Subjects -> METEOROLOGY (Total: 113 journals)
 Showing 1 - 36 of 36 Journals sorted alphabetically Acta Meteorologica Sinica       (Followers: 4) Advances in Atmospheric Sciences       (Followers: 45) Advances in Climate Change Research       (Followers: 39) Advances in Meteorology       (Followers: 28) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 10) Aeolian Research       (Followers: 6) Agricultural and Forest Meteorology       (Followers: 20) American Journal of Climate Change       (Followers: 34) Atmósfera       (Followers: 3) Atmosphere       (Followers: 29) Atmosphere-Ocean       (Followers: 16) Atmospheric and Oceanic Science Letters       (Followers: 13) Atmospheric Chemistry and Physics (ACP)       (Followers: 48) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 16) Atmospheric Environment       (Followers: 75) Atmospheric Environment : X       (Followers: 3) Atmospheric Research       (Followers: 71) Atmospheric Science Letters       (Followers: 40) Boundary-Layer Meteorology       (Followers: 32) Bulletin of Atmospheric Science and Technology       (Followers: 5) Bulletin of the American Meteorological Society       (Followers: 51) Carbon Balance and Management       (Followers: 5) Ciencia, Ambiente y Clima       (Followers: 3) Climate       (Followers: 6) Climate and Energy       (Followers: 7) Climate Change Economics       (Followers: 33) Climate Change Responses       (Followers: 18) Climate Dynamics       (Followers: 44) Climate of the Past (CP)       (Followers: 5) Climate of the Past Discussions (CPD) Climate Policy       (Followers: 51) Climate Research       (Followers: 6) Climate Resilience and Sustainability       (Followers: 21) Climate Risk Management       (Followers: 7) Climate Services       (Followers: 3) Climatic Change       (Followers: 68) Current Climate Change Reports       (Followers: 10) Developments in Atmospheric Science       (Followers: 31) 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: 9) Energy & Environment       (Followers: 24) Environmental and Climate Technologies       (Followers: 4) Environmental Dynamics and Global Climate Change       (Followers: 17) Frontiers in Climate       (Followers: 3) GeoHazards       (Followers: 2) Global Meteorology       (Followers: 18) International Journal of Atmospheric Sciences       (Followers: 23) International Journal of Biometeorology       (Followers: 1) International Journal of Climate Change Strategies and Management       (Followers: 27) International Journal of Climatology       (Followers: 30) International Journal of Environment and Climate Change       (Followers: 12) International Journal of Image and Data Fusion       (Followers: 2) Journal of Agricultural Meteorology Journal of Applied Meteorology and Climatology       (Followers: 36) Journal of Atmospheric and Oceanic Technology       (Followers: 34) Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 210) Journal of Atmospheric Chemistry       (Followers: 22) Journal of Climate       (Followers: 57) Journal of Climate Change       (Followers: 16) Journal of Climatology       (Followers: 3) Journal of Hydrology and Meteorology       (Followers: 36) 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: 17) Journal of Space Weather and Space Climate       (Followers: 28) Journal of the Atmospheric Sciences       (Followers: 84) Journal of the Meteorological Society of Japan       (Followers: 6) Journal of Weather Modification       (Followers: 2) Large Marine Ecosystems       (Followers: 1) 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: 27) 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: 16) Monthly Weather Review       (Followers: 33) Nature Climate Change       (Followers: 144) Nature Reports Climate Change       (Followers: 39) Nīvār npj Climate and Atmospheric Science       (Followers: 6) Open Atmospheric Science Journal       (Followers: 4) Open Journal of Modern Hydrology       (Followers: 7) 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: 6) The Quarterly Journal of the Royal Meteorological Society       (Followers: 28) Theoretical and Applied Climatology       (Followers: 13) Tropical Cyclone Research and Review Urban Climate       (Followers: 4) Weather       (Followers: 18) Weather and Climate Dynamics Weather and Climate Extremes       (Followers: 16) Weather and Forecasting       (Followers: 27) 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: 32      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1573-1472 - ISSN (Online) 0006-8314 Published by Springer-Verlag  [2658 journals]
• Analysis of Coastal Fog from a Ship During the C-FOG Campaign

