scholarly journals Turbulence vertical structure of the boundary layer during the afternoon transition

2014 ◽  
Vol 14 (23) ◽  
pp. 32491-32533 ◽  
Author(s):  
C. Darbieu ◽  
F. Lohou ◽  
M. Lothon ◽  
J. Vilà-Guerau de Arellano ◽  
F. Couvreux ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Structure ◽  
Second Phase ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Surface Measurements ◽  
Vertical Evolution ◽  
Two Phases ◽  
Surface Buoyancy

Abstract. We investigate the decay of planetary boundary layer (PBL) turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field experiment by several meteorological surface stations, sounding balloons, radars, lidars, and two aircraft flying extensively during the afternoon transition. We analyzed a case study based on some of those observations and Large-Eddy Simulation (LES) data focusing on the turbulent vertical structure throughout the afternoon transition. The decay of turbulence is quantified through the temporal and vertical evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic length scales of turbulence, (3) the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to (1) characterize the variation of the turbulent decay with height and (2) study the distribution of turbulence over eddy size. This study points out the LES ability to reproduce the turbulence evolution throughout the afternoon. LES and observations agree that the afternoon transition can be divided in two phases: (1) a first phase during which the TKE decays with a low rate, with no significant change in turbulence characteristics, (2) a second phase characterized by a larger TKE decay rate and a change spectral shape, implying an evolution of eddy size distribution and energy cascade from low to high wavenumber. The changes observed either on TKE decay (during the first phase) or on the vertical wind spectra shape (during the second phase of the afternoon transition) occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.

scholarly journals Turbulence vertical structure of the boundary layer during the afternoon transition

2015 ◽  
Vol 15 (17) ◽  
pp. 10071-10086 ◽  
Author(s):  
C. Darbieu ◽  
F. Lohou ◽  
M. Lothon ◽  
J. Vilà-Guerau de Arellano ◽  
F. Couvreux ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Structure ◽  
Wave Number ◽  
Second Phase ◽  
High Wave Number ◽  
Eddy Simulation ◽  
Surface Measurements ◽  
Vertical Evolution ◽  
Two Phases ◽  
Surface Buoyancy

Abstract. We investigate the decay of planetary boundary layer (PBL) turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field experiment by several meteorological surface stations, sounding balloons, radars, lidars and two aircraft during the afternoon transition. We analysed a case study based on some of these observations and large-eddy simulation (LES) data focusing on the turbulent vertical structure throughout the afternoon transition. The decay of turbulence is quantified through the temporal and vertical evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic length scales of turbulence and (3) the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to characterize the variation in the turbulent decay with height and study the distribution of turbulence over eddy size. This study highlights the LES ability to reproduce the turbulence evolution throughout the afternoon. LESs and observations agree that the afternoon transition can be divided in two phases: (1) a first phase during which the TKE decays at a low rate, with no significant change in turbulence characteristics, and (2) a second phase characterized by a larger TKE decay rate and a change in spectral shape, implying an evolution of eddy size distribution and energy cascade from low to high wave number. The changes observed either in TKE decay (during the first phase) or in the vertical wind spectra shape (during the second phase of the afternoon transition) occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.

scholarly journals Seamless Stratocumulus Simulation across the Turbulent Gray Zone

2014 ◽  
Vol 142 (4) ◽  
pp. 1655-1668 ◽  
Author(s):  
I. A. Boutle ◽  
J. E. J. Eyre ◽  
A. P. Lock
Keyword(s):  
Boundary Layer ◽  
Prediction Models ◽  
Weather Prediction ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Aircraft Observations ◽  
Microphysical Parameterization ◽  
Grid Length ◽  
Numerical Weather Prediction Models

Abstract A pragmatic approach for representing partially resolved turbulence in numerical weather prediction models is introduced and tested. The method blends a conventional boundary layer parameterization, suitable for large grid lengths, with a subgrid turbulence scheme suitable for large-eddy simulation. The key parameter for blending the schemes is the ratio of grid length to boundary layer depth. The new parameterization is combined with a scale-aware microphysical parameterization and tested on a case study forecast of stratocumulus evolution. Simulations at a range of model grid lengths between 1 km and 100 m are compared to aircraft observations. The improved microphysical representation removes the correlation between precipitation rate and model grid length, while the new turbulence parameterization improves the transition from unresolved to resolved turbulence as grid length is reduced.

scholarly journals A Case Study of Convective Boundary Layer Development during IHOP_2002: Numerical Simulations Compared to Observations

2008 ◽  
Vol 136 (7) ◽  
pp. 2305-2320 ◽  
Author(s):  
Robert J. Conzemius ◽  
Evgeni Fedorovich
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Convective Boundary ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Boundary Layer Development ◽  
Large Eddy ◽  
Atmospheric Observations

Abstract Results are presented from a combined numerical and observational study of the convective boundary layer (CBL) diurnal evolution on a day of the International H2O Project (IHOP_2002) experiment that was marked by the passage of a dryline across part of the Oklahoma and Texas Panhandles. The initial numerical setup was based on observational data obtained from IHOP_2002 measurement platforms and supplementary datasets from surrounding locations. The initial goals of the study were as follows: (i) numerical investigation of the structure and evolution of the relatively shallow and homogeneous CBL east of the dryline by means of large-eddy simulation (LES), (ii) evaluation of LES predictions of the sheared CBL growth against lidar observations of the CBL depth evolution, and (iii) comparison of the simulated turbulence structures with those observed by lidar and vertically pointing radar during the CBL evolution. In the process of meeting these goals, complications associated with comparisons between LES predictions and atmospheric observations of sheared CBLs were encountered, adding an additional purpose to this study, namely, to convey and analyze these issues. For a period during mid- to late morning, the simulated CBL evolution was found to be in fair agreement with atmospheric lidar and radar observations, and the simulated entrainment dynamics were consistent with those from previous studies. However, CBL depths, determined from lidar data, increased at a faster rate than in the simulations during the afternoon, and the wind direction veered in the simulations more than in the observations. The CBL depth discrepancy can be explained by a dryline solenoidal circulation reported in other studies of the 22 May 2002 case. The discrepancy in winds can be explained by time variation of the large-scale pressure gradient, which was not included in LES.

