scholarly journals Simulating Real Atmospheric Boundary Layers at Gray-Zone Resolutions: How Do Currently Available Turbulence Parameterizations Perform?

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 345 ◽  
Author(s):  
Paula Doubrawa ◽  
Domingo Muñoz-Esparza
Keyword(s):  
Boundary Layer ◽  
Turbulent Transport ◽  
Model Performance ◽  
Wrf Model ◽  
Turbulent Energy ◽  
Complex Problem ◽  
Gray Zone ◽  
Horizontal Structure ◽  
One Dimensional ◽  
Dimensional Boundary

Recent computational and modeling advances have led a diverse modeling community to experiment with atmospheric boundary layer (ABL) simulations at subkilometer horizontal scales. Accurately parameterizing turbulence at these scales is a complex problem. The modeling solutions proposed to date are still in the development phase and remain largely unvalidated. This work assesses the performance of methods currently available in the Weather Research and Forecasting (WRF) model to represent ABL turbulence at a gray-zone grid spacing of 333 m. We consider three one-dimensional boundary layer parameterizations (MYNN, YSU and Shin-Hong) and coarse large-eddy simulations (LES). The reference dataset consists of five real-case simulations performed with WRF-LES nested down to 25 m. Results reveal that users should refrain from coarse LES and favor the scale-aware, Shin-Hong parameterization over traditional one-dimensional schemes. Overall, the spread in model performance is large for the cellular convection regime corresponding to the majority of our cases, with coarse LES overestimating turbulent energy across scales and YSU underestimating it and failing to reproduce its horizontal structure. Despite yielding the best results, the Shin-Hong scheme overestimates the effect of grid dependence on turbulent transport, highlighting the outstanding need for improved solutions to seamlessly parameterize turbulence across scales.

scholarly journals MODELING TURBULENT BOTTOM BOUNDARY LAYER DYNAMICS

1986 ◽  
Vol 1 (20) ◽  
pp. 110 ◽  
Author(s):  
Y.P. Sheng
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Boundary Layers ◽  
Turbulent Transport ◽  
Complex Problem ◽  
Comprehensive Model ◽  
Bottom Boundary ◽  
Bottom Boundary Layers ◽  
Dimensional Boundary ◽  
Boundary Layer Dynamics

This paper presents a modeling approach aimed at solving a complete hierarchy of turbulent bottom boundary layers which are often encountered in practical coastal and oceanographic engineering problems. The practical problem is extremely complex due to the presence and interaction of competing processes. A comprehensive model is thus needed to first provide fundamental understanding of a variety of turbulent bottom boundary layers before any simple model for the complex problem can be meaningfully constructed. This paper presents a comprehensive second-order closure model of turbulent transport and in addition, discusses some applications of the model to wave boundary layer, wave-current boundary layer, sediment-laden boundary layer and two-dimensional boundary layer. Example is provided to show how such a comprehensive model may be used to guide the development of a simple model.

Low-level wind profiles at an Antarctic coastal station

1989 ◽  
Vol 1 (2) ◽  
pp. 169-178 ◽  
Author(s):  
J.C. King
Keyword(s):  
Boundary Layer ◽  
Temperature Profiles ◽  
Pressure Gradients ◽  
Synoptic Scale ◽  
Layer Model ◽  
Coastal Station ◽  
One Dimensional ◽  
Dimensional Boundary ◽  
Sloping Surface ◽  
Wind Profiles

Wind and temperature profiles in the lowest 2000 m of the atmosphere at Halley (75°35′S, 26°50′W) have been analysed. Surface winds blow most frequently from the sector 090° ± 45° but the 2000 m wind direction is much more evenly distributed and appears to be determined by synoptic-scale pressure gradients. A simple one-dimensional boundary layer model, which includes the effects of stably-stratified air overlying a sloping surface, is able to reproduce some of the features of the observed profiles.

scholarly journals Dynamics of eddying abyssal mixing layers over rough topography

2022 ◽  
Author(s):  
Henri Drake ◽  
Xiaozhou Ruan ◽  
Raffaele Ferrari ◽  
Andreas Thurnherr ◽  
Kelly Ogden ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Small Scale ◽  
One Dimensional ◽  
Basin Scale ◽  
Dimensional Boundary ◽  
Mid Atlantic Ridge ◽  
Non Local ◽  
The One ◽  
Abyssal Mixing

