Subjects -> METEOROLOGY (Total: 112 journals)
 Showing 1 - 36 of 36 Journals sorted alphabetically Acta Meteorologica Sinica       (Followers: 3) Advances in Atmospheric Sciences       (Followers: 43) Advances in Climate Change Research       (Followers: 31) Advances in Meteorology       (Followers: 24) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 7) Aeolian Research       (Followers: 6) Agricultural and Forest Meteorology       (Followers: 18) American Journal of Climate Change       (Followers: 31) Atmósfera       (Followers: 3) Atmosphere       (Followers: 26) Atmosphere-Ocean       (Followers: 15) Atmospheric and Oceanic Science Letters       (Followers: 11) Atmospheric Chemistry and Physics (ACP)       (Followers: 48) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 15) Atmospheric Environment       (Followers: 73) Atmospheric Environment : X       (Followers: 3) Atmospheric Research       (Followers: 69) Atmospheric Science Letters       (Followers: 36) Boundary-Layer Meteorology       (Followers: 31) Bulletin of Atmospheric Science and Technology       (Followers: 1) Bulletin of the American Meteorological Society       (Followers: 51) Carbon Balance and Management       (Followers: 4) Change and Adaptation in Socio-Ecological Systems       (Followers: 5) Ciencia, Ambiente y Clima       (Followers: 3) Climate       (Followers: 6) Climate and Energy       (Followers: 4) Climate Change Economics       (Followers: 26) Climate Change Research Letters       (Followers: 7) Climate Change Responses       (Followers: 12) Climate Dynamics       (Followers: 44) Climate of the Past (CP)       (Followers: 5) Climate of the Past Discussions (CPD) Climate Policy       (Followers: 44) Climate Research       (Followers: 6) Climate Resilience and Sustainability       (Followers: 13) Climate Risk Management       (Followers: 6) Climate Services       (Followers: 3) Climate Summary of South Africa       (Followers: 2) Climatic Change       (Followers: 66) Current Climate Change Reports       (Followers: 8) Developments in Atmospheric Science       (Followers: 28) Dynamics and Statistics of the Climate System       (Followers: 5) Dynamics of Atmospheres and Oceans       (Followers: 19) Earth Perspectives - Transdisciplinarity Enabled Economics of Disasters and Climate Change       (Followers: 3) Energy & Environment       (Followers: 24) Environmental and Climate Technologies       (Followers: 4) Environmental Dynamics and Global Climate Change       (Followers: 8) Frontiers in Climate       (Followers: 3) GeoHazards       (Followers: 2) Global Meteorology       (Followers: 17) International Journal of Atmospheric Sciences       (Followers: 22) International Journal of Biometeorology       (Followers: 1) International Journal of Climate Change Strategies and Management       (Followers: 22) International Journal of Climatology       (Followers: 31) International Journal of Environment and Climate Change       (Followers: 5) International Journal of Image and Data Fusion       (Followers: 2) Journal of Agricultural Meteorology Journal of Applied Meteorology and Climatology       (Followers: 35) Journal of Atmospheric and Oceanic Technology       (Followers: 34) Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 198) Journal of Atmospheric Chemistry       (Followers: 21) Journal of Climate       (Followers: 54) Journal of Climate Change       (Followers: 3) Journal of Climatology       (Followers: 3) Journal of Hydrology and Meteorology       (Followers: 29) Journal of Hydrometeorology       (Followers: 11) Journal of Integrative Environmental Sciences       (Followers: 4) Journal of Meteorological Research       (Followers: 1) Journal of Meteorology and Climate Science       (Followers: 14) Journal of Space Weather and Space Climate       (Followers: 27) Journal of the Atmospheric Sciences       (Followers: 81) Journal of the Meteorological Society of Japan       (Followers: 6) Journal of Weather Modification       (Followers: 2) Large Marine Ecosystems       (Followers: 1) Mathematics of Climate and Weather Forecasting       (Followers: 6) Mediterranean Marine Science       (Followers: 1) Meteorologica       (Followers: 2) Meteorological Applications       (Followers: 4) Meteorological Monographs       (Followers: 2) Meteorologische Zeitschrift       (Followers: 3) Meteorology and Atmospheric Physics       (Followers: 26) Mètode Science Studies Journal : Annual Review Michigan Journal of Sustainability       (Followers: 1) Modeling Earth Systems and Environment       (Followers: 1) Monthly Notices of the Royal Astronomical Society       (Followers: 13) Monthly Weather Review       (Followers: 34) Nature Climate Change       (Followers: 134) Nature Reports Climate Change       (Followers: 37) Nīvār npj Climate and Atmospheric Science       (Followers: 3) Open Atmospheric Science Journal       (Followers: 2) Open Journal of Modern Hydrology       (Followers: 6) Revista Brasileira de Meteorologia Revista Iberoamericana de Bioeconomía y Cambio Climático Russian Meteorology and Hydrology       (Followers: 3) Space Weather       (Followers: 25) Studia Geophysica et Geodaetica Tellus A       (Followers: 22) Tellus B       (Followers: 21) The Cryosphere (TC)       (Followers: 5) The Cryosphere Discussions (TCD)       (Followers: 4) The Quarterly Journal of the Royal Meteorological Society       (Followers: 27) Theoretical and Applied Climatology       (Followers: 13) Tropical Cyclone Research and Review       (Followers: 1) Urban Climate       (Followers: 4) Weather       (Followers: 19) Weather and Climate Dynamics Weather and Climate Extremes       (Followers: 16) Weather and Forecasting       (Followers: 28) Weatherwise       (Followers: 4) 气候与环境研究       (Followers: 1)
Similar Journals
 Boundary-Layer MeteorologyJournal Prestige (SJR): 1.262 Citation Impact (citeScore): 2Number of Followers: 31      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1573-1472 - ISSN (Online) 0006-8314 Published by Springer-Verlag  [2656 journals]
• Neighbourhood-Scale Flow Regimes and Pollution Transport in Cities
• Abstract: 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 density within neighbourhoods. One of these flow regimes distributes pollutants in counter-intuitive ways, such as producing pollution ‘hot spots’ in patches of lower frontal-area density. The regimes provide the first quantitative definition of the ‘urban background’, which can be used for more precisely targeted pollution monitoring. They also provide a conceptual basis for further research into neighbourhood-scale air-pollution problems, such as parametrizations in mesoscale models, and the transport of fluid constituents in other porous media.
PubDate: 2021-05-01

