scholarly journals How Does Cyclogenesis Commence Given a Favorable Tropical Environment?

2021 ◽  
Vol 8 (1) ◽  
pp. 20
Author(s):  
Galina Levina
Keyword(s):  
Mirror Symmetry ◽  
Large Scale ◽  
Extreme Event ◽  
Three Dimensional ◽  
Tropical Environment ◽  
Tropical Cyclogenesis ◽  
Near Surface ◽  
Helical Turbulence ◽  
Vortical Hot Towers ◽  
Operational Diagnosis

In a series of collaborative Russian–American works (Levina and Montgomery, 2009–2015), we applied the fundamental ideas of self-organization in turbulence with broken mirror symmetry, the so-called “helical” turbulence. In this context, tropical cyclogenesis is considered as a threshold extreme event in the three-dimensional helical moist convective atmospheric turbulence of a vorticity-rich environment of a pre-depression zone. This allowed us to discover a large-scale vortex instability and answer the question “When will cyclogenesis commence given a favorable tropical environment?”. The new instability emerges against the background of seemingly disorganized convection, without a well-defined center of near-surface circulation and noticeably precedes the formation of a tropical depression. This can give the fundamental ground and quantitative substantiation for the term “Potential Tropical Cyclone” as a beginning of TC genesis. In the present work, we explore in detail the crucial role of special convective coherent structures of cloud scales—vortical hot towers (VHTs)—in the formation and maintenance of the secondary circulation and, therefore, of the whole mesoscale vortex system. On this basis, we propose how the onset of large-scale instability, i.e., the beginning of TC genesis, can be diagnosed exactly and distantly with VHTs patterns in the field of temperature (satellite data) and vertical helicity (cloud-resolving numerical analysis). The present research is intended to contribute to a recently initiated development of operational diagnosis of the beginning of TC genesis based on GOES Imagery and supported by cloud-resolving numerical modeling.

Diagnosis of Pre-Depression Large-Scale Vortex Instability in the Tropical Atmosphere

2021 ◽  
Author(s):  
Galina Levina
Keyword(s):  
Mirror Symmetry ◽  
Large Scale ◽  
Tropical Cyclogenesis ◽  
Theoretical Ground ◽  
Tropical Atmosphere ◽  
Vortex Instability ◽  
Turbulent Vortex ◽  
Convective Clouds ◽  
Vortical Hot Towers ◽  
Large Scale Vortex

<p>An approach is proposed [1] for determining the precise time of the start of tropical cyclogenesis, which includes a combined analysis of data from cloud-resolving numerical modeling and GOES Imagery. The approach is based on the similarity of patterns in the fields of vertical helicity (numerical simulation) and temperature (satellite data), allowing for the localization of intense rotating convective clouds known as the Vortical Hot Towers. As a theoretical ground, we applied a hypothesized (to date) interpretation of tropical cyclogenesis as a large-scale instability caused by the mechanism of the turbulent vortex dynamo in the atmosphere [1,2], and with bearing in mind the crucial role of Vortical Hot Towers in providing the dynamo-effect [2]. In this context, birth of a hurricane is considered as an extreme threshold event in the helical atmospheric turbulence of a vorticity-rich environment of a pre-depression cyclonic recirculation zone. Helical turbulence is characterized by the broken mirror symmetry and permits an existence of inverse energy cascade in three-dimensional cases. In order to trace and analyze processes of self-organization in the tropical atmosphere, that span scales from convective clouds with horizontal dimensions of 1-5 km to mesoscale vortices of hundreds of kilometers, we used the post-processing [1-3] of data from cloud-resolving numerical simulations [4].  Implementation of the proposed approach revealed that large-scale vortex instability can begin a few hours, or even dozens of hours, before the formation of the Tropical Depression. This work was supported by the research project “Monitoring” No. 01200200164.</p><p>References</p><p>[1] Levina, G. V., 2020. Birth of a hurricane: early detection of large-scale vortex instability. J. Phys.: Conf. Ser., <strong>1640  </strong>012023,  doi:10.1088/1742-6596/1640/1/012023</p><p>[2] Levina, G. V., 2018. On the path from the turbulent vortex dynamo theory to diagnosis of tropical cyclogenesis. Open J. Fluid Dyn., <strong>8,</strong> 86–114,  https:<strong>//</strong>doi.org/10.4236/ojfd.2018.81008</p><p>[3] Levina, G. V. and M. T. Montgomery, 2015. When will Cyclogenesis Commence Given a Favorable Tropical Environment?  Procedia IUTAM, <strong>17</strong><strong>,</strong> 59–68, https://doi.org/10.1016/j.piutam.2015.06.010</p><p>[4] Montgomery, M. T., M. E.  Nicholls, T. A. Cram, and A. B. Saunders, 2006: A vortical hot tower route to tropical cyclogenesis. J. Atmos. Sci., 63, 355–386,  https://doi.org/10.1175/JAS3604.1</p>

