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Boundary-Layer Meteorology
Journal Prestige (SJR): 1.262
Citation Impact (citeScore): 2
Number of Followers: 30  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1573-1472 - ISSN (Online) 0006-8314
Published by Springer-Verlag Homepage  [2467 journals]
  • Correction to: Anisotropic Turbulence in the Radiatively Driven Convective
           Layer in a Small Shallow Ice-Covered Lake: An Observational Study

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      PubDate: 2023-03-24
       
  • A Study on Measuring the Wind Field in the Air Using a Multi-rotor UAV
           Mounted with an Anemometer

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      Abstract: Abstract Compared to conventional wind field measurement methods such as wind masts or wind towers, UAV-based measurement is a relatively new approach to making wind field measurements. In the present study, a method for measuring wind field by using a six-rotor UAV mounted with an ultrasonic anemometer was established, and the feasibility thereof in wind field measurement was tested. Firstly, the influence of the UAS fuselage attitude on the accuracy of wind measurement results was analysed by means of wind tunnel testing. The results show that the average wind speed obtained by the UAV anemometry system (UAS) was slightly larger, but the average wind speed obtained by the UAS was consistent with that obtained by the Cobra anemometer after the modification of the fuselage attitude coefficient. Secondly, the wind field measurement results obtained by the UAS and the wind tower were compared, and the revised wind speed, wind direction, turbulence intensity and other parameters obtained by the UAS were found to be consistent with those of the anemometers at the same height on the wind tower. The difference was within 5%, and the longitudinal fluctuating wind power spectra obtained by the two were almost the same, being in good agreement with the Von Karman spectrum. Finally, the UAS was used to measure the wind field characteristic parameters of a certain site, which were compared with the corresponding parameters of national regulations. The feasibility of the UAS in measuring the air wind field was verified. These research results provide a reference for further research into UAV wind measurement methods.
      PubDate: 2023-03-19
       
  • A Note on Friction Velocity and Viscous Effect for Idealized Urban Canopy
           Flows

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      Abstract: Abstract Friction velocity is one of the important scaling parameters in atmospheric boundary layer studies. However, several definitions of friction velocity exist in the literature: e.g. estimated from the total drag force or used only pressure drag, etc. In this study, a series of large-eddy simulation (LES) calculations were carried out to evaluate the impact of various definitions on the friction velocity for idealized urban geometries, i.e. staggered array of cubes with different packing densities and wind directions. We first compared the normalized velocity fields with the literature data for the case with a packing density of \(25\%\) . The results show that the LES data normalized by the friction velocity derived from the Reynolds stress using the extrinsic spatial average is more consistent with the direct numerical simulation data. Furthermore, when varying the wind direction, the distribution of Reynolds stress and pressure drag show significant change in streamwise and spanwise directions. We further found that for packing density of \(44.44\%\) , the frictional drag accounts for more than a quarter of the total drag, and even higher than the pressure drag in parallel wind direction. This leads to the deviation of friction velocity estimated from the pressure drag and that calculated from the total drag force up to 33%. Such characteristic of viscous effect challenges the assumption widely used in wind tunnel experiments and urban canopy parameterizations that the contribution of viscous force is negligible, especially for ultra-dense arrays.
      PubDate: 2023-03-17
       
  • Midday Boundary-Layer Collapse in the Altiplano Desert: The Combined
           Effect of Advection and Subsidence

