scholarly journals Evaluation of large-eddy simulations forced with mesoscale model output for a multi-week period during a measurement campaign

2017 ◽  
Vol 17 (11) ◽  
pp. 7083-7109 ◽  
Author(s):  
Rieke Heinze ◽  
Christopher Moseley ◽  
Lennart Nils Böske ◽  
Shravan Kumar Muppa ◽  
Vera Maurer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mesoscale Model ◽  
Large Eddy Simulations ◽  
Model Output ◽  
Synoptic Scale ◽  
High Definition ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Lidar Measurements ◽  
The Mean

Abstract. Large-eddy simulations (LESs) of a multi-week period during the HD(CP)2 (High-Definition Clouds and Precipitation for advancing Climate Prediction) Observational Prototype Experiment (HOPE) conducted in Germany are evaluated with respect to mean boundary layer quantities and turbulence statistics. Two LES models are used in a semi-idealized setup through forcing with mesoscale model output to account for the synoptic-scale conditions. Evaluation is performed based on the HOPE observations. The mean boundary layer characteristics like the boundary layer depth are in a principal agreement with observations. Simulating shallow-cumulus layers in agreement with the measurements poses a challenge for both LES models. Variance profiles agree satisfactorily with lidar measurements. The results depend on how the forcing data stemming from mesoscale model output are constructed. The mean boundary layer characteristics become less sensitive if the averaging domain for the forcing is large enough to filter out mesoscale fluctuations.

scholarly journals Evaluation of large-eddy simulations forced with mesoscale model output for a multi-week period during a measurement campaign

2016 ◽  
Author(s):  
Rieke Heinze ◽  
Christopher Moseley ◽  
Lennart Nils Böske ◽  
Shravan Muppa ◽  
Vera Maurer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mesoscale Model ◽  
Large Eddy Simulations ◽  
Model Output ◽  
Synoptic Scale ◽  
High Definition ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Lidar Measurements ◽  
The Mean

Abstract. Large-eddy simulations (LES) of a multi-week period during the HD(CP)2 (High-Definition Clouds and Precipitation for advancing Climate Prediction) Observational Prototype Experiment (HOPE) conducted in Germany are evaluated with respect to mean boundary layer quantities and turbulence statistics. Two LES models are used in a semi-idealized setup through forcing with mescoscale model output to account for the synoptic-scale conditions. Evaluation is performed based on the HOPE observations. The mean boundary layer characteristics like the boundary layer depth are in a principal agreement with observations. Simulating shallow-cumulus layers in agreement with the measurements poses a challenge for both LES models. Variance profiles agree satisfactorily with lidar measurements. The results depend on how the forcing data stemming from mesoscale model output is constructed. The mean boundary layer characteristics become less sensitive if the averaging domain for the forcing is large enough to filter out mesoscale fluctuations.

scholarly journals Departure from <i>K</i>-theory in the planetary boundary layer

2020 ◽  
Author(s):  
Pedro Santos ◽  
Alfredo Peña ◽  
Jakob Mann
Keyword(s):  
Wind Speed ◽  
Mesoscale Model ◽  
Vertical Gradient ◽  
Large Eddy Simulations ◽  
Horizontal Velocity ◽  
Model Output ◽  
Energy Applications ◽  
Large Eddy ◽  
Momentum Fluxes ◽  
The Mean

Abstract. It is well known that when eddies are small, the eddy fluxes can be directly related to the mean vertical gradients, the so-called K-theory, but such relation becomes weaker the larger the coherent structures. Here, we show that this relation does not hold at heights relevant for wind energy applications. The relation implies that the angle (β) between the vector of vertical flux of horizontal momentum and the vector of the mean vertical gradient of horizontal velocity is zero, i.e., the vectors are aligned. This is not what we observe from measurements performed both offshore and onshore. We quantify the misalignment of β using measurements from a long-range Doppler profiling lidar and large-eddy simulations. We also use mesoscale model output from the New European Wind Atlas project to compare with the lidar-observed vertical profiles of wind speed, wind direction, momentum fluxes, and the angle between the horizontal velocity vector and the momentum flux vector up to 500 m both offshore and onshore, hence covering the rotor areas of modern wind turbines and beyond. The results show that within the range 100–500 m, β = −18° offshore and β = 12° onshore, on average. However, the large-eddy simulations show β ≈ 0°, partly confirming previous modeling results. We illustrate that mesoscale model output matches the observed mean wind speed and momentum fluxes well, but that this model output has significant deviations with the observations when looking at the turning of the wind.

