scholarly journals Imported and Storm-Generated Near-Ground Vertical Vorticity in a Simulated Supercell*

2014 ◽  
Vol 71 (8) ◽  
pp. 3027-3051 ◽  
Author(s):  
Johannes M. L. Dahl ◽  
Matthew D. Parker ◽  
Louis J. Wicker
Keyword(s):  
High Resolution ◽  
Vortex Line ◽  
Vertical Component ◽  
Fluid Volume ◽  
Line Segments ◽  
Vertical Vorticity ◽  
Vorticity Vector ◽  
Barotropic Vorticity

Abstract The authors use a high-resolution supercell simulation to investigate the source of near-ground vertical vorticity by decomposing the vorticity vector into barotropic and nonbarotropic parts. This way, the roles of ambient and storm-generated vorticity can be isolated. A new Lagrangian technique is employed in which material fluid volume elements are tracked to analyze the rearrangement of ambient vortex-line segments. This contribution is interpreted as barotropic vorticity. The storm-generated vorticity is treated as the residual between the known total vorticity and the barotropic vorticity. In the simulation the development of near-ground vertical vorticity is an outflow phenomenon. There are distinct “rivers” of cyclonic shear vorticity originating from the base of downdrafts that feed into the developing near-ground vortex. The origin of these rivers of vertical vorticity is primarily horizontal baroclinic production, which is maximized in the lowest few hundred meters AGL. Subsequently, this horizontal vorticity is tilted upward while the parcels are still descending. The barotropic vorticity remains mostly streamwise along the analyzed trajectories and does not acquire a large vertical component as the parcels reach the ground. Thus, the ambient vorticity that is imported into the storm contributes only a small fraction of the total near-ground vertical vorticity.

Transition of Near-Ground Vorticity Dynamics During Tornadogenesis

2021 ◽  
Keyword(s):  
Vortex Dynamics ◽  
Vertical Component ◽  
Considerable Change ◽  
The Other ◽  
Surface Drag ◽  
Vortex Patch ◽  
Vertical Vorticity ◽  
Corner Flow ◽  
Vorticity Vector ◽  
Vorticity Dynamics

Abstract Although much is known about the environmental conditions necessary for tornadogenesis, the near-ground vorticity dynamics during the tornadogenesis process itself are still somewhat poorly understood. For instance, seemingly contradicting mechanisms responsible for large near-ground vertical vorticity can be found in the literature. Broadly, these mechanisms can be sorted into two classes, one being based on upward tilting of mainly baroclinically produced horizontal vorticity in descending air (here called downdraft mechanism), while in the other the horizontal vorticity vector is abruptly tilted upward practically at the surface by a strong updraft gradient (referred to as in-and-up mechanism). In this study, full-physics supercell simulations and highly idealized simulations show that both mechanisms play important roles during tornadogenesis. Pretornadic vertical vorticity maxima are generated via the downdraft mechanism, while the dynamics of a fully developed vortex are dominated by the in-and-up mechanism. Consequently, a transition between the two mechanisms occurs during tornadogenesis. This transition is a result of axisymmetrization of the pretornadic vortex patch and intensification via vertical stretching. These processes facilitate the development of the corner flow, which enables production of vertical vorticity by upward tilting of horizontal vorticity practically at the surface, i.e. the in-and-up mechanism. The transition of mechanisms found here suggests that early stages of tornado formation rely on the downdraft mechanism, which is often limited to a small vertical component of baroclinically generated vorticity. Subsequently, a larger supply of horizontal vorticity (produced baroclinically or via surface drag, or even imported from the environment) may be utilized, which marks a considerable change in the vortex dynamics.

scholarly journals A Framework for Automatic Building Detection from Low-Contrast Satellite Images

Symmetry ◽  
2018 ◽  
Vol 11 (1) ◽  
pp. 3 ◽  
Author(s):  
Muhammad Aamir ◽  
Yi-Fei Pu ◽  
Ziaur Rahman ◽  
Muhammad Tahir ◽  
Hamad Naeem ◽  
...  
Keyword(s):  
High Resolution ◽  
High Performance ◽  
Satellite Images ◽  
Discrete Wavelet ◽  
Building Detection ◽  
Detection Scheme ◽  
Low Contrast ◽  
Line Segments ◽  
High Resolution Satellite Images ◽  
Wide Range

