Analysis of small-scale patterns of atmospheric motion in a sheared, convective boundary layer

1996 ◽  
Vol 101 (D5) ◽  
pp. 9391-9411 ◽  
Author(s):  
F. L. Ludwig ◽  
R. L. Street ◽  
J. M. Schneider ◽  
K. R. Costigan
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Small Scale ◽  
Convective Boundary ◽  
Atmospheric Motion ◽  
Sheared 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.

scholarly journals Bulk Models of the Sheared Convective Boundary Layer: Evaluation through Large Eddy Simulations

2007 ◽  
Vol 64 (3) ◽  
pp. 786-807 ◽  
Author(s):  
Robert Conzemius ◽  
Evgeni Fedorovich
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Entrainment Rate ◽  
Convective Boundary ◽  
Surface Shear ◽  
Large Eddy ◽  
Entrainment Zone ◽  
Sheared Convective Boundary Layer ◽  
Bulk Model ◽  
Approach Zero

Abstract A set of first-order model (FOM) equations, describing the sheared convective boundary layer (CBL) evolution, is derived. The model output is compared with predictions of the zero-order bulk model (ZOM) for the same CBL type. Large eddy simulation (LES) data are employed to test both models. The results show an advantage of the FOM over the ZOM in the prediction of entrainment, but in many CBL cases, the predictions by the two models are fairly close. Despite its relative simplicity, the ZOM is able to quantify the effects of shear production and dissipation in an integral sense—as long as the constants describing the integral dissipation of shear- and buoyancy-produced turbulence kinetic energy (TKE) are prescribed appropriately and the shear is weak enough that the denominator of the ZOM entrainment equation does not approach zero, causing a numerical instability in the solutions. Overall, the FOM better predicts the entrainment rate due to its ability to avoid this instability. Also, the FOM in a more physically consistent manner reproduces the sheared CBL entrainment zone, whose depth is controlled by a balance among shear generation, buoyancy consumption, and dissipation of TKE. Such balance is manifested by nearly constant values of Richardson numbers observed in the entrainment zone of simulated sheared CBLs. Conducted model tests support the conclusion that the surface shear generation of TKE and its corresponding dissipation, as well as the nonstationary terms, can be omitted from the integral TKE balance equation.

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 Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings

2015 ◽  
Vol 15 (8) ◽  
pp. 4241-4257 ◽  
Author(s):  
H. P. Pietersen ◽  
J. Vilà-Guerau de Arellano ◽  
P. Augustin ◽  
A. van de Boer ◽  
O. de Coster ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Surface Heterogeneity ◽  
Small Scale ◽  
Mountain Range ◽  
Convective Boundary ◽  
Data Set ◽  
Local Boundary ◽  
Heat And Moisture

Abstract. We study the influence of the large-scale atmospheric contribution to the dynamics of the convective boundary layer (CBL) in a situation observed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. We employ two modeling approaches, the mixed-layer theory and large-eddy simulation (LES), with a complete data set of surface and upper-air atmospheric observations, to quantify the contributions of the advection of heat and moisture, and subsidence. We find that by only taking surface and entrainment fluxes into account, the boundary-layer height is overestimated by 70%. Constrained by surface and upper-air observations, we infer the large-scale vertical motions and horizontal advection of heat and moisture. Our findings show that subsidence has a clear diurnal pattern. Supported by the presence of a nearby mountain range, this pattern suggests that not only synoptic scales exert their influence on the boundary layer, but also mesoscale circulations. LES results show a satisfactory correspondence of the vertical structure of turbulent variables with observations. We also find that when large-scale advection and subsidence are included in the simulation, the values for turbulent kinetic energy are lower than without these large-scale forcings. We conclude that the prototypical CBL is a valid representation of the boundary-layer dynamics near regions characterized by complex topography and small-scale surface heterogeneity, provided that surface- and large-scale forcings are representative for the local boundary layer.

scholarly journals Bulk models of sheared boundary layer convection

2019 ◽  
Vol 55 (2) ◽  
pp. 3-16
Author(s):  
A. V. Debolskiy ◽  
V. M. Stepanenko ◽  
A. V. Glazunov ◽  
S. S. Zilitinkevich
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Convective Boundary Layer ◽  
Integral Model ◽  
Published Data ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Average Wind ◽  
Sheared Convective Boundary Layer ◽  
Convective Layer

The paper discusses approaches to the construction of integral models of the convective boundary layer (CBL), based on the concept of complete mixing. To test analytic bulk models and the basic hypotheses of similarity, we use the results of eddy modeling (LES – Large Eddy Simulation). The empirical constants of the CBL integral models obtained according to the LES data for the case of free convection, are in good agreement with the previously published data of laboratory experiments. It is also shown that the flow of kinetic energy from the upper boundary of the CPS, carried out by gravitational waves, is small compared with other components of the balance of turbulent kinetic energy (TKE) in the convective layer. Parametrization of TKE generation for the case of sheared convective boundary layer in terms of the friction velocity and the average wind velocity in the CBL derived; resulting dimensionless constants are obtained from LES data. The results of the work allow us to formulate an integral model of the shear KPS suitable for practical use.

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