Abstract: This work presents ship-based measurements of fog off St John’s, Newfoundland, on 13 September 2018 during the Coastal Fog field campaign. The measurements included cloud-particle spectra, cloud-base height and aerosol backscatter, radiation, turbulence, visibility, and sea-surface temperature. Radiosonde soundings were made at intervals of less than 2 h. Fog occurred in two episodes during the passage of an eastward-moving synoptic low-pressure system. The boundary-layer structure during the first fog episode consisted of three layers, separated by two saturated temperature inversions, and capped by a subsidence inversion. The lowest layer was fog, and the upper layers were cloud. The second fog episode consisted of one well-mixed fog layer capped by a subsidence inversion. Low wind speeds and stable stratification maintained low surface-layer turbulence during fog. Droplet size distributions had typical bimodal distributions. The visibility correlated with the droplet number concentration and liquid water content. The air temperature was higher than the sea-surface temperature for the first 30 min of the first fog episode but was lower than the sea for the remainder of all fog. The sensible heat flux was upward, from sea to air, for the first 62% of the first fog episode and then reversed to downward, from air to sea, for the remainder of the first fog episode and the second fog episode. The counter-gradient heat fluxes observed (i.e., opposite to what is expected from the instantaneous air–sea temperature difference) appear to be related to turbulence, entrainment, and stratification in the fog layer that overwhelmed the influence of the air–sea temperature difference. While the synoptic-scale dynamics preconditioned the area for fog formation, the final step of fog appearance in this case was nuanced by stratification–turbulence interactions, local advective processes, and microphysical environment.
PubDate: 2021-10-11

• Study of Stratus-Lowering Marine-Fog Events Observed During C-FOG

Abstract: Two stratus-lowering marine fog events observed on 28 September and 4 October 2018 during the Coastal Fog (C-Fog) field campaign that took place offshore of eastern Canada from 1 September to 6 October 2018 are described. In situ, profiling, and remote sensing observations were made at selected land sites in eastern Newfoundland, Nova Scotia, and aboard the research vessel Hugh R. Sharp cruising in adjoining coastal waters. Synoptic-scale analysis shows that both fog episodes result from the interaction between synoptic-scale surface-level low-pressure systems and a contiguous high-pressure system. At the same time, back trajectories reveal that the bulk of the fog layer is formed due to differential advection. The diameter of the fog droplets at the surface gradually decreases from the centre of the fog layer to its leading/trailing edges. The bimodal fog-droplet diameter distribution with peaks at 5–10 µm and 20–25 µm provide clues on droplet collision and coalescence processes. The observed difference between microphysical variables and droplet distribution between the two fog events and within the same fog layer might be governed by the atmospheric-boundary-layer (e.g., humidity conditions and turbulence) that prevailed in the fog layer. Overall, it is concluded that the life cycle of observed stratus-lowering coastal-fog episodes depends on synoptic conditions and atmospheric-boundary-layer characteristics such as stability, cloud-top cooling, and entrainment.
PubDate: 2021-10-11

• A Review of Coastal Fog Microphysics During C-FOG

Abstract: Our goal is to provide an overview of the microphysical measurements made during the C-FOG (Toward Improving Coastal Fog Prediction) field project. In addition, we evaluate microphysical parametrizations using the C-FOG dataset. The C-FOG project is designed to advance understanding of liquid fog formation, particularly its development and dissipation in coastal environments, so as to improve fog predictability and monitoring. The project took place along eastern Canada’s (Nova Scotia and Newfoundland) coastlines and open water environments from August−October 2018, where environmental conditions play an important role for late-season fog formation. Visibility, wind speed, and atmospheric turbulence along coastlines are the most critical weather-related factors affecting marine transportation and aviation. In the analysis, microphysical observations are summarized first and then, together with three-dimensional wind components, used for fog intensity (visibility) evaluation. Results suggest that detailed microphysical observations collected at the supersites and aboard the Research Vessel Hugh R. Sharp are useful for developing microphysical parametrizations. The fog life cycle and turbulence-kinetic-energy dissipation rate are strongly related to each other. The magnitudes of three-dimensional wind fluctuations are higher during the formation and dissipation stages. An array of cutting-edge instruments used for data collection provides new insight into the variability and intensity of fog (visibility) and microphysics. It is concluded that further modifications in microphysical observations and parametrizations are needed to improve fog predictability of numerical-weather-prediction models.
PubDate: 2021-10-11