• Revisiting Raupach’s Flow-Sheltering Paradigm
• Abstract: 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. A large computational domain is used to study the behaviours of the wall-shear stress in both the near-wake and the far-wake regions. Aside from a low wall-shear stress region in the near-wake as one would expect from the flow-sheltering paradigm, a high-stress region is found in the far-wake. The presence of such a high-stress region challenges the well-established flow sheltering paradigm and is also counter-intuitive. Detailed analysis of the vortical structures shows that the high wall-shear stress region is a consequence of the horse-shoe-vortex-induced downwash motion in the far-wake.
PubDate: 2021-05-01

• Improving Numerical Dispersion Modelling in Built Environments with Data
Assimilation Using the Iterative Ensemble Kalman Smoother
• Abstract: 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 is difficult but crucial. When observations of the wind speed and turbulence or pollutant concentration are available inside the domain, they provide supplementary information via data assimilation, to enhance the simulation accuracy by modifying the boundary conditions. Among the existing data assimilation methods, the iterative ensemble Kalman smoother (IEnKS) is adapted to urban-scale simulations. This method has already been found to increase the accuracy of wind-resource assessment. Here we assess the ability of the IEnKS method to improve scalar-dispersion modelling—an important component of air-quality modelling—by assimilating perturbed measurements inside the urban canopy. To test the data assimilation method in urban conditions, we use the observations provided by the Mock Urban Setting Test field campaign and consider cases with neutral and stable conditions, and the boundary conditions consisting of the horizontal velocity components and turbulence. We prove the capacity of the IEnKS method to assimilate observations of velocity as well as pollutant concentration. In both cases, the accuracy of pollutant concentration estimates is enhanced by 40–60%. We also show that assimilating both types of observations allows further improvements of turbulence predictions by the model.
PubDate: 2021-05-01

