Over the past few years large-eddy simulation (LES) has demonstrated success in modelling continental radiation fog, and several recent studies have used LES to investigate the sensitivity of fog formation to physical processes such as turbulent mixing and surface heat and moisture exchange, as well as to the parametrization of microphysical processes such as cloud droplet activation. Here we extend

For a family of relatively common problems in micrometeorology, whose forms previously required iterative or indirect treatment, analytical solution is possible via the Lambert-W function. Use of this function reduces computational time and the need for approximations, while offering a clearer view of the character and solution of such problems. This note provides a generalized form for such problems

A large-eddy simulation model is coupled with a Lagrangian cloud model to study marine fog. In this model, aerosols and droplets are treated from a Lagrangian frame of reference, in contrast to the traditional bulk and bin microphysical models. Droplet growth via condensation is governed by Köhler theory and environmental conditions local to the droplet. Coupling to the vapour and temperature fields

Air-pollution modelling at the local scale requires accurate meteorological inputs such as from the velocity field. These meteorological fields are generally simulated with microscale models (here Code_Saturne), which are forced with boundary conditions provided by larger scale models or observations. Local atmospheric simulations are very sensitive to the boundary conditions, whose accurate estimation

The relationship between the wind speed derived from the outputs of a numerical-weather-prediction model and from observations is explored using statistical and machine-learning models. Eight years of wind-speed measurements at a height of 10 m (from 2010 to 2017) from 171 stations spread over mainland France and Corsica are used for reference. Operational analyses from the European Center for Medium

Open cellular convection (OCC) over, for example, the North Sea is often observed in connection with cold-air outbreaks. It is accompanied by large temporal and spatial variability in wind speed, which affects offshore wind energy in the area. This study uses the global Model for Prediction Across Scales (MPAS), with regional mesh refinement down to convection-permitting scales of 2 km, to simulate

To simulate the airflow through a wind farm across a wide range of atmospheric conditions, microscale models (e.g., large-eddy simulation, LES, models) have to be coupled with mesoscale models, because microscale models lack the atmospheric physical processes to represent time-varying local forcing. Here we couple mesoscale model outputs to a LES solver by applying mesoscale momentum- and temperature-budget

In north-west China, extensive areas of gravel desert exist, whose surface properties have an important effect on the wind-erosion threshold friction velocity \( u_{*t} \). In this study, we use four models and field observations of gravel mass fraction, soil physical crust, and soil clay content to assess the effect of gravel-surface properties on the value of \( u_{*t} \). Results show that gravel

In this commentary, we revisit Raupach’s flow-sheltering paradigm that asserts reduced wall-shear stress behind a surface roughness element (MR Raupach in Boundary-Layer Meteorol, 60(4):375–395, 1992). Direct numerical simulations of a turbulent boundary layer over a wall-mounted rectangular roughness are conducted we consider roughness with three different aspect ratios and flows at two Reynolds numbers

Cities intimately intermingle people and air pollution. It is very difficult to monitor or model neighbourhood-scale pollutant transport explicitly. One computationally efficient way is to treat neighbourhoods as patches of porous media to which the flow adjusts. Here we use conceptual arguments and large-eddy simulation to formulate two flow regimes based on the size of patches of different frontal-area

Observations from the 2014 Arctic Clouds in Summer Experiment indicate that, in summer, warm-air advection over melting sea-ice results in a strong surface melting feedback forced by a very strong surface-based temperature inversion and fog formation exerting additional heat flux on the surface. Here, we analyze this case further using a combination of reanalysis dataset and satellite products in a

Observations of the near-surface components of the vegetated terrestrial air–surface system during and around the complete solar eclipse of 21 August 2017 were made in the U.S.A. at three sites of intensive measurement in Tennessee and at a number of locations in Idaho. Data obtained relate to a variety of surfaces, from barren to forest. Results reveal details of how the atmospheric, vegetative, and

Some 60 years ago, six researchers obtained a semi-empirical equation that describes how the stability correction function for the mean velocity profile (\(\phi _\mathrm{m}\)) in the atmospheric surface layer varies with the stability parameter—the famous O’KEYPS equation. Their derivations are essentially based on interpolation of the turbulent eddy viscosity between neutral and convective conditions

Five planetary-boundary-layer parametrizations of the Weather Research and Forecasting model are compared with respect to their ability to simulate the very stable and the weakly stable regimes of the stable boundary layer. This is performed for single column models where the large-scale mechanical forcing is represented by geostrophic wind speeds ranging from 0.5 to 12 m \(\hbox {s}^{-1}\). The performance

In a recent study (Želi et al. in Bound Layer Meteorol 176:229–249, 2020), we have shown that the explicit algebraic Reynolds-stress (EARS) model, implemented in a single-column context, is able to capture the main features of a stable atmospheric boundary layer (ABL) for a range of stratification levels. We here extend the previous study and show that the same formulation and calibration of the EARS