scholarly journals Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer

2009 ◽  
Vol 137 (3) ◽  
pp. 1083-1110 ◽  
Author(s):  
Andrew S. Ackerman ◽  
Margreet C. vanZanten ◽  
Bjorn Stevens ◽  
Verica Savic-Jovcic ◽  
Christopher S. Bretherton ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Cloud Water ◽  
Large Eddy Simulations ◽  
Cloud Base ◽  
Entrainment Rate ◽  
Liquid Water Path ◽  
Average Maximum ◽  
Large Eddy ◽  
The Mean

Abstract Cloud water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from 11 groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. Including drizzle in the simulations reduces convective intensity, increases boundary layer stratification, and decreases LWP for nearly all models. Including cloud water sedimentation substantially decreases entrainment, decreases convective intensity, and increases LWP for most models. In nearly all cases, LWP responds more strongly to cloud water sedimentation than to drizzle. The omission of cloud water sedimentation in simulations is strongly discouraged, regardless of whether or not precipitation is present below cloud base.

scholarly journals Comparison of Large Eddy Simulations of a convective boundary layer with wind LIDAR measurements

2012 ◽  
Vol 8 (1) ◽  
pp. 83-86 ◽  
Author(s):  
J. G. Pedersen ◽  
M. Kelly ◽  
S.-E. Gryning ◽  
R. Floors ◽  
E. Batchvarova ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Geostrophic Wind ◽  
Large Eddy Simulations ◽  
Horizontal Wind ◽  
Convective Boundary ◽  
Horizontal Wind Speed ◽  
Large Eddy ◽  
Lidar Measurements ◽  
Wind Lidar

Abstract. Vertical profiles of the horizontal wind speed and of the standard deviation of vertical wind speed from Large Eddy Simulations of a convective atmospheric boundary layer are compared to wind LIDAR measurements up to 1400 m. Fair agreement regarding both types of profiles is observed only when the simulated flow is driven by a both time- and height-dependent geostrophic wind and a time-dependent surface heat flux. This underlines the importance of mesoscale effects when the flow above the atmospheric surface layer is simulated with a computational fluid dynamics model.

Large Eddy Simulations of Thermal Boundary Layer Spatial Development in a Turbulent Channel Flow

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Marc Sanchez ◽  
Frédéric Aulery ◽  
Adrien Toutant ◽  
Françoise Bataille
Keyword(s):  
Boundary Layer ◽  
Channel Flow ◽  
Thermal Boundary Layer ◽  
Turbulent Channel Flow ◽  
Spatial Development ◽  
Large Eddy Simulations ◽  
Boundary Layer Development ◽  
Large Eddy ◽  
The Mean ◽  
Heat Transfers

This article presents Large Eddy Simulations of thermal boundary layer spatial development in a low-Mach number turbulent channel flow. A coupling between isothermal biperiodic channel and anisothermal open channel is done to obtain a fully developed turbulent inlet. The interaction between a high temperature gradient and a turbulent flow is studied during the thermal boundary layer development. Turbulence and temperature quantities are analyzed for both streamwise and wall-normal directions. The results show how the asymmetrical heating modifies the velocity of the flow. The correlation between turbulence and heat transfers is studied. The mean and the fluctuation profiles are found to be asymmetrical. They evolve along the channel and are perturbed by the thermal gradient. Fluctuation destruction and creation areas in the length of the channel are highlighted.

scholarly journals Vertical transport of pollutants by shallow cumuli from large eddy simulations

2012 ◽  
Vol 12 (23) ◽  
pp. 11319-11327 ◽  
Author(s):  
G. Chen ◽  
H. Xue ◽  
G. Feingold ◽  
X. Zhou
Keyword(s):  
Boundary Layer ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Vertical Transport ◽  
Large Eddy Simulations ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Upward Transport ◽  
Lower Boundary Layer

