Turbulence Fine Structure, Intermittency, and Large-Scale Interactions in the Stable Boundary Layer and Residual Layer: Correlative High-Resolution Measurements and Direct Numerical Simulations

Abstract The evolution of the stable boundary layer is simulated using an idealized single-column model of pressure-driven flow coupled to a surface energy budget. Several commonly used parameterizations of turbulence are examined. The agreement between the simulated wind and temperature profiles and tower observations from the Cabauw tower is generally good given the simplicity of the model. The collapse and recovery of turbulence is explored in the presence of a large-scale pressure gradient, but excluding transient submesoscale atmospheric forcings such as internal waves and density-driven currents. The sensitivity tests presented here clarify the role of both rotation and the surface energy budget in the collapse and recovery of turbulence for the pressure-driven dry stable boundary layer (SBL). Conditions of stability are affected strongly by the geostrophic winds, the cloud cover, and the thermal conductivity of the surface. Inertial oscillations and the subsurface temperature have a weaker influence. Particularly noteworthy is the relationship between SBL regime and the relative importance of the terms in the surface energy budget.

Download Full-text

A Businger Mechanism for Intermittent Bursting in the Stable Boundary Layer

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0309.1 ◽

2020 ◽

Vol 77 (10) ◽

pp. 3343-3360

Author(s):

Steven J. A. van der Linden ◽

Bas J. H. van de Wiel ◽

Igor Petenko ◽

Chiel C. van Heerwaarden ◽

Peter Baas ◽

...

Keyword(s):

Boundary Layer ◽

Stable Boundary Layer ◽

Large Scale ◽

Lower Layer ◽

Unstable Wave ◽

Turbulent Friction ◽

Stable Boundary ◽

Flow Acceleration ◽

Boundary Layer Height ◽

Entire Sequence

AbstractHigh-resolution large-eddy simulations of the Antarctic very stable boundary layer reveal a mechanism for systematic and periodic intermittent bursting. A nonbursting state with a boundary layer height of just 3 m is alternated by a bursting state with a height of ≈5 m. The bursts result from unstable wave growth triggered by a shear-generated Kelvin–Helmholtz instability, as confirmed by linear stability analysis. The shear at the top of the boundary layer is built up by two processes. The upper, quasi-laminar layer accelerates due to the combined effect of the pressure force and rotation by the Coriolis force, while the lower layer decelerates by turbulent friction. During the burst, this shear is eroded and the initial cause of the instability is removed. Subsequently, the interfacial shear builds up again, causing the entire sequence to repeat itself with a time scale of ≈10 min. Despite the clear intermittent bursting, the overall change of the mean wind profile is remarkably small during the cycle. This enables such a fast erosion and recovery of the shear. This mechanism for cyclic bursting is remarkably similar to the mechanism hypothesized by Businger in 1973, with one key difference. Whereas Businger proposes that the flow acceleration in the upper layer results from downward turbulent transfer of high-momentum flow, the current results indicate no turbulent activity in the upper layer, hence requiring another source of momentum. Finally, it would be interesting to construct a climatology of shear-generated intermittency in relation to large-scale conditions to assess the generality of this Businger mechanism.

Download Full-text

High-Resolution In Situ Profiling through the Stable Boundary Layer: Examination of the SBL Top in Terms of Minimum Shear, Maximum Stratification, and Turbulence Decrease

Journal of the Atmospheric Sciences ◽

10.1175/jas3671.1 ◽

2006 ◽

Vol 63 (4) ◽

pp. 1291-1307 ◽

Cited By ~ 35

Author(s):

B. B. Balsley ◽

R. G. Frehlich ◽

M. L. Jensen ◽

Y. Meillier

Keyword(s):

