scholarly journals Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

2016 ◽  
Vol 16 (2) ◽  
pp. 651-674 ◽  
Author(s):  
M. Jähn ◽  
D. Muñoz-Esparza ◽  
F. Chouza ◽  
O. Reitebuch ◽  
O. Knoth ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Potential Temperature ◽  
Vertical Mixing ◽  
Large Eddy Simulations ◽  
Inertial Subrange ◽  
Trade Wind ◽  
Lidar Data ◽  
Raman Lidar ◽  
Large Eddy

Abstract. Large eddy simulations (LESs) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude potential temperature perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind and Raman lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to “gray zone modeling” when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ≈ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the downwind vertical wind structure. Additionally, the model results accurately reproduce the development of the daytime convective boundary layer measured by the Raman lidar.

scholarly journals Investigations of boundary layer structure, cloud characteristics and vertical mixing of aerosols at Barbados with large eddy simulations

2015 ◽  
Vol 15 (16) ◽  
pp. 22637-22699 ◽  
Author(s):  
M. Jähn ◽  
D. Muñoz-Esparza ◽  
F. Chouza ◽  
O. Reitebuch
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Vertical Mixing ◽  
Atmospheric Stability ◽  
Large Eddy Simulations ◽  
Inertial Subrange ◽  
Trade Wind ◽  
Lidar Data ◽  
Large Eddy ◽  
Wind Lidar

Abstract. Large eddy simulations (LES) are performed for the area of the Caribbean island Barbados to investigate island effects on boundary layer modification, cloud generation and vertical mixing of aerosols. Due to the presence of a topographically structured island surface in the domain center, the model setup has to be designed with open lateral boundaries. In order to generate inflow turbulence consistent with the upstream marine boundary layer forcing, we use the cell perturbation method based on finite amplitude perturbations. In this work, this method is for the first time tested and validated for moist boundary layer simulations with open lateral boundary conditions. Observational data obtained from the SALTRACE field campaign is used for both model initialization and a comparison with Doppler wind lidar data. Several numerical sensitivity tests are carried out to demonstrate the problems related to "gray zone modeling" when using coarser spatial grid spacings beyond the inertial subrange of three-dimensional turbulence or when the turbulent marine boundary layer flow is replaced by laminar winds. Especially cloud properties in the downwind area west of Barbados are markedly affected in these kinds of simulations. Results of an additional simulation with a strong trade-wind inversion reveal its effect on cloud layer depth and location. Saharan dust layers that reach Barbados via long-range transport over the North Atlantic are included as passive tracers in the model. Effects of layer thinning, subsidence and turbulent downward transport near the layer bottom at z ~ 1800 m become apparent. The exact position of these layers and strength of downward mixing is found to be mainly controlled atmospheric stability (especially inversion strength) and wind shear. Comparisons of LES model output with wind lidar data show similarities in the formation of the daytime convective plume and the mean vertical wind structure.

scholarly journals Large-eddy simulations of the Northeastern US coastal marine boundary layer

2020 ◽  
Vol 1618 ◽  
pp. 062038
Author(s):  
Lawrence C. Cheung ◽  
Colleen M. Kaul ◽  
Alan S. Hsieh ◽  
Myra L. Blaylock ◽  
Matthew J. Churchfield
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Large Eddy Simulations ◽  
Coastal Marine ◽  
Large Eddy

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.

Exploring microphysical properties of marine boundary layer clouds through network analysis

2021 ◽  
Author(s):  
Lucile Ricard ◽  
Athanasios Nenes ◽  
Jakob Runge ◽  
Paraskevi Georgakaki
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Network Analysis ◽  
Marine Boundary Layer ◽  
Large Eddy Simulations ◽  
Dynamical Structure ◽  
Boundary Layer Clouds ◽  
Microphysical Properties ◽  
Spatial Coverage ◽  
Large Eddy

<p>Aerosol-cloud interactions remain the largest uncertainty in assessments of anthropogenic climate forcing, while the complexity of these interactions require methods that enable abstractions and simplifications that allow their improved treatment in climate models. Marine boundary layer clouds are an important component of the climate system as their large albedo and spatial coverage strongly affect the planetary radiative balance. High resolution simulations of clouds provide an unprecedented understanding of the structure and behavior of these clouds in the marine atmosphere, but the amount of data is often too large and complex to be useful in climate simulations. Data reduction and inference methods provide a way that to reduce the complexity and dimensionality of datasets generated from high-resolution Large Eddy Simulations.</p><p>In this study we use network analysis, (the δ-Maps method) to study the complex interaction between liquid water, droplet number and vertical velocity in Large Eddy Simulations of Marine Boundary Layer clouds. δ-Maps identifies domains that are spatially contiguous and possibly overlapping and characterizes their connections and temporal interactions. The objective is to better understand microphysical properties of marine boundary layer clouds, and how they are impacted by the variability in aerosols. Here we will capture the dynamical structure of the cloud fields predicted by the MIMICA Large Eddy Simulation (LES) model. The networks inferred from the different simulation fields are compared between them (intra-comparisons) using perturbations in initial conditions and aerosol, using a set of four metrics. The networks are then evaluated for their differences, quantifying how much variability is inherent in the LES simulations versus the robust changes induced by the aerosol fields. </p>

scholarly journals A Revised Conceptual Model of the Tropical Marine Boundary Layer. Part I: Statistical Characterization of the Variability Inherent in the Wintertime Trade Wind Regime over the Western Tropical Atlantic