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      Abstract: Abstract Observations in the Altiplano region of the Atacama Desert show that the atmospheric boundary layer (ABL) suddenly collapses at noon. This rapid decrease occurs simultaneously to the entrance of a thermally driven, regional flow that causes a rise in wind speed and a marked temperature decrease. We identify the main drivers that cause the observed ABL collapse by using a land–atmosphere model. The free atmosphere lapse rate and regional forcings, such as advection of mass and cold air as well as subsidence, are first estimated by combining observations from a comprehensive field campaign and a regional model. Then, to disentangle the ABL collapse, we perform a suite of numerical experiments with increasing level of complexity: from only considering local land–atmosphere interactions, to systematically including the regional contributions of mass advection, cold air advection, and subsidence. Our results show that non-local processes related to the arrival of the regional flow are the main factors explaining the boundary-layer collapse. The advection of a shallower boundary layer ( \(\approx -250\)  m h \(^{-1}\) at noon) causes an immediate decrease in the ABL height (h) at midday. This occurs simultaneously with the arrival of a cold air mass, which reaches a strength of \(\approx -4\)  K h \(^{-1}\) at 1400 LT. These two external forcings become dominant over entrainment and surface processes that warm the atmosphere and increase h. As a consequence, the ABL growth is capped during the afternoon. Finally, a wind divergence of \(\approx 8 \times 10^{-5}\)  s \(^{-1}\) contributes to the collapse by causing subsidence motions over the ABL from 1200 LT onward. Our findings show the relevance of treating large and small-scale processes as a continuum to be able to understand the ABL dynamics.
      PubDate: 2023-03-17
       
  • Large-Eddy Simulation of Reynolds Stress Budgets in and Above Forests in
           Neutral Atmospheric Boundary Layers

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      Abstract: Abstract Large-eddy simulations (LESs) of inversion-capped neutral atmospheric boundary layers (ABLs) are augmented to earlier small-domain LESs of a sparse forest and field observation to evaluate the budgets of all non-negligible resolved-scale Reynolds stress components. The focus is on the atmospheric surface layer comprised of the roughness sublayer (RSL) in and above horizontally homogeneous forests and the inertial sublayer (ISL) above the RSL over flat terrain. The greater LES domain and ABL depths result in greater depths of both the RSL and the ISL. A key result is that in the upper portions of the canopy and above, pressure redistribution is a major sink of normal stress in the horizontal direction with mean shear production as a major source, whereas in the horizontal direction absent of mean shear production and in the vertical direction, pressure redistributions are major sources of normal stresses. In the lower portions of the canopy where mean shear production and turbulent transport are much reduced, pressure redistributions are major sources of horizontal velocity variances but a major sink of vertical velocity variance. Pressure transport is a greater source of vertical velocity variance than turbulent transport from the ground level to just under the treetops where it transitions to a major sink up to about 1.5 times the canopy height. This greater significance of pressure transport over turbulent transport increases with increased vegetation area index (VAI). The impact of increased value of geostrophic wind speed is negligible compared to that of increased value of VAI on enhancing normalized budget terms in the vicinity of treetops.
      PubDate: 2023-03-13
       
  • Observed Budgets of Turbulence Kinetic Energy, Heat Flux, and Temperature
           Variance Under Convective and Stable Conditions

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      Abstract: Abstract The terms of the budget equations for turbulence kinetic energy (TKE), heat, flux, and temperature variance are evaluated observationally using 4 levels of turbulence observations made over a period of 10 months at a 30-m tower in southern Brazil. All terms are evaluated, except those associated with horizontal transport or pressure perturbations, which were not observed. The analysis is split between daytime, convective conditions and night-time, stable conditions. In both cases, the terms are initially shown in their original dimensional form as a function of the mean wind speed at 3 m, and the observations are then classified by net radiation. During the day, the TKE budget is dominated by shear and buoyant production, while dissipation is the main removal mechanism and the residual analysis indicates that the pressure transport term is positive near the surface. At night, the TKE budget is dominated by shear production and destruction by dissipation, while the buoyant destruction is about an order of magnitude smaller than both. The inferred role of pressure transport depends on the turbulence regime. In the daytime heat flux budget the dominant production mechanism varies between gradient and buoyant production, depending on mean wind speed and net radiation, while most of the destruction is mainly attributed to the pressure covariance term, inferred from the budget residual. At night, buoyancy becomes a relevant destruction mechanism, and its relationship with gradient production is related to the stable boundary layer turbulence regime. Temperature variance budget is a balance between gradient production and dissipation both at day and night, in which case the residual is larger and its possible causes are discussed. Dimensionless expressions for the dominant terms in the three budgets considered are compared to the data, as a function of the stability parameter.
      PubDate: 2023-03-13
       