The vertical structure of mid-latitude marine stratocumulus simulated by large eddy simulation

2020 ◽  
Author(s):  
Yangze Ren ◽  
Huiwen Xue
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Cellular Structure ◽  
Large Scale ◽  
Vertical Structure ◽  
Temperature Inversion ◽  
Liquid Water Content ◽  
Marine Stratocumulus ◽  
Eddy Simulation ◽  
Large Eddy

<p>Cloud feedback in mid-latitude marine stratocumulus is not clearly understood due to few reliable observations. Stratocumulus cloud is the most frequent and extensive cloud type over mid-latitude marine areas and has strong short-wave radiative effect. In this study, large eddy simulation (LES) is used to resolve the vertical structure of mid-latitude marine stratocumulus. We find that, in the wintertime over North Pacific, stratocumulus cloud often forms in regions of high pressure and large-scale sinking motion, and can remain in steady-state for a couple of days. We then choose two typical cases to do LES simulation: One has a lower cloud top height and a stronger temperature inversion (case l), without mesoscale cellular structure; the other has a higher cloud top height and a weaker temperature inversion (case h), with closed-cell cellular structure. The liquid water content profiles are adiabatic, and the boundary layer is well-mixed for both cases. In case l, the main source of turbulent kinetic energy (TKE) is from cloud top long-wave radiative cooling for the entire boundary layer. In case h, TKE production due to cloud-top longwave cooling is only significant in the cloud layer, and the subcloud layer TKE is mainly from surface processes.</p>

scholarly journals Predictability of Dry Convective Boundary Layers: An LES Study

2016 ◽  
Vol 73 (7) ◽  
pp. 2715-2727 ◽  
Author(s):  
Siddhartha Mukherjee ◽  
Jerôme Schalkwijk ◽  
Harmen J. J. Jonker
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Strong Dependence ◽  
Second Phase ◽  
Error Growth ◽  
Convective Boundary ◽  
Boundary Layer Height ◽  
Eddy Simulation ◽  
Convective Boundary Layers ◽  
Two Phases

Abstract The predictability horizon of convective boundary layers is investigated in this study. Large-eddy simulation (LES) and direct numerical simulation (DNS) techniques are employed to probe the evolution of perturbations in identical twin simulations of a growing dry convective boundary layer. Error growth typical of chaotic systems is observed, marked by two phases. The first comprises an exponential error growth as , with δ0 as the initial error, δ(t) as the error at time t, and Λ as the Lyapunov exponent. This phase is independent of the perturbation wavenumber, and the perturbation energy grows following a self-similar spectral shape dominated by higher wavenumbers. The nondimensional error growth rate in this phase shows a strong dependence on the Reynolds number (Re). The second phase involves saturation of the error. Here, the error growth follows Lorenz dynamics with a slower saturation of successively larger scales. An analysis of the spectral decorrelation times reveals two regimes: an Re-independent regime for scales larger than the boundary layer height and an Re-dependent regime for scales smaller than , which are found to decorrelate substantially faster for increasing Reynolds numbers.

A Comparison of Roll and Nonroll Convection and the Subsequent Deepening Moist Convection: An LEM Case Study Based on SCMS Data

2009 ◽  
Vol 137 (1) ◽  
pp. 350-365 ◽  
Author(s):  
Qian Huang ◽  
John H. Marsham ◽  
Douglas J. Parker ◽  
Wenshou Tian ◽  
Tammy Weckwerth
Keyword(s):  
Boundary Layer ◽  
Wind Shear ◽  
Moist Convection ◽  
Convective Boundary ◽  
Obukhov Length ◽  
A Value ◽  
Large Eddy ◽  
Wind Shears ◽  
Surface Buoyancy

Abstract Rolls observed during the Small Cumulus Microphysical Study (SCMS) field campaign are simulated using a large eddy model (LEM). The simulated boundary layer properties were in a good agreement with sounding profiles and aircraft observations, and the observed boundary layer rolls were reproduced by the model. Rolls started to decay when −Zi/L exceeded a threshold, with a value between 5 and 45. Here Zi and L refer to the height of the top of convective boundary layer and the Monin–Obukhov length, respectively. This value was found to depend on a nondimensional combination of the low-level wind shear, the height of the CBL, and the eddy velocity scale. Larger surface buoyancy fluxes and smaller shears gave higher thresholds. For the case modeled, rolls persisted for surface buoyancy fluxes less than 110 W m−2, and formed for boundary layer wind shears greater than 5 × 10−3 s−1, which is consistent with previous studies. The simulated roll convection was compared with a nonroll simulation, which was identical except for the wind and the wind shear used. In both the roll and nonroll cases the variability in convective inhibition (CIN) was dominated by the variability in the source air, rather than the lifting of the top of the boundary layer by the convection. Stronger moist updrafts existed in the nonroll convection, whereas roll convection gave a more symmetrical distribution of up and downdrafts, with stronger downdrafts than the nonroll case. The nonroll convection simulations have lower minimum values of CIN and clouds develop 15 min earlier in this case.

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