Subjects -> METEOROLOGY (Total: 106 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: 50) Advances in Meteorology       (Followers: 27) Advances in Statistical Climatology, Meteorology and Oceanography       (Followers: 11) Aeolian Research       (Followers: 7) Agricultural and Forest Meteorology       (Followers: 20) American Journal of Climate Change       (Followers: 37) Atmósfera       (Followers: 2) Atmosphere       (Followers: 33) Atmosphere-Ocean       (Followers: 16) Atmospheric and Oceanic Science Letters       (Followers: 13) Atmospheric Chemistry and Physics (ACP)       (Followers: 43) Atmospheric Chemistry and Physics Discussions (ACPD)       (Followers: 15) Atmospheric Environment       (Followers: 72) Atmospheric Environment : X       (Followers: 3) Atmospheric Research       (Followers: 73) 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: 63) Carbon Balance and Management       (Followers: 6) Ciencia, Ambiente y Clima       (Followers: 1) Climate       (Followers: 8) Climate and Energy       (Followers: 6) Climate Change Economics       (Followers: 44) Climate Change Responses       (Followers: 23) Climate Dynamics       (Followers: 45) Climate Law       (Followers: 6) Climate of the Past (CP)       (Followers: 6) Climate of the Past Discussions (CPD)       (Followers: 1) Climate Policy       (Followers: 51) Climate Research       (Followers: 9) Climate Resilience and Sustainability       (Followers: 21) Climate Risk Management       (Followers: 10) Climate Services       (Followers: 4) Climatic Change       (Followers: 69) Current Climate Change Reports       (Followers: 17) Dynamics and Statistics of the Climate System       (Followers: 6) Dynamics of Atmospheres and Oceans       (Followers: 19) Earth Perspectives - Transdisciplinarity Enabled       (Followers: 1) Economics of Disasters and Climate Change       (Followers: 13) Energy & Environment       (Followers: 24) Environmental and Climate Technologies       (Followers: 3) Environmental Dynamics and Global Climate Change       (Followers: 21) Frontiers in Climate       (Followers: 4) GeoHazards       (Followers: 2) Global Meteorology       (Followers: 20) International Journal of Atmospheric Sciences       (Followers: 25) International Journal of Biometeorology       (Followers: 3) International Journal of Climate Change Strategies and Management       (Followers: 29) International Journal of Climatology       (Followers: 28) International Journal of Environment and Climate Change       (Followers: 20) International Journal of Image and Data Fusion       (Followers: 3) Journal of Agricultural Meteorology Journal of Applied Meteorology and Climatology       (Followers: 42) Journal of Atmospheric and Oceanic Technology       (Followers: 33) Journal of Atmospheric and Solar-Terrestrial Physics       (Followers: 133) Journal of Atmospheric Chemistry       (Followers: 23) Journal of Climate       (Followers: 56) Journal of Climate Change and Health       (Followers: 4) Journal of Climatology       (Followers: 4) Journal of Hydrology and Meteorology       (Followers: 39) Journal of Hydrometeorology       (Followers: 10) Journal of Integrative Environmental Sciences       (Followers: 4) Journal of Meteorological Research       (Followers: 2) Journal of Meteorology and Climate Science       (Followers: 21) Journal of Space Weather and Space Climate       (Followers: 30) Journal of the Atmospheric Sciences       (Followers: 83) Journal of the Meteorological Society of Japan       (Followers: 7) Journal of Weather Modification       (Followers: 4) Mediterranean Marine Science       (Followers: 2) Meteorologica       (Followers: 2) Meteorological Applications       (Followers: 4) Meteorological Monographs       (Followers: 1) Meteorologische Zeitschrift       (Followers: 4) Meteorology and Atmospheric Physics       (Followers: 29) 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: 30) Nature Climate Change       (Followers: 145) Nature Reports Climate Change       (Followers: 40) Nīvār       (Followers: 1) npj Climate and Atmospheric Science       (Followers: 6) Open Atmospheric Science Journal       (Followers: 6) Open Journal of Modern Hydrology       (Followers: 5) Revista Iberoamericana de Bioeconomía y Cambio Climático       (Followers: 1) Russian Meteorology and Hydrology       (Followers: 4) Space Weather       (Followers: 27) Studia Geophysica et Geodaetica       (Followers: 1) Tellus A       (Followers: 21) Tellus B       (Followers: 20) The Cryosphere (TC)       (Followers: 8) The Quarterly Journal of the Royal Meteorological Society       (Followers: 32) Theoretical and Applied Climatology       (Followers: 14) Tropical Cyclone Research and Review       (Followers: 1) Urban Climate       (Followers: 5) Weather       (Followers: 20) Weather and Climate Dynamics       (Followers: 1) Weather and Climate Extremes       (Followers: 18) Weather and Forecasting       (Followers: 43) Weatherwise       (Followers: 18) 气候与环境研究       (Followers: 2)
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  [2469 journals]
• Unique Windward Measurements and a Mesoscale Simulation of an Extremely
Long-Lasting Severe Bora Event

Abstract: Abstract Unique data from a 100-m meteorological mast located on the windward side of the Dinaric Alps, Croatia, are compared to high-resolution Weather Research and Forecasting (WRF) model simulations. This was performed for an especially strong and long-lasting (more than 20 days) wintertime bora event. The agreement between the measurements on the mast and the respective WRF simulation was generally very good, even with respect to the time series