• The Role of Atmospheric Stability and Turbulence in Offshore Wind-Farm
Wakes in the German Bight

Abstract: Airborne meteorological in situ measurements as well as stationary measurements at the offshore masts FINO1 and FINO3 in the German Bight are evaluated in order to examine the hypothesis that the wake dissipation downstream of large offshore wind farms depends on atmospheric stability. A long-term study of the mast data for the years 2016 and 2017 demonstrates a clear dependence of stability on the wind direction. Stable conditions are predominantly expected during southerly winds coming from the land. The analysis of various stability and turbulence criteria shows that the lapse rate is the most robust parameter for stability classification in the German Bight, but further implies that stability depends on the measurement height. A near-surface (0 to 30 m), predominantly convective, layer is present and more stable conditions are found aloft (55 to 95 m). Combing the stability data with the airborne measurements of the offshore wind-farm wakes reveals the trend of a correlation between longer wake lengths and an increase in the initial wind-speed deficit downwind of a wind farm with stronger thermal stability. However, the stability correlation criteria with the wake length downstream of the four investigated wind farms, Godewind, Amrumbank West, Meerwind Süd/Ost, and Nordsee Ost, contain large variance. It is assumed that the observed scattering is due to the influence of the wind-farm architecture and temperature inversions around hub height. These, however, are crucial for the classification of stability and illustrate the complexity of a clear stability metric.
PubDate: 2021-10-10

• Cold-Air Pool Processes in the Inn Valley During Föhn: A Comparison of
Four Cases During the PIANO Campaign

Abstract: We present a comprehensive analysis of four south föhn events observed during the Penetration and Interruption of Alpine Foehn (PIANO) field campaign in the Inn Valley, Austria, in the vicinity of Innsbruck. The goal is to detect and quantify processes of cold-air pool (CAP) erosion by föhn as well as processes of föhn breakdown. Despite differences in föhn breakthrough and strength, the four cases exhibit similarities in CAP evolution: initially, the CAP experienced strongest warming in the centre of Innsbruck, where the föhn jet from the Wipp Valley interacted with the CAP in the Inn Valley. The resulting shear-flow instability at the föhn–CAP interface caused turbulent CAP erosion and, together with vertical warm-air advection, led to CAP depression over the city centre. This depression drove pre-föhn westerlies near the surface that caused cold-air advection inside the CAP west of the city centre and warm-air advection in the east. Ultimately, the latter contributed to stronger CAP erosion in the east than in the west. This stronger heating also explains the preferential initial föhn breakthrough at the valley floor east of Innsbruck. In two of the cases, subsequent westward propagation of the föhn–CAP boundary across the city accompanied by northerly (deflected) föhn winds led to a complete föhn breakthrough. Föhn breakdown occurred either by a backflow of the CAP remnant or by a cold-frontal passage. This study emphasizes the importance of both turbulence and advection in the CAP heat budget and reveal their large spatio–temporal variability.
PubDate: 2021-10-10

• Correction to: Atmospheric Turbulence Measurements at a Coastal Zone with
and without Fog

PubDate: 2021-10-06

• The Convective-Atmospheric-Boundary-Layer Height and its dependence upon
Meteorological Variables At a Tropical Coastal Station during Onshore and
Offshore Flows

