The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Evgeni Fedorovich - One of the best experts on this subject based on the ideXlab platform.
-
Structure Functions and Structure Parameters of Velocity Fluctuations in Numerically Simulated Atmospheric Convective Boundary Layer Flows
Journal of the Atmospheric Sciences, 2020Co-Authors: Jeremy A. Gibbs, Evgeni FedorovichAbstract:AbstractWe extend our previous study, which dealt with structure functions of potential temperature fluctuations, and focus on the characteristics of second-order velocity structure functions and corresponding structure parameters in the atmospheric Convective Boundary Layer. We consider the three previously reported methods to compute the structure parameters of turbulent velocity fields: the direct method, the true spectral method, and the approximate spectral method. The methods are evaluated using high-resolution gridded numerical data from large-eddy simulations of shear-free and shear-driven Convective Boundary Layers. Results indicate that the direct and true spectral methods are more suitable than the approximate spectral method, which overestimates the structure parameters of velocity as a result of assuming the inertial-subrange shape of the velocity spectrum for all turbulence scales. Results also suggest that structure parameters of vertical velocity fluctuations are of limited utility because of violations of local isotropy, especially in shear-free Convective Boundary Layers.
-
Impact of Aerosol Shortwave Radiative Heating on Entrainment in the Atmospheric Convective Boundary Layer: A Large-Eddy Simulation Study
Journal of the Atmospheric Sciences, 2019Co-Authors: Cheng Liu, Evgeni Fedorovich, Jianping Huang, Yongwei Wang, Xuhui LeeAbstract:AbstractEntrainment is critical to the development of the atmospheric Convective Boundary Layer (CBL), but little is known about how entrainment is impacted by the aerosol radiative effect. An aero...
-
Evaluation of an LES-Based Wind Profiler Simulator for Observations of a Daytime Atmospheric Convective Boundary Layer
Journal of Atmospheric and Oceanic Technology, 2008Co-Authors: Danny Scipion, Evgeni Fedorovich, Phillip B. Chilson, Robert D. PalmerAbstract:Abstract The daytime atmospheric Convective Boundary Layer (CBL) is characterized by strong turbulence that is primarily caused by buoyancy forced from the heated underlying surface. The present study considers a combination of a virtual radar and large eddy simulation (LES) techniques to characterize the CBL. Data representative of a daytime CBL with wind shear were generated by LES and used in the virtual Boundary Layer radar (BLR) with both vertical and multiple off-vertical beams and frequencies. To evaluate the virtual radar, a multiple radar experiment (MRE) was conducted using five virtual radars with common resolution volumes at two different altitudes. Three-dimensional wind fields were retrieved from the virtual radar data and compared with the LES output. It is shown that data produced from the virtual BLR are representative of what one expects to retrieve using a real BLR and the measured wind fields match those of the LES. Additionally, results from a frequency domain interferometry (FDI) com...
-
Effects of wind shear on the atmospheric Convective Boundary Layer structure and evolution
Acta Geophysica, 2007Co-Authors: Evgeni Fedorovich, Robert J. ConzemiusAbstract:The article reviews past accomplishments and recent advances in conceptual understanding, numerical simulation, and physical interpretation of the wind shear phenomena in the atmospheric Convective Boundary Layer.
-
dynamics of sheared Convective Boundary Layer entrainment part i methodological background and large eddy simulations
Journal of the Atmospheric Sciences, 2006Co-Authors: Robert J. Conzemius, Evgeni FedorovichAbstract:Abstract The reported study examines the dynamics of entrainment and its effects on the evolution of the dry atmospheric Convective Boundary Layer (CBL) when wind shear is present. The sheared CBL can be studied by means of direct measurements in the atmosphere, laboratory studies, and numerical techniques. The advantages and disadvantages of each technique are discussed in the present paper, which also describes the methodological background for studying the dynamics of entrainment in sheared CBLs. For the reported study, large-eddy simulation (LES) was chosen as the primary method of Convective entrainment investigation. Twenty-four LES runs were conducted for CBLs growing under varying conditions of surface buoyancy flux, free-atmospheric stratification, and wind shear. The simulations were divided into three categories: CBL with no mean wind (NS), CBL with a height-constant geostrophic wind of 20 m s−1 (GC), and CBL with geostrophic wind shear (GS). In the simulated cases, the sheared CBLs grew fastes...
Frederic Hourdin - One of the best experts on this subject based on the ideXlab platform.
-
A Thermal Plume Model for the Convective Boundary Layer: Representation of Cumulus Clouds
Journal of the Atmospheric Sciences, 2008Co-Authors: Catherine Rio, Frederic HourdinAbstract:The ``thermal plume model,{''} a mass-flux scheme combined with a\nclassical diffusive approach, originally developed to represent\nturbulent transport in the dry Convective Boundary Layer, is extended\nhere to the representation of cloud processes. The modified\nparameterization is validated in a 1D configuration against results of\nlarge eddy simulations (LES), as well as in a 3D configuration against\nin situ measurements, for a series of cases of dry and cloudy Convective\nBoundary Layers. Accounting for coherent structures of the mixed Layer\nwith the mass-flux scheme improves the representation of the diurnal\ncycle of the Boundary Layer, particularly its progressive deepening\nduring the day and the associated near-surface drying. Results also\nunderline the role of the prescription of the mixing of air between the\nplume and its environment, and of submean-plume fluctuations.
