Download or read book Turbulent Characteristics in the Hurricane Boundary Layer written by Sunwei Li and published by . This book was released on 2012 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the medium between the sea surface and the upper atmosphere in a hurricane, the Hurricane Boundary Layer (HBL) plays a key role in the overall dynamics of a tropical cyclone, and therefore turbulence exchanges within the HBL deserve a thorough investigation. However, since it is dangerous and difficult to take direct measurements within the HBL, studies of the HBL turbulence processes based on direct observations are rare. Thanks to the newly developed dropwindsonde equipped with a Global Position System (GPS) receiver, it is now possible to measure wind velocities and other meteorological variables with an unprecedented accuracy and resolution in the HBL. To fully utilize dropwindsonde measurements, it is necessary to thoroughly understand its motion characteristics in the measured wind field since its horizontal motions are usually reported as wind measurements. For that reason, the dropwindsonde motion in a pseudo-stochastic wind field with known statistics is simulated. The simulation results illustrate the importance of the wind finding equations introduced by Hock and Franklin (1999) which calculate local winds from dropwindsonde motions. The simulation results show that they are important in reproducing both mean and turbulent wind structures in the HBL. One of its basic assumptions that the dropwindsonde drag coefficient is a constant regardless of the angle of attack is, however, invalidated by the wind tunnel tests conducted in this study. Given that this assumption is essential in both deriving the wind finding equations and in conducting the numerical dropwindsonde motion simulation described above, it is necessary to adapt the dropwindsonde motion model and to repeat the motion simulation to recheck the validity of the wind finding equations demonstrated in the previous simulation. The results validates the wind finding equations although it is derived based on a false assumption that the dropwindsonde drag coefficient is a constant regardless of angles of attack. Moreover, through analyzing the adapted dropwindsonde motion model, a new approach to estimate the vertical wind is proposed which is shown to increase the accuracy in vertical wind estimation by nearly 70%. Based on the findings derived in the dropwindsonde motion simulations, an in-house software package is designed to process the actual dropwindsonde measurements gathered from 1997 to 2010. The in-house software package, showing an effectiveness equivalent to other widely used processing systems, gives users more control over the processing and compositing procedures used to derive the desired statistics of the measured wind field. With the help of this software package, dropwindsonde measurements are processed and composited to produce the mean, turbulence intensity, and turbulent length scale profiles of the HBL. While the mean wind structure confirms the findings made by several previous studies, the turbulence structure reveals that the turbulence diffusivity formulation currently used by the Yonsei University planetary boundary layer scheme, or the YSU scheme, in Weather Research and Forecasting Model(WRF), a widely used hurricane wind simulation package, correctly simulate turbulent mixing in the HBL up to 200m from the sea surface. In a theoretical discussion of the validity of the YSU scheme, it is found that both the velocity scale and height scale used in its turbulence diffusivity formulation should be revised to take into consideration the special turbulence characteristics in the HBL. For the purpose of checking the turbulence diffusivity formulation used in the YSU scheme, high resolution numerical simulations of an idealized tropical cyclone are conducted using WRF. The simulation results show that only revising the HBL height calculation is not adequate to improve the numerical simulation of hurricanes. Therefore, a deeper investigation of the YSU scheme in simulating the HBL turbulence is required.