  • Evaluation of Surface Layer Stability Functions and Their Extension to
           First Order Turbulent Closures for Weakly and Strongly Stratified Stable
           Boundary Layer

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      Abstract: Abstract In this study, we utilize a generalization of Monin–Obukhov similarity theory to construct first order turbulent closures for single-column models of the atmospheric boundary layer (ABL). A set of widely used universal functions for dimensionless gradients is evaluated. Two test cases based on Large-Eddy Simulations (LES) experimental setups are considered – weakly stable ABL (GABLS1; Beare et al. in Bound Layer Meteorol 118(2):247–272, 2006), and very strongly stratified ABL (van der Linden et al. in Bound Layer Meteorol 173(2):165–192, 2019). The comparison shows that approximations obtained using a linear dimensionless velocity gradient tend to match the LES data more closely. In particular, the EFB (Energy- and Flux- Budget) closure proposed by Zilitinkevich et al. (Bound Layer Meteorol 146(3):341–373, 2013) has the best performance for the tests considered here. We also test surface layer “bulk formulas” based on these universal functions. The same LES data are utilized for comparison. The setup showcases the behavior of surface scheme, when one assumes that the velocity and temperature profiles in ABL are represented correctly. The advantages and disadvantages of different surface schemes are revealed.
      PubDate: 2023-03-06
       
  • How Do Dust Devil-Like Vortices Depend on Model Resolution' A Grid
           Convergence Study Using Large-Eddy Simulation

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      Abstract: Abstract Dust devils are organized convective vortices with pressure drops of hundreds of pascals that spirally lift surface material into the air. This material modifies the radiation budget by contributing to the atmospheric aerosol concentration. Quantification of this contribution requires good knowledge of the dust devil statistics and dynamics. The latter can also help to understand vortex genesis, evolution and decay, in general. Dust devil-like vortices are numerically investigated mainly by large-eddy simulation (LES). A critical parameter in these simulations is the grid spacing, which has a great influence on the dust devil statistics. So far, it is unknown which grid size is sufficient to capture dust devils accurately. We investigate the convergence of simulated convective vertical vortices that resemble dust devils by using the LES model PALM. We use the nesting capabilities of PALM to explore grid spacings from 10 to 0.625 m. Grid spacings of 1 m or less have never been used for the analysis of dust devil-like vortices that develop in a horizontal domain of more than 10 km \(^2\) . Our results demonstrate that a minimum resolution of 1.25 m is necessary to achieve a convergence for sample-averaged quantities like the core pressure drop. This grid spacing or smaller should be used for future quantifications of dust devil sediment fluxes. However, sample maxima of the investigated dust devil population and peak velocity values of the general flow show no convergence. If a qualitative description of the dust devil flow pattern is sufficient, we recommend a grid spacing of 2.5 m or smaller.
      PubDate: 2023-03-06
       
  • Drag Coefficient and Turbulence Mixing Length of Local Climate Zone-Based
           Urban Morphologies Derived Using Obstacle-Resolving Modelling

