The Experts below are selected from a list of 21993 Experts worldwide ranked by ideXlab platform
Matthew D. Parker - One of the best experts on this subject based on the ideXlab platform.
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The 6 May 2010 Elevated Supercell during VORTEX2
Monthly Weather Review, 2017Co-Authors: Christopher W. Macintosh, Matthew D. ParkerAbstract:AbstractAn elevated supercell from the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) on 6 May 2010 is investigated. Observations show that the supercell formed over a stable inversion and was likely decoupled from the surface. Quintessential features of a supercell were present, including a hook echo (albeit bent anticyclonically) and midlevel mesocyclone, and the storm was quasi steady during the observing period. A weak surface cold pool formed, but it was apparently devoid of air originating from midlevels. Idealized modeling using near-storm soundings is employed to clarify the structure and maintenance of this supercell. The simulated storm is decoupled from the surface by the stable layer. Additionally, the reflectivity structure of the simulated supercell is strikingly similar to the observed storm, including its peculiar anticyclonic-curving hook echo. Air parcels above 1 km reached their LFCs as a result of the simulated supercell’s own dynamic lifting, which li...
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Simulated Supercells in Nontornadic and Tornadic VORTEX2 Environments
Monthly Weather Review, 2016Co-Authors: Brice E. Coffer, Matthew D. ParkerAbstract:AbstractThe composite near-storm environments of nontornadic and tornadic Supercells sampled during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) both appear to be generally favorable for Supercells and tornadoes. It has not been clear whether small differences between the two environments (e.g., more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite) are actually determinative of storms’ tornadic potential. From the VORTEX2 composite environments, simulations of a nontornadic and a tornadic supercell are used to investigate storm-scale differences that ultimately favor tornadogenesis or tornadogenesis failure. Both environments produce strong Supercells with robust midlevel mesocyclones and hook echoes, though the tornadic supercell has a more intense low-level updraft and develops a tornado-like vortex exceeding the EF3 wind speed threshold. In contrast, the nontornadic supercell only produces shallow vortic...
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Composite VORTEX2 Supercell Environments from Near-Storm Soundings
Monthly Weather Review, 2014Co-Authors: Matthew D. ParkerAbstract:AbstractThree-dimensional composite analyses using 134 soundings from the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) reveal the nature of near-storm variability in the environments of supercell thunderstorms. Based upon the full analysis, it appears that vertical wind shear increases as one approaches a supercell within the inflow sector, providing favorable conditions for supercell maintenance (and possibly tornado formation) despite small amounts of low-level cooling near the storm. The seven analyzed tornadic Supercells have a composite environment that is clearly more impressive (in terms of widely used metrics) than that of the five analyzed nontornadic Supercells, including more convective available potential energy (CAPE), more vertical wind shear, higher boundary layer relative humidity, and lower tropospheric horizontal vorticity that is more streamwise in the near-storm inflow. The widely used supercell composite parameter (SCP) and significant tornado param...
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A numerical investigation of Supercells in landfalling tropical cyclones
Geophysical Research Letters, 2011Co-Authors: M. J. Morin, Matthew D. ParkerAbstract:[1] Supercell thunderstorms are known to occur in the outer rainbands of tropical cyclones (TCs), and these cells are of interest because they are occasionally tornadic. A series of multi-scale quasi-idealized TC simulations are used to study the development of outer rainband Supercells. Within the environment of landfalling TCs, the sea-to-land transition of the rainbands is found to locally benefit supercell development onshore due in part to (1) enhanced surface-based destabilization during the day and (2) increased surface friction slowing and backing the low-level winds. Landfall time of day is shown to have a substantial impact on the average number, strength, and lifetime of the ensemble of simulated Supercells. These idealized simulations represent a first attempt at controlled hypothesis tests for supercell and tornado ingredients within the context of a highly resolved parent TC.
Paul Markowski - One of the best experts on this subject based on the ideXlab platform.
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near ground vertical vorticity in supercell thunderstorm models
Journal of the Atmospheric Sciences, 2017Co-Authors: Richard Rotunno, Paul Markowski, George H BryanAbstract:AbstractNumerical models of supercell thunderstorms produce near-ground rotation about a vertical axis (i.e., vertical vorticity) after the development of rain-cooled outflows and downdrafts. The physical processes involved in the production of near-ground vertical vorticity in simulated Supercells have been a subject of discussion in the literature for over 30 years. One cause for this lengthy discussion is the difficulty in applying the principles of inviscid vorticity dynamics in a continuous fluid to the viscous evolution of discrete Eulerian simulations. The present paper reports on a Lagrangian analysis of near-ground vorticity from an idealized-supercell simulation with enhanced vertical resolution near the lower surface. The parcel that enters the low-level maximum of vertical vorticity has a history of descent during which its horizontal vorticity is considerably enhanced. In its final approach to this region, the parcel’s enhanced horizontal vorticity is tilted to produce vertical vorticity, whi...
