scholarly journals Numerical Simulation of Tornadogenesis in an Outer-Rainband Minisupercell of Typhoon Shanshan on 17 September 2006

2009 ◽  
Vol 137 (12) ◽  
pp. 4238-4260 ◽  
Author(s):  
Wataru Mashiko ◽  
Hiroshi Niino ◽  
Teruyuki Kato
Keyword(s):  
Momentum Equation ◽  
Precipitation Pattern ◽  
Streamwise Vorticity ◽  
Convective Storms ◽  
Low Level ◽  
Budget Analysis ◽  
Rapid Amplification ◽  
The Right ◽  
Left Front ◽  
Gust Front

Abstract On 17 September 2006, three tornadoes occurred along the east coast of Kyusyu Island in western Japan during the passage of an outer rainband in the right-front quadrant of Typhoon Shanshan. To clarify the structure of the tornado-producing storms and the mechanism of tornadogenesis, quadruply nested numerical simulations were performed using a nonhydrostatic model with an innermost horizontal grid spacing of 50 m. Several simulated convective storms in the outermost rainband exhibited characteristics of a minisupercell. One storm had a strong rotating updraft of more than 30 m s−1 and a large vertical vorticity exceeding 0.06 s−1. This storm spawned a tornado when the low-level mesocyclone intensified. The tornado was generated on the rear-flank gust front near the mesocyclone center when a secondary rear-flank downdraft (RFD) surge advanced cyclonically around the low-level mesocyclone and overtook the rear-flank gust front at its left-front edge. Backward trajectories and vorticity budget analysis along the trajectories indicate that the secondary RFD surge played a key role in tornadogenesis by barotropically transporting the large streamwise vorticity associated with the environmental low-level veering shear toward the surface. When the secondary RFD outflow surge boundary reached the rear-flank gust front, the horizontal convergence was enhanced, contributing to the rapid amplification of the vertically tilted streamwise vorticity. The diagnostics of the vertical momentum equation and several sensitivity experiments demonstrated that precipitation loading in the area of a hook-shaped precipitation pattern was crucial to the behavior of the RFD and the subsequent tornadogenesis.

The Anatomy of a Series of Cloud Bursts that Eclipsed the US Rainfall Record

2021 ◽  
Keyword(s):  
Deep Convection ◽  
Vertical Motion ◽  
Precipitable Water ◽  
Radar Data ◽  
Data Sets ◽  
Streamwise Vorticity ◽  
Convective Storms ◽  
Low Level ◽  
The Us ◽  
The Right

Abstract A series of extreme cloudbursts occurred on 14 April 2018 over the northern slopes of the island of Kaua‘i. The storm inundated some areas with 1262 mm (∼50”) of rainfall in a 24-hr period, eclipsing the previous 24-hr US rainfall record of 1100 mm (42”) set in Texas in 1979. Three periods of intense rainfall are diagnosed through detailed analysis of National Weather Service operational and special data sets. On the synoptic scale, a slowly southeastward propagating trough aloft over a deep layer of low level moisture (>40 mm of total precipitable water) produced prolonged instability over Kaua‘i. Enhanced NE to E low level flow impacted Kaua‘i’s complex terrain, which includes steep north and eastward facing slopes and cirques. The resulting orographic lift initiated deep convection. The wind profile exhibited significant shear in the troposphere and streamwise vorticity within the convective storm inflow. Evidence suggests that large directional shear in the boundary layer, paired with enhanced orographic vertical motion, produced rotating updrafts within the convective storms. Mesoscale rotation is manifest in the radar data during the latter two periods and reflectivity cores are observed to propagate both to the left and to the right of the mean shear, which is characteristic of supercells. The observations suggest that the terrain configuration in combination with the windshear separates the area of updrafts from the downdraft section of the storm, resulting in almost continuous heavy rainfall over Waipā Garden.

scholarly journals A Numerical Study of the 6 May 2012 Tsukuba City Supercell Tornado. Part I: Vorticity Sources of Low-Level and Midlevel Mesocyclones