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      Abstract: Abstract Large-eddy microscale simulations of eleven local climate zone-based (LCZ) urban morphologies with various building plane and frontal area density are used to investigate the flow characteristics and provide vertical profiles of velocity, sectional drag coefficient, and turbulence mixing length. The urban morphologies are procedurally generated to mimick real urban districts. The simulations are performed with the MesoNH-IBM meteorological research model, which allows to represent explicitly the obstacles and to account for the impact of the large scale turbulence structures on the urban canopy layer (UCL). The results show that, in heterogeneous building height UCLs, the streamwise velocity profile is not exponential, the mixing length is not constant and the equivalent sectional drag coefficient formula based on bulk morphology parameters is not valid. Comparatively to an non-urban mixing length increasing linearly with the distance from the ground, the UCL mixing length is higher for \(z/h_\textrm{mean} \in [0 - \approx 0.75]\) , because of the turbulent structures generated by the buildings and lower above, because of the shear generated at the building roofs. These differences extend up to several times the mean building height. The vertical profile of the dispersive momentum flux (DMF) in the UCL is in agreement with the literature; positive DMF is found upstream of the buildings whereas negative DMF is localized downstream. Although the DMF is lower than the turbulent momentum flux for most of the LCZs, it is not negligible for midrise and highrise LCZs. The large-scale atmospheric boundary-layer turbulence has a negligible influence on most of the investigated horizontally-averaged quantities. This suggests that considering a neutral stratification and a wind flow aligned with the buildings, most of the turbulence within the UCL is generated by the buildings themselves.
      PubDate: 2023-03-01
       
  • Turbulence Organization and Mean Profile Shapes in the Stably Stratified
           Boundary Layer: Zones of Uniform Momentum and Air Temperature

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      Abstract: Abstract A persistent spatial organization of eddies is identified in the lowest portion of the stably stratified planetary boundary layer. The analysis uses flow realizations from published large-eddy simulations (Sullivan et al. in J Atmos Sci 73(4):1815–1840, 2016) ranging in stability from near-neutral to almost z-less stratification. The coherent turbulent structure is well approximated as a series of uniform momentum zones (UMZs) and uniform temperature zones (UTZs) separated by thin layers of intense gradients that are significantly greater than the mean. This pattern yields stairstep-like instantaneous flow profiles whose shape is distinct from the mean profiles that emerge from long-term averaging. However, the scaling of the stairstep organization is closely related to the resulting mean profiles. The differences in velocity and temperature across the thin gradient layers remain proportional to the surface momentum and heat flux conditions regardless of stratification. The vertical thickness of UMZs and UTZs is proportional to height above the surface for near-neutral and weak stratification, but becomes thinner and less dependent on height as the stability increases. Deviations from the logarithmic mean profiles for velocity and temperature observed under neutral conditions are therefore predominately due to the reduction in eddy size with increasing stratification, which is empirically captured by existing Monin–Obukhov similarity relations for momentum and heat. The zone properties are additionally used to explain trends in the turbulent Prandtl number, thus providing a connection between the eddy organization, mean profiles, and turbulent diffusivity in stably stratified conditions.
      PubDate: 2023-03-01
       
  • Robustness of the Mean Flow Similarity in an Urban Roughness Sublayer to
           Different Inflow Properties

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      Abstract: Abstract This study uses a numerical simulation to examine the local mean flow similarity within an urban roughness sublayer (RSL). The simulations are conducted using a realistic building geometry for the central area of Tokyo under three different inflow conditions. The inflow properties are controlled by changing the surface geometries in the upwind direction, which results in various ratios of boundary-layer height to roughness height in the target region. The local mean wind velocities within the RSL, which vary significantly in space, are proportional to each other in all simulations, regardless of the inflow conditions. The velocity within the RSL is represented by the friction velocity, which is estimated from the Reynolds stress profile in the inertial sublayer. The behaviour of the wake turbulence behind isolated high-rise buildings differs considerably among the inflow conditions. Velocity persists for long distances downstream in cases with a low boundary- layer height relative to an isolated building, whereas it diffuses rapidly in cases with a higher boundary-layer height. This effect can propagate into the RSL and modify the mean flow similarity within the sublayer.
      PubDate: 2023-03-01
       
  • An Asymptotic Theory for the Flow over Heterogeneous Roughness

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      Abstract: Abstract The flow over arbitrary roughness changes is investigated, revisiting the analysis of Belcher et al. (Q J R Meteorol Soc 116:611–635, 1990) regarding surface-roughness heterogeneity. The proposed theory is restricted to steady neutral boundary layers over flat regions with changes of roughness sufficiently slow and mild to inhibit the growth of nonlinear terms. The approach is based on a triple-deck decomposition of the flow above the roughness, although only the first two layers are interactive at leading order. Two experimental datasets (one with a smooth-to-rough and the other with a rough-to-smooth transition) are used to validate the theory. The latter is further compared against two large-eddy simulations featuring chessboard patterns of alternating surface roughness with relatively short and long length scales, respectively. All the comparisons show that the proposed theory is able to reasonably assess the wind-field perturbation due to the roughness heterogeneity, supporting the use of the model to quickly assess the effect of roughness changes in the flow field.
      PubDate: 2023-03-01
       