• Jagadish Chandran Kaimal (1930–2021)
• PubDate: 2021-04-28

• Thermal Submesoscale Motions in the Nocturnal Stable Boundary Layer. Part
1: Detection and Mean Statistics
• Abstract: Submesoscale motions within the stable boundary layer were detected during the Shallow Cold Pool Experiment conducted in the Colorado plains, Colorado, U.S.A. in 2012. The submesoscale motion consisted of two air layers creating a well-defined front with a sharp temperature gradient, and further-on referred to as a thermal submesofront (TSF). The semi-stationary TSFs and their advective velocities are detected and determined by the fibre-optic distributed-sensing (FODS) technique. An objective detection algorithm utilizing FODS measurements is able to detect the TSF boundary, which enables a detailed investigation of its spatio–temporal statistics. The novel approach in data processing is to conditionally average any parameter depending on the distance between a TSF boundary and the measurement location. By doing this, a spatially-distributed feature like TSFs can be characterized by point observations and processes at the TSF boundary can be investigated. At the TSF boundary, the air layers converge, creating an updraft, strong static stability, and vigorous mixing. Further, the TSF advective velocity of TSFs is an order of magnitude lower than the mean wind speed. Despite being gentle, the topography plays an important role in TSF formation. Details on generating mechanisms and implications of TSFs on the stable boundary layer are discussed in Part 2.
PubDate: 2021-04-28

• Thermal Submeso Motions in the Nocturnal Stable Boundary Layer. Part 2:
Generating Mechanisms and Implications
• Abstract: In the stable boundary layer, thermal submesofronts (TSFs) are detected during the Shallow Cold Pool experiment in the Colorado plains, Colorado, USA in 2012. The topography induces TSFs by forming two different air layers converging on the valley-side wall while being stacked vertically above the valley bottom. The warm-air layer is mechanically generated by lee turbulence that consistently elevates near-surface temperatures, while the cold-air layer is thermodynamically driven by radiative cooling and the corresponding cold-air drainage decreases near-surface temperatures. The semi-stationary TSFs can only be detected, tracked, and investigated in detail when using fibre-optic distributed sensing (FODS), as point observations miss TSFs most of the time. Neither the occurrence of TSFs nor the characteristics of each air layer are connected to a specific wind or thermal regime. However, each air layer is characterized by a specific relationship between the wind speed and the friction velocity. Accordingly, a single threshold separating different flow regimes within the boundary layer is an oversimplification, especially during the occurrence of TSFs. No local forcings or their combination could predict the occurrence of TSFs except that they are less likely to occur during stronger near-surface or synoptic-scale flow. While classical conceptualizations and techniques of the boundary layer fail in describing the formation of TSFs, the use of spatially continuous data obtained from FODS provide new insights. Future studies need to incorporate spatially continuous data in the horizontal and vertical planes, in addition to classic sensor networks of sonic anemometry and thermohygrometers to fully characterize and describe boundary-layer phenomena.
PubDate: 2021-04-28

• Land-Use Improvements in the Weather Research and Forecasting Model over
Complex Mountainous Terrain and Comparison of Different Grid Sizes
• Abstract: Weather forecasts over mountainous terrain are challenging due to the complex topography that is necessarily smoothed by actual local-area models. As complex mountainous territories represent 20% of the Earth’s surface, accurate forecasts and the numerical resolution of the interaction between the surface and the atmospheric boundary layer are crucial. We present an assessment of the Weather Research and Forecasting model with two different grid spacings (1 km and 0.5 km), using two topography datasets (NASA Shuttle Radar Topography Mission and Global Multi-resolution Terrain Elevation Data 2010, digital elevation models) and four land-cover-description datasets (Corine Land Cover, U.S. Geological Survey land-use, MODIS30 and MODIS15, Moderate Resolution Imaging Spectroradiometer land-use). We investigate the Ortles Cevadale region in the Rhaetian Alps (central Italian Alps), focusing on the upper Forni Glacier proglacial area, where a micrometeorological station operated from 28 August to 11 September 2017. The simulation outputs are compared with observations at this micrometeorological station and four other weather stations distributed around the Forni Glacier with respect to the latent heat, sensible heat and ground heat fluxes, mixing-layer height, soil moisture, 2-m air temperature, and 10-m wind speed. The different model runs make it possible to isolate the contributions of land use, topography, grid spacing, and boundary-layer parametrizations. Among the considered factors, land use proves to have the most significant impact on results.
PubDate: 2021-04-28