The abyssal overturning circulation is thought to be primarily driven by small-scale turbulent mixing. Diagnosed watermass transformations are dominated by rough topography "hotspots", where the bottom-enhancement of mixing causes the diffusive buoyancy flux to diverge, driving widespread downwelling in the interior—only to be overwhelmed by an even stronger upwelling in a thin Bottom Boundary Layer (BBL). These watermass transformations are significantly underestimated by one-dimensional sloping boundary layer solutions, suggesting the importance of three-dimensional physics. Here, we use a hierarchy of models to generalize this one-dimensional boundary layer approach to three-dimensional eddying flows over realistically rough topography. When applied to the Mid-Atlantic Ridge in the Brazil Basin, the idealized simulation results are roughly consistent with available observations. Integral buoyancy budgets isolate the physical processes that contribute to realistically strong BBL upwelling. The downwards diffusion of buoyancy is primarily balanced by upwelling along the canyon flanks and the surrounding abyssal hills. These flows are strengthened by the restratifying effects of submesoscale baroclinic eddies on the canyon flanks and by the blocking of along-ridge thermal wind within the canyon. Major topographic sills block along-thalweg flows from restratifying the canyon trough, resulting in the continual erosion of the trough's stratification. We propose simple modifications to the one-dimensional boundary layer model which approximate each of these three-dimensional effects. These results provide \textit{local} dynamical insights into mixing-driven abyssal overturning, but a complete theory will also require the non-local coupling to the basin-scale circulation.

scholarly journals Diapycnal Transport near a Sloping Bottom Boundary

2020 ◽  
Vol 50 (11) ◽  
pp. 3253-3266
Author(s):  
R. M. Holmes ◽  
Trevor J. McDougall
Keyword(s):  
Boundary Layer ◽  
Mixing Layer ◽  
Buoyancy Flux ◽  
Bottom Boundary ◽  
One Dimensional ◽  
Dimensional Boundary ◽  
Velocity Changes ◽  
Stratified Ocean ◽  
The One ◽  
Sloping Bottom

AbstractThe diapycnal motion in the stratified ocean near a sloping bottom boundary is studied using analytical solutions from one-dimensional boundary layer theory. Bottom-intensification of the diapycnal mixing intensity ensures that in the stratified mixing layer (SML), where isopycnals are relatively flat, the diapycnal motion is downward toward denser fluid. In contrast, convergence of the diffusive buoyancy flux near the seafloor drives diapycnal upwelling in what we define as the bottom boundary layer (BBL). Much of the one-dimensional BBL is characterized by a stratification only slightly reduced from that in the SML because the maximum in the buoyancy flux at the top of the BBL, where the diapycnal velocity changes sign, must occur in well-stratified fluid. The diapycnal upwelling in the BBL is determined by variations not only in the magnitude of the buoyancy gradient but also in the curvature of isopycnals. The net diapycnal upwelling is concentrated in the bottom half of the BBL where the magnitude of the buoyancy gradient changes most rapidly. The curvature effect drives upwelling near the seafloor that only makes a significant contribution to the net upwelling for steep slopes. The structure of the diapycnal velocity in this stratified BBL differs from the case of a turbulent well-mixed BBL that has been assumed in some recent theoretical studies on bottom-intensified mixing. This work therefore extends recent theories in a way that should be more applicable to abyssal ocean observations where well-mixed BBLs are not common.

scholarly journals Explicit Filtering and Reconstruction to Reduce Grid Dependence in Convective Boundary Layer Simulations Using WRF-LES

2019 ◽  
Vol 147 (5) ◽  
pp. 1805-1821 ◽  
Author(s):  
Jason S. Simon ◽  
Bowen Zhou ◽  
Jeffrey D. Mirocha ◽  
Fotini Katopodes Chow
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Mixed Model ◽  
Potential Temperature ◽  
Wrf Model ◽  
Turbulence Models ◽  
Reconstruction Technique ◽  
Gray Zone ◽  
Turbulent Structures ◽  
Convective Boundary

Abstract As model grid resolutions move from the mesoscale to the microscale, turbulent structures represented in atmospheric boundary layer simulations change dramatically. At intermediate resolutions, the so-called gray zone, turbulent motions are not resolved accurately, posing a challenge to numerical simulations. The representation of turbulence is also highly sensitive to the choice of closure model. Here, we examine explicit filtering and reconstruction in the gray zone as a technique to better represent atmospheric turbulence. The convective boundary layer is simulated using the Weather Research and Forecasting (WRF) Model with horizontal resolutions ranging from 25 m to 1 km. Four large-eddy simulation (LES) turbulence models are considered: the Smagorinsky model, the TKE-1.5 model, and two versions of the dynamic reconstruction model (DRM). The models are evaluated by their ability to produce consistent mean potential temperature profiles, heat and momentum fluxes, velocity fields, and turbulent kinetic energy spectra as the grids become coarser. The DRM, a mixed model that uses an explicit filtering and reconstruction technique to account for resolvable subfilter-scale (RSFS) stresses, performs very well at resolutions of 500 m and 1 km without any special tuning, whereas the Smagorinsky and TKE-1.5 models produce heavily grid-dependent results.

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