scholarly journals A Spatial Filter Approach to Evaluating the Role of Convection on the Evolution of a Mesoscale Vortex

2013 ◽  
Vol 70 (7) ◽  
pp. 1954-1976 ◽  
Author(s):  
Glenn A. Creighton ◽  
Robert E. Hart ◽  
Philip Cunningham
Keyword(s):  
Three Dimensional ◽  
Spatial Separation ◽  
Spatial Filter ◽  
Tropical Cyclogenesis ◽  
Moist Convection ◽  
Mesoscale Vortex ◽  
Convective Scale ◽  
Vortical Hot Towers ◽  
Order Of Magnitude ◽  
Deep Moist Convection

Abstract A new spatial filter is proposed that exploits a spectral gap in power between the convective scale and the system (“vortex”) scale during tropical cyclone (TC) genesis simulations. Using this spatial separation, this study analyzes idealized three-dimensional numerical simulations of deep moist convection in the presence of a symmetric midlevel vortex to quantify and understand the energy cascade between the objectively defined convective scale and system scale during the early stages of tropical cyclogenesis. The simulations neglect surface momentum, heat, and moisture fluxes to focus on generation and enhancement of vorticity within the interior to more completely close off the energy budget and to be consistent for comparison with prior benchmark studies of modeled TC genesis. The primary contribution to system-scale intensification comes from the convergence of convective-scale vorticity that is supplied by vortical hot towers (VHTs). They contribute more than the convergence of system-scale vorticity to the spinup of vorticity in these simulations by an order of magnitude. Analysis of the change of circulation with time shows an initial strengthening of the surface vortex, closely followed by a growth of the mid- to upper-level circulation. This evolution precludes any possibility of a stratiform precipitation–induced top-down mechanism as the primary contributor to system-scale spinup in this simulation. Instead, an upscale cascade of rotational kinetic energy during vortex mergers is responsible for spinup of the simulated mesoscale vortex. The spatial filter employed herein offers an alternative approach to the traditional symmetry–asymmetry paradigm, acknowledges the highly asymmetric evolution of the system-scale vortex itself, and may prove useful to future studies on TC genesis.

Analytic investigations of the effects of near‐surface three‐dimensional galvanic scatterers on MT tensor decompositions

Geophysics ◽  
1991 ◽  
Vol 56 (4) ◽  
pp. 496-518 ◽  
Author(s):  
R. W. Groom ◽  
R. C. Bailey
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Magnetic Scattering ◽  
Impedance Tensor ◽  
Data Set ◽  
Near Surface ◽  
Eigenvalue Estimates ◽  
Polarization Azimuth ◽  
Local Current ◽  
Scattering Operators