Abstract: The height of the atmospheric boundary layer (ABL) plays a crucial role in the vertical transport of energy, moisture, and pollutants from the surface. We investigate the development of the convective ABL (CABL) height over a tropical coastal station and quantify its variations with the shortwave radiative flux, near-surface air temperature (Tair), soil skin temperature, soil moisture content, lower tropospheric thermal structure, and virtual potential temperature lapse rate (VPLR) during onshore and offshore flows, based on multi-year (2012–2017) observations carried out using a microwave radiometer profiler and in situ probes at Thumba (8.5° N, 77° E), located in the south-west of Indian Peninsula. The maximum CABL height increases linearly with the VPLR at the rate of 140 to 200 m per °C km−1 (correlation coefficient of 0.82 to 0.92) during different seasons. The delayed onset of daytime onshore flow results in a greater CABL height as continental conditions persist longer, allowing more CABL growth, whereas the earlier arrival of the onshore flow leads to early development of a thermal internal boundary layer with a lower CABL height. When offshore flow prevails, the CABL develops like the continental CABL, with a peak CABL height greater than that during onshore flow by about 300 m. The onset of onshore flow lowers the daytime increase in Tair by about 2 °C. Such quantifications for distinct flow conditions are very sparse over tropical coastal regions and would be useful for understanding coastal air-pollution dispersal as well as validation and improvements in numerical modelling of the CABL under different wind conditions.
PubDate: 2021-10-06

• A Feasibility Study for Determining the Sensible Heat Flux to and from
Small Green Roofs

Abstract: Eddy covariance is an established technique for registering sensible heat fluxes. However, this method is less adequate for smaller surfaces that cannot match the associated footprint. As an alternative technique, a recently constructed acoustic anemometer (Ly-ATOM) is tested, which operates horizontally at an extension of circa 1 m and a data-acquisition frequency of 1 Hz. The Ly-ATOM device reproduces both the acoustic virtual temperature and the horizontal wind components registered by a three-dimensional sonic anemometer. As this Ly-ATOM device can be applied much closer to the ground compared with a sonic anemometer, the size of the related source area is significantly reduced (by a factor of 25). Two methods are used to retrieve the sensible heat flux from variance characteristics of temperature and the horizontal wind components recorded by the Ly-ATOM device: combining the flux-variance-similarity and alternative-flux-variance methods for use in unstable and stable stratification, respectively, yields good results for the sonic measurements. Therefore, these methods can be applied to the Ly-ATOM device as well. In investigating the sensitivity to detect modified surface characteristics, specifically increased evapotranspiration and decreased surface albedo, the Ly-ATOM device proves to be superior to the sonic anemometer which is more vertically removed from the surface of interest.
PubDate: 2021-10-01
DOI: 10.1007/s10546-021-00646-w

• Atmospheric-Boundary-Layer-Height Variation over Mountainous and Urban
Sites in Beijing as Derived from Radar Wind-Profiler Measurements

Abstract: The evolution of the atmospheric boundary layer (ABL) varies greatly with terrain, so that the spatial and temporal variabilities of the ABL height remain poorly understood over complex terrain. Using radar wind-profiler measurements obtained from rural mountainous (Yanqing) and adjoining urban-plain (Haidian) landscapes of Beijing, China in 2019, ABL heights are calculated based on a normalized signal-to-noise-ratio threshold. The seasonally contrasting features of ABL height variation and growth rate over the two sites are revealed for clear-sky conditions. Interestingly, the ABL in spring remains suppressed during the morning and evolves rapidly in the afternoon over Haidian; however, a usual diurnal ABL evolution is observed over Yanqing. During the winter, more rapid evolution of the ABL is observed over Haidian, although on average the daytime ABL height remains less than 800 m above ground level. The growth rate of ABL height is found to undergo a more pronounced seasonal variation over Haidian while being relatively less variable over Yanqing. As expected, the lowest (highest) growth rate of 90 m h−1 (188 m h−1) occurs in winter (summer) over Haidian. The analysis of the seasonal variations in wind profiles reveals deeper insights into the development of the local plain-to-mountain flow circulation over the region and possible implications on the contrasting seasonal ABL variations, particularly during the spring and summer. Additionally, the slower ABL evolution over Haidian in autumn and winter could be associated with an aerosol-induced stable ABL as well as stronger urban heat accumulation. The findings have implications for the better understanding of air pollution meteorology in regions with mountainous terrain.
PubDate: 2021-10-01
DOI: 10.1007/s10546-021-00639-9

• Alternative Anisotropic Formulations for Eddy-Viscosity Models in the
Weather Research and Forecasting Model