• Numerical Prediction of the Boundary-Layer Flow Over the Bolund Hill:
Assessment of Turbulence Models and Advection Schemes
• Abstract: The WindStation software package is applied to simulate the wind field over the Bolund hill. The standard, ReNormalization Group (RNG), realizable, and limited-length k−ε turbulence models are tested, along with the quadratic upstream interpolation for convective kinetics (QUICK) and hybrid advection schemes. Comparisons with experimental results are made for the speed-up and turbulence kinetic energy (TKE) increase. The adopted mesh is Cartesian uniform in the horizontal plane and terrain following with a variable expansion factor in the vertical direction. The QUICK advection scheme leads to better agreement with the experimental data than the hybrid scheme, in particular for the TKE increase. The RNG and standard k−ε turbulence models show the best performance for speed-up and for TKE increase, respectively.
PubDate: 2021-04-21

• Assessing the Surface-Layer Stability over China Using Long-Term
Wind-Tower Network Observations
• Abstract: Surface-layer stability is important in many processes, such as in the surface energy budget, atmospheric pollution, and boundary-layer parametrizations. Most previous studies on stability, however, conducted either theoretical or observational investigations at specific sites, thus leaving a gap with regard to the large-scale pattern. Here, wind-speed and temperature observations at multiple heights from the wind-tower network of China are used to estimate low-level stability during the 2009–2016 period. A series of data-quality-control procedures are conducted and data from 170 wind towers with more than 2 years of valid observations are selected. The degree of stability is classified by the Obukhov length, which is derived from the wind speed and temperature at 10 m and 70 m above ground level, combined with information regarding the roughness length. Overall, the occurrence frequency of surface-layer instability exhibits significant temporal and spatial variability, being particularly larger in spring and summer than in autumn and winter. The maximum frequency of summertime instability occurs in the time period 1000–1200 local solar time, approximately 2 h earlier than in autumn. Geographically, the peak instability frequency occurs much earlier in the day in north-west China than in other regions, likely owing to the arid and semi-arid land cover. Also noteworthy is the steady increase in instability frequency observed during the period analyzed here, likely resulting from the reduction in the vertical gradient of wind speed. Our findings call for explicit consideration of stability variability in the wind-energy industry and in fundamental boundary-layer investigations in China.
PubDate: 2021-04-21

• Wind-Tunnel Simulation of Approximately Horizontally Homogeneous Stable
Atmospheric Boundary Layers
• Abstract: Two cases of an overlying inversion imposed on a stable boundary layer are investigated, extending the work of Hancock and Hayden (Boundary-Layer Meteorol 168:29–57, 2018; 175:93–112, 2020). Vertical profiles of Reynolds stresses and heat flux show closely horizontally homogeneous behaviour over a streamwise fetch of more than eight boundary-layer heights. However, profiles of mean temperature and velocity show closely horizontally homogeneous behaviour only in the top two-thirds of the boundary layer. In the lower one-third the temperature decreases with fetch, directly as a consequence of heat transfer to the surface. A weaker effect is seen in the mean velocity profiles, curiously, such that the gradient Richardson number is invariant with fetch, while various other quantities are not. Stability leads to a ‘blocking’ of vertical influence. Inferred aerodynamic and thermal roughness lengths increase with fetch, while the former is constant in the neutral case, as expected. Favourable validation comparisons are made against two sets of local-scaling systems over the full depth of the boundary layer. Close concurrence is seen for all stable cases for z/L < 0.2, where z and L are the vertical height and local Obukhov length, respectively, and over most of the layer for some quantities.
PubDate: 2021-04-21