An outcropping hemispherical inhomogeneity embedded in a two‐dimensional (2-D) earth is used to model the effects of three‐dimensional (3-D) near‐surface electromagnetic (EM) “static” distortion. Analytical solutions are first derived for the galvanic electric and magnetic scattering operators of the heterogeneity. To represent the local distortion by 3-D structures of fields which were produced by a large‐scale 2-D structure, these 3-D scattering operators are applied to 2-D electric and magnetic fields derived by numerical modeling to synthesize an MT data set. Synthetic noise is also included in the data. These synthetic data are used to study the parameters recovered by several published methods for decomposing or parameterizing the measured MT impedance tensor. The stability of these parameters in the presence of noise is also examined. The parameterizations studied include the conventional 2-D parameterization (Swift, 1967), Eggers’s (1982) and Spitz’s (1985) eigenstate formulations, LaTorraca et al.’s (1986) SVD decomposition, and the Groom and Bailey (1989) method designed specifically for 3-D galvanic electric scattering. The relationships between the impedance or eigenvalue estimates of each method and the true regional impedances are examined, as are the azimuthal (e.g., regional 2-D strike, eigenvector orientation and local strike) and ellipticity parameters. The 3-D structure causes the conventional 2-D estimates of impedances to be site‐dependent mixtures of the regional impedance responses, with the strike estimate being strongly determined by the orientation of the local current. For strong 3-D electric scattering, the local current polarization azimuth is mainly determined by the local 3-D scattering rather than the regional currents. There are strong similarities among the 2-D rotation estimates of impedance and the eigenvalue estimates of impedance both by Eggers’s and Spitz’s first parameterization as well as the characteristic values of LaTorraca et al. There are striking similarities among the conventional estimate of strike, the orientations given by the Eggers’s, Spitz’s (Q), and LaTorraca et al.’s decompositions, as well as the estimate of local current polarization azimuth given by Groom and Bailey. It was found that one of the ellipticities of Eggers, LaTorraca et al., and Spitz is identically zero for all sites and all periods, indicating that one eigenvalue or characteristic value is linearly polarized. There is strong evidence that this eigenvalue is related to the local current. For these three methods, the other ellipticity differs from zero only when there are significant differences in the phases of the regional 2-D impedances (i.e., strong 2-D inductive effects), implying the second ellipticity indicates a multidimensional inductive response. Spitz’s second parameterization (U), and the Groom and Bailey decomposition, were able to recover information regarding the actual regional 2-D strike and the separate character of the 2-D regional impedances. Unconstrained, both methods can suffer from noise in their ability to resolve structural information especially when the current distortion causes the impedance tensor to be approximately singular. The method of Groom and Bailey, designed specifically for quantifying the fit of the measured tensors to the physics of the parameterization, constraining a model, and resolving parameters, can recover much of the information in the two regional impedances and some information about the local structure.

scholarly journals Influence of Boundary Layer Structure and Low-Level Jet on PM2.5 Pollution in Beijing: A Case Study

2019 ◽  
Vol 16 (4) ◽  
pp. 616 ◽  
Author(s):  
Yucong Miao ◽  
Shuhua Liu ◽  
Li Sheng ◽  
Shunxiang Huang ◽  
Jian Li
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Layer Structure ◽  
Three Dimensional ◽  
Near Surface ◽  
Thermally Induced ◽  
Low Level ◽  
Relative Contribution ◽  
Low Level Jet ◽  
Meteorological Observations