Using data for 3 days in the Cooperative Atmosphere-Surface Exchange Study 1997 field experiment that are analyzed in LeMone et al. (Boundary-Layer Meteorol 104:1–52, 2002, hereafter L2002), it is shown that direct radiative heating can have a significant role in warming the nearly cloudless fair-weather convective boundary layer (CBL). Radiative heating becomes especially important in the presence

Accurate measurements of the depth of the convective boundary layer (CBL) are fundamental for understanding and forecasting weather, air quality, and climate. However, the CBL depth (BLD) shows significant spatial and temporal variability, which is challenging to measure and model. Ceilometer instruments, which estimate the CBL depth from aerosol layers, are relatively cheap, have high temporal resolution

We propose a method for estimating the convective-heat-transfer coefficient (CHTC) distribution on building walls by using the water-evaporation method involving filter paper and three-dimensional laser scanning, and demonstrates consistency with the gravimetric evaporation method. The theory and method are established based on the convective heat- and mass-transfer analogy and a near-infrared laser-scanning

Formation of coastal fog was observed near the southern tip of Nova Scotia when warm, humid air was advected towards the shore over an area of colder water. The sea-surface temperature in the colder and higher salinity patch near the coast was below 14 °C compared to that of the surrounding sea of ≈ 17–18 °C. Measurements of stratification, currents, and the dissipation rate of turbulence kinetic energy

A model for the spectrum of the lateral velocity component \(S_v(f)\) is developed for a frequency range from about 0.2 \(\hbox {day}^{-1}\) to the turbulence inertial subrange, with the intent of improving the calculation of flow meandering over areas the size of offshore wind farms and clusters. These sizes can correspond to a temporal scale of several hours, much larger than the validity limit of

The development and assessment of subgrid-scale (SGS) models for large-eddy simulations of the atmospheric boundary layer is an active research area. In this study, we compare the performance of the classical Smagorinsky model, the Lagrangian-averaged scale-dependent (LASD) model, and the anisotropic minimum dissipation (AMD) model. The LASD model has been widely used in the literature for 15 years

We review developments in the field of boundary-layer flow over complex topography, focussing on the period from 1970 to the present day. The review follows two parallel strands: the impact of hills on flow in the atmospheric boundary layer and gravity-driven flows on hill slopes initiated by heating or cooling of the surface. For each strand we consider the understanding that has resulted from analytic

We describe and explain the turbulent processes at play in the lower part of the urban boundary layer through performing a large-eddy simulation of the flow over an urban-like canopy composed of a staggered array of cubes with a packing density of 25%. The simulation models neutral thermal conditions at a Reynolds number (based on both velocity at the top of the domain and the domain height) of \(Re

Polarization lidar observations were made to study the transport of an elevated aerosol layer over Gadanki, India (13.45° N, 79.17° E) during the pre-monsoon period of the year 2009. Observations show significant aerosol layering within and above the boundary layer. Coordinated observations with radiosondes were carried out from 2 to 10 April 2009. Temporal and spatial variations of the parameters

Large-eddy simulations of nine idealized heterogeneous urban morphologies with identical building density and frontal area index are used to explore the impact of heterogeneity on urban airflow. The fractal-like urban morphologies were generated with a new open-source Urban Landscape Generator tool (doi:10.5281/zenodo.3747475). The vertical structure of mean flow and the dispersive vertical momentum

The shear-stress cospectrum and the horizontal and vertical temperature-flux cospectra in the convective boundary layer (CBL) are predicted using the multi-point Monin–Obukhov similarity (MMO theory). MMO theory was recently proposed and then derived from first principles by Tong and Nguyen (Journal of the Atmospheric Sciences, 2015, Vol. 72, 4337 – 4348) and Tong and Ding (Journal of Fluid Mechanics

Studying the microclimate of plant canopies has long motivated scientists in various research fields such as agronomy, ecology or silviculture, and almost a century has passed since the first measurements of wind speed in a forest stand were published in the scientific literature. The behaviour of wind in canopies is an essential component of their microclimate, which largely conditions the rate of

Peatlands often experience turbulent sheltering from their surrounding upland forests, which results in spatially variable surface–atmosphere exchanges of momentum, heat, and moisture produced by flow-separation dynamics, which suppresses the transport of such scalars in the sheltered region while promoting transport in the reattachment zone. With evapotranspiration being the dominant source of water

We report the ability of an urban canopy model, coupled with a regional climate model, to simulate energy fluxes, the intra-urban variability of air temperature, urban-heat-island characteristics, indoor temperature variation, as well as anthropogenic heat emissions, in Berlin, Germany. A building energy model is implemented into the Double Canyon Effect Parametrization, which is coupled with the mesoscale