  • Machine Learning Weather Analogs for Near-Surface Variables

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      Abstract: Abstract Numerical weather prediction models and high-performance computing have significantly improved our ability to model near-surface variables, but their uncertainty quantification still remains a challenging task. Ensembles are usually produced to depict a series of possible future states of the atmosphere, as a means to quantify the prediction uncertainty, but this requires multiple instantiation of the model, leading to an increased computational cost. Weather analogs, alternatively, can be used to generate ensembles without repeated model runs. The analog ensemble (AnEn) is a technique to identify similar weather patterns for near-surface variables and quantify forecast uncertainty. Analogs are chosen based on a similarity metric that calculates the weighted multivariate Euclidean distance. However, identifying optimal weights for similarity metric becomes a bottleneck because it involves performing a constrained exhaustive search. As a result, only a few predictors were selected and optimized in previous AnEn studies. A new machine learning similarity metric is proposed to improve the theoretical framework on how weather analogs are identified. First, a deep learning network is trained to generate latent features using all the temporal multivariate input predictors. Analogs are then selected in this latent space, rather than the original predictor space. The proposed method does not require prior predictor selection and an exhaustive search, thus presenting a significant computational benefit and scalability. It is tested for surface wind speed and solar irradiance forecasts in Pennsylvania from 2017 to 2019. Results show that the proposed method is capable of handling a large number of predictors, and it outperforms the original similarity metric in RMSE, bias, and CRPS. Since the data-driven transformation network is trained using the historical record, the proposed method has been found to be more flexible for searching through a longer record.
      PubDate: 2023-03-01
       
  • An Improved Fringe-Region Technique for the Representation of Gravity
           Waves in Large Eddy Simulation with Application to Wind Farms

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      Abstract: Abstract Large eddy simulations (LESs) of the atmospheric boundary layer are often performed using pseudo-spectral methods, which adopt a fringe-region approach to introduce inflow boundary conditions. However, we notice that a standard fringe-region technique excites spurious gravity waves when stratified atmospheres are considered, therefore enhancing the amount of energy reflected from the top of the domain and perturbing the velocity and pressure fields downstream. In this work, we develop a new fringe-region method that imposes the inflow conditions while limiting spurious effects on the surrounding flow. This is achieved by locally damping the convective term in the vertical momentum equation. We first apply the standard and wave-free fringe-region techniques to two-dimensional inviscid-flow simulations subjected to 169 different atmospheric states. A similar study is performed on a three-dimensional domain using a couple of atmospheric states. In all cases, the new fringe-region technique outperforms the standard method, imposing the inflow conditions with a minimal impact on the surrounding flow. Moreover, we also investigate the performance of two already existing non-reflective upper boundary conditions, that is, a Rayleigh damping layer (RDL) and a radiation condition (RC). Results highlight the importance of carefully tuning the RDL to limit the distortion of the numerical solution. Also, we find that the tuned RDL outperforms the RC in all cases. Finally, the tuned RDL together with the wave-free fringe-region method is applied to an LES of a wind farm operating in a conventionally neutral boundary layer, for which we measure a reflectivity of only \(0.75\%\) .
      PubDate: 2023-03-01
       
  • Effects of Urban Surface Roughness on Potential Sources of Microplastics
           in the Atmospheric Boundary Layer