Beijing experiences frequent PM2.5 pollution, which is influenced by the planetary boundary layer (PBL) structure/process. Partly due to a lack of appropriate observations, the impacts of PBL on PM2.5 pollution are not yet fully understood. Combining wind-profiler data, radiosonde measurements, near-surface meteorological observations, aerosol measurements, and three-dimensional simulations, this study investigated the influence of PBL structure and the low-level jet (LLJ) on the pollution in Beijing from 19 to 20 September 2015. The evolution of the LLJ was generally well simulated by the model, although the wind speed within the PBL was overestimated. Being influenced by the large-scale southerly prevailing winds, the aerosols emitted from the southern polluted regions could be easily transported to Beijing, contributing to ~68% of the PM2.5 measured in Beijing on 20 September. The relative contribution of external transport of PM2.5 to Beijing was high in the afternoon (≥80%), which was related to the strong southerly PBL winds and the presence of thermally-induced upslope winds. On 20 September, the LLJ in Beijing demonstrated a prominent diurnal variation, which was predominant in the morning and after sunset. The occurrence of the LLJ could enhance the dilution capacity in Beijing to some extent, which favors the dilution of pollutants at a local scale. This study has important implications for better understanding the complexity of PBL structure/process associated with PM2.5 pollution in Beijing.

scholarly journals Seismic and gravity constraints on the crustal architecture of the Intermontane terranes, central Yukon

2017 ◽  
Vol 54 (7) ◽  
pp. 798-811 ◽  
Author(s):  
Andrew J. Calvert ◽  
Nathan Hayward ◽  
Rajesh Vayavur ◽  
Maurice Colpron
Keyword(s):  
Large Scale ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Three Dimensional ◽  
Flower Structure ◽  
Alluvial Deposits ◽  
Near Surface ◽  
Clastic Rocks ◽  
Reflection Data ◽  
First Arrival

In 2004, two seismic reflection lines were shot across the Mesozoic Whitehorse trough and adjacent terranes. Three-dimensional first-arrival tomographic inversion is used to constrain lithology to 800–1200 m depth, and surface structures are extrapolated into the middle crust using the coincident reflection data. In the Yukon–Tanana terrane, the metasedimentary Snowcap assemblage is characterized by velocities of 4.5–5.5 km/s, while in Quesnellia, velocities of 5.0–6.0 km/s occur at 500 m depth, and probably represent igneous rocks of the Tatchun batholith. Across the Whitehorse trough, velocities >4.0 km/s correspond to clastic rocks of the Jurassic Laberge and Triassic Lewes River groups; velocities <4.0 km/s probably present the clastic Jurassic to Cretaceous Tantalus Formation. Several near-surface units with velocities of 2.0–3.0 km/s are identified; some correlate well with volcanic rocks of the Upper Cretaceous Carmacks Group, but others could be attributable to alluvial deposits or faulting. The Big Salmon fault is interpreted to dip southwest, implying that rocks of the Yukon–Tanana terrane extend beneath Quesnellia. Stikinia and Quesnellia underlie up to 5–8 km of Triassic to Early Cretaceous sedimentary strata, and appear to be a single allochthon within an 18–20 km deep synform above the Yukon–Tanana terrane, which we name the Northern Intermontane synform. In general, reflection geometries in the upper crust are complex, but are consistent with large-scale imbricate structures that have been dissected into numerous blocks by displacement along moderately to steeply dipping strike-slip faults, which may be part of a crustal-scale flower structure extending to the base of the crust.

scholarly journals The interplay between helicity and rotation in turbulence: implications for scaling laws and small-scale dynamics

2010 ◽  
Vol 368 (1916) ◽  
pp. 1635-1662 ◽  
Author(s):  
A. Pouquet ◽  
P. D. Mininni
Keyword(s):  
Turbulent Flows ◽  
Mirror Symmetry ◽  
Scaling Laws ◽  
Three Dimensional ◽  
Wide Distribution ◽  
Turbulence Theory ◽  
Small Scale ◽  
Helical Turbulence ◽  
Weak Turbulence Theory ◽  
Astrophysical Flows