Abstract: The Weather Research and Forecasting (WRF) model is used to simulate multiple convective-boundary-layer cases on grids with horizontal resolutions of 100 m and 1.2 km to evaluate the Smagorinsky–Lilly turbulence closure on highly anisotropic grids for numerical weather prediction (NWP). The Smagorinsky–Lilly closure is used with its standard isotropic and anisotropic formulations as distributed with the WRF model, as well as an anisotropic form where the resolved strain-rate tensor is partitioned into horizontal and vertical components, and an isotropic form which scales with height near the surface, following implementations used in other NWP models. Finally, a novel anisotropic length scale is proposed based on using normal-direction grid spacing so that the vertical (horizontal) length scale is a function of the horizontal (vertical) resolution. The formulations are evaluated by comparing their development of resolved turbulence kinetic energy, potential temperature and velocity profiles, and planar velocity fields. The different forms behave very similarly on the 100-m grid, but significant differences are seen on the 1.2-km grid. When compared to the high-resolution results, notable improvements are seen on the 1.2-km grid using the modifications to the Smagorinsky–Lilly closure introduced here in the WRF model, particularly for the normal-direction anisotropic form which agrees very well with the high-resolution results with a much lower sensitivity to the tuning coefficient than the other formulations.
PubDate: 2021-10-01
DOI: 10.1007/s10546-021-00642-0

• Urban Boundary Layers Over Dense and Tall Canopies

Abstract: Wind-tunnel experiments were carried out on four urban morphologies: two tall canopies with uniform height and two super-tall canopies with a large variation in element heights (where the maximum element height is more than double the average canopy height, $$h_{max}=2.5h_{avg}$$ ). The average canopy height and packing density are fixed across the surfaces to $$h_{avg} = 80~\hbox {mm}$$ , and $$\lambda _{p} = 0.44$$ , respectively. A combination of laser Doppler anemometry and direct-drag measurements are used to calculate and scale the mean velocity profiles with the boundary-layer depth $$\delta$$ . In the uniform-height experiment, the high packing density results in a ‘skimming flow’ regime with very little flow penetration into the canopy. This leads to a surprisingly shallow roughness sublayer (depth  $$\approx 1.15h_{avg}$$ ), and a well-defined inertial sublayer above it. In the heterogeneous-height canopies, despite the same packing density and average height, the flow features are significantly different. The height heterogeneity enhances mixing, thus encouraging deep flow penetration into the canopy. A deeper roughness sublayer is found to exist extending up to just above the tallest element height (corresponding to $$z/h_{avg} = 2.85$$ ), which is found to be the dominant length scale controlling the flow behaviour. Results point toward the existence of a constant-stress layer for all surfaces considered herein despite the severity of the surface roughness ( $$\delta /h_{avg} = 3 - 6.25$$ ). This contrasts with the previous literature.
PubDate: 2021-10-01
DOI: 10.1007/s10546-021-00635-z

• Coherent Eddies Transporting Passive Scalars Through the Plant Canopy
Revealed by Large-Eddy Simulations Using the Lattice Boltzmann Method

Abstract: A double-distribution-function lattice Boltzmann model for large-eddy simulations of a passive scalar field in a neutrally stratified turbulent flow is described. In simulations of the scalar turbulence within and above a homogeneous plant canopy, the model’s performance is found to be comparable with that of a conventional large-eddy simulation model based on the Navier–Stokes equations and a scalar advection–diffusion equation in terms of the mean turbulence statistics, budgets of the second moments, power spectra, and spatial two-point correlation functions. For a top-down scalar, for which the plant canopy serves as a distributed sink, the variance and flux of the scalar near the canopy top are predominantly determined by sweep motions originating far above the canopy. These sweep motions, which have spatial scales much larger than the canopy height, penetrate deep inside the canopy and cause scalar sweep events near the canopy floor. By contrast, scalar ejection events near the canopy floor are induced by coherent eddies generated near the canopy top. The generation of such eddies is triggered by the downward approach of massive sweep motions to existing wide regions of weak ejective motions from inside to above the canopy. The non-local transport of scalars from above the canopy to the canopy floor, and vice versa, is driven by these eddies of different origins. Such non-local transport has significant implications for the scalar variance and flux budgets within and above the canopy, as well as the transport of scalars emitted from the underlying soils to the atmosphere.
PubDate: 2021-10-01
DOI: 10.1007/s10546-021-00633-1