Download or read book A Study on the Turbulent Characteristics Within the Hurricane Boundary Layer written by Sunwei Li and published by . This book was released on 2012 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the medium between the sea surface and the upper atmosphere in a hurricane, the Hurricane Boundary Layer (HBL) plays a key role in the overall dynamics of a tropical cyclone, and therefore turbulence exchanges within the HBL deserve a thorough investigation. However, since it is dangerous and difficult to take direct measurements within the HBL, studies of the HBL turbulence processes based on direct observations are rare. Thanks to the newly developed dropwindsonde equipped with a Global Position System (GPS) receiver, it is now possible to measure wind velocities and other meteorological variables with an unprecedented accuracy and resolution in the HBL. To fully utilize dropwindsonde measurements, it is necessary to thoroughly understand its motion characteristics in the measured wind field since its horizontal motions are usually reported as wind measurements. For that reason, the dropwindsonde motion in a pseudo-stochastic wind field with known statistics is simulated. The simulation results illustrate the importance of the wind finding equations introduced by Hock and Franklin (1999) which calculate local winds from dropwindsonde motions. The simulation results show that they are important in reproducing both mean and turbulent wind structures in the HBL. One of its basic assumptions that the dropwindsonde drag coefficient is a constant regardless of the angle of attack is, however, invalidated by the wind tunnel tests conducted in this study. Given that this assumption is essential in both deriving the wind finding equations and in conducting the numerical dropwindsonde motion simulation described above, it is necessary to adapt the dropwindsonde motion model and to repeat the motion simulation to recheck the validity of the wind finding equations demonstrated in the previous simulation. The results validates the wind finding equations although it is derived based on a false assumption that the dropwindsonde drag coefficient is a constant regardless of angles of attack. Moreover, through analyzing the adapted dropwindsonde motion model, a new approach to estimate the vertical wind is proposed which is shown to increase the accuracy in vertical wind estimation by nearly 70%. Based on the findings derived in the dropwindsonde motion simulations, an in-house software package is designed to process the actual dropwindsonde measurements gathered from 1997 to 2010. The in-house software package, showing an effectiveness equivalent to other widely used processing systems, gives users more control over the processing and compositing procedures used to derive the desired statistics of the measured wind field. With the help of this software package, dropwindsonde measurements are processed and composited to produce the mean, turbulence intensity, and turbulent length scale profiles of the HBL. While the mean wind structure confirms the findings made by several previous studies, the turbulence structure reveals that the turbulence diffusivity formulation currently used by the Yonsei University planetary boundary layer scheme, or the YSU scheme, in Weather Research and Forecasting Model(WRF), a widely used hurricane wind simulation package, correctly simulate turbulent mixing in the HBL up to 200m from the sea surface. In a theoretical discussion of the validity of the YSU scheme, it is found that both the velocity scale and height scale used in its turbulence diffusivity formulation should be revised to take into consideration the special turbulence characteristics in the HBL. For the purpose of checking the turbulence diffusivity formulation used in the YSU scheme, high resolution numerical simulations of an idealized tropical cyclone are conducted using WRF. The simulation results show that only revising the HBL height calculation is not adequate to improve the numerical simulation of hurricanes. Therefore, a deeper investigation of the YSU scheme in simulating the HBL turbulence is required.

Download or read book Turbulence Structure of the Hurricane Boundary Layer Between the Outer Rainbands written by and published by . This book was released on 2009 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt: As part of the Coupled Boundary Layers Air-Sea Transfer (CBLAST)-Hurricane program, flights were conducted to directly measure turbulent fluxes and turbulence properties in the high-wind boundary layer of hurricanes between the outer rainbands. For the first time, vertical profiles of normalized momentum fluxes, sensible heat and humidity fluxes, and variances of three-dimensional wind velocities and specific humidity are presented for the hurricane boundary layer with surface wind speeds ranging from 20 to 30 m/s. The turbulent kinetic energy budget is estimated, indicating that the shear production and dissipation are the major source and sink terms, respectively. The imbalance in the turbulent kinetic energy budget indicates that the unmeasured terms, such as horizontal advection, may be important in hurricane boundary layer structure and dynamics. Finally, the thermodynamic boundary layer height, estimated based on the virtual potential temperature profiles, is roughly half of the boundary layer height estimated from the momentum flux profiles. The latter height where momentum and humidity fluxes tend to vanish is close to that of the inflow layer and also of the maximum in the tangential velocity profiles.