2016 ◽  
Vol 144 (3) ◽  
pp. 1069-1092 ◽  
Author(s):  
Wataru Mashiko
Keyword(s):  
Numerical Study ◽  
Streamwise Vorticity ◽  
Retrograde Motion ◽  
Low Level ◽  
Vortex Lines ◽  
Supercell Storm ◽  
Nested Grids ◽  
Generation Mechanisms ◽  
Eastern Japan ◽  
Gust Front

Abstract On 6 May 2012, an F3 supercell tornado, one of the most destructive tornadoes ever recorded in Japan, hit Tsukuba City in eastern Japan and caused severe damage. To clarify the generation mechanisms of the tornadic storm and tornado, high-resolution numerical simulations were conducted under realistic environmental conditions using triply nested grids. The innermost simulation with a 50-m mesh successfully reproduced the Tsukuba City tornadic supercell storm. In this study (the first of a two-part study), the vorticity sources responsible for mesocyclogenesis prior to tornadogenesis were investigated by analyzing vortex lines and the evolution of circulation of the mesocyclones. Vortex lines that passed through the midlevel mesocyclone (4-km height) originated from the environmental streamwise vorticity, whereas the low-level mesocyclone and low-level mesoanticyclone were connected by several arching vortex lines over the rear-flank downdraft associated with the hook-shaped distribution of hydrometeors (hereafter hook echo). Most of the circulation for the circuit surrounding the midlevel mesocyclone was conserved, although the baroclinity associated with positive buoyancy within the storm led to an up-and-down trend. The circulation of the material circuit encircling the low-level mesocyclone showed a gradual increase caused by baroclinity along the forward-flank gust front. Friction also had a positive net effect on the circulation. In contrast, most of the negative circulation of the low-level mesoanticyclone was rapidly acquired owing to baroclinity around the tip of the hook echo. Just after tornadogenesis, the low-level mesocyclone intensified significantly and developed upward, which caused retrograde motion of the midlevel mesocyclone.

Simulated Changes in Storm Morphology Associated with a Sea-Breeze Air Mass

2020 ◽  
Author(s):  
Joshua Hartigan ◽  
Robert A. Warren ◽  
Joshua S. Soderholm ◽  
Harald Richter
Keyword(s):  
Front Propagation ◽  
Sea Breeze ◽  
Wind Fields ◽  
Air Mass ◽  
Convective Storms ◽  
Low Level ◽  
Environmental Air ◽  
Homogeneous Environment ◽  
Gust Front

AbstractThe central east coast of Australia is frequently impacted by large hail and damaging winds associated with severe convective storms, with individual events recording damages exceeding AU$1 billion. These storms present a significant challenge for forecasting due to their development in seemingly marginal environments. They often have been observed to intensify upon approaching the coast, with case studies and climatological analyses indicating that interactions with the sea breeze are key to this process. The relative importance of the additional lifting and vorticity along the sea-breeze front compared to the change to a cooler, moister air mass with stronger low-level shear behind the front has yet to be investigated. Here, the role of the sea-breeze air mass is isolated using idealized numerical simulations of storms developing in a horizontally homogeneous environment. The base-state substitution (BSS) modeling technique is utilized to introduce the sea-breeze air mass following initial storm development. Compared to a simulation without BSS, the storm is longer lived and more intense, ultimately developing supercell characteristics including increased updraft rotation, deviant motion to the left of the mean wind vector, and a strong reflectivity gradient on the inflow edge. Separately simulating the changes in the thermodynamic and wind fields reveals that the enhanced storm longevity and intensity are primarily due to the latter. The change in the low-level environmental winds slows gust front propagation, allowing the storm to continue to ingest warm, potentially buoyant environmental air. At the same time, increased low-level shear promotes the development of persistent updraft rotation causing the storm to transition from a multicell to a supercell.