Invariance properties of physical systems govern their behaviour: energy conservation in turbulence drives a wide distribution of energy among modes, as observed in geophysical or astrophysical flows. In ideal hydrodynamics, the role of the invariance of helicity (correlation between velocity and its curl, measuring departures from mirror symmetry) remains unclear since it does not alter the energy spectrum. However, in the presence of rotation, significant differences emerge between helical and non-helical turbulent flows. We first briefly outline some of the issues such as the partition of energy and helicity among modes. Using massive numerical simulations, we then show that small-scale structures and their intermittency properties differ according to whether helicity is present or not, in particular with respect to the emergence of Beltrami core vortices that are laminar helical vertical updraft vortices. These results point to the discovery of a small parameter besides the Rossby number, a fact that would relate the problem of rotating helical turbulence to that of critical phenomena, through the renormalization group and weak-turbulence theory. This parameter can be associated with the adimensionalized ratio of the energy to helicity flux to small scales, the three-dimensional energy cascade being weak and self-similar.

Using NOGAPS Singular Vectors to Diagnose Large-scale Influences on Tropical Cyclogenesis

2011 ◽  
Author(s):  
Sharanya J. Majumdar ◽  
Melinda S. Peng ◽  
Carolyn A. Reynolds ◽  
James D. Doyle ◽  
Chun-Chieh Wu ◽  
...  
Keyword(s):  
Large Scale ◽  
Tropical Cyclogenesis ◽  
Singular Vectors

scholarly journals A Review on Additive Manufacturing Possibilities for Electrical Machines

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1940
Author(s):  
Muhammad Usman Naseer ◽  
Ants Kallaste ◽  
Bilal Asad ◽  
Toomas Vaimann ◽  
Anton Rassõlkin
Keyword(s):  
Additive Manufacturing ◽  
Large Scale ◽  
Three Dimensional ◽  
Electrical Machines ◽  
Electromagnetic Properties ◽  
Scale Production ◽  
Performance Parameters ◽  
Large Scale Production ◽  
One Step ◽  
Manufacturing Techniques

This paper presents current research trends and prospects of utilizing additive manufacturing (AM) techniques to manufacture electrical machines. Modern-day machine applications require extraordinary performance parameters such as high power-density, integrated functionalities, improved thermal, mechanical & electromagnetic properties. AM offers a higher degree of design flexibility to achieve these performance parameters, which is impossible to realize through conventional manufacturing techniques. AM has a lot to offer in every aspect of machine fabrication, such that from size/weight reduction to the realization of complex geometric designs. However, some practical limitations of existing AM techniques restrict their utilization in large scale production industry. The introduction of three-dimensional asymmetry in machine design is an aspect that can be exploited most with the prevalent level of research in AM. In order to take one step further towards the enablement of large-scale production of AM-built electrical machines, this paper also discusses some machine types which can best utilize existing developments in the field of AM.

scholarly journals Vibration characteristics of triple-gear-rotor system in compressed air energy storage under variable torque load

2021 ◽  
Vol 104 (1) ◽  
pp. 003685042098705
Author(s):  
Xinran Wang ◽  
Yangli Zhu ◽  
Wen Li ◽  
Dongxu Hu ◽  
Xuehui Zhang ◽  
...  
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Element Model ◽  
Rotor System ◽  
Dynamic Responses ◽  
System Response ◽  
Rotating Speed ◽  
Torque Load ◽  
Set Up ◽  
Two Stages

This paper focuses on the effects of the off-design operation of CAES on the dynamic characteristics of the triple-gear-rotor system. A finite element model of the system is set up with unbalanced excitations, torque load excitations, and backlash which lead to variations of tooth contact status. An experiment is carried out to verify the accuracy of the mathematical model. The results show that when the system is subjected to large-scale torque load lifting at a high rotating speed, it has two stages of relatively strong periodicity when the torque load is light, and of chaotic when the torque load is heavy, with the transition between the two states being relatively quick and violent. The analysis of the three-dimensional acceleration spectrum and the meshing force shows that the variation in the meshing state and the fluctuation of the meshing force is the basic reasons for the variation in the system response with the torque load. In addition, the three rotors in the triple-gear-rotor system studied show a strong similarity in the meshing states and meshing force fluctuations, which result in the similarity in the dynamic responses of the three rotors.

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