• Evaluation and Applications of Multi-Instrument Boundary-Layer
Thermodynamic Retrievals

Abstract: Recent reports have highlighted the need for improved observations of the atmosphere boundary layer. In this study, we explore the combination of ground-based active and passive remote sensors deployed for thermodynamic profiling to analyze various boundary-layer observation strategies. Optimal-estimation retrievals of thermodynamic profiles from Atmospheric Emitted Radiance Interferometer (AERI) observed spectral radiance are compared with and without the addition of active sensor observations from a May–June 2017 observation period at the Atmospheric Radiation Measurement Southern Great Plains site. In all, three separate thermodynamic retrievals are considered here: retrievals including AERI data only, retrievals including AERI data and Vaisala water vapour differential-absorption lidar data, and retrievals including AERI data and Raman lidar data. First, the three retrievals are compared to each other and to reference radiosonde data over the full observation period to obtain a bulk understanding of their differences and characterize the impact of clouds on these retrieved profiles. These analyses show that the most significant differences are in the water vapour field, where the active sensors are better able to represent the moisture gradient in the entrainment zone near the boundary-layer top. We also explore how differences in retrievals may affect results of applied analyses including land–atmosphere coupling, convection indices, and severe storm environmental characterization. Overall, adding active sensors to the optimal-estimation retrieval shows some added information, particularly in the moisture field. Given the costs of such platforms, the value of that added information must be weighed for the application at hand.
PubDate: 2021-10-01
DOI: 10.1007/s10546-021-00640-2

• Coherent Flow Structures and Pollutant Dispersion in a Street Canyon

Abstract: Coherent flow structures and pollutant dispersion in a spanwise-long street canyon are investigated using a parallelized large-eddy-simulation model. Low- and high-concentration branches, starting from the downwind top corner and upwind bottom corner, respectively, are detected in the time-averaged field of pollutant concentration, and detailed structures of in-canyon flow and pollutant dispersion following the two branches are demonstrated. When turbulent eddies impinge on the upper downwind wall, low- and high-concentration blobs with U-shaped flow structures appear and move downward. The downdrafts tilt away from the downwind bottom corner and impinge on the canyon bottom, driving horizontally diverging flows. Cellular structures of low-concentration centres and high-concentration edges are induced by the downdrafts and diverging flows. The diverging flows push low-concentration air toward the downwind and upwind building walls, resulting in local divergence and convergence of pollutants on both walls. Time series of pollutant concentration at multiple points illustrate that pollutant concentration at the pedestrian level is highly sensitive to the diverging flows. The multiresolution spectra show that time scales of variations of pollutant concentration and vertical velocity component increase from the canyon top to the pedestrian-level centre, indicating longer time-scale flow structures are dominant inside the street canyon. The multiresolution cospectra also show that the time scale of vertical turbulent transport of pollutants increases from the canyon top to the pedestrian-level centre. At the two bottom corners, however, short and long time-scale transports occur together, confirming that the low-concentration diverging flows transport pollutants downward while short time-scale turbulence transports pollutants upward.
PubDate: 2021-09-28

• Katabatic Flow Structures Indicative of the Flux Dissimilarity for Stable
Stratification