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Comparison of the Tornadic and Nontornadic Supercells Intercepted by VORTEX2 on 10 June 2010
Monthly Weather Review, 2016Co-Authors: Alicia Klees, Paul Markowski, Yvette Richardson, Christopher C. Weiss, Joshua Wurman, Karen KosibaAbstract:AbstractOn 10 June 2010, the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) armada collected a rare set of observations of a nontornadic and a tornadic supercell evolving in close proximity to each other. The storms and their environments were analyzed using single- and dual-Doppler radar, mobile mesonet, deployable surface mesonet, and mobile sounding data, with the goal of understanding why one supercell produced no tornadoes while the other produced at least two. Outflow temperature deficits were similar for the two storms, both within the normal range for weakly tornadic Supercells but somewhat cold relative to significantly tornadic Supercells. The storms formed in a complex environment, with slightly higher storm-relative helicity near the tornadic supercell. The environment evolved significantly in time, with large thermodynamic changes and increases in storm-relative helicity, leading to conditions much more favorable for tornadogenesis. After a few hours, a new s...
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Supercell Low-Level Mesocyclones in Simulations with a Sheared Convective Boundary Layer
Monthly Weather Review, 2015Co-Authors: Christopher J. Nowotarski, Paul Markowski, Yvette Richardson, George H BryanAbstract:AbstractSimulations of supercell thunderstorms in a sheared convective boundary layer (CBL), characterized by quasi-two-dimensional rolls, are compared with simulations having horizontally homogeneous environments. The effects of boundary layer convection on the general characteristics and the low-level mesocyclones of the simulated Supercells are investigated for rolls oriented either perpendicular or parallel to storm motion, as well as with and without the effects of cloud shading.Bulk measures of storm strength are not greatly affected by the presence of rolls in the near-storm environment. Though boundary layer convection diminishes with time under the anvil shadow of the Supercells when cloud shading is allowed, simulations without cloud shading suggest that rolls affect the morphology and evolution of supercell low-level mesocyclones. Initially, CBL vertical vorticity perturbations are enhanced along the supercell outflow boundary, resulting in nonnegligible near-ground vertical vorticity regardles...
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The origins of vortex sheets in a simulated supercell thunderstorm
Monthly Weather Review, 2014Co-Authors: Paul Markowski, Yvette Richardson, George H BryanAbstract:AbstractThis paper investigates the origins of the (cyclonic) vertical vorticity within vortex sheets that develop within a numerically simulated supercell in a nonrotating, horizontally homogeneous environment with a free-slip lower boundary. Vortex sheets are commonly observed along the gust fronts of supercell storms, particularly in the early stages of storm development. The “collapse” of a vortex sheet into a compact vortex is often seen to accompany the intensification of rotation that occasionally leads to tornadogenesis. The vortex sheets predominantly acquire their vertical vorticity from the tilting of horizontal vorticity that has been modified by horizontal buoyancy gradients associated with the supercell’s cool low-level outflow. If the tilting is within an ascending airstream (i.e., the horizontal gradient of vertical velocity responsible for the tilting resides entirely within an updraft), the vertical vorticity of the vortex sheet nearly vanishes at the lowest model level for horizontal wi...
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multiscale processes leading to Supercells in the landfalling outer rainbands of hurricane katrina 2005
Weather and Forecasting, 2011Co-Authors: Benjamin Green, Fuqing Zhang, Paul MarkowskiAbstract:AbstractShallow Supercells are frequently observed within the outer rainbands—both onshore and offshore—of landfalling tropical cyclones (TCs). Such Supercells can produce tornadoes along the coast even when the center of the parent TC is hundreds of kilometers from land, as was the case with Hurricane Katrina (2005). A convection-permitting simulation with 1.5-km grid spacing in the innermost domain is used in conjunction with radar, radiosonde, and surface observations to investigate the multiscale conditions conducive to Supercells in the landfalling outer rainbands of Katrina. Several hours before the eye of the TC made landfall, a baroclinic zone developed along the coast; this front strongly influenced the horizontal distributions of cell-relative helicity and CAPE such that the largest values of these parameters were located over land and water, respectively. An example of a tornadic supercell in the outer rainbands of Katrina is examined. This cell intensified just before landfall and spawned a to...
Fumiyasu Oba - One of the best experts on this subject based on the ideXlab platform.