Building detection in satellite images has been considered an essential field of research in remote sensing and computer vision. There are currently numerous techniques and algorithms used to achieve building detection performance. Different algorithms have been proposed to extract building objects from high-resolution satellite images with standard contrast. However, building detection from low-contrast satellite images to predict symmetrical findings as of past studies using normal contrast images is considered a challenging task and may play an integral role in a wide range of applications. Having received significant attention in recent years, this manuscript proposes a methodology to detect buildings from low-contrast satellite images. In an effort to enhance visualization of satellite images, in this study, first, the contrast of an image is optimized to represent all the information using singular value decomposition (SVD) based on the discrete wavelet transform (DWT). Second, a line-segment detection scheme is applied to accurately detect building line segments. Third, the detected line segments are hierarchically grouped to recognize the relationship of identified line segments, and the complete contours of the building are attained to obtain candidate rectangular buildings. In this paper, the results from the method above are compared with existing approaches based on high-resolution images with reasonable contrast. The proposed method achieves high performance thus yields more diversified and insightful results over conventional techniques.

Visual search strategies in lab and life

2020 ◽  
Author(s):  
Anna Nowakowska ◽  
Amelia R. Hunt ◽  
Alasdair D F Clarke
Keyword(s):  
Individual Differences ◽  
Visual Search ◽  
High Resolution ◽  
Search Efficiency ◽  
Complex Objects ◽  
Line Segments ◽  
Surface Level ◽  
Dramatic Shift ◽  
The Individual ◽  
Lines Of Evidence

To what extent can our eye movement be thought of as efficient, that is, targeting locations where high resolution is needed to differentiate objects? Previous research reported conflicting conclusions: people are near-optimal, random, or even counter-optimal, according to different lines of evidence. Researchers tend to use the simplest possible environments to measure search efficiency, assuming these will minimize the individual differences in experience that could introduce unnecessary variation in behaviour. Here we measured the efficiency of 30 participants as they searched through simple line segment stimuli and through a set of complex icons. We observed a dramatic shift from highly variable strategies with the line segments, to uniformly efficient search with the icons. These results demonstrate that changing what may initially appear to be irrelevant, surface-level details of the task can lead to large changes in measured behaviour, and that visual primitives are not always representative of more complex objects.

Threading dislocations with edge components in GaN epilayers grown on Al2O3 substrates

2001 ◽  
Vol 16 (9) ◽  
pp. 2550-2555 ◽  
Author(s):  
Junyong Kang ◽  
Tomoya Ogawa
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Transmission Electron Microscope ◽  
The Other ◽  
Threading Dislocations ◽  
Line Segments ◽  
Bright Line ◽  
Transmission Electron ◽  
Dislocation Interactions

Two types of threading dislocations with edge components were investigated by a high-resolution transmission electron microscope in undoped GaN epilayers grown on Al2O3 substrates. One is a fully filled core with regular contraction and stretch of bright dots, and the other is incompletely filled with one bright dot less and irregular contraction and stretch of bright dots. The bright dots were distorted and degenerated into bright line segments at cores in areas with smaller local dislocation intervals. The calculated results suggested that the distorted bright regions are attributable to the glide and/or climb caused by nearby dislocation interactions.

scholarly journals Assessing the accuracy of SRTM altitude data for the hilly area in northeastern Romania

2018 ◽  
Author(s):  
Mihai Niculita
Keyword(s):  
High Resolution ◽  
Vertical Component ◽  
Hilly Area ◽  
The Earth ◽  
Vertical Datum ◽  
North Eastern ◽  
Elevation Data ◽  
Horizontal Wavelength ◽  
Acquisition Method ◽  
Srtm Data

SRTM data is still one of the most used data in geosciences for various purposes: geomorphometric analysis, environmental covariate modelling or geomorphic change detection. Although high resolution national/regional DEMs exist, very often accessing them is expensive, or their coverage is not complete over specific areas (only floodplains or cities are covered). Because of this SRTM still remains the best choice when elevation data is needed for regional/national or global areas. In order to assess the correctness of SRTM data to depict the real shape of Earth surface we used a regional high resolution DEM which cover a part of the hilly area of north-eastern Romanian. Both DEMs were converted to the same horizontal and vertical datum (Stereo 70 Romanian projection and the EGG97 geoid), interpolated to the same grid size and position and compared using raster algebra. The horizontal x and y components and the vertical component errors were assessed. The results show that the errors of the SRTM model are well consistent with its acquisition method (the presence of the trees and the topographic shadow) and does represent reasonably well the Earth’s surface in the study area. Anyhow, the resolution of the Earth features depicted on the SRTM model is limited by the acquisition method and does not incorporate landforms which have a vertical and horizontal wavelength under 100 m.