Boundary Layer ◽

Energy Dissipation ◽

High Resolution ◽

Stable Boundary Layer ◽

Dissipation Rate ◽

Energy Dissipation Rate ◽

Horizontal Wind ◽

Small Scale ◽

Stable Boundary ◽

Stable Conditions

Abstract Some 50 separate high-resolution profiles of small-scale turbulence defined by the energy dissipation rate (ɛ), horizontal wind speed, and temperature from near the surface, through the nighttime stable boundary layer (SBL), and well into the residual layer are used to compare the various definitions of SBL height during nighttime stable conditions. These profiles were obtained during postmidnight periods on three separate nights using the Tethered Lifting System (TLS) during the Cooperative Atmosphere–Surface Exchange Study (CASES-99) campaign in east-central Kansas, October 1999. Although the number of profiles is insufficient to make any definitive conclusions, the results suggest that, under most conditions, the boundary layer top can be reasonably estimated in terms of a very significant decrease in the energy dissipation rate (i.e., the mixing height) with height. In the majority of instances this height lies slightly below the height of a pronounced minimum in wind shear and slightly above a maximum in N 2, where N is the Brunt–Väisälä frequency. When combined with flux measurements and vertical velocity variance data obtained from the nearby 55-m tower, the results provide additional insights into SBL processes, even when the boundary layer, by any definition, extends to heights well above the top of the tower. Both the TLS profiles and tower data are then used for preliminary high-resolution studies into various categories of SBL structure, including the so-called upside-down boundary layer.

Download Full-text

On Thermally Forced Circulations over Heated Terrain

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-0199.1 ◽

2013 ◽

Vol 70 (6) ◽

pp. 1690-1709 ◽

Cited By ~ 24

Author(s):

Daniel J. Kirshbaum

Keyword(s):

Boundary Layer ◽

Heat Source ◽

Stable Boundary Layer ◽

Large Scale ◽

Numerical Models ◽

Theoretical Models ◽

Static Stability ◽

Boussinesq System ◽

Stable Boundary ◽

Convection Initiation

Abstract A combination of analytical and numerical models is used to gain insight into the dynamics of thermally forced circulations over diurnally heated terrain. Solutions are obtained for two-layer flows (representing the boundary layer and the overlying free troposphere) over an isolated mountainlike heat source. A scaling based on the linearized Boussinesq system of equations is developed to quantify the strength of thermally forced updrafts and to identify three flow regimes, each with distinct dynamics and parameter sensitivities. This scaling closely matches corresponding numerical simulations in two of these regimes: the first characterized by a weakly stable boundary layer and significant background winds and the second by a strongly stable boundary layer. In the third regime, characterized by weak winds and weak boundary layer stability, this scaling is outperformed by a fundamentally different scaling based on thermodynamic heat engines. Within this regime, the inability of wind ventilation or static stability to diminish the buoyancy over the heat source leads to intense updrafts that are controlled by nonlinear dynamics. These nonlinearities create a positive feedback loop between the thermal forcing and vorticity that rapidly strengthens the circulation and contracts its central updraft into a narrow core. As the circulation intensifies under daytime heating, the warmest surface-based air is ventilated into the upper boundary layer, where it spreads laterally to occupy a broader area and, ultimately, restrain the circulation strength. The success demonstrated herein of simple theoretical models at predicting key aspects of thermally forced circulations offers hope for improved parameterization of related processes (e.g., convection initiation and aerosol venting) in large-scale models.

Download Full-text

Stable Boundary Layer Depth from High-Resolution Measurements of the Mean Wind Profile

Journal of Applied Meteorology and Climatology ◽

10.1175/2009jamc2168.1 ◽

2010 ◽

Vol 49 (1) ◽

pp. 20-35 ◽

Cited By ~ 27

Author(s):

Yelena L. Pichugina ◽

Robert M. Banta

Keyword(s):