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finite size corrections for defect involving vertical transitions in supercell calculations
Physical Review B, 2020Co-Authors: Tomoya Gake, Christoph Freysoldt, Yu Kumagai, Fumiyasu ObaAbstract:A correction method for vertical transition levels (VTLs) involving defect states calculated with a supercell technique is formulated and its effectiveness is systematically verified with ten defects in prototypical materials: cubic-BN, GaN, MgO, and 3C-SiC. Without any corrections, the absolute errors are around 1 eV with moderate size Supercells in most cases. In contrast, when our correction method is adopted, the absolute errors are reduced and become less than 0.12 eV in all the cases. Our correction scheme is general and will have the potential for wide application as it is adaptive for evaluating various quantities at fixed geometry, as represented by those relevant to the generalized Koopmans' theorem.
George H Bryan - One of the best experts on this subject based on the ideXlab platform.
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near ground vertical vorticity in supercell thunderstorm models
Journal of the Atmospheric Sciences, 2017Co-Authors: Richard Rotunno, Paul Markowski, George H BryanAbstract:AbstractNumerical models of supercell thunderstorms produce near-ground rotation about a vertical axis (i.e., vertical vorticity) after the development of rain-cooled outflows and downdrafts. The physical processes involved in the production of near-ground vertical vorticity in simulated Supercells have been a subject of discussion in the literature for over 30 years. One cause for this lengthy discussion is the difficulty in applying the principles of inviscid vorticity dynamics in a continuous fluid to the viscous evolution of discrete Eulerian simulations. The present paper reports on a Lagrangian analysis of near-ground vorticity from an idealized-supercell simulation with enhanced vertical resolution near the lower surface. The parcel that enters the low-level maximum of vertical vorticity has a history of descent during which its horizontal vorticity is considerably enhanced. In its final approach to this region, the parcel’s enhanced horizontal vorticity is tilted to produce vertical vorticity, whi...
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Supercell Low-Level Mesocyclones in Simulations with a Sheared Convective Boundary Layer
Monthly Weather Review, 2015Co-Authors: Christopher J. Nowotarski, Paul Markowski, Yvette Richardson, George H BryanAbstract:AbstractSimulations of supercell thunderstorms in a sheared convective boundary layer (CBL), characterized by quasi-two-dimensional rolls, are compared with simulations having horizontally homogeneous environments. The effects of boundary layer convection on the general characteristics and the low-level mesocyclones of the simulated Supercells are investigated for rolls oriented either perpendicular or parallel to storm motion, as well as with and without the effects of cloud shading.Bulk measures of storm strength are not greatly affected by the presence of rolls in the near-storm environment. Though boundary layer convection diminishes with time under the anvil shadow of the Supercells when cloud shading is allowed, simulations without cloud shading suggest that rolls affect the morphology and evolution of supercell low-level mesocyclones. Initially, CBL vertical vorticity perturbations are enhanced along the supercell outflow boundary, resulting in nonnegligible near-ground vertical vorticity regardles...
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The origins of vortex sheets in a simulated supercell thunderstorm
Monthly Weather Review, 2014Co-Authors: Paul Markowski, Yvette Richardson, George H BryanAbstract:AbstractThis paper investigates the origins of the (cyclonic) vertical vorticity within vortex sheets that develop within a numerically simulated supercell in a nonrotating, horizontally homogeneous environment with a free-slip lower boundary. Vortex sheets are commonly observed along the gust fronts of supercell storms, particularly in the early stages of storm development. The “collapse” of a vortex sheet into a compact vortex is often seen to accompany the intensification of rotation that occasionally leads to tornadogenesis. The vortex sheets predominantly acquire their vertical vorticity from the tilting of horizontal vorticity that has been modified by horizontal buoyancy gradients associated with the supercell’s cool low-level outflow. If the tilting is within an ascending airstream (i.e., the horizontal gradient of vertical velocity responsible for the tilting resides entirely within an updraft), the vertical vorticity of the vortex sheet nearly vanishes at the lowest model level for horizontal wi...
Richard L. Thompson - One of the best experts on this subject based on the ideXlab platform.
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Choosing a Universal Mean Wind for Supercell Motion Prediction
Journal of Operational Meteorology, 2014Co-Authors: Matthew J. Bunkers, Roger Edwards, Richard L. Thompson, David A. Barber, Jonathan GarnerAbstract:The 06-km AGL mean wind has been used widely in operations to predict supercell motion. However, when a supercell is low-topped or elevated, its motion may be poorly predicted with this default mean wind— which itself could be height-based or pressure-weighted. This information suggests that a single, fixed layer is inappropriate for some situations, and thus various mean-wind parameters are explored herein. A dataset of 583 observed and 829 Rapid Update Cycle supercell soundings was assembled. When the mean wind is computed using pressure weighting for an effective inflow-layer as the base, and 65% of the most-unstable equilibrium level height as the top, the result is that better supercell motion predictions can be obtained for low-topped and elevated Supercells. Such a mean-wind modification would come at the cost of only a minor increase in mean absolute error for the entire sample of supercell cases considered.