Abstract: Based on observations over an alpine glacier, we investigate the turbulent flux dissimilarity between momentum and sensible heat transfer in a stably stratified katabatic flow. The flux correlation coefficient RF is employed as a measure of variable levels of the flux similarity, which are found to be modulated by the anisotropy of turbulence. In the katabatic wind regime over this glacier, heat is transported more efficiently than momentum. Based on quadrant analysis, the sweep–ejection differences in the flux fraction constitute turbulence characteristics in terms of the velocity aspect ratio, which unravel dissimilar transport of momentum and heat. Moreover, an innovative method is established for connecting quadrant analysis and cospectral analysis, whereby the hyperbolic quadrant hole size is coupled to the frequency underlying the fast Fourier transform. In extending applications of octant analysis, we introduce a hypothetical octant hole, whose size is solicited as a proxy for the amplitude scale of fluctuating fluxes. The contributions to $${R}_{F}$$ can then be quantified for eddy structures that are associated with different amplitude scales. The katabatic flow structures identified from octant analysis differ in their behaviour so helping illuminate the outcome of flux dissimilarity. Exhibited as a statistical behaviour regardless of amplitude scale, along-wind rapid motions of heated air parcels can modify fractional contributions to the heat flux instead of the momentum flux, with reductions in $${R}_{F}$$ related to decreasing heat-flux fractions. Besides, along-wind slow motions of cooled air parcels cannot modify the flux fractions for both momentum and heat. Thus, the flux dissimilarity due to low-speed low-temperature eddies cannot be explicable in terms of the flux fractions alone. These findings are an incipient step towards physical understanding of the turbulent flux dissimilarity for a stably stratified katabatic flow.
PubDate: 2021-09-14
DOI: 10.1007/s10546-021-00660-y

• On the Effect of a Low-level Jet on Atmospheric Pollutant Dispersion: A
Case Study Over a Coastal Complex Domain, Employing High-Resolution
Modelling

Abstract: A low-level-jet (LLJ) event that occurred over a coastal area in complex terrain is analyzed to investigate its effect on the dispersion of potential air pollutants released in the area. The atmospheric model RAMS (Regional Atmospheric Modeling System) is employed with a high vertical resolution close to the surface, adopting a rarely used nesting approach, in order to allow a detailed analysis of the flow and to characterize the specific features of the LLJ. After a comparison with meteorological variables measured by radiosondes, numerical experiments are performed adding a scalar tracer in the simulation. As a first test, the tracer is distributed uniformly throughout the domain to follow the dynamics of the LLJ and its effect on the tracer dispersion. Then, continuous releases from virtual point sources are simulated to address their possible impact in the area under LLJ conditions. This allows the identification of “hotspots” of pollutant accumulation due to very local circulations and convective cells that develop from the combined effect of terrain-induced flow and the interaction of the LLJ flow with complex topography. An original mass analysis is applied on the dispersion results for an advanced exploration of the LLJ impact on the tracer. The RAMS model provides reliable results demonstrating that with which atmospheric numerical models are useful tools with which to study LLJ dynamics and their effect on local circulation and pollutant dispersion.
PubDate: 2021-09-14
DOI: 10.1007/s10546-021-00661-x

• Anisotropy of Unstably Stratified Near-Surface Turbulence

Abstract: Classic Monin–Obukov similarity scaling states that in a stationary, horizontally homogeneous flow, in the absence of subsidence, turbulence is dictated by the balance between shear production and buoyancy production/destruction, whose ratio is characterized by a single universal scaling parameter. An evident breakdown in scaling is observed though, through large scatter in traditional scaling relations for the horizontal velocity variances under unstable stratification, or more generally in complex flow conditions. This breakdown suggests the existence of processes other than local shear and buoyancy that modulate near-surface turbulence. Recent studies on the role of anisotropy in similarity scaling have shown that anisotropy, even if calculated locally, may encode the information about these missing processes. We therefore examine the possible processes that govern the degree of anisotropy in convective conditions. We first use the reduced turbulence-kinetic-energy budget to show that anisotropy in convective conditions cannot be uniquely described by a balance of buoyancy and shear production and dissipation, but that other terms in the budget play an important role. Subsequently, we identify a ratio of local time scales that acts as a proxy for the anisotropic state of convective turbulence. This ratio can be used to formulate a new non-dimensional group. Results show that building on this approach the role of anisotropy in scaling relations over complex terrain can be placed into a more generalized framework.
PubDate: 2021-09-01
DOI: 10.1007/s10546-021-00634-0

• Velocity and Temperature Dissimilarity in the Surface Layer Uncovered by
the Telegraph Approximation

