scholarly journals Observations and Numerical Simulations of Subrotor Vortices during T-REX

2009 ◽  
Vol 66 (5) ◽  
pp. 1229-1249 ◽  
Author(s):  
James D. Doyle ◽  
Vanda Grubišić ◽  
William O. J. Brown ◽  
Stephan F. J. De Wekker ◽  
Andreas Dörnbrack ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Wind Shear ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Vortex Sheet ◽  
Small Scale ◽  
Wind Profiler ◽  
Strong Wind ◽  
Transient Nature

Abstract High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of ∼500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.

scholarly journals Wind shear over the Nice Côte d'Azur airport: case studies

2013 ◽  
Vol 13 (9) ◽  
pp. 2223-2238 ◽  
Author(s):  
A. Boilley ◽  
J.-F. Mahfouf
Keyword(s):  
Numerical Simulation ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Wind Shear ◽  
Horizontal Wind ◽  
Wind Profiler ◽  
Measurement Campaign ◽  
Wind Lidar ◽  
Real Time Applications ◽  
Wind Shears

Abstract. The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating an horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

How does vertical wind shear influence entrainment in squall lines?

2021 ◽  
Author(s):  
Jake P. Mulholland ◽  
John M. Peters ◽  
Hugh Morrison
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Vertical Wind ◽  
Squall Line ◽  
Cold Pool ◽  
Low Level ◽  
Boundary Shear ◽  
Squall Lines ◽  
Outflow Boundary

AbstractThe influence of vertical wind shear on updraft entrainment in squall lines is not well understood. To address this knowledge gap, a suite of high-resolution idealized numerical model simulations of squall lines were run in various vertical wind shear (hereafter “shear”) environments to study the effects of shear on entrainment in deep convective updrafts. Low-level horizontal mass flux into the leading edge of the cold pool was strongest in the simulations with the strongest low-level shear. These simulations consequently displayed wider updrafts, less entrainment-driven dilution, and larger buoyancy than the simulations with comparatively weak low-level shear. An analysis of vertical accelerations along trajectories that passed through updrafts showed larger net accelerations from buoyancy in the simulations with stronger low-level shear, which demonstrates how less entrainment-driven dilution equated to stronger updrafts. The effects of upper-level shear on entrainment and updraft vertical velocities were generally less pronounced than the effects of low-level shear. We argue that in addition to the outflow boundary-shear interactions and their effect on updraft tilt established by previous authors, decreased entrainment-driven dilution is yet another beneficial effect of strong low-level shear on squall line updraft intensity.

Retrieved Thermodynamic Structure of Hurricane Rita (2005) from Airborne Multi-Doppler Radar Data

2021 ◽  
Author(s):  
Annette M. Boehm ◽  
Michael M. Bell
Keyword(s):  
Wind Shear ◽  
Doppler Radar ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
Radar Data ◽  
Vertical Wind ◽  
Vertical Acceleration ◽  
Hurricane Rita ◽  
Doppler Radar Data

AbstractThe newly developed SAMURAI-TR is used to estimate three-dimensional temperature and pressure perturbations in Hurricane Rita on 23 September 2005 from multi-Doppler radar data during the RAINEX field campaign. These are believed to be the first fully three-dimensional gridded thermodynamic observations from a TC. Rita was a major hurricane at this time and was affected by 13 m s−1 deep-layer vertical wind shear. Analysis of the contributions of the kinematic and retrieved thermodynamic fields to different azimuthal wavenumbers suggests the interpretation of eyewall convective forcing within a three-level framework of balanced, quasi-balanced, and unbalanced motions. The axisymmetric, wavenumber-0 structure was approximately in thermal-wind balance, resulting in a large pressure drop and temperature increase toward the center. The wavenumber-1 structure was determined by the interaction of the storm with environmental vertical wind shear resulting in a quasi-balance between shear and shear-induced kinematic and thermo-dynamic perturbations. The observed wavenumber-1 thermodynamic asymmetries corroborate results of previous studies on the response of a vortex tilted by shear, and add new evidence that the vertical motion is nearly hydrostatic on the wavenumber-1 scale. Higher-order wavenumbers were associated with unbalanced motions and convective cells within the eyewall. The unbalanced vertical acceleration was positively correlated with buoyant forcing from thermal perturbations and negatively correlated with perturbation pressure gradients relative to the balanced vortex.

scholarly journals Wind-Driven Hydrodynamics in the Shallow, Micro-Tidal Estuary at the Fangar Bay (Ebro Delta, NW Mediterranean Sea)

2020 ◽  
Vol 10 (19) ◽  
pp. 6952
Author(s):  
Marta F-Pedrera Balsells ◽  
Manel Grifoll ◽  
Manuel Espino ◽  
Pablo Cerralbo ◽  
Agustín Sánchez-Arcilla
Keyword(s):  
Numerical Experiments ◽  
Field Data ◽  
Three Dimensional ◽  
Estuarine Circulation ◽  
Water Circulation ◽  
Ebro Delta ◽  
Small Scale ◽  
Strong Wind ◽  
Axially Symmetric ◽  
Nw Mediterranean

