scholarly journals Turbulent Velocity-Variance Profiles in the Stable Boundary Layer Generated by a Nocturnal Low-Level Jet

2006 ◽  
Vol 63 (11) ◽  
pp. 2700-2719 ◽  
Author(s):  
Robert M. Banta ◽  
Yelena L. Pichugina ◽  
W. Alan Brewer
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Strong Wind ◽  
Surface Exchange ◽  
Stable Boundary ◽  
Low Level ◽  
Stable Conditions ◽  
Velocity Scale ◽  
Low Level Jet ◽  
Wind Profiles

Abstract Profiles of mean winds and turbulence were measured by the High Resolution Doppler lidar in the strong-wind stable boundary layer (SBL) with continuous turbulence. The turbulence quantity measured was the variance of the streamwise wind velocity component σ2u. This variance is a component of the turbulence kinetic energy (TKE), and it is shown to be numerically approximately equal to TKE for stable conditions—profiles of σ2u are therefore equivalent to profiles of TKE. Mean-wind profiles showed low-level jet (LLJ) structure for most of the profiles, which represented 10-min averages of mean and fluctuating quantities throughout each of the six nights studied. Heights were normalized by the height of the first LLJ maximum above the surface ZX, and the velocity scale used was the speed of the jet UX, which is shown to be superior to the friction velocity u* as a velocity scale. The major results were 1) the ratio of the maximum value of the streamwise standard deviation to the LLJ speed σu/UX was found to be 0.05, and 2) the three most common σ2u profile shapes were determined by stability (or Richardson number Ri). The least stable profile shapes had the maximum σ2u at the surface decreasing to a minimum at the height of the LLJ; profiles that were somewhat more stable had constant σ2u through a portion of the subjet layer; and the most stable of the profiles had a maximum of σ2u aloft, although it is important to note that the Ri for even the most stable of the three profile categories averaged less than 0.20. The datasets used in this study were two nights from the Cooperative Atmosphere–Surface Exchange Study 1999 campaign (CASES-99) and four nights from the Lamar Low-Level Jet Project, a wind-energy experiment in southeast Colorado, during September 2003.

The Response of Simulated Nocturnal Convective Systems to a Developing Low-Level Jet

2010 ◽  
Vol 67 (10) ◽  
pp. 3384-3408 ◽  
Author(s):  
Adam J. French ◽  
Matthew D. Parker
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Wind Shear ◽  
Squall Line ◽  
Stable Boundary ◽  
Low Level ◽  
Convective Systems ◽  
Squall Lines ◽  
Central United States ◽  
Low Level Jet

Abstract Some recent numerical experiments have examined the dynamics of initially surface-based squall lines that encounter an increasingly stable boundary layer, akin to what occurs with the onset of nocturnal cooling. The present study builds on that work by investigating the added effect of a developing nocturnal low-level jet (LLJ) on the convective-scale dynamics of a simulated squall line. The characteristics of the simulated LLJ atop a simulated stable boundary layer are based on past climatological studies of the LLJ in the central United States. A variety of jet orientations are tested, and sensitivities to jet height and the presence of low-level cooling are explored. The primary impacts of adding the LLJ are that it alters the wind shear in the layers just above and below the jet and that it alters the magnitude of the storm-relative inflow in the jet layer. The changes to wind shear have an attendant impact on low-level lifting, in keeping with current theories for gust front lifting in squall lines. The changes to the system-relative inflow, in turn, impact total upward mass flux and precipitation output. Both are sensitive to the squall line–relative orientation of the LLJ. The variations in updraft intensity and system-relative inflow are modulated by the progression of the low-level cooling, which mimics the development of a nocturnal boundary layer. While the system remains surface-based, the below-jet shear has the largest impact on lifting, whereas the above-jet shear begins to play a larger role as the system becomes elevated. Similarly, as the system becomes elevated, larger changes to system-relative inflow are observed because of the layer of potentially buoyant inflowing parcels becoming confined to the layer of the LLJ.

Spectra, variances and length scales in a marine stable boundary layer dominated by a low level jet

1995 ◽  
Vol 76 (3) ◽  
pp. 211-232 ◽  
Author(s):  
Ann-Sofi Smedman ◽  
Hans Bergstr�m ◽  
Ulf H�gstr�m
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Length Scales ◽  
Stable Boundary ◽  
Low Level ◽  
Low Level Jet

scholarly journals Lidar study of wind turbulence, low level jet streams, and atmospheric internal waves in the boundary layer of atmosphere

2018 ◽  
Vol 176 ◽  
pp. 06005
Author(s):  
Viktor Banakh ◽  
Igor Smalikho
Keyword(s):  
Boundary Layer ◽  
Internal Waves ◽  
Stable Boundary Layer ◽  
Dissipation Rate ◽  
Jet Streams ◽  
Stable Boundary ◽  
Low Level ◽  
Experimental Campaign ◽  
Wind Turbulence ◽  
Low Level Jet

The results of lidar study of wind turbulence, low level jet streams, and internal atmospheric waves in the stable boundary layer of atmosphere on the coast of Lake Baikal are presented. Few events of the atmospheric internal waves (AIWs) were registered during the experimental campaign. All the registered AIWs were observed in the presence of low level jet streams. Two dimensional time–height patterns of the wind turbulence dissipation rate during AIW events were obtained as well.

Intermittent Bursting of Turbulence in a Stable Boundary Layer with Low-level Jet

2007 ◽  
Vol 126 (3) ◽  
pp. 349-363 ◽  
Author(s):  
Yuji Ohya ◽  
Reina Nakamura ◽  
Takanori Uchida
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Stable Boundary ◽  
Low Level ◽  
Low Level Jet

scholarly journals Ventilation of a Mid-Size City under Stable Boundary Layer Conditions: A Simulation Using the LES Model PALM

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 401
Author(s):  
Jonathan Biehl ◽  
Bastian Paas ◽  
Otto Klemm
Keyword(s):  
Boundary Layer ◽  
Stable Boundary Layer ◽  
Passive Scalar ◽  
City Center ◽  
Street Canyons ◽  
Stable Boundary ◽  
Northwest Germany ◽  
Stable Conditions ◽  
Les Model ◽  
The City

City centers have to cope with an increasing amount of air pollution. The supply of fresh air is crucial yet difficult to ensure, especially under stable conditions of the atmospheric boundary layer. This case study used the PArallelized Large eddy simulation (LES) Model PALM to investigate the wind field over an urban lake that had once been built as a designated fresh air corridor for the city center of Münster, northwest, Germany. The model initialization was performed using the main wind direction and stable boundary layer conditions as input. The initial wind and temperature profiles included a weak nocturnal low-level jet. By emitting a passive scalar at one point on top of a bridge, the dispersion of fresh air could be traced over the lake’s surface, within street canyons leading to the city center and within the urban boundary layer above. The concept of city ventilation was confirmed in principle, but the air took a direct route from the shore of the lake to the city center above a former river bed and its adjoining streets rather than through the street canyons. According to the dispersion of the passive scalar, half of the city center was supplied with fresh air originating from the lake. PALM proved to be a useful tool to study fresh air corridors under stable boundary layer conditions.

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