Abstract. This study investigates the vertical transport of a passive tracer in a shallow cumulus boundary layer using large eddy simulations. The tracer source is at the surface in one case, and in the inversion layer in the other case. Results show that shallow cumulus clouds can significantly enhance vertical transport of the tracer in both cases. In the case with surface-borne pollutants, cloudy regions are responsible for the upward transport, due to the intense updrafts in cumulus clouds. In the case where pollutants are aloft, cloud-free regions are responsible for the downward transport, but the downward transport mainly occurs in thin regions around cloud edges. This is consistent with previous aircraft measurements of downdrafts around cumulus clouds and indicates that the downward transport is also cloud-induced. Cumulus convection is therefore able to both vent pollutants upward from the surface and fumigate pollutants in the inversion layer downward into the lower boundary layer.

scholarly journals Departure from Flux-Gradient Relation in the Planetary Boundary Layer

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 672
Author(s):  
Pedro Santos ◽  
Alfredo Peña ◽  
Jakob Mann
Keyword(s):  
Wind Speed ◽  
Mesoscale Model ◽  
Large Eddy Simulations ◽  
Horizontal Velocity ◽  
Vertical Profiles ◽  
Height Range ◽  
Flux Gradient ◽  
Large Eddy ◽  
Momentum Fluxes ◽  
The Mean

It is well known that when eddies are small, the eddy fluxes can be directly related to the mean vertical gradients, the so-called flux-gradient relation, but such a relation becomes weaker the larger the coherent structures. Here, we show that this relation does not hold at heights relevant for wind energy applications. The flux–gradient relation assumes that the angle (β) between the vector of vertical flux of horizontal momentum and the vector of the mean vertical gradient of horizontal velocity is zero, i.e., these vectors are aligned. Our observations do not support this assumption, either onshore or offshore. Here, we present analyses of a misalignment between these vectors from a Doppler wind lidar observations and large-eddy simulations. We also use a real-time mesoscale model output for inter-comparison with the lidar-observed vertical profiles of wind speed, wind direction, momentum fluxes, and the angle between the horizontal velocity vector and the momentum flux vector up to 500 m, both offshore and onshore. The observations show this within the height range 100–500 m, β=−18∘ offshore and β=−12∘ onshore, on average. However, the large-eddy simulations show β≈0∘ both offshore and onshore. We show that observed and mesoscale-simulated vertical profiles of mean wind speed and momentum fluxes agree well; however, the mesoscale results significantly deviate from the wind-turning observations.

scholarly journals Vertical transport of pollutants by shallow cumuli from large eddy simulations

2012 ◽  
Vol 12 (5) ◽  
pp. 11391-11413
Author(s):  
G. Chen ◽  
H. Xue ◽  
G. Feingold ◽  
X. Zhou
Keyword(s):  
Boundary Layer ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Vertical Transport ◽  
Large Eddy Simulations ◽  
Cumulus Clouds ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Dry Convection ◽  
Lower Boundary Layer

Abstract. This study investigates the vertical transport of a passive tracer in a shallow cumulus boundary layer using large eddy simulations. The tracer source is at the surface in one case, and in the inversion layer in the other case. Results show that shallow cumulus clouds can significantly enhance vertical transport of the tracer in both cases. In the case with surface-borne pollutants, cloudy regions are responsible for the upward transport, due to the intense updrafts in cumulus clouds. In the case where pollutants are aloft, cloud-free regions are responsible for the downward transport, but the downward transport mainly occurs in thin regions around cloud edges. This is consistent with previous aircraft measurements of downdrafts around cumulus clouds and indicates that the downward transport is also cloud-induced. We also preformed cloud-free sensitivity runs for the two cases. Results show that this dry convection can neither transport the surface-borne pollutants into the inversion layer, nor transport pollutants from the inversion layer downward to the lower boundary layer. Cumulus convection is therefore more effective than dry convection at venting pollutants upward from the surface, and fumigating pollutants in the inversion layer downward into the lower boundary layer.

scholarly journals Using the Sensitivity of Large-Eddy Simulations to Evaluate Atmospheric Boundary Layer Models

2012 ◽  
Vol 69 (5) ◽  
pp. 1582-1601 ◽  
Author(s):  
Gilles Bellon ◽  
Bjorn Stevens
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Stationary State ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Tropospheric Temperature ◽  
Unstable Regime ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Bulk Model