Inland freshwater bodies form the largest natural source of carbon to the atmosphere. To study this contribution to the atmospheric carbon cycle, eddy-covariance flux measurements at lake sites have become increasingly popular. The eddy-covariance method is derived for solely local processes from the surface (lake). Non-local processes, such as entrainment or advection, would add erroneous contributions

We investigate sensible and latent heat exchange between evaporating saline droplets and carrier air by performing direct numerical simulation (DNS) of an idealized flow modelling the marine atmospheric boundary layer. Turbulent, droplet-laden Couette airflow over a waved water surface is considered in the DNS under two different sets of bulk air and water temperatures, \( T_{a} = -\, 10\,^{\circ}{\hbox{C}}

Mesoscale simulations are typically performed at coarse resolutions that do not adequately represent underlying topography; nesting large-eddy simulations within a mesoscale model can better resolve terrain and hence capture topographically-induced stable flow phenomena. In the case of the Mountain Terrain Atmospheric Modelling and Observations (MATERHORN) program, large temperature fluctuations were

We use a database of direct numerical simulations to evaluate parametrizations for energy dissipation rate in stably stratified flows. We show that shear-based formulations are more appropriate for stable boundary layers than commonly used buoyancy-based formulations. As part of the derivations, we explore several length scales of turbulence and investigate their dependence on local stability.

We investigate the impact of wildfires on surface energy exchange through the assessment of six California wildfires that occurred in the last 20 years. A burned–unburned binary mask was generated from the MODIS approximate date of burn product and implemented into the Simplified Simple Biosphere model for a series of simulations. Model performance was evaluated against the North American Land Data

We have identified certain fundamental limitations of a mixing-length parametrization used in a popular turbulent kinetic energy-based subgrid-scale model. Replacing this parametrization with a more physically realistic one significantly improves the overall quality of the large-eddy simulation (LES) of stable boundary layers. For the range of grid sizes considered here (specifically, 1 m–12.5 m),

A wind-wave generation model over an ice-covered sea is proposed. The wind velocity over the ice upper surface is decomposed into the mean velocity profile of the boundary-layer flow and small perturbations, while the ice cover is modelled as a viscoelastic layer, with the water part modelled as an inviscid fluid. The present model is based on two-dimensional linear flow-instability theory, with no-slip

Over the last 50 years the large-eddy simulation (LES) technique has developed into one of the most prominent numerical tools used to study transport processes in the atmospheric boundary layer (ABL). This review examines development of the technique as a tool for ABL research, integration with state-of-the-art scientific computing resources, and some key application areas. Analysis of the published

Representing land–atmosphere exchange processes at the ground surface of numerical-weather-prediction models remains a challenge in spite of the recent advances in computing. Previous studies investigating the effects of spatial surface heterogeneities have been viewed from a turbulence perspective, mostly assuming the existence of a blending length scale above which surface-induced perturbations are

Katabatic winds are very frequent but poorly understood or simulated over steep slopes. This study focuses on a katabatic jet above a steep alpine slope. We assess the buoyancy terms in both the turbulence kinetic energy (TKE) and the Reynolds shear-stress budget equations. We specifically focus on the contribution of the slope-normal and along-slope turbulent sensible heat fluxes to these terms. Four

An experimental field campaign is designed to unveil mechanisms responsible for turbulent exchange processes when mechanical and thermal effects are entwined. The focus is an urban street canyon with a mean aspect ratio H/W of 1.65 in the business centre of a mid-size Italian city (H is the mean building height and W is the mean canyon width). The exchange processes can be characterized by time scales

The precise determination of evapotranspiration rate is challenging because it is a quantity that is difficult to measure and to parametrize. Direct estimates include the determination of the change of mass of a volume of soil and vegetation that evapotranspirates using lysimeters, or direct measurements of turbulent water vapour fluxes by eddy-covariance systems. Parametrized estimates that make use

We review the efforts made by the scientific community in more than seventy years to elucidate the behaviour of concentration fluctuations arising from localized atmospheric releases of dynamically passive and non-reactive scalars. Concentration fluctuations are relevant in many fields including the evaluation of toxicity, flammability, and odour nuisance. Characterizing concentration fluctuations

The \(\hbox {CO}_2\) flux from spume droplets occurs in two steps. First, the initial droplet–air gas concentration gradient \(\nabla C\) is immediately removed with no change in the droplet solubility. Then, the solubility changes with droplet temperature T and radius r evolution, but the flux maintains the condition \(\nabla C=0\). The gas content of a droplet can be determined by \(\nabla C=0\)

