scholarly journals Structure of the Atmospheric Boundary Layer in the Vicinity of a Developing Upslope Flow System: A Numerical Model Study

2010 ◽  
Vol 67 (4) ◽  
pp. 1171-1185 ◽  
Author(s):  
Stefano Serafin ◽  
Dino Zardi
Keyword(s):  
Boundary Layer ◽  
Layer Structure ◽  
Flow Region ◽  
Energy Budgets ◽  
Thermal Plume ◽  
Water Tank ◽  
Convective Boundary ◽  
System A ◽  
Sequence Of Events ◽  
Model Study

Abstract The development of a morning upslope flow is studied by means of idealized numerical simulations. In particular, two cases are examined: a plane slope connecting a lower plain and an elevated plateau and a symmetric mountain in the middle of a uniform plain. The analysis examines various steepness cases and aims at understanding the processes occurring in the area of transition between the upslope flow region and the convective boundary layers (CBLs) growing nearby. A characteristic sequence of events is recognized in the simulations, and their relationship with the along-slope variability of the thermal energy and turbulent kinetic energy budgets is studied. Features occurring after the onset of the upslope wind include a transient depression in the boundary layer depth at the base of the slope and the formation of elevated turbulent layers above the CBL, caused by the divergence of turbulent flow from a thermal plume at the slope top. Numerical evidence agrees well with the results of previous experiments, including both field campaigns and water tank models. It is observed that the occurrence of streamwise inhomogeneities in the upslope flow field favors the occurrence of a multilayered vertical structure of the CBL near heated slopes. Multiple layering appears to be a transient feature, only persisting until sufficient heating causes the merging of the CBL with the overlying elevated turbulent layers. The analysis suggests that the slope steepness is an important factor in determining the speed at which the boundary layer structure near a slope evolves in time: in particular, the development of the wind system appears to occur faster in the vicinity of a steeper slope.

Aspects of the convective boundary layer structure over complex terrain

1998 ◽  
Vol 32 (7) ◽  
pp. 1323-1348 ◽  
Author(s):  
M. Kossmann ◽  
R. Vögtlin ◽  
U. Corsmeier ◽  
B. Vogel ◽  
F. Fiedler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Complex Terrain ◽  
Layer Structure ◽  
Convective Boundary ◽  
Boundary Layer Structure

A Thermal Plume Model for the Convective Boundary Layer: Representation of Cumulus Clouds

2008 ◽  
Vol 65 (2) ◽  
pp. 407-425 ◽  
Author(s):  
Catherine Rio ◽  
Frédéric Hourdin
Keyword(s):  
Boundary Layer ◽  
Mass Flux ◽  
Convective Boundary Layer ◽  
Turbulent Transport ◽  
Thermal Plume ◽  
Cumulus Clouds ◽  
Convective Boundary ◽  
Near Surface ◽  
Plume Model ◽  
Surface Drying

Abstract The “thermal plume model,” a mass-flux scheme combined with a classical diffusive approach, originally developed to represent turbulent transport in the dry convective boundary layer, is extended here to the representation of cloud processes. The modified parameterization is validated in a 1D configuration against results of large eddy simulations (LES), as well as in a 3D configuration against in situ measurements, for a series of cases of dry and cloudy convective boundary layers. Accounting for coherent structures of the mixed layer with the mass-flux scheme improves the representation of the diurnal cycle of the boundary layer, particularly its progressive deepening during the day and the associated near-surface drying. Results also underline the role of the prescription of the mixing of air between the plume and its environment, and of submean-plume fluctuations.

scholarly journals The performance of RAMS in representing the convective boundary layer structure in a very steep valley

2005 ◽  
Vol 5 (1-2) ◽  
pp. 35-62 ◽  
Author(s):  
Stephan F. J. De Wekker ◽  
D. G. Steyn ◽  
J. D. Fast ◽  
M. W. Rotach ◽  
S. Zhong
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Layer Structure ◽  
Convective Boundary ◽  
Boundary Layer Structure

scholarly journals The Universality of the Normalized Vertical Velocity Variance in Contrast to the Horizontal Velocity Variance in the Convective Boundary Layer

2019 ◽  
Vol 76 (5) ◽  
pp. 1437-1456 ◽  
Author(s):  
Bowen Zhou ◽  
Shiwei Sun ◽  
Jianning Sun ◽  
Kefeng Zhu
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Surface Heating ◽  
Turbulent Velocity ◽  
Energy Budgets ◽  
Convective Boundary ◽  
Stability Range ◽  
Homogeneous Surface ◽  
Large Eddy ◽  
Velocity Variance

Abstract The vertical turbulent velocity variance normalized by the convective velocity squared as a function of the boundary layer depth–normalized height [i.e., ] in the convective boundary layer (CBL) over a homogeneous surface exhibits a near-universal profile, as demonstrated by field observations, laboratory experiments, and numerical simulations. The profile holds over a wide CBL stability range set by the friction velocity, CBL depth, and surface heating. In contrast, the normalized horizontal turbulent velocity variance increases monotonically with decreasing stability. This study investigates the independence of the profile to changes in CBL stability, or more precisely, wind shear. Large-eddy simulations of several convective and neutral cases are performed by varying surface heating and geostrophic winds. Analysis of the turbulent kinetic energy budgets reveals that the conversion term between and depends almost entirely on buoyancy. This explains why does not vary with shear, which is a source to only. Further analysis through rotational and divergent decomposition suggests that the near-universal profile of is fundamentally related to the dynamics and interactions of local and nonlocal CBL turbulence. Specifically, the preferential interactions between local wavenumbers and the downscale energy cascade of CBL turbulence offer plausible explanations to the universal profile of .

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