scholarly journals Large eddy simulation of boundary-layer turbulence over the heterogeneous surface in the Source Region of the Yellow River

2021 ◽  
Author(s):  
Yunshuai Zhang ◽  
Qian Huang ◽  
Yaoming Ma ◽  
Jiali Luo ◽  
Chan Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Yellow River ◽  
Source Region ◽  
Turbulent Intensity ◽  
The Yellow River ◽  
Lake Basin ◽  
Convective Boundary ◽  
Boundary Layer Turbulence ◽  
Large Eddy

Abstract. Lake breezes are proved by downdrafts and the divergence flows of zonal wind in the source region of the Yellow River in the daytime based on ERA-Interim reanalysis data. In order to depict the effect of the circulations induced by surface anomaly heating (patches) on the boundary-layer turbulence, the large eddy model was used to produce a set of 1D strip-like surface heat flux distributions based on observations, which obtained by a field campaign in the Ngoring Lake Basin in the summer of 2012. The simulations show that for the cases without ambient winds, patch-induced circulations (SCs) enhance the turbulent kinetic energy (TKE) and then modify the spatial distribution of TKE. Based on phase-averaged analysis, which separates the attribution from the SCs and the background turbulence, the SCs contribute no more than 10 % to the vertical turbulent intensity, but their contributions to the heat flux can be up to 80 %. The lake patches produce consistent spatial distributions of wind speed and turbulent stress over the lake–land boundary, and the obvious change of turbulent momentum flux over the boundary of patches can not be neglected. In the entrainment layer, the convective rolls still persist under stronger geostrophic winds of 7–11 m s−1. The increased downdrafts, which mainly occur over the lake patches and carry more warm, dry air down from the free atmosphere. In general, the SCs promote the growth of convective boundary layer, while the background flows inhibit it. The background winds also weaken the patch-induced turbulent intensity, heat flux, and convective intensity.

scholarly journals Large eddy simulation of boundary-layer turbulence over the heterogeneous surface in the source region of the Yellow River

2021 ◽  
Vol 21 (20) ◽  
pp. 15949-15968
Author(s):  
Yunshuai Zhang ◽  
Qian Huang ◽  
Yaoming Ma ◽  
Jiali Luo ◽  
Chan Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Yellow River ◽  
Source Region ◽  
Turbulent Intensity ◽  
Internal Boundary ◽  
The Yellow River ◽  
Background Wind ◽  
Boundary Layer Turbulence ◽  
Large Eddy

Abstract. Lake breezes are proved by downdrafts and the divergence flows of zonal wind in the source region of the Yellow River (SRYR) in the daytime based on ERA-Interim reanalysis data. In order to depict the effect of the circulations induced by surface anomaly heating (patches) on the boundary-layer turbulence, the UK Met Office Large Eddy Model was used to produce a set of 1D strip-like surface heat flux distributions based on observations, which were obtained by a field campaign in the Ngoring Lake basin in the summer of 2012. The simulations show that for the cases without background wind, patch-induced circulations (SCs) promote the growth of convective boundary layer (CBL), enhance the turbulent kinetic energy (TKE), and then modify the spatial distribution of TKE. Based on phase-averaged analysis, which separates the attribution from the SCs and the background turbulence, the SCs contribute no more than 10 % to the vertical turbulent intensity, but their contributions to the heat flux can be up to 80 %. The thermal internal boundary layer (TIBL) reduces the wind speed and forms the stable stratification, which produces the obvious change of turbulent momentum flux and heat flux over the heterogeneous surfaces. The increased downdrafts, which mainly occur over the lake patches, carry more warm, dry air down from the free atmosphere. The background wind inhibits the SCs and the development of the CBL; it also weakens the patch-induced turbulent intensity, heat flux, and convective intensity.