• The Impact of Atmosphere–Ocean–Wave Coupling on the Near-Surface Wind
Speed in Forecasts of Extratropical Cyclones
• Abstract: Accurate modelling of air–sea surface exchanges is crucial for reliable extreme surface wind-speed forecasts. While atmosphere-only weather forecast models represent ocean and wave effects through sea-state independent parametrizations, coupled multi-model systems capture sea-state dynamics by integrating feedbacks between the atmosphere, ocean and wave model components. Here, we investigate the sensitivity of extreme surface wind speeds to air–sea exchanges at the kilometre scale using coupled and uncoupled configurations of the Met Office’s UK Regional Coupled Environmental Prediction system. The case period includes the passage of extra-tropical cyclones Helen, Ali, and Bronagh, which brought maximum gusts of 36 m s $$^{-1}$$ over the UK. Compared with the atmosphere-only results, coupling to the ocean decreases the domain-average sea-surface temperature by up to 0.5 K. Inclusion of coupling to waves reduce the 98th percentile 10-m wind speed by up to 2 m s $$^{-1}$$ as young, growing wind waves reduce the wind speed by increasing the sea-surface aerodynamic roughness. Impacts on gusts are more modest, with local reductions of up to 1 m s $$^{-1}$$ , due to enhanced boundary-layer turbulence which partially offsets air–sea momentum transfer. Using a new drag parametrization based on the Coupled Ocean–Atmosphere Response Experiment 4.0 parametrization, with a cap on the neutral drag coefficient and reduction for wind speeds exceeding 27 m s $$^{-1}$$ , the atmosphere-only model achieves equivalent impacts on 10-m wind speeds and gusts as from coupling to waves. Overall, the new drag parametrization achieves the same 20% improvement in forecast 10-m wind-speed skill as coupling to waves, with the advantage of saving the computational cost of the ocean and wave models.
PubDate: 2021-04-20

• Discriminating Fog and Rain at the Kilometre Scale Using the Extinction
from Collocated Infrared and Microwave Scintillometers
• Abstract: We investigate the path-averaged visibility and discrimination of fog and rain events using a two-wavelength (near-infrared and microwave) scintillometer system. These systems are normally used to measure near-surface turbulent heat fluxes on scales of $${\mathscr {O}}$$ (1 km). Fog attenuates electromagnetic radiation as a function of the wavelength and droplet-size spectra with a known refractive index. Near-infrared (0.88   $$\upmu$$ m) radiation is highly attenuated by fog whereas fog is translucent to microwave (1860   $$\upmu$$ m) radiation which propagates with minimal attenuation. During liquid precipitation events, both near-infrared and microwave radiation are attenuated to similar levels. Observations from the Coastal-Fog campaign, dubbed the C-FOG experiment, conducted along the east coast of Newfoundland, Canada, are used. Both near-infrared and microwave scintillometers are used to differentiate between fog, precipitation, and clear-sky conditions along a 1444-m path length. We lay the groundwork for using a two-wavelength scintillometer system for fog–rain discrimination and visibility measurements. The scintillometer provides path-averaged extinction values compared to typical point measurements of visibility. Results suggest that scintillometer data can effectively discriminate between rain and fog as well as provide path-averaged visibility, which was found to be $$\approx$$ 10% greater than point-visibility measurements. Measurements of attenuation in the near-infrared and microwave regimes can improve numerical weather prediction of fog visibility by providing ground-based data on the same length scales as typical grid resolutions.
PubDate: 2021-04-11

• A Seasonal Climatology of the Mexico City Atmospheric Boundary Layer
• Abstract: Lower tropospheric thermal structure greatly affects atmospheric boundary-layer (ABL) stability and mixing processes with the free troposphere. In particular, in polluted urban zones, ABL stratification becomes a key variable in air quality research. This study focuses on generating a climatology (1990–2017) of the seasonal variability of ABL thermal structure in Mexico City by way of radiosonde analysis. Thermal inversion intensity and frequency are shown to be greater during winter and spring, a behaviour which coincides with greater pollutant concentrations. Higher concentrations are found during the dry season (November to May) than during the rainy months. In addition, significantly higher than normal surface pollutant concentrations are found on days with simple thermal inversion layers as well as during multilayer inversion days. Furthermore, stable layers, determined by potential temperature, are found throughout the year but more frequently during winter, whereas stable layers based on the virtual potential temperature prevail all year. In regions of complex terrain, such multiple stable layers have also been identified by previous authors. Additionally, the most unstable surface layers (in which the bulk Richardson number ( $${Ri}_{\mathrm {B}}$$ ) is small) develop during the rainy season, whereas during winter there are more levels in the vertical column with higher $${Ri}_{\mathrm {B}}$$ values. Although the Mexico City ABL and pollution episodes have been widely studied, this represents the first long-term investigation to consider the thermal stability of the ABL. Therefore, the present study provides a baseline for further research employing different observational techniques and high-resolution numerical models.
PubDate: 2021-04-06

