scholarly journals Properties of a Simulated Convective Boundary Layer in an Idealized Supercell Thunderstorm Environment

2014 ◽  
Vol 142 (11) ◽  
pp. 3955-3976 ◽  
Author(s):  
Christopher J. Nowotarski ◽  
Paul M. Markowski ◽  
Yvette P. Richardson ◽  
George H. Bryan
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Convective Available Potential Energy ◽  
Vertical Wind Shear ◽  
Surface Fluxes ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Sensitivity Tests ◽  
Supercell Thunderstorms ◽  
Background Shear

Abstract Nearly all previous numerical simulations of supercell thunderstorms have neglected surface fluxes of heat, moisture, and momentum. This choice precludes horizontal inhomogeneities associated with dry boundary layer convection in the near-storm environment. As part of a broader study on how mature supercell thunderstorms are affected by a convective boundary layer (CBL) with quasi-two-dimensional features (i.e., boundary layer rolls), this paper documents the methods used to develop a realistic CBL in an idealized environment supportive of supercells. The evolution and characteristics of the modeled CBL, including the horizontal variability of thermodynamic and kinematic quantities known to affect supercell evolution, are presented. The simulated rolls result in periodic bands of perturbations in temperature, moisture, convective available potential energy (CAPE), vertical wind shear, and storm-relative helicity (SRH). Vertical vorticity is shown to arise within the boundary layer through the tilting of ambient horizontal vorticity associated with the background shear by vertical velocity perturbations in the turbulent CBL. Sensitivity tests suggest that 200-m horizontal grid spacing is adequate to represent rolls using a large-eddy simulation (LES) approach.

scholarly journals Modifications to the Near-Storm Environment Induced by Simulated Supercell Thunderstorms

2015 ◽  
Vol 144 (1) ◽  
pp. 273-293 ◽  
Author(s):  
Christopher J. Nowotarski ◽  
Paul M. Markowski
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Convective Boundary ◽  
Roll Vortices ◽  
Sensitivity Tests ◽  
Supercell Thunderstorms ◽  
Sheared Convective Boundary Layer ◽  
Outflow Boundary ◽  
Cloud Ice ◽  
Ice Water

Abstract This study investigates the changes that simulated supercell thunderstorms impart on their surroundings. Supercells are simulated in a strongly sheared convective boundary layer comprising horizontal roll vortices. In sensitivity tests, the effects of cloud shading on the near-storm environment are explored through the removal of cloud ice, water, and hydrometeor effects on parameterized radiation. All of the simulated supercells increase the low-level shear in their proximal environment; however, this effect is more pronounced when cloud shading is included. Shading stabilizes the boundary layer beneath the cirrus anvil, diminishes boundary layer rolls and their attendant thermodynamic perturbations, and reduces the intensity of resolved turbulent mixing in the convective boundary layer. Anvil shading also acts to reduce the buoyancy of inflow air and the horizontal buoyancy gradient along the forward-flank outflow boundary.

scholarly journals Mid-latitude convective boundary-layer electricity: A study by large-eddy simulation

2020 ◽  
Vol 244 ◽  
pp. 105035 ◽  
Author(s):  
S.V. Anisimov ◽  
S.V. Galichenko ◽  
A.A. Prokhorchuk ◽  
K.V. Aphinogenov
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Convective Boundary Layer ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy

Influence of Swell on Marine Surface-Layer Structure

2020 ◽  
Vol 77 (5) ◽  
pp. 1865-1885 ◽  
Author(s):  
Qingfang Jiang
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Convective Boundary Layer ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Convective Boundary ◽  
Stable Conditions ◽  
Marine Surface Layer ◽  
Marine Surface

Abstract The influence of swell on turbulence and scalar profiles in a marine surface layer and underlying physics is examined in this study through diagnosis of large-eddy simulations (LES) that explicitly resolve the surface layer and underlying swell. In general, under stable conditions, the mean wind and scalar profiles can be significantly modified by swell. The influence of swell on wind shear, turbulence structure, scalar profiles, and evaporation duct (ED) characteristics becomes less pronounced in a more convective boundary layer, where the buoyancy production of turbulence is significant. Dynamically, swell has little direct impact on scalar profiles. Instead it modifies the vertical wind shear by exerting pressure drag on the wave boundary layer. The resulting redistribution of vertical wind shear leads to changes in turbulence production and therefore turbulence mixing of scalars. Over swell, the eddy diffusivities from LES systematically deviate from the Monin–Obukhov similarity theory (MOST) prediction, implying that MOST becomes invalid over a swell-dominated sea. The deviations from MOST are more pronounced in a neutral or stable boundary layer under relatively low winds and less so in a convective boundary layer.

scholarly journals Comparison of Convective Boundary Layer Velocity Spectra Retrieved from Large- Eddy-Simulation and Weather Research and Forecasting Model Data

2014 ◽  
Vol 53 (2) ◽  
pp. 377-394 ◽  
Author(s):  
Jeremy A. Gibbs ◽  
Evgeni Fedorovich
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Wrf Model ◽  
Velocity Fields ◽  
Weather Research And Forecasting ◽  
Small Scale ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Velocity Spectra

AbstractAs computing capabilities expand, operational and research environments are moving toward the use of finescale atmospheric numerical models. These models are attractive for users who seek an accurate description of small-scale turbulent motions. One such numerical tool is the Weather Research and Forecasting (WRF) model, which has been extensively used in synoptic-scale and mesoscale studies. As finer-resolution simulations become more desirable, it remains a question whether the model features originally designed for the simulation of larger-scale atmospheric flows will translate to adequate reproductions of small-scale motions. In this study, turbulent flow in the dry atmospheric convective boundary layer (CBL) is simulated using a conventional large-eddy-simulation (LES) code and the WRF model applied in an LES mode. The two simulation configurations use almost identical numerical grids and are initialized with the same idealized vertical profiles of wind velocity, temperature, and moisture. The respective CBL forcings are set equal and held constant. The effects of the CBL wind shear and of the varying grid spacings are investigated. Horizontal slices of velocity fields are analyzed to enable a comparison of CBL flow patterns obtained with each simulation method. Two-dimensional velocity spectra are used to characterize the planar turbulence structure. One-dimensional velocity spectra are also calculated. Results show that the WRF model tends to attribute slightly more energy to larger-scale flow structures as compared with the CBL structures reproduced by the conventional LES. Consequently, the WRF model reproduces relatively less spatial variability of the velocity fields. Spectra from the WRF model also feature narrower inertial spectral subranges and indicate enhanced damping of turbulence on small scales.

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