Large eddy simulation of boundary-layer turbulence over different underlying surfaces in the Source Region of the Yellow River, northeastern Tibetan Plateau

2020 ◽  
Author(s):  
Yunshuai Zhang ◽  
Qian Huang ◽  
Yaoming Ma
Keyword(s):  
Boundary Layer ◽  
Tibetan Plateau ◽  
Turbulence Intensity ◽  
Yellow River ◽  
Source Region ◽  
Horizontal Resolution ◽  
The Yellow River ◽  
Lake Basin ◽  
Small Range ◽  
Large Eddy

<p>In order to study the characteristics of turbulence over the homogeneous and inhomogeneous underlying surfaces and its effects on the transport of material and energy in the Source Region of the Yellow River (SRYR), northeast of the Tibetan Plateau. We use the GPS sounding data and eddy covariance data observed during a field experiment in the Ngoring Lake Basin in summer 2012, and for the first time large eddy simulations are performed to investigate the characteristics of the fine turbulence structure in the convective boundary layer (CBL) of the two different underlying surfaces (grassland and lake) in the SRYR. It shows that the simulated CBLs of grassland and lake in the SRYR is in good agreement with the observations, but the characteristics of the turbulence structure in the CBLs are obviously different. The spatio-temporal distribution of turbulence energy and the structure characteristics of thermal bubbles in the CBL above the grassland are consistent with those of the typical thermally driven CBL above the land. Convective rolls are simulated in the shear dominant CBL above the lake. Turbulence intensity in the surface layer above the grassland is higher, while it is larger at the top of CBL above the lake due to the strong entrainment. We also found that the simulations are sensitive to the horizontal resolution on the two different homogeneous underlying surfaces. The higher horizontal resolution should applied to the CBL above the lake to improve the accuracy in the simulation of turbulence kinetic energy and turbulence flux of the surface layer and the entrainment layer, while avoiding underestimating the turbulence flux due to the small range of the waves simulated at low resolution. For the CBL of the grassland, it is suggested that the grid distance should be between 200 m-300 m, which can save the calculation time, also can give the turbulence flux and the fine turbulence structure. In addition, 3-D simulations are also performed to figure out the differences of turbulence intensity over homogeneous and inhomogeneous underlying surfaces. It is found that lake breeze induced by surface inhomogeneity would enhance the wind shear, decreasing the intensity of vertical turbulence and increasing that of horizontal turbulence.</p>

scholarly journals Resolution Dependence of Turbulent Structures in Convective Boundary Layer Simulations

Atmosphere ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 986 ◽  
Author(s):  
Mary-Jane M. Bopape ◽  
Robert S. Plant ◽  
Omduth Coceal
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Convective Boundary Layer ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Quadrant Analysis ◽  
Turbulent Structures ◽  
Convective Boundary ◽  
Large Eddy ◽  
Lower Boundary Layer

Large-eddy simulations are performed using the U.K. Met Office Large Eddy Model to study the effects of resolution on turbulent structures in a convective boundary layer. A standard Smagorinsky subgrid scheme is used. As the grid length is increased, the diagnosed height of the boundary layer increases, and the horizontally- and temporally-averaged temperature near the surface and in the inversion layer increase. At the highest resolution, quadrant analysis shows that the majority of events in the lower boundary layer are associated with cold descending air, followed by warm ascending air. The largest contribution to the total heat flux is made by warm ascending air, with associated strong thermals. At lower resolutions, the contribution to the heat flux from cold descending air is increased, and that from cold ascending air is reduced in the lower boundary layer; around the inversion layer, however, the contribution from cold ascending air is increased. Calculations of the heating rate show that the differences in cold ascending air are responsible for the warm bias below the boundary layer top in the low resolution simulations. Correlation length and time scales for coherent resolved structures increase with increasing grid coarseness. The results overall suggest that differences in the simulations are due to weaker mixing between thermals and their environment at lower resolutions. Some simple numerical experiments are performed to increase the mixing in the lower resolution simulations and to investigate backscatter. Such simulations are successful at reducing the contribution of cold ascending air to the heat flux just below the inversion, although the effects in the lower boundary layer are weaker.

scholarly journals Estimates of Daily Evapotranspiration in the Source Region of the Yellow River Combining Visible/Near-Infrared and Microwave Remote Sensing

2020 ◽  
Vol 13 (1) ◽  
pp. 53
Author(s):  
Rong Liu ◽  
Jun Wen ◽  
Xin Wang ◽  
Zuoliang Wang ◽  
Yu Liu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Energy Distribution ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Yellow River ◽  
Source Region ◽  
The Yellow River ◽  
Effective Energy ◽  
Meteorological Satellite