• Limitations of an Eddy-Covariance System in Measuring Low Ammonia Fluxes
• Abstract: Green manuring of legume crops can improve soil fertility and sustainability. To evaluate its agronomic and environmental effectiveness, gaseous losses of ammonia (NH3) in the surface layer need to be quantified by direct measurements in the field. However, the application of the eddy-covariance technique to atmospheric NH3 is challenging: its high reactivity, water solubility, and low background concentrations all hinder the response time of closed-path sensors for fast measurements of NH3 concentration. Ammonia emissions following green manuring were measured for 21 days using a flux system equipped with a fast-pulsed quantum-cascade tunable-infrared-laser spectrometer. The noisy cross-covariance function for this configuration indicates flux measurements are close to the limit of detection; the low signal-to-noise ratio further increases the uncertainties, introducing a mirroring effect on the fluxes, which results in the rapid alternation between emission and deposition, within the limit of detection (around 13 and 20 ng m−2 s−1, at the 95 and 99% confidence limits, respectively). An evaluation of the measurement errors is presented, focussing on three technical aspects of the eddy-covariance system: (1) time lag, (2) random error, and (3) limit of detection. The NH3 fluxes measured by the spectrometer are close to its limit of detection, with a random error of the same order as the flux.
PubDate: 2021-04-06

• Gravel-Desert Surface Properties and Their Influences on the Wind-Erosion
Threshold Friction Velocity in North-West China
• Abstract: 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 coverage in north-west China ranges between 0.07 and 1.00 (with a mean of 0.67), and about 81% of the sites investigated are covered by soil physical crust. Clay content is 2.4% on average in the study region, less than 2% in 52.1% of that region, and between 2 and 4% in the remaining study regions. The four regions where clay content is greater than the mean include the western Alxa Plain, the alluvial fan of the western Alxa Plain, the northern Alxa Plain, and the Hexi Corridor. In the study region, the value of $$u_{*t}$$ ranges between 0.12 and 0.78 m s−1 (with a mean of 0.45 m s−1). Soil moisture, gravel coverage, and soil physical crust all affect the magnitude of $$u_{*t}$$ . A principal component analysis indicates that the soil crust contributes of about 62% of the $$u_{{*{\text{t}}}}$$ variations, soil moisture 25%, and surface roughness 9%. A variance analysis shows clear spatial differences in the magnitude of $$u_{*t}$$ in north-west China due to the spatial variations in gravel land-surface properties.
PubDate: 2021-04-01

• Analysis of Pollutant Entrainment from Localized Sources in a Street
Network
• Abstract: The propagation of a pollutant emitted from localized sources both within and above a regular street network is studied by analyzing data from direct numerical simulations of passive scalar dispersion. Two wind directions are considered, corresponding to aligned and oblique flow with respect to the street axes. Particular attention is paid to the role of entrainment of the scalar into the urban canopy from an elevated source and re-entrainment of material originally released further upstream from a ground source. The variation of concentration differences and vertical fluxes between the streets and the air above as a function of distance reveals important differences between the rate of lateral and vertical mixing for the two sources. Detrainment and entrainment need a longer fetch to equilibrate for the elevated source than for the ground source. There are large differences between the advection and detrainment velocities for the aligned and oblique cases, so that a change in wind direction could affect ventilation efficiency considerably. Time scales associated with different dispersion processes are computed and the time of first appearance of the scalar from the onset of release in different streets is mapped. It is shown that re-entrainment can provide a shortcut dispersion pathway for reaching certain parts of the network. This is particularly striking in the case of oblique flow, when material can be transferred by entrainment up to twice as rapidly as by advection. Taken together, these results highlight the overall message that vertical exchange is a two-way process and that entrainment needs to be considered in the context of emergency response as well as urban ventilation.
PubDate: 2021-01-21
DOI: 10.1007/s10546-020-00598-7