This article investigates water circulation in small-scale (~10 km2), shallow (less than 4 m) and micro-tidal estuaries. The research characterizes the hydrodynamic wind response in these domains using field data from Fangar Bay (Ebro Delta) jointly with three-dimensional numerical experiments in an idealized domain. During calm periods, field data in Fangar Bay show complex water circulation in the inner part of the estuary owing to its shallow depths and positive estuarine circulation in the mouth. Numerical experiments are conducted to investigate wind-induced water circulation due to laterally varying bathymetry. For intense up-bay wind conditions (wind intensities greater than 9 m·s−1), an axially symmetric transverse structure occurs with outflow in the central channel axis and inflow in the lateral shallow areas. These numerical results explain the water circulation observed in Fangar Bay during strong wind episodes, highlighting the role of the bathymetry in a small-scale environment. During these episodes, the water column tends to homogenize rapidly in Fangar Bay, breaking the stratification and disrupting estuarine circulation, consistent with other observations in similar domains.

scholarly journals The Fermi bubbles inflated by winds from the accretion flow in Sgr A*

2014 ◽  
Vol 10 (S312) ◽  
pp. 137-138
Author(s):  
Guobin Mou
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Small Scale ◽  
Observational Constraints ◽  
Accretion Flow ◽  
Accretion Flows ◽  
The Past ◽  
Sgr A ◽  
Hydrodynamical Simulations

AbstractBy performing three-dimensional hydrodynamical simulations, we show that the Fermi bubbles could be inflated by winds launched from the “past” hot accretion flow in Sgr A*. The parameters of the accretion flow required in the model are consistent with those obtained independently from other observational constraints. The wind parameters are taken from small scale MHD numerical simulations of hot accretion flows.

Direct Numerical Simulations of Transitional Separation–Bubble Development in Swept–Blade Flow Conditions

2012 ◽  
Author(s):  
Joshua R. Brinkerhoff ◽  
Metin I. Yaras
Keyword(s):  
Boundary Layer ◽  
Numerical Simulations ◽  
Shear Layer ◽  
Pressure Field ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Direct Numerical Simulations ◽  
Small Scale ◽  
Flow Conditions ◽  
Crossflow Instability

This paper describes numerical simulations of the instability mechanisms in a separation bubble subjected to a three-dimensional freestream pressure distribution. Two direct numerical simulations are performed of a separation bubble with laminar separation and turbulent reattachment under low freestream turbulence at flow Reynolds numbers and streamwise pressure distributions that approximate the conditions encountered on the suction side of typical low-pressure gas-turbine blades with blade sweep angles of 0° and 45°. The three-dimensional pressure field in the swept configuration produces a crossflow-velocity component in the laminar boundary layer upstream of the separation point that is unstable to a crossflow instability mode. The simulation results show that crossflow instability does not play a role in the development of the boundary layer upstream of separation. An increase in the amplification rate and most amplified disturbance frequency is observed in the separated-flow region of the swept configuration, and is attributed to boundary-layer conditions at the point of separation that are modified by the spanwise pressure gradient. This results in a slight upstream movement of the location where the shear layer breaks down to small-scale turbulence and modifies the turbulent mixing of the separated shear layer to yield a downstream shift in the time-averaged reattachment location. The results demonstrate that although crossflow instability does not appear to have a noticeable effect on the development of the transitional separation bubble, the 3D pressure field does indirectly alter the separation-bubble development by modifying the flow conditions at separation.

scholarly journals Numerical Simulations of Bow Echo Formation Following a Squall Line–Supercell Merger

2014 ◽  
Vol 142 (12) ◽  
pp. 4791-4822 ◽  
Author(s):  
Adam J. French ◽  
Matthew D. Parker
Keyword(s):  
Numerical Simulations ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Direct Result ◽  
Squall Line ◽  
Cold Pool ◽  
Surface Winds ◽  
Sensitivity Tests ◽  
Bow Echo ◽  
Inflow Jet

Abstract Output from idealized numerical simulations is used to investigate the storm-scale processes responsible for squall-line evolution following a merger with an isolated supercell. A simulation including a squall line–supercell merger is compared to one using the same initial squall line and background environment without the merger. These simulations reveal that while bow echo formation is favored by the strongly sheared background environment, the merger produces a more compact bowing structure owing to a locally enhanced rear-inflow jet. The merger also represents a favored location for severe weather production relative to other portions of the squall line, with surface winds, vertical vorticity, and rainfall all being maximized in the vicinity of the merger. An analysis of storm-scale processes reveals that the premerger squall line weakens as it encounters outflow from the preline supercell, and the supercell becomes the leading edge of the merged system. Subsequent localized strengthening of the cold pool and rear-inflow jet produce a compact, intense bow echo local to the merger, with a descending rear-inflow jet creating a broad swath of damaging surface winds. These features, common to severe bow echoes, are shown to be a direct result of the merger in the present simulations, and are diminished or absent in the no-merger simulation. Sensitivity tests reveal that mergers in a weaker vertical wind shear environment do not produce an enhanced bow echo structure, and only produce a localized region of marginally enhanced surface winds. Additional tests demonstrate that the details of postmerger evolution vary with merger location along the line.