Abstract: The physicist and mathematician Shang-Keng Ma once commented that “the simplest possible variable is one that can have two values. If there is only one value, no variation is possible." Guided by this dictum, the telegraphic approximation (TA) is applied to the streamwise velocity component and air temperature time series acquired in the first metre above the salt flats of Utah, USA. The TA technique removes amplitude variations and retains only zero-crossing behaviour in a turbulent series, thereby allowing for an isolated examination of the role of clustering in intermittency. By applying the TA technique, clustering properties are analyzed to uncover dissimilarity in temperature and velocity across unstable, near-neutral, and stable atmospheric stratification. The spectral exponents of the original and of the TA series are examined, with the inertial-subrange behaviour conforming to prior empirical relations and the energy-containing range exhibiting deviations. These two distinct scale regimes are observed in the standard deviations of the running density fluctuations of the TA series, delineating scaling behaviour between fine and large scales. In the fine scales, clustering is not appreciably affected by the stability regime and is higher than in the large scales. In the large scales, the temperature series exhibits stronger clustering with increasing stability, and higher clustering compared with the streamwise velocity component series under stable conditions. Amplitude variations are shown to mitigate intermittency in the small scales of velocity, but play only a minor role in intermittency for temperature. Last, the inter-pulse period probability distributions are explored and implications to self-organized criticality as models for TA turbulence are discussed.
PubDate: 2021-09-01
DOI: 10.1007/s10546-021-00632-2

• A Simple Mixing-Length Model for Urban Canopy Flows

Abstract: Urban canopy models (UCMs) developed based on Prandtl mixing-length theory provide a simple method for predicting urban flows. In the existing models, the Prandtl mixing length and the sectional drag coefficient of buildings are usually assumed to be uniform with height within urban canopies. This leads to exponential vertical profiles of the time-averaged and horizontally space-averaged streamwise velocity component within urban canopies, which was recently found to be inaccurate. In this study, in order to improve the current UCM predictions, a new mixing-length parametrization is proposed for urban canopy flows by considering the strong shear layer at the canopy roof level. It assumes that, within the shear layer, the mixing length increases linearly with the distance from the canopy roof level with a proportionality constant approximately equal to 0.8. Using the new parametrization, good predictions of the space-averaged mean wind profiles are obtained against building-resolved large-eddy simulation and direct numerical simulation results.
PubDate: 2021-08-03
DOI: 10.1007/s10546-021-00650-0

• Intermittent Surface Renewals and Methane Hotspots in Natural Peatlands

Abstract: Peatlands account for a large fraction of global methane ( $$\mathrm {CH_4}$$ ) emissions. These environments exchange $$\mathrm {CH_4}$$ with the atmosphere via three main mechanisms: diffusion through the peat and water, plant-mediated diffusion, and sporadic release of $$\mathrm {CH_4}$$ bubbles. While rapid advances have been made in measuring $$\mathrm {CH_4}$$ fluxes above peatlands on sub-daily time scales, partitioning $$\mathrm {CH_4}$$ fluxes into ebullition and background diffusion remains a formidable challenge. Such partitioning is becoming necessary for future projection of methane concentration as atmospheric, hydrologic, and edaphic drivers of these two types of methane releases may differ significantly. Using surface renewal theory, a framework for partitioning measured methane fluxes based on the mass transfer mechanism is introduced with the overall objective of characterizing the intermittency of $$\mathrm {CH_4}$$ source and its strength at the ground. This approach is tested using a large dataset of measured turbulent air velocity and multiple scalar concentrations (including heat, water vapour, and carbon dioxide) for flow above a boreal peatland in Finland. The transport efficiencies of different gas transfer mechanisms are then evaluated for scalars characterized by background diffusion (e.g., water vapour) or by intermittent sources (e.g., methane). Whether environmental variables such as water-table levels and atmospheric conditions have a signature on the occurrence of $$\mathrm {CH_4}$$ hotspots is then investigated. Building upon the classical surface renewal theory, this work introduces a novel approach for inferring the intermittent nature of scalar sources at the ground and for exploring how non-homogeneity affects the efficiency of gas turbulent transport in the atmospheric surface layer.
PubDate: 2021-07-04
DOI: 10.1007/s10546-021-00637-x

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