• Modelling Soil Moisture in Hyper-Arid Conditions
• Abstract: In most land-surface models, the evolution of soil moisture is governed by soil-hydraulic processes. In hyper-arid soils, these processes break down, but soil moisture continues to show clear temporal variations, suggesting that other processes may be at work. We hypothesize that moisture in such soils varies due to evaporation in the soil and to vapour fluxes at the air–soil interface. To test this, we include vapour exchange between the air and soil in a land-surface model, apply the model to a desert site, and compare the simulated and observed soil moisture. The good agreement between the simulations and observations confirms our hypothesis. Using the model results, we examine the interactions between the soil-moisture and soil-vapour phases and influences of the soil-vapour phase on the surface energy balance.
PubDate: 2021-01-21
DOI: 10.1007/s10546-020-00596-9

• Real-Time Tracer Dispersion Simulations in Oklahoma City Using the Locally
Mesh-Refined Lattice Boltzmann Method
• Abstract: We present ensemble-based large-eddy simulations based on a lattice Boltzmann method for a realistic urban area. A plume-dispersion model enables a real-time simulation over several kilometres by applying a local mesh-refinement method. We assess plume-dispersion problems in the complex urban environment of Oklahoma City on 16 July using realistic mesoscale velocity boundary conditions produced by the Weather Research and Forecasting model, as well as building structures and a plant-canopy model introduced into the plume-dispersion model. Ensemble calculations are performed to reduce uncertainties in the macroscale boundary conditions due to turbulence, which cannot be determined by the mesoscale model. The statistics of the plume-dispersion field, as well as mean and maximum concentrations, show that ensemble calculations improve the accuracy of the simulations. Factor-of-2 agreement is found between the ensemble-averaged concentrations based on the simulations over a 4.2 × 4.2 × 2.5 km2 area with 2-m resolution with the plume-dispersion model and the observations.
PubDate: 2021-01-21
DOI: 10.1007/s10546-020-00594-x

• Investigation of Spatial and Temporal Wind-Speed Variability During Open
Cellular Convection with the Model for Prediction Across Scales in
Comparison with Measurements
• Abstract: 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 an OCC episode in the North Sea, with a focus on wind-speed variability. Modelled data are combined with wind speeds retrieved from satellite data and in situ measurements to investigate the spatial and temporal variability of offshore wind speeds under OCC conditions from a synoptic to mesoscale perspective, and to examine the model’s ability to represent the OCC structures and wind-speed variability. The model can simulate realistic OCC structures and mesoscale wind-speed variability within the limits set by the effective model resolution. Under OCC conditions, significant differences from climatological conditions are found in the spatial wind-speed power spectrum and in 10-min wind-speed step changes. The very high horizontal mesh-cell spacing in the refinement region of 2 km, and the focus on OCC wind-speed variability, makes this the first investigation of this kind using the MPAS modelling framework with mesh refinement.
PubDate: 2021-01-14
DOI: 10.1007/s10546-020-00591-0

• Coupling Mesoscale Budget Components to Large-Eddy Simulations for
Wind-Energy Applications
• Abstract: 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 components from the Weather Research and Forecasting model to the governing equations of the Simulator fOr Wind Farm Applications model. We test whether averaging the budget components affects the LES results with regard to quantities of interest to wind energy. Our study focuses on flat terrain during a quiescent diurnal cycle. The simulation results are compared with observations from a 200-m tall meteorological tower and a wind-profiling radar, by analyzing time series, profiles, rotor-averaged quantities, and spectra. While results show that averaging reduces the spatio-temporal variability of the mesoscale momentum-budget components, when coupled with the LES model, the mesoscale bias (in comparison with observations of wind speed and direction, and potential temperature) is not reduced. In contrast, the LES technique can correct for shear and veer. In both cases, however, averaging the budget components shows no significant impact on the mean flow quantities in the microscale and is not necessary when coupling mesocale budget components to the LES model.
PubDate: 2021-01-14
DOI: 10.1007/s10546-020-00584-z

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