Storm-Relative Helicity Revealed from Polarimetric Radar Measurements

2009 ◽  
Vol 66 (3) ◽  
pp. 667-685 ◽  
Author(s):  
Matthew R. Kumjian ◽  
Alexander V. Ryzhkov
Keyword(s):  
Strong Positive Correlation ◽  
Convective Storms ◽  
Low Level ◽  
Initial Drop ◽  
Size Sorting ◽  
Radar Measurements ◽  
Microphysical Processes ◽  
Differential Sedimentation ◽  
The Right ◽  
Differential Reflectivity

Abstract The dual-polarization radar variables are especially sensitive to the microphysical processes of melting and size sorting of precipitation particles. In deep convective storms, polarimetric measurements of such processes can provide information about the airflow in and around the storm that may be used to elucidate storm behavior and evolution. Size sorting mechanisms include differential sedimentation, vertical transport, strong rotation, and wind shear. In particular, winds that veer with increasing height typical of supercell environments cause size sorting that is manifested as an enhancement of differential reflectivity (ZDR) along the right or inflow edge of the forward-flank downdraft precipitation echo, which has been called the ZDR arc signature. In some cases, this shear profile can be augmented by the storm inflow. It is argued that the magnitude of this enhancement is related to the low-level storm-relative environmental helicity (SRH) in the storm inflow. To test this hypothesis, a simple numerical model is constructed that calculates trajectories for raindrops based on their individual sizes, which allows size sorting to occur. The modeling results indicate a strong positive correlation between the maximum ZDR in the arc signature and the low-level SRH, regardless of the initial drop size distribution aloft. Additional observational evidence in support of the conceptual model is presented. Potential changes in the ZDR arc signature as the supercell evolves and the low-level mesocyclone occludes are described.

scholarly journals Quadrant-Dependent Evolution of Low-Level Tangential Wind of a Tropical Cyclone in the Shear Flow

2016 ◽  
Vol 73 (3) ◽  
pp. 1159-1177 ◽  
Author(s):  
Jian-Feng Gu ◽  
Zhe-Min Tan ◽  
Xin Qiu
Keyword(s):  
Tropical Cyclone ◽  
Shear Flow ◽  
Vertical Wind Shear ◽  
Intensity Change ◽  
Low Level ◽  
Budget Analysis ◽  
Steady Stage ◽  
Tangential Wind ◽  
Low Level Jet ◽  
The Right

Abstract This study investigates the quadrant-by-quadrant evolution of the low-level tangential wind near the eyewall of an idealized simulated mature tropical cyclone embedded in a unidirectional shear flow. It is found that the quadrant-averaged tangential wind in the right-of-shear quadrants weakens continuously, while that in the left-of-shear quadrants experiences a two-stage evolution: a quasi-steady stage followed by a weakening stage after the imposing of vertical wind shear. This leads to a larger weakening rate in the right-of-shear and a stronger jet in the left-of-shear quadrants. The budget analysis shows that the quadrant-dependent evolution of tangential wind is controlled through the balance between the generalized Coriolis force (GCF; i.e., the radial advection of absolute angular momentum) and the advection terms. The steady decreasing of the GCF is primarily responsible for the continuous weakening of jet strength in the right-of-shear quadrants. For the left-of-shear quadrants, the quasi-steady stage is due to the opposite contributions by the enhanced GCF and negative tendency of advections cancelling out each other. The later weakening stage is the result of both the decreased GCF and the negative tangential advection. The combination of storm-relative flows at vortex scale and the convection strength both within and outside the eyewall determines the evolution of boundary layer inflow asymmetries, which in turn results in the change of GCF, leading to the quadrant-dependent evolution of low-level jet strength and thus the overall storm intensity change.

scholarly journals Wintertime Supercell Thunderstorms in a Subtropical Environment: Numerical Simulation

2009 ◽  
Vol 137 (7) ◽  
pp. 2175-2202 ◽  
Author(s):  
Chung-Chieh Wang ◽  
George Tai-Jen Chen ◽  
Shan-Chien Yang ◽  
Kazuhisa Tsuboki
Keyword(s):  
Taiwan Strait ◽  
Vertical Shear ◽  
Diagnostic Study ◽  
Grid Spacing ◽  
Thermodynamic Structure ◽  
Low Level ◽  
Budget Analysis ◽  
The Taiwan Strait ◽  
The Right ◽  
Subtropical Environment