Abstract A simple framework to study the sensitivity of atmospheric boundary layer (ABL) models to the large-scale conditions and forcings is introduced. This framework minimizes the number of parameters necessary to describe the large-scale conditions, subsidence, and radiation. Using this framework, the sensitivity of the stationary ABL to the large-scale boundary conditions [underlying sea surface temperature (SST) and overlying humidity and temperature in the free troposphere] is investigated in large-eddy simulations (LESs). For increasing SST or decreasing free-tropospheric temperature, the LES exhibits a transition from a cloud-free, well-mixed ABL stationary state, through a cloudy, well-mixed stationary state and a stable shallow cumulus stationary state, to an unstable regime with a deepening shallow cumulus layer. For a warm SST, when increasing free-tropospheric humidity, the LES exhibits a transition from a stable shallow cumulus stationary state, through a stable cumulus-under-stratus stationary state, to an unstable regime with a deepening, cumulus-under-stratus layer. For a cool SST, when increasing the free-tropospheric humidity, the LES stationary state exhibits a transition from a cloud-free, well-mixed ABL regime, through a well-mixed cumulus-capped regime, to a stratus-capped regime with a decoupling between the subcloud and cloud layers. This dataset can be used to evaluate other ABL models. As an example, the sensitivity of a bulk model based on the mixing-line model is presented. This bulk model reproduces the LES sensitivity to SST and free-tropospheric temperature for the stable and unstable shallow cumulus regimes, but it is less successful at reproducing the LES sensitivity to free-tropospheric humidity for both shallow cumulus and well-mixed regimes.

scholarly journals Coherent structure of the convective boundary layer derived from large-eddy simulations

1989 ◽  
Vol 200 ◽  
pp. 511-562 ◽  
Author(s):  
Helmut Schmidt ◽  
Ulrich Schumann
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Large Scale ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Stable Layer ◽  
Convective Boundary ◽  
Velocity Fluctuations ◽  
Large Eddy ◽  
The Mean

Turbulence in the convective boundary layer (CBL) uniformly heated from below and topped by a layer of uniformly stratified fluid is investigated for zero mean horizontal flow using large-eddy simulations (LES). The Rayleigh number is effectively infinite, the Froude number of the stable layer is 0.09 and the surface roughness height relative to the height of the convective layer is varied between 10−6 and 10−2. The LES uses a finite-difference method to integrate the three-dimensional grid-volume-averaged Navier–Stokes equations for a Boussinesq fluid. Subgrid-scale (SGS) fluxes are determined from algebraically approximated second-order closure (SOC) transport equations for which all essential coefficients are determined from the inertial-range theory. The surface boundary condition uses the Monin–Obukhov relationships. A radiation boundary condition at the top of the computational domain prevents spurious reflections of gravity waves. The simulation uses 160 × 160 × 48 grid cells. In the asymptotic state, the results in terms of vertical mean profiles of turbulence statistics generally agree very well with results available from laboratory and atmospheric field experiments. We found less agreement with respect to horizontal velocity fluctuations, pressure fluctuations and dissipation rates, which previous investigations tend to overestimate. Horizontal spectra exhibit an inertial subrange. The entrainment heat flux at the top of the CBL is carried by cold updraughts and warm downdraughts in the form of wisps at scales comparable with the height of the boundary layer. Plots of instantaneous flow fields show a spoke pattern in the lower quarter of the CBL which feeds large-scale updraughts penetrating into the stable layer aloft. The spoke pattern has also been found in a few previous investigations. Small-scale plumes near the surface and remote from strong updraughts do not merge together but decay while rising through large-scale downdraughts. The structure of updraughts and downdraughts is identified by three-dimensional correlation functions and conditionally averaged fields. The mean circulation extends vertically over the whole boundary layer. We find that updraughts are composed of quasi-steady large-scale plumes together with transient rising thermals which grow in size by lateral entrainment. The skewness of the vertical velocity fluctuations is generally positive but becomes negative in the lowest mesh cells when the dissipation rate exceeds the production rate due to buoyancy near the surface, as is the case for very rough surfaces. The LES results are used to determine the root-mean-square value of the surface friction velocity and the mean temperature difference between the surface and the mixed layer as a function of the roughness height. The results corroborate a simple model of the heat transfer in the surface layer.

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