Boundary Layer ◽

High Resolution ◽

Wind Speed ◽

Stable Boundary Layer ◽

Type I ◽

Profile Data ◽

Zero Crossing ◽

Stable Boundary ◽

Type Iii ◽

The Mean

Abstract The depth h of the stable boundary layer (SBL) has long been an elusive measurement. In this diagnostic study the use of high-quality, high-resolution (Δz = 10 m) vertical profile data of the mean wind U(z) and streamwise variance σu2(z) is investigated to see whether mean-profile features alone can be equated with h. Three mean-profile diagnostics are identified: hJ, the height of maximum low-level-jet (LLJ) wind speed U in the SBL; h1, the height of the first zero crossing or minimum absolute value of the magnitude of the shear ∂U/∂z profile above the surface; and h2, the minimum in the curvature ∂2U/∂z2 profile. Boundary layer BL here is defined as the surface-based layer of significant turbulence, so the top of the BL was determined as the first significant minimum in the σu2(z) profile, designated as hσ. The height hσ was taken as a reference against which the three mean-profile diagnostics were tested. Mean-wind profiles smooth enough to calculate second derivatives were obtained by averaging high-resolution Doppler lidar profile data, taken during two nighttime field programs in the Great Plains, over 10-min intervals. Nights are chosen for study when the maximum wind speed in the lowest 200 m exceeded 5 m s−1 (i.e., weak-wind, very stable BLs were excluded). To evaluate the three diagnostics, data from the 14-night sample were divided into three profile shapes: Type I, a traditional LLJ structure with a distinct maximum or “nose,” Type II, a “flat” structure with constant wind speed over a significant depth, and Type III, having a layered structure to the shear and turbulence in the lower levels. For Type I profiles, the height of the jet nose hJ, which coincided with h1 and h2 in this case, agreed with the reference SBL depth to within 5%. The study had two major results: 1) among the mean-profile diagnostics for h, the curvature depth h2 gave the best results; for the entire sample, h2 agreed with hσ to within 12%; 2) considering the profile shapes, the layered Type III profiles gave the most problems. When these profiles could be identified and eliminated from the sample, regression and error statistics improved significantly: mean relative errors of 8% for hJ and h1, and errors of <5% for h2, were found for the sample of only Type I and II profiles.

Download Full-text

A Businger Mechanism for Intermittent Bursting in the Stable Boundary Layer

10.5194/egusphere-egu2020-5227 ◽

2020 ◽

Author(s):

Steven van der Linden ◽

Bas van de Wiel ◽

Igor Petenko ◽

Chiel van Heerwaarden ◽

Peter Baas ◽

...

Keyword(s):

Boundary Layer ◽

Stable Boundary Layer ◽

Large Scale ◽

Lower Layer ◽

Turbulent Transport ◽

Base Flow ◽

Unstable Wave ◽

Turbulent Friction ◽

Stable Boundary ◽

Boundary Layer Height

<p>High-resolution large-eddy simulations of the Antarctic very stable boundary layer reveal a mechanism for systematic and periodic intermittent bursting. A non-bursting state with a boundary-layer height of just 3 m is alternated by a bursting state with a height of &#8776;5 m. The bursts result from unstable wave growth triggered by a shear-generated Kelvin-Helmholtz instability, as confirmed by linear stability analysis. The shear at the top of the boundary layer is built up by two processes. The upper, quasi-laminar layer accelerates due to the combined effect of the pressure force and rotation by the Coriolis force, while the lower layer decelerates by turbulent friction. During the burst, this shear is eroded and the initial cause of the instability is removed. Subsequently, the interfacial shear builds up again, causing the entire sequence to repeat itself with a timescale of 10 min. Despite the clear intermittent bursting, the overall change of the mean wind profile is remarkably small during the cycle. This enables such a fast erosion and recovery of the shear. This mechanism for cyclic bursting is remarkably similar to the mechanism hypothesized by Businger in 1973. In his proposed mechanism, the momentum in the upper layer is increased by the downward turbulent transport of high-momentum flow. From the results, it appears that such transfer is not possible as the turbulent activity above the base flow is negligible. Finally, it would be interesting to construct a climatology of shear-generated intermittency in relation to large-scale conditions to assess the generality of this Businger mechanism.</p>

Download Full-text