Following an earlier diagnostic study, the present paper performs numerical simulations of the rare wintertime supercell storms during 19–20 December 2002 in a subtropical environment near Taiwan. Using Japan Meteorology Agency (JMA) 20-km analyses and horizontal grid spacing of 1.5 and 0.5 km, the Cloud-Resolving Storm Simulator (CReSS) of Nagoya University successfully reproduced the three major storms at the correct time and location, but the southern storm decayed too early over the Taiwan Strait. The two experiments produce similar overall results, suggesting that the 1.5-km grid spacing is sufficient even for storm dynamics. Model results are further used to examine the storm structure, kinematics, splitting process, and the variation in the mesoscale environment. Over the Taiwan Strait, the strong surface northeasterly flow enhanced low-level vertical shear and helped the storms evolve into isolated supercells. Consistent with previous studies, the vorticity budget analysis indicates that midlevel updraft rotation arose mainly from the tilting effect, and was reinforced by vertical stretching at the supercell stage. As the ultimate source of vorticity generation, the horizontal vorticity (vertical shear) was altered by the baroclinic (solenoidal) effect around the warm-core updraft, as well as the tilting of vertical vorticity onto, and rotation of vortex tubes in the x–y plane, forming a counterclockwise pattern that pointed generally northward (westward) at the right (left) flanks of the updraft. In both runs, model storms travel about 15°–20° to the left of the actual storms, and they are found to be quite sensitive to the detailed low-level thermodynamic structure of the postfrontal atmosphere and the intensity of the storms themselves, in particular whether or not the existing instability can be released by forced uplift at the gust front. In this regard, the finer 0.5-km grid did produce stronger storms that maintained longer across the strait. The disagreement in propagation direction between the model and real storms is partially attributed to the differences in environment, while the remaining part is most likely due to differences not reflected in gridded analyses. Since the conditions (in both the model and real atmosphere) over the Taiwan Strait are not uniform and depend on many detailed factors, it is anticipated that a successful simulation that agrees with the observation in all aspects over data-sparse regions like this one will remain a challenging task in the foreseeable future.

The Multiple-Vortex Structure of the El Reno, Oklahoma, Tornado on 31 May 2013

2018 ◽  
Vol 146 (8) ◽  
pp. 2483-2502 ◽  
Author(s):  
Howard B. Bluestein ◽  
Kyle J. Thiem ◽  
Jeffrey C. Snyder ◽  
Jana B. Houser
Keyword(s):  
Doppler Radar ◽  
Radar Data ◽  
Rapid Scan ◽  
X Band ◽  
Close Range ◽  
Formation And Evolution ◽  
Using Data ◽  
Secondary Vortices ◽  
The Right ◽  
Gust Front

Abstract This study documents the formation and evolution of secondary vortices associated within a large, violent tornado in Oklahoma based on data from a close-range, mobile, polarimetric, rapid-scan, X-band Doppler radar. Secondary vortices were tracked relative to the parent circulation using data collected every 2 s. It was found that most long-lived vortices (those that could be tracked for ≥15 s) formed within the radius of maximum wind (RMW), mainly in the left-rear quadrant (with respect to parent tornado motion), passing around the center of the parent tornado and dissipating closer to the center in the right-forward and left-forward quadrants. Some secondary vortices persisted for at least 1 min. When a Burgers–Rott vortex is fit to the Doppler radar data, and the vortex is assumed to be axisymmetric, the secondary vortices propagated slowly against the mean azimuthal flow; if the vortex is not assumed to be axisymmetric as a result of a strong rear-flank gust front on one side of it, then the secondary vortices moved along approximately with the wind.