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      Abstract: Abstract Understanding the local transport of microplastics (MPs) emitted from the urban environment, such as those from vehicle tire wearing in streets and highways, is a necessary first step for quantifying their global transport cycle. By approximating microplastics as heavy particles, we conduct numerical simulations using large-eddy simulations (LESs) to understand how spatially organized sources and complex urban surface roughness affect their transport. Three sets of cases are considered, namely: (i) spatially uniform source and (ii) spatially organized source, and (iii) spatially organized source with explicitly resolved roughness elements, respectively. Results suggest that for a spatially organized source without buildings, source heterogeneity in streamwise direction only influences the vertical concentration profile up to \(z/L_z=0.11\) . In contrast, that in spanwise direction influences the profile till \(z/L_z=0.58\) , where z and \(L_z\) are the vertical coordinate and the domain height, respectively. Simulations with buildings reveal that the buildings impede the transport of particles and particles accumulate on the leeward side of the buildings, which are characterized by wake turbulence and relatively quiescent flow. Within the canopy sub-layer, the gravitational settling effect of the particles becomes more significant because of the reduced wind. Because of that, the escape fraction of particles is smaller than in cases with no buildings and it decreases with increasing building height h and increasing building plan area fraction \(\lambda _p\) . Finally, by finding suitable scalar displacement height \(d_s\) and scalar roughness length \(z_{os}\) , we find that similar to a passive scalar, an inertial sub-layer (ISL) still exists for heavy particles. This study highlights that for spatially organized particle sources, the momentum sinks due to urban roughness and the gravitational settling jointly affect the transport of heavy particles, which implies that the surface heterogeneity effect can be substantial in quantifying the atmospheric transport of microplastics of urban origins.
      PubDate: 2023-03-01
       
  • CityTransformer: A Transformer-Based Model for Contaminant Dispersion
           Prediction in a Realistic Urban Area

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      Abstract: Abstract We develop a Transformer-based deep learning model to predict the plume concentrations in the urban area in statistically stationary flow conditions under a stationary and homogeneous forcing. Our model has two distinct input layers: Transformer layers for sequential data and convolutional layers in convolutional neural networks for image-like data. Our model can predict the plume concentration from realistically available data such as the time series monitoring data at a few observation stations, and the building shapes and the source location. It is shown that the model can give reasonably accurate prediction in less than a second. It is also shown that exactly the same model can be applied to predict the source location and emission rate, which also gives reasonable prediction accuracy.
      PubDate: 2023-03-01
       
  • Entrainment Rates and Their Synoptic Dependence on Wind Speed Aloft in
           California's Central Valley

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      Abstract: Abstract Daytime atmospheric boundary layer (ABL) dynamics—including potential temperature budgets, water vapour budgets, and entrainment rates—are presented from in situ flight data taken on six afternoons near Fresno in the San Joaquin Valley (SJV) of California during July/August 2016. The flights took place as a part of the California Baseline Ozone Transport Study aimed at investigating transport pathways of air entering the Central Valley from offshore and mixing down to the surface. Midday entrainment velocity estimates ranged from 0.8 to 5.4 cm s−1 and were derived from a combination of continuously determined ABL heights during each flight and model-derived subsidence rates, which averaged -2.0 cm s−1 in the flight region. A strong correlation was found between entrainment velocity (normalized by the convective velocity scale) and an inverse bulk ABL Richardson number, suggesting that wind shear at the ABL top plays a significant role in driving entrainment. Similarly, we found a strong correlation between the entrainment efficiency (the ratio of entrainment to surface heat fluxes with an average of 0.23 ± 0.15) and the wind speed at the ABL top. We explore the synoptic conditions that generate higher winds near the ABL top and propose that warm anomalies in the southern Sierra Nevada mountains promote increased entrainment. Additionally, a method is outlined to estimate turbulence kinetic energy, convective velocity scale (w*), and the surface sensible heat flux in the ABL from a slow, airborne wind measurement system using mixed-layer similarity theory.
      PubDate: 2023-03-01
       
  • Dynamic Mechanisms Associated with the Structure and Evolution of Roll
           Vortices and Coherent Turbulence in the Hurricane Boundary Layer: A Large
           Eddy Simulation During the Landfall of Hurricane Harvey