Mesoscale-to-microscale coupling (MMC) aims to address the limited scope of traditional large-eddy simulations by driving the microscale flow with information concerning large-scale weather patterns provided by mesoscale models. We present a new offline MMC technique for horizontally homogeneous microscale flow conditions, in which internal forcing terms are computed based on mesoscale time–height

Surface turbulent fluxes provide a key boundary condition for the prediction of weather, hydrology, and atmospheric carbon dioxide. The turbulence cospectrum is assumed to typically follow a −7/3 power-law scaling, which is used for the high-frequency spectral correction of eddy-covariance data. The derivation of this scaling is mostly grounded on dimensional analysis. The dimensional analysis or cospectral

Atmospheric boundary-layer dynamics over heterogeneous surfaces is significant to a wide array of geophysical and engineering applications. Yet, despite over five decades of intense efforts by the research community, numerous open research questions remain. This underlines the complexity of the physical processes that are excited by heterogeneity, the multitude of patterns and manifestations that it

The stably stratified atmospheric boundary layer (SBL) has been found in previous studies to display distinct regimes of behaviour. In particular, a contrast is often drawn between the weakly (wSBL) and very (vSBL) stable boundary layers. Time series of SBL regime affiliation obtained from hidden Markov model analyses of data from three different towers at the Los Alamos National Laboratory are used

An overview is given of 50-year Cabauw observations and research on the structure and dynamics of the atmospheric boundary layer. It is shown that over time this research site with its 200-m meteorological tower has grown into an atmospheric observatory with a comprehensive observational program encompassing almost all aspects of the atmospheric column including its boundary conditions. This is accomplished

Two well-developed sea-breeze cases in the La Plata River region, selected from a 5-month summer period, are studied using local observations, satellite images, and hydrostatic boundary-layer model simulations. Both the northern and southern coast cases are characterized by offshore regional flow that help develop stronger sea breezes due to enhanced horizontal convergence by the opposing flow. The

Physical processes represented by the Monin–Obukhov bulk formula for momentum are investigated with field observations. We discuss important differences between turbulent mixing by the most energetic non-local, large, coherent turbulence eddies and local turbulent mixing as traditionally represented by K-theory (analog to molecular diffusion), especially in consideration of developing surface-layer

A sonic anemometer is employed to investigate turbulent statistical characteristics and meteorological properties associated with a local windstorm known as the Vento Norte (Portuguese for north wind), which is observed in central Rio Grande do Sul state situated in southern Brazil. The Vento Norte consists of persistent and warm northerly gusts of moderate to strong magnitude that occur just downstream

In polar regions, where the boundary layer is often stably stratified, atmospheric models produce large biases depending on the boundary-layer parametrizations and the parametrization of the exchange of energy at the surface. This model intercomparison focuses on the very stable stratification encountered over the Antarctic Plateau in 2009. Here, we analyze results from 10 large-eddy-simulation (LES)

In the original publication, Figures 1 and 2 are subject to Crown Copyright.

During nocturnal cooling over land, the 10-m wind speed falls to very low values in many parts of the world while the absolute sensible heat flux increases initially after sunset but reaches a maximum before decreasing later in the night. In contrast, a one-dimensional numerical model predicts that the nocturnal wind speed is constant after an initial reduction at the evening transition. The difference

Boundary-layer schemes are essential components of numerical weather-forecasting and climate models. From simple beginnings 50 years ago, they have grown in sophistication and detail. Here, we review development and discuss the key processes to be represented and how they have most commonly been parametrized. We conclude by discussing the challenges posed by ever-increasing model resolution and a growing

Large-eddy simulation (LES) experiments have been performed using the Parallelized LES Model (PALM). A methodology for validating and understanding LES results for plume dispersion and concentration fluctuations in an atmospheric-like flow is presented. A wide range of grid resolutions is shown to be necessary for investigating the convergence of statistical characteristics of velocity and scalar fields

A simple analytical model is developed for the flow downwind of a step change of the aerodynamic roughness length in the atmospheric boundary layer. The region downwind of the roughness transition is assumed to be composed of two equilibrium layers, corresponding to the downwind and upwind conditions, and separated by a third, transition, layer. The key assumption in deriving the model is that the

The problem of realizability of the second-order turbulence closure models (parametrization schemes) is addressed through the consideration of the so-called “stability functions”. The emphasis is on the turbulence kinetic energy–scalar variance (TKESV) closure scheme that carries prognostic transport equations for the turbulence kinetic energy (TKE) and for the variances and covariance of two quasi-conservative

On the Greenland ice sheet, the sensible heat flux is the second largest source of energy for surface melt. Yet in atmospheric models, the surface turbulent heat fluxes are always indirectly estimated using a bulk turbulence parametrization, which needs to be constrained by long-term and continuous observations. Unfortunately, such observations are challenging to obtain in remote polar environments