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convective modes for significant severe thunderstorms in the contiguous united states part ii supercell and qlcs tornado environments
Weather and Forecasting, 2012Co-Authors: Richard L. Thompson, Bryan T Smith, Jeremy S Grams, Andrew R Dean, Chris BroylesAbstract:AbstractA sample of 22 901 tornado and significant severe thunderstorm events, filtered on an hourly 40-km grid, was collected for the period 2003–11 across the contiguous United States (CONUS). Convective mode was assigned to each case via manual examination of full volumetric radar data (Part I of this study), and environmental information accompanied each grid-hour event from the hourly objective analyses calculated and archived at the Storm Prediction Center (SPC). Sounding-derived parameters related to Supercells and tornadoes formed the basis of this investigation owing to the dominance of right-moving Supercells in tornado production and the availability of supercell-related convective parameters in the SPC environmental archive. The tornado and significant severe thunderstorm events were stratified by convective mode and season. Measures of buoyancy discriminated most strongly between supercell and quasi-linear convective system (QLCS) tornado events during the winter, while bulk wind differences ...
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the optimal bulk wind differential depth and the utility of the upper tropospheric storm relative flow for forecasting Supercells
Weather and Forecasting, 2008Co-Authors: Adam L. Houston, Richard L. Thompson, Roger EdwardsAbstract:Abstract An analysis of 4 yr of Rapid Update Cycle-2 (RUC-2) derived soundings in proximity to radar-observed Supercells and nonSupercells is conducted in an effort to answer two questions: 1) over what depth is the fixed-layer bulk wind differential (BWD; the vector difference between the wind velocity at a given level and the wind velocity at the surface) the best discriminator between supercell and nonsupercell environments and 2) does the upper-tropospheric storm-relative flow (UTSRF) discriminate between the environments of Supercells and nonSupercells? Previous climatologies of sounding-based supercell forecast parameters have documented the ability of the 0–6-km BWD in delineating supercell from nonsupercell environments. However, a systematic examination of a wide range of layers has never been documented. The UTSRF has previously been tested as a parameter for discriminating between supercell and nonsupercell environments and there is some evidence that Supercells may be sensitive to the UTSRF. H...
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Effective Storm-Relative Helicity and Bulk Shear in Supercell Thunderstorm Environments
Weather and Forecasting, 2007Co-Authors: Richard L. Thompson, Corey M. Mead, Roger EdwardsAbstract:Abstract A sample of 1185 Rapid Update Cycle (RUC) model analysis (0 h) proximity soundings, within 40 km and 30 min of radar-identified discrete storms, was categorized by several storm types: significantly tornadic Supercells (F2 or greater damage), weakly tornadic Supercells (F0–F1 damage), nontornadic Supercells, elevated right-moving Supercells, storms with marginal supercell characteristics, and nonSupercells. These proximity soundings served as the basis for calculations of storm-relative helicity and bulk shear intended to apply across a broad spectrum of thunderstorm types. An effective storm inflow layer was defined in terms of minimum constraints on lifted parcel CAPE and convective inhibition (CIN). Sixteen CAPE and CIN constraint combinations were examined, and the smallest CAPE (25 and 100 J kg−1) and largest CIN (−250 J kg−1) constraints provided the greatest probability of detecting an effective inflow layer within an 835-supercell subset of the proximity soundings. Effective storm-relativ...
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characteristics of vertical wind profiles near Supercells obtained from the rapid update cycle
Weather and Forecasting, 2003Co-Authors: Paul Markowski, Christina Hannon, Jeffrey Frame, Elise Lancaster, Albert Pietrycha, Roger Edwards, Richard L. ThompsonAbstract:Abstract Over 400 vertical wind profiles in close proximity to nontornadic and tornadic supercell thunderstorms are examined. The profiles were obtained from the Rapid Update Cycle (RUC) model/analysis system. Ground-relative wind speeds throughout the lower and middle troposphere are larger, on average, in tornadic supercell environments than in nontornadic supercell environments. The average vertical profiles of storm-relative wind speed, vertical wind shear, hodograph curvature, crosswise and streamwise vorticity, and storm-relative helicity are generally similar above 1 km in the tornadic and nontornadic supercell environments, with differences that are either not statistically significant or not what most would regard as meteorologically significant. On the other hand, considerable differences are found in these average vertical profiles within 1 km of the ground, with environments associated with significantly tornadic Supercells (those producing tornadoes of at least F2 intensity) having substantia...