Download or read book Turbulent Characteristics in the Surface Boundary Layer written by Manuel Armendariz and published by . This book was released on 1968 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: The turbulent characteristics of the first 62 meters of the atmosphere over White Sands Missile Range, New Mexico, have been intensively studied using data collected from an instrumented tower. It is demonstrated that important turbulence characteristics such as standard deviation of wind direction, longitudinal intensity of turbulence, and the ratio of the lateral intensity of turbulence to longitudinal intensity of turbulence are dependent upon the height of the wind measurement, the surface roughness, and the stability of the atmosphere. In particular, it is shown that the lateral intensity of turbulence is affected more by stability changes than by roughness or height of the measurement. The longitudinal intensity of turbulence, however, is affected by roughness and height of measurement as well as by the stability of the atmosphere.

Download or read book Turbulence Characteristics in the Stable Atmospheric Boundary Layer written by Yinguo Cheng and published by . This book was released on 2004 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characteristics of Turbulence Within an Internal Boundary Layer written by R. A. Antonia and published by . This book was released on 1973 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Low layer Features to Two Limited area Hurricane Regimes written by Michael S. Moss and published by . This book was released on 1977 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: Extrapolation of the data to the surface yields a stress that agrees very well with that calculated from a diagnostic application of the Deardorff parameterization scheme. The virtual heat flux profile, determined entirely from conventional measurements, is fairly consistent with that observed in the fair weather trade wind regime. From near-surface extrapolated momentum and virtual heat fluxes, a Monin-Obukov length is computed to indicate that the low-layer turbulence is principally shear-induced. This indication is substantiated by the budget of turbulence kinetic energy, which shows an overall predominance of shear over buoyancy production. In the lowest levels there is an approximate balance among shear production, convergence of the vertical transport, and viscous dissipation of the turbulence kinetic energy. At the upper mixed-layer levels, all of the calculable production terms are negligible in comparison with destruction through dissipation.

Download or read book Characteristics of Turbulence in the Atmospheric Boundary Layer written by Sture Wickerts and published by . This book was released on 1978 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book On the Estimation from Bulk Data of Boundary Layer Variables and Cloud Base Mass Flux in Mature Hurricanes written by Michael S. Moss and published by . This book was released on 1975 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characteristics of Winds and Turbulence in the Planetary Boundary Layer written by Steven R. Hanna and published by . This book was released on 1969 with total page 61 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Characteristics of Boundary Layer Turbulence in Developing Annular Flows written by A. B. Thornton-Trump and published by . This book was released on 1972 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Observed Characteristics of Turbulence in the Atmospheric Boundary Layer Over Mountainous Terrain written by David C. Hahn and published by . This book was released on 1980 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Study of Turbulent Boundary Layer Structure written by John Leask Lumley and published by . This book was released on 1986 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Statistical characteristics of turbulence and the budget of turbulent energy in the surface boundary layer written by Kenji Kai and published by . This book was released on 1982 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Investigation of turbulent boundary layer characteristics with particular reference to the effects of heat transfer and pressure gradient written by H. D. Harris and published by . This book was released on 1970 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Investigation of Turbulent Boundary Layer Characteristics with Particular Reference to the Effects of Heat Transfer and Pressure Gradient written by Harry David Harris and published by . This book was released on 1970 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced Numerical Modeling and Data Assimilation Techniques for Tropical Cyclone Predictions written by U.C. Mohanty and published by Springer. This book was released on 2016-11-21 with total page 762 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book deals primarily with monitoring, prediction and understanding of Tropical Cyclones (TCs). It was envisioned to serve as a teaching and reference resource at universities and academic institutions for researchers and post-graduate students. It has been designed to provide a broad outlook on recent advances in observations, assimilation and modeling of TCs with detailed and advanced information on genesis, intensification, movement and storm surge prediction. Specifically, it focuses on (i) state-of-the-art observations for advancing TC research, (ii) advances in numerical weather prediction for TCs, (iii) advanced assimilation and vortex initialization techniques, (iv) ocean coupling, (v) current capabilities to predict TCs, and (vi) advanced research in physical and dynamical processes in TCs. The chapters in the book are authored by leading international experts from academic, research and operational environments. The book is also expected to stimulate critical thinking for cyclone forecasters and researchers, managers, policy makers, and graduate and post-graduate students to carry out future research in the field of TCs.