scholarly journals EXTRACTION OF HUMAN SETTLEMENTS FROM HIGH RESOLUTION REMOTE SENSING IMAGERY BY FUSING BOTH RIGHT-ANGLE CORNERS AND RIGHT-ANGLE SIDES

2017 ◽  
Vol XLII-2/W7 ◽  
pp. 803-807
Author(s):  
X. G. Lin ◽  
X. G. Ning
Keyword(s):  
Remote Sensing ◽  
High Resolution ◽  
Local Region ◽  
Human Settlement ◽  
Human Settlements ◽  
Line Segments ◽  
Remote Sensing Imagery ◽  
Image Conversion ◽  
The Right

A method for human settlements extraction from high resolution remote sensing imagery using feature-level-based fusion of right-angle-corners and right-angle-sides is proposed in this paper. First, the corners and line segments are detected, the right-angle-corners and right-angle-sides are determined by cross verification of the detected corners and line segments, and these two types of features are rasterized. Second, a human settlement index image is built based on the density and distance of the right-angle-corners and right-angle-sides in a local region. Finally, the polygons of human settlements are generated through binary thresholding of the index image, conversion from raster format to vector format, and sieving. Three images are used for testing the proposed method. The experimental results suggest that our proposed method has higher accuracy than the existed method. Specifically, the correctness, completeness, and quality of our method are 6.76 %, 10.12 %, 12.14 % respectively higher than the existed method.

The Role of Kinetic Boundary Conditions in Generating Type II Solutions for Rayleigh-Benard Convection

1985 ◽  
Vol 6 (2) ◽  
pp. 216-219 ◽  
Author(s):  
J. O. Murphy ◽  
N. Yannios
Keyword(s):  
Vertical Component ◽  
Single Mode ◽  
Convection Cell ◽  
Type I ◽  
Type Ii ◽  
Vertical Vorticity ◽  
Bénard Convection ◽  
Benard Convection ◽  
Rayleigh Benard Convection ◽  
Rayleigh Benard

A new family of solutions for stationary convection (Murphy and Lopez 1984) has been established which exists within the astrophysical range of parameter values — large Rayleigh number and low Prandtl number. These single mode Type II solutions, which have a non-zero component of vertical vorticity, apparently do not exist at higher Prandtl numbers and are characterized by a lower vertical velocity and heat flux, when compared to the equivalent single mode Type I solutions for Rayleigh — Benard convection with zero vertical vorticity. In turn the vertical component of vorticity associated with Type II solutions is responsible for modifying the horizontal components of the velocity field to establish cyclonic or swirling type solutions within the hexagonal convection cell.

scholarly journals Assessing the accuracy of SRTM altitude data for the hilly area in northeastern Romania

2018 ◽  
Author(s):  
Mihai Niculita
Keyword(s):  
High Resolution ◽  
Vertical Component ◽  
Hilly Area ◽  
The Earth ◽  
Vertical Datum ◽  
North Eastern ◽  
Elevation Data ◽  
Horizontal Wavelength ◽  
Acquisition Method ◽  
Srtm Data

SRTM data is still one of the most used data in geosciences for various purposes: geomorphometric analysis, environmental covariate modelling or geomorphic change detection. Although high resolution national/regional DEMs exist, very often accessing them is expensive, or their coverage is not complete over specific areas (only floodplains or cities are covered). Because of this SRTM still remains the best choice when elevation data is needed for regional/national or global areas. In order to assess the correctness of SRTM data to depict the real shape of Earth surface we used a regional high resolution DEM which cover a part of the hilly area of north-eastern Romanian. Both DEMs were converted to the same horizontal and vertical datum (Stereo 70 Romanian projection and the EGG97 geoid), interpolated to the same grid size and position and compared using raster algebra. The horizontal x and y components and the vertical component errors were assessed. The results show that the errors of the SRTM model are well consistent with its acquisition method (the presence of the trees and the topographic shadow) and does represent reasonably well the Earth’s surface in the study area. Anyhow, the resolution of the Earth features depicted on the SRTM model is limited by the acquisition method and does not incorporate landforms which have a vertical and horizontal wavelength under 100 m.

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