that occurs in Earth's atmosphere, and the organization of various types of clouds in larger weather systems such as fronts, thunderstorms, and hurricanes.This book is aimed specifically at graduate students, advanced undergraduates, practicing researchers either already in atmospheric science or moving in from a related scientific field, and operational meteorologists. Some prior knowledge of atmospheric dynamics and physics is helpful, but a thorough overview of the necessary prerequisites is supplied. Provides a complete treatment of clouds integrating the analysis of air motions with cloud structure, microphysics, and precipitation mechanics Describes and explains the basic types of clouds and cloud systems that occur in the atmosphere-fog, stratus, stratocumulus, altocumulus, altostratus, cirrus, thunderstorms, tornadoes, waterspouts, orographically induced clouds, mesoscale convection complexes, hurricanes, fronts, and extratropical cyclones Presents a photographic guide, presented in the first chapter, linking the examination of each type of cloud with an image to enhance visual retention and understanding Summarizes the fundamentals, both observational and theoretical, of atmospheric dynamics, thermodynamics, cloud microphysics, and radar meteorology, allowing each type of cloud to be examined in depth Integrates the latest field observations, numerical model simulations, and theory Supplies a theoretical treatment suitable for the advanced undergraduate or graduate level