The spatial variation of surface net radiation, soil heat flux, sensible heat flux, and latent heat flux at different times of the day over the northern Tibetan Plateau were estimated using the Surface Energy Balance System algorithm, data from the FY-2G geostationary meteorological satellite, and microwave data from the FY-3C polar-orbiting meteorological satellite. In addition, the evaporative fraction was analyzed, and the total evapotranspiration (ET) was obtained by the effective evaporative fraction to avoid the error from accumulation. The hourly change of latent heat flux presented a sound unimodal diurnal variation. The results showed the regional ET ranged between 2.0 and 4.0 mm over the Source Region of the Yellow River. The conditional expectations of surface energy components during the experimental period of the study area were statistically analyzed, and the correspondence between different surface temperatures and the effective energy distribution was examined. The effective energy distribution of the surface changed significantly with the increase in temperature; in particular, when the surface temperature exceeded 290 K, the effective energy was mainly used for surface ET. The aim of this study was to avoid the use of surface meteorological observations that are not readily available over large areas, and the findings lay a foundation for the commercialization of land surface evapotranspiration.

Impact of Aerosol Shortwave Radiative Heating on Entrainment in the Atmospheric Convective Boundary Layer: A Large-Eddy Simulation Study

2019 ◽  
Vol 76 (3) ◽  
pp. 785-799 ◽  
Author(s):  
Cheng Liu ◽  
Evgeni Fedorovich ◽  
Jianping Huang ◽  
Xiao-Ming Hu ◽  
Yongwei Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Radiative Heating ◽  
Radiative Effect ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Aerosol Radiative

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 aerosol radiation transfer model is used in conjunction with large-eddy simulation (LES) to quantify the impact of aerosol shortwave radiative heating on entrainment and thermodynamics of an idealized dry CBL under aerosol-loading conditions. An entrainment equation is derived within the framework of a zero-order model (ZOM) with the aerosol radiative heating effect included; the equation is then examined against the LES outputs for varying aerosol optical depths (AODs) and free-atmosphere stratification scenarios. The results show that the heat flux profiles become more nonlinear in shape as compared to the case of the clean (no aerosol pollution) CBL, with the degree of nonlinearity being highly dependent on the AOD of the layer for the given type of radiation-absorbing aerosols. As AOD increases, less solar radiation reaches the surface and thus the surface heat flux becomes smaller, and both actual (LES) and ZOM-derived entrainment flux ratios decrease. This trend is opposite to the clean CBL where the LES-predicted flux ratios show an increasing trend with diminishing surface heat flux, while the ZOM-calculated flux ratio remains constant. The modified dimensionless entrainment rate closely follows the −1 power law with a modified Richardson number. The study suggests that including the aerosol radiative effect may improve numerical air quality predictions for heavy-air-pollution events.

scholarly journals The Effect of Aerosol Radiative Heating on Turbulence Statistics and Spectra in the Atmospheric Convective Boundary Layer: A Large-Eddy Simulation Study

Atmosphere ◽  
2018 ◽  
Vol 9 (9) ◽  
pp. 347 ◽  
Author(s):  
Cheng Liu ◽  
Jianping Huang ◽  
Evgeni Fedorovich ◽  
Xiao-Ming Hu ◽  
Yongwei Wang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Radiative Heating ◽  
Turbulence Statistics ◽  
Convective Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Aerosol Pollution ◽  
Velocity Spectra ◽  
Aerosol Radiative

Turbulence statistics and spectra in a radiatively heated convective boundary layer (CBL) under aerosol pollution conditions are less investigated than their counterparts in the clear CBL. In this study, a large-eddy simulation (LES) coupled with an aerosol radiative transfer model is employed to determine the impact of aerosol radiative heating on CBL turbulence statistics. One-dimensional velocity spectra and velocity–temperature cospectra are invoked to characterize the turbulence flow in the CBL with varying aerosol pollution conditions. The results show that aerosol heating makes the profiles of turbulent heat flux curvilinear, while the total (turbulent plus radiative) heat flux profile retains the linear relationship with height throughout the CBL. The horizontal and vertical velocity variances are reduced significantly throughout the radiatively heated CBL with increased aerosol optical depth (AOD). The potential temperature variance is also reduced, especially in the entrainment zone and near the surface. The velocity spectral density tends to be smaller overall, and the peak of the velocity spectra is shifted toward larger wavenumbers as AOD increases. This shift reveals that the energy-containing turbulent eddies become smaller, which is also supported by visual inspection of the vertical velocity pattern over horizontal planes. The modified CBL turbulence scales for velocity and temperature are found to be applicable for normalizing the corresponding profiles, indicating that a correction factor for aerosol radiative heating is needed for capturing the general features of the CBL structure in the presence of aerosol radiative heating.

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