scholarly journals LES on Plume Dispersion in the Convective Boundary Layer Capped by a Temperature Inversion

2008 ◽  
Vol 3 (4) ◽  
pp. 519-532 ◽  
Author(s):  
Hiromasa NAKAYAMA ◽  
Tetsuro TAMURA ◽  
Satoshi ABE
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Temperature Inversion ◽  
Plume Dispersion ◽  
Convective Boundary

scholarly journals Scalar Turbulence in Convective Boundary Layers by Changing the Entrainment Flux

2013 ◽  
Vol 70 (1) ◽  
pp. 248-265 ◽  
Author(s):  
Alessandra S. Lanotte ◽  
Irene M. Mazzitelli
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Spatial Scales ◽  
Surface Flux ◽  
Scalar Fields ◽  
Temperature Inversion ◽  
Trace Gas ◽  
Free Atmosphere ◽  
Convective Boundary ◽  
Homogeneous Surface

Abstract A large-eddy simulation model is adopted to investigate the evolution of scalars transported by atmospheric cloud-free convective boundary layer flows. Temperature fluctuations due to the ground release of sensible heat and concentration fluctuations of a trace gas emitted at the homogeneous surface are mixed by turbulence within the unstable boundary layer. On the top, the entrainment zone is varied to obtain two distinct situations: (i) the temperature inversion is strong and the trace gas increment across the entrainment region is small, yielding to a small top flux with respect to the surface emission; (ii) the temperature inversion at the top of the convective boundary layer is weak, and the scalar increment large enough to achieve a concentration flux toward the free atmosphere that overwhelms the surface flux. In both cases, an estimation of the entrainment flux is obtained within a simple model, and it is tested against numerical data. The evolution of the scalar profiles is discussed in terms of the different entrainment–surface flux ratios. Results show that, when entrainment at the top of the boundary layer is weak, temperature and trace gas scalar fields are strongly correlated, particularly in the lower part of the boundary layer. This means that they exhibit similar behavior from the largest down to the smallest spatial scales. However, when entrainment is strong, as moving from the surface, differences in the transport of the two scalars arise. Finally, it is shown that, independently of the scalar regime, the temperature field exhibits more intermittent fluctuations than the trace gas.

scholarly journals Ship plume dispersion rates in convective boundary layers for chemistry models

2008 ◽  
Vol 8 (2) ◽  
pp. 6793-6824
Author(s):  
F. Chosson ◽  
R. Paoli ◽  
B. Cuenot
Keyword(s):  
Boundary Layer ◽  
Dilution Rate ◽  
Convective Boundary Layer ◽  
Time Scale ◽  
High Dispersion ◽  
Minor Effect ◽  
Plume Rise ◽  
Plume Dispersion ◽  
Convective Boundary ◽  
The Impact

Abstract. Detailed ship plume simulations in various convective boundary layer situations have been performed using a Lagrangian Dispersion Model driven by a Large Eddy Simulation Model. The simulations focus on early stage (1–2 h) of plume dispersion regime and take into account the effects of plume rise on dispersion. Results are presented in an attempt to provide to chemical modellers community a realistic description of the impact of characteristic dispersion on exhaust ship plume chemistry. Plume dispersion simulations are used to derive analytical dilution rate functions. Even though results exhibit striking effects of plume rise parameter on dispersion patterns, it is shown that initial buoyancy fluxes at ship stack have minor effect on plume dilution rate. After initial high dispersion regimes a simple characteristic dilution time scale can be used to parameterize the subgrid plume dilution effects in large scale chemistry models. The results show that this parameter is directly related to the typical turn-over time scale of the convective boundary layer.

scholarly journals The Turbulent Structure and Diurnal Growth of the Saharan Atmospheric Boundary Layer

2015 ◽  
Vol 72 (2) ◽  
pp. 693-713 ◽  
Author(s):  
L. Garcia-Carreras ◽  
D. J. Parker ◽  
J. H. Marsham ◽  
P. D. Rosenberg ◽  
I. M. Brooks ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Temperature Inversion ◽  
Residual Layer ◽  
Turbulent Structure ◽  
Radiosonde Data ◽  
Convective Boundary ◽  
Boundary Layer Processes

Abstract The turbulent structure and growth of the remote Saharan atmospheric boundary layer (ABL) is described with in situ radiosonde and aircraft measurements and a large-eddy simulation model. A month of radiosonde data from June 2011 provides a mean profile of the midday Saharan ABL, which is characterized by a well-mixed convective boundary layer, capped by a small temperature inversion (<1 K) and a deep, near-neutral residual layer. The boundary layer depth varies by up to 100% over horizontal distances of a few kilometers due to turbulent processes alone. The distinctive vertical structure also leads to unique boundary layer processes, such as detrainment of the warmest plumes across the weak temperature inversion, which slows down the warming and growth of the convective boundary layer. As the boundary layer grows, overshooting plumes can also entrain free-tropospheric air into the residual layer, forming a second entrainment zone that acts to maintain the inversion above the convective boundary layer, thus slowing down boundary layer growth further. A single-column model is unable to accurately reproduce the evolution of the Saharan boundary layer, highlighting the difficulty of representing such processes in large-scale models. These boundary layer processes are special to the Sahara, and possibly hot, dry, desert environments in general, and have implications for the large-scale structure of the Saharan heat low. The growth of the boundary layer influences the vertical redistribution of moisture and dust, and the spatial coverage and duration of clouds, with large-scale dynamical and radiative implications.

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