Economic and Social Rights, Budgets and the Convention on the Rights of the Child

2013 ◽  
Vol 21 (2) ◽  
pp. 248-277 ◽  
Author(s):  
Aoife Nolan
Keyword(s):  
Decision Making ◽  
Social Rights ◽  
Child Rights ◽  
Rights Of The Child ◽  
Budget Analysis ◽  
Key Issues ◽  
Significant Obstacle ◽  
The Right ◽  
The Relationship

Recent years have seen an explosion in methodologies for monitoring children’s economic and social rights (ESR). Key examples include the development of indicators, benchmarks, child rights-based budget analysis and child rights impact assessments. The Committee on the Right of the Child has praised such tools in its work and has actively promoted their usage. Troublingly, however, there are serious shortcomings in the Committee’s approach to the ESR standards enshrined in the UN Convention on the Rights of the Child (CRC), which threaten to impact upon the efficacy of such methodologies. This article argues that the Committee has failed to engage with the substantive obligations imposed by Article 4 and many of the specific ESR guaranteed in the CRC in sufficient depth. As a result, that body has not succeeded in outlining a coherent, comprehensive child rights-specific ESR framework. Using the example of child rights-based budget analysis, the author claims that this omission constitutes a significant obstacle to those seeking to evaluate the extent to which states have met their ESR-related obligations under the CRC. The article thus brings together and addresses key issues that have so far received only very limited critical academic attention, namely, children’s ESR under the CRC, the relationship between budgetary decision-making and the CRC, and child rights-based budget analysis.

Examining Terrain Effects on an Upstate New York Tornado Event Utilizing a High-Resolution Model Simulation

2021 ◽  
Author(s):  
Luke J. LeBel ◽  
Brian H. Tang ◽  
Ross A. Lazear
Keyword(s):  
New York ◽  
High Resolution ◽  
Wind Shear ◽  
Model Simulation ◽  
Wrf Model ◽  
Severe Weather ◽  
Streamwise Vorticity ◽  
Low Level ◽  
Severe Convection ◽  
The Impact

AbstractThe complex terrain at the intersection of the Mohawk and Hudson valleys of New York has an impact on the development and evolution of severe convection in the region. Specifically, previous research has concluded that terrain-channeled flow in the Mohawk and Hudson valleys likely contributes to increased low-level wind shear and instability in the valleys during severe weather events such as the historic 31 May 1998 event that produced a strong (F3) tornado in Mechanicville, New York.The goal of this study is to further examine the impact of terrain channeling on severe convection by analyzing a high-resolution WRF model simulation of the 31 May 1998 event. Results from the simulation suggest that terrain-channeled flow resulted in the localized formation of an enhanced low-level moisture gradient, resembling a dryline, at the intersection of the Mohawk and Hudson valleys. East of this boundary, the environment was characterized by stronger low-level wind shear and greater low-level moisture and instability, increasing tornadogenesis potential. A simulated supercell intensified after crossing the boundary, as the larger instability and streamwise vorticity of the low-level inflow was ingested into the supercell updraft. These results suggest that terrain can have a key role in producing mesoscale inhomogeneities that impact the evolution of severe convection. Recognition of these terrain-induced boundaries may help in anticipating where the risk of severe weather may be locally enhanced.

scholarly journals Structure of the SAD mutation and the location of control sites at silent mating type genes in Saccharomyces cerevisiae.

1984 ◽  
Vol 4 (7) ◽  
pp. 1278-1285 ◽  
Author(s):  
J Hicks ◽  
J Strathern ◽  
A Klar ◽  
S Ismail ◽  
J Broach
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Mating Type ◽  
Control Site ◽  
Left Hand ◽  
Low Level ◽  
Flanking Sequences ◽  
Mating Type Genes ◽  
Weak Expression ◽  
The Right ◽  
Flanking Regions

The SAD mutation, an extra mating type cassette, has been shown to arise from an unequal mitotic crossover between the MAT and HMR loci, resulting in the formation of a hybrid cassette and a duplication of the MAT-HMR interval. The SAD cassette contains the "a" information and left-hand flanking regions from the parental HMRa cassette and the right-hand flanking sequences of the parental MAT cassette. This arrangement of flanking sequences causes a leaky but reproducible mating phenotype correlated with a low-level expression of the cassette as measured by RNA blotting. This weak expression is attributed to the loss of one flanking control site normally present at the silent HM storage loci.

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