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      Abstract: Abstract Roll vortices are a series of large-scale turbulent eddies that nearly align with the mean wind direction and prevail in the hurricane boundary layer. In this study, the one-way nested WRF-LES model simulation results from Li et al. (J Atmos Sci 78(6):1847–1867, https://doi.org/10.1175/JAS-D-20-0270.1, 2021) are used to examine the structure and generation mechanism of roll vortices and associated coherent turbulence in the hurricane boundary layer during the landfall of Hurricane Harvey from 00 UTC 25 to 18 UTC 27 August 2017. Results indicate that roll vortices prevail in the hurricane boundary layer. The intense roll vortices and associated large turbulent eddies above them (at a height of ~ 200 to 3000 m) accumulate within a hurricane radius of 20–40 km. Their intensity is proportional to hurricane intensity during the simulation period. Before and during hurricane landfall, strong inflow convergence leads to horizontal advection of roll vortices throughout the entire hurricane boundary layer. Combined with the strong wind shear, the strongest roll vortices and associated large turbulent eddies are generated near the eyewall with suitable thermodynamic (Richardson number at around − 0.2 to 0.2) and dynamic conditions (strong negative inflow wind shear). After landfall, the decayed inflow weakens the inflow convergence and quickly reduces the strong roll vortices and associated large turbulent eddies. Diagnosis of vertical turbulent kinetic energy indicates that atmospheric pressure perturbation, caused by horizontal convergence, transfers the horizontal component of turbulence to the vertical component with a mean wavelength of about 1 km. The buoyancy term is weak and negative, and the large turbulent eddies are suppressed.
      PubDate: 2023-03-01
       
  • The Effect of Submeso Motions on the Budgets of the Mean Turbulent Kinetic
           Energy and Temperature Variance in the Stable Atmospheric Surface Layer

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      Abstract: Abstract By considering turbulence observations in the atmospheric stable surface layer over complex terrain, we study the effect of submeso motions on the budgets of the mean turbulent kinetic energy (TKE) and (half) the temperature variance. Different averaging times are considered (i.e., 100 s and 30 min), to filter out or retain the submeso contributions to second-order moments. Furthermore, results are interpreted by introducing four parameters that express the relative submeso contribution to the TKE, the temperature variance, and the vertical fluxes of heat and momentum. Four regimes are identified according to these four submeso parameters and the budgets are evaluated for these regimes. A balance among production, buoyancy (for the TKE) and dissipation occurs for the two regimes characterized by small submeso contribution to the fluxes, while an unbalance occurs for the other two regimes, where the submeso contribution to the fluxes is large. Instead, the budgets are independent of the magnitude of the submeso contribution to the TKE and the temperature variance.
      PubDate: 2023-02-03
       
  • Aerosols, Clusters, Greenhouse Gases, Trace Gases and Boundary-Layer
           Dynamics: on Feedbacks and Interactions

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      Abstract: Abstract Turbulence is the key process transporting material and energy in the atmosphere. Furthermore, turbulence causes concentration fluctuations, influencing different atmospheric processes such as deposition, chemical reactions, formation of low-volatile vapours, formation of new aerosol particles and their growth in the atmosphere, and the effect of aerosol particles on boundary-layer meteorology. In order to analyse the connections, interactions and feedbacks relating those different processes require a deep understanding of atmospheric turbulence mechanisms, atmospheric chemistry and aerosol dynamics. All these processes will further influence air pollution and climate. The better we understand these processes and their interactions and associated feedback, the more effectively we can mitigate air pollution as well as mitigate climate forcers and adapt to climate change. We present several aspects on the importance of turbulence including how turbulence is crucial for atmospheric phenomena and feedbacks in different environments. Furthermore, we discuss how boundary-layer dynamics links to aerosols and air pollution. Here, we present also a roadmap from deep understanding to practical solutions.
      PubDate: 2023-01-20
       
 
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