2013 ◽  
Vol 70 (10) ◽  
pp. 3005-3024 ◽  
Author(s):  
Jennifer L. Davison ◽  
Robert M. Rauber ◽  
Larry Di Girolamo ◽  
Margaret A. LeMone
Keyword(s):  
Boundary Layer ◽  
Wind Direction ◽  
Rain Rate ◽  
Marine Boundary Layer ◽  
Potential Temperature ◽  
Statistical Characteristics ◽  
Trade Wind ◽  
Statistical Characterization ◽  
Wide Range ◽  
Rate Method

Abstract This paper investigates wintertime tropical marine boundary layer (TMBL) statistical characteristics over the western North Atlantic using the complete set of island-launched soundings from the Rain in Cumulus over the Ocean (RICO) experiment. The soundings are subdivided into undisturbed and disturbed classifications using two discriminators: 1) dates chosen by Global Energy and Water Cycle Experiment (GEWEX) Cloud System Studies (GCSS) investigators to construct the mean RICO sounding and 2) daily average rain rates. A wide range of relative humidity (RH) values was observed between the surface and 8.0 km. At 2.0 km, half the RH values were within 56%–89%; at 4.0 km, half were within 13%–61%. The rain-rate method of separating disturbed and undisturbed soundings appears more meaningful than the GCSS method. The median RH for disturbed conditions using the rain-rate method showed moister conditions from the surface to 8.0 km, with maximum RH differences of 30%–40%. Moist air generally extended higher on disturbed than undisturbed days. Based on equivalent potential temperature, wind direction, and RH analyses, the most common altitude marking the TMBL top was about 4.0 km. Temperature inversions (over both 50- and 350-m intervals) were observed at every altitude above 1.2 km; there were no dominant inversion heights and most of the inversions were weak. Wind direction analyses indicated that winds within the TMBL originated from more tropical latitudes on disturbed days. The analyses herein suggest that the RICO profile used to initialize many model simulations of this environment represents only a small subset of the broad range of possible conditions characterizing the wintertime trades.

scholarly journals On the Application of the Dynamic Smagorinsky Model to Large-Eddy Simulations of the Cloud-Topped Atmospheric Boundary Layer

2006 ◽  
Vol 63 (2) ◽  
pp. 526-546 ◽  
Author(s):  
M. P. Kirkpatrick ◽  
A. S. Ackerman ◽  
D. E. Stevens ◽  
N. N. Mansour
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Dynamic Model ◽  
Potential Temperature ◽  
Large Eddy Simulations ◽  
Small Scale ◽  
Subgrid Scale ◽  
Smagorinsky Model ◽  
Marine Stratocumulus ◽  
Large Eddy

Abstract In this paper the dynamic Smagorinsky model originally developed for engineering flows is adapted for simulations of the cloud-topped atmospheric boundary layer in which an anelastic form of the governing equations is used. The adapted model accounts for local buoyancy sources, vertical density stratification, and poor resolution close to the surface and calculates additional model coefficients for the subgrid-scale fluxes of potential temperature and total water mixing ratio. Results obtained with the dynamic model are compared with those obtained using two nondynamic models for simulations of a nocturnal marine stratocumulus cloud deck observed during the first research flight of the second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field experiment. The dynamic Smagorinsky model is found to give better agreement with the observations for all parameters and statistics. The dynamic model also gives improved spatial convergence and resolution independence over the nondynamic models. The good results obtained with the dynamic model appear to be due primarily to the fact that it calculates minimal subgrid-scale fluxes at the inversion. Based on other results in the literature, it is suggested that entrainment in the DYCOMS-II case is due predominantly to isolated mixing events associated with overturning internal waves. While the behavior of the dynamic model is consistent with this entrainment mechanism, a similar tendency to switch off subgrid-scale fluxes at an interface is also observed in a case in which gradient transport by small-scale eddies has been found to be important. This indicates that there may be problems associated with the application of the dynamic model close to flow interfaces. One issue here involves the plane-averaging procedure used to stabilize the model, which is not justified when the averaging plane intersects a deforming interface. More fundamental, however, is that the behavior may be due to insufficient resolution in this region of the flow. The implications of this are discussed with reference to both dynamic and nondynamic subgrid-scale models, and a new approach to turbulence modeling for large-eddy simulations is proposed.

scholarly journals Characteristics of Decaying Convective Boundary Layers Revealed by Large-Eddy Simulations

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 434 ◽  
Author(s):  
Seung-Bu Park ◽  
Jong-Jin Baik
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Time Scale ◽  
Potential Temperature ◽  
Large Eddy Simulations ◽  
Quadrant Analysis ◽  
Convective Boundary ◽  
Near Surface ◽  
Large Eddy ◽  
Downward Propagation

The decay of the Convective Boundary Layer (CBL) is studied using large-eddy simulations of free and advective CBLs, in which surface heat supply is suddenly cut off. After the cutoff, coherent convective circulations last about one convective time scale and then fade away. In the mixed layer, the decay time scale increases with height, indicating that nonlocal eddies decay slower than near-surface local eddies. The slower decay of turbulence in the middle of CBL than near-surface turbulence is reconfirmed from the analysis of pattern correlations of perturbations of vertical velocity. Perturbations of potential temperature and scalar concentration decay faster and slower than vertical velocity perturbations, respectively. A downward propagation of negative heat flux and its oscillation are found and a quadrant analysis reveals that warmer air sinking events are responsible for the downward propagation. The fourth quadrant events seem to be induced by demixing of air parcels, entrained from above the CBL. The advective CBL simulation with geostrophic wind illustrates that near-surface eddies are mechanically generated and they decelerate flow from the bottom up in the CBL/residual layer. The two-dimensional spectra show the height- and scale-dependent characteristics of decaying convective turbulence again in the free and advective boundary layer simulations.

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