-
parameterization of the dry Convective Boundary Layer based on a mass flux representation of thermals
Journal of the Atmospheric Sciences, 2002Co-Authors: Frederic Hourdin, Fleur Couvreux, Laurent MenutAbstract:Presented is a mass flux parameterization of vertical transport in the Convective Boundary Layer. The formulation of the new parameterization is based on an idealization of thermal cells or rolls. The parameterization is validated by comparison to large eddy simulations (LES). It is also compared to classical Boundary Layer schemes on a
Donald A. Nield - One of the best experts on this subject based on the ideXlab platform.
-
natural Convective Boundary Layer flow of a nanofluid past a vertical plate a revised model
International Journal of Thermal Sciences, 2014Co-Authors: A. V. Kuznetsov, Donald A. NieldAbstract:Abstract The problem of natural Convective Boundary-Layer flow of a nanofluid past a vertical plate is revisited. The model, which includes the effects of Brownian motion and thermophoresis, is revised so that the nanofluid particle fraction on the Boundary is passively rather than actively controlled. In this respect the model is more realistic physically than that employed by previous authors.
-
double diffusive natural Convective Boundary Layer flow of a nanofluid past a vertical plate
International Journal of Thermal Sciences, 2011Co-Authors: A. V. Kuznetsov, Donald A. NieldAbstract:The double-diffusive natural Convective Boundary-Layer flow of a nanofluid past a vertical plate is studied analytically. The model used for the binary nanofluid incorporates the effects of Brownian motion and thermophoresis. In addition the thermal energy equations include regular diffusion and cross-diffusion terms. A similarity solution is presented. Numerical calculations were performed in order to obtain correlation formulas giving the reduced Nusselt number as a function of the various relevant parameters.
-
natural Convective Boundary Layer flow of a nanofluid past a vertical plate
International Journal of Thermal Sciences, 2010Co-Authors: A. V. Kuznetsov, Donald A. NieldAbstract:The natural Convective Boundary-Layer flow of a nanofluid past a vertical plate is studied analytically. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. A similarity solution is presented. This solution depends on a Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. For various values of Pr and Le, the variation of the reduced Nusselt number with Nr, Nb and Nt is expressed by correlation formulas. It was found that the reduced Nusselt number is a decreasing function of each of Nr, Nb and Nt.
Bruce Ainslie - One of the best experts on this subject based on the ideXlab platform.
-
A Simple Model for Pollution Dispersion in a Convective Boundary Layer
Journal of Applied Meteorology and Climatology, 2006Co-Authors: Roland B. Stull, Bruce AinslieAbstract:Abstract A simplified model for dispersion in a Convective Boundary Layer is presented and is used to diagnose crosswind-integrated concentrations, ground-level concentrations, and vertical plume spread over flat terrain for various release heights. The model parameterizes the long-wavelength oscillation of the time-averaged plume centerline versus downwind distance under unstable conditions, using a simple sine wave. This wave is phase shifted to account for the influence of source height and is damped toward the mid–mixed Layer to account for the well-mixed end state of Convective dispersion. This model represents an improvement over a previous model in two ways. First, vertical dispersion about the oscillating time-averaged centerline is parameterized using a lognormal distribution instead of a Gaussian distribution so as to give better ground-level concentration. Second, to account for the addition of surface-Layer shear-generated turbulence to a Convective Boundary Layer, the wavelength of the time-a...
Frank Beyrich - One of the best experts on this subject based on the ideXlab platform.
-
Aspects of the Convective Boundary Layer structure over complex terrain
Atmospheric Environment, 1998Co-Authors: M. Kossmann, Norbert Kalthoff, R. Vögtlin, Ulrich Corsmeier, Bernhard Vogel, Franz Fiedler, H.-j. Binder, Frank BeyrichAbstract:Abstract Measurements are presented of the development of the Convective Boundary Layer in the transition zone from the Upper Rhine valley to the Northern Black Forest during one special observation period of the TRACT campaign conducted in September 1992. The data used in this study were obtained from airborne instruments as well as from ground-based stations. The analysed Boundary Layer structure shows a strong influence of the underlying terrain. Until noon, a nearly terrain following capping inversion developed. However, advective processes proved to play an important role in the Boundary Layer structure over the hilly terrain. So, the large-scale air flow caused suppression of the Convective Boundary Layer growth at the mountain ridge by forcing the capping inversion towards the elevation of the terrain. A mountain induced secondary circulation system was observed on the western facing slopes of the Black Forest. This secondary circulation system affected the heat budget and therefore the growth of the Convective Boundary Layer over the mountain slopes. The advection of cold air by up-slope winds lowered the heating rate near the ground and was able to generate an inversion above the up-slope wind Layer. In the late afternoon, the terrain following structure of the capping inversion diminished and the capping inversion tended to form a horizontal plane. Prognostic formulae for Boundary Layer growth are discussed for different sites of the terrain. While in the valley good agreement is found between calculated and observed Boundary Layer depths, the calculations for the mountain ridge overestimate the obserations by up to a factor of 5 if a Boundary Layer growth equation derived for homogeneous terrain is used.
-
Mixing-height estimation in the Convective Boundary Layer using sodar data
Boundary-Layer Meteorology, 1995Co-Authors: Frank BeyrichAbstract:Sodar has been used for about 20 years to determine mixing height. However, estimation of the height of a Convective Boundary Layer (CBL) that exceeds the sodar-probing range is still an unsolved question. As one possible way, it is suggested that one adapt a simple mixed-Layer model to sodar observations during the morning growth period of the CBL, when its top can be clearly detected. Results are compared with other methods for CBL-height estimation from sodar data that have been proposed in the literature. Finally, some prognostic aspects are discussed.