scholarly journals Research Aircraft and Wind Profiler Observations in Gastineau Channel during a Taku Wind Event*

2006 ◽  
Vol 21 (4) ◽  
pp. 489-501 ◽  
Author(s):  
Nicholas A. Bond ◽  
Carl F. Dierking ◽  
James D. Doyle
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Naval Research ◽  
Wind Profiler ◽  
Mean Flow ◽  
Gap Flow ◽  
Wind Event ◽  
Research Aircraft ◽  
Downslope Flow

Abstract The flow in Gastineau Channel near Juneau, Alaska, during the moderate Taku wind event of 18 October 2004 is examined using observations from the University of Wyoming’s King Air research aircraft, two wind profilers, and surface weather stations. These data sources reveal low-level winds directed down the central portion of Gastineau Channel, that is, gap flow. Farther down the channel, and above this gap flow, the winds were strongly cross channel in association with the downslope flow that characterizes Taku events. The transition region between these two flows included strong vertical wind shear and severe turbulence; measurements from the King Air indicate turbulent kinetic energy locally exceeding 50 m2 s−2. A high-resolution simulation of this case using the Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System reproduced the observed character of the mean flow. This case illustrates the hazard to aviation posed by even a moderate Taku wind event and shows the value of a wind profiler for monitoring the vertical wind shear responsible for the hazard.

Processes Controlling the Structure and Longevity of Two Quasi-Linear Convective Systems Crossing the Southern New England Coast

2013 ◽  
Vol 141 (11) ◽  
pp. 3710-3734 ◽  
Author(s):  
Kelly Lombardo ◽  
Brian A. Colle
Keyword(s):  
New York ◽  
New York City ◽  
York City ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Vertical Wind ◽  
Cold Pool ◽  
Convective Systems ◽  
Atlantic Coastal

Abstract This paper explores the structural evolution and physical processes that explain the modification of two quasi-linear convective systems (QLCSs) that encountered the densely populated New York City–Atlantic coastal region. One QLCS on 31 May 2002 traversed the Atlantic coastal boundary with little change in its intensity, producing widespread severe wind damage across New York City and Long Island. During this event, warm air advection at 925 hPa helped destabilize the layer above this level over the coastal zone, while the marine boundary layer deepened below this level. The 0–3-km line-perpendicular vertical wind shear was relatively strong, which supported ascent along the leading edge of the diabatically generated cold pool. The surface-based convective system became slightly elevated as it moved over the marine waters. In contrast, the 23 July 2002 QLCS decayed upon encountering the Atlantic coastline, despite its coincidence with a surface cold front. The most unstable CAPE values during this decaying event were 400–800 J kg−1 greater than the sustaining 31 May event, though the 0–3-km vertical wind shear was approximately half. Weaker shear likely contributed to limited ascent along the leading edge of the surface based cold pool, and ultimately the demise of the convective line. Sensitivity tests highlight the importance of the relationship between the cold pool and vertical shear during these two events, and illustrate the limited role of the marine layer in modifying the evolution of these two convective systems.

scholarly journals Estimating the Maximum Vertical Velocity at the Leading Edge of a Density Current

2020 ◽  
Vol 77 (11) ◽  
pp. 3683-3700
Author(s):  
Dylan W. Reif ◽  
Howard B. Bluestein ◽  
Tammy M. Weckwerth ◽  
Zachary B. Wienhoff ◽  
Manda B. Chasteen
Keyword(s):  
Vertical Velocity ◽  
Wind Shear ◽  
Potential Temperature ◽  
Vertical Wind Shear ◽  
Mesoscale Convective System ◽  
Leading Edge ◽  
Density Current ◽  
Convective System ◽  
Density Currents ◽  
Spatiotemporal Resolution

AbstractThe maximum upward vertical velocity at the leading edge of a density current is commonly <10 m s−1. Studies of the vertical velocity, however, are relatively few, in part owing to the dearth of high-spatiotemporal-resolution observations. During the Plains Elevated Convection At Night (PECAN) field project, a mobile Doppler lidar measured a maximum vertical velocity of 13 m s−1 at the leading edge of a density current created by a mesoscale convective system during the night of 15 July 2015. Two other vertically pointing instruments recorded 8 m s−1 vertical velocities at the leading edge of the density current on the same night. This study describes the structure of the density current and attempts to estimate the maximum vertical velocity at their leading edges using the following properties: the density current depth, the slope of its head, and its perturbation potential temperature. The method is then be applied to estimate the maximum vertical velocity at the leading edge of density currents using idealized numerical simulations conducted in neutral and stable atmospheres with resting base states and in neutral and stable atmospheres with vertical wind shear. After testing this method on idealized simulations, this method is then used to estimate the vertical velocity at the leading edge of density currents documented in several previous studies. It was found that the maximum vertical velocity can be estimated to within 10%–15% of the observed or simulated maximum vertical velocity and indirectly accounts for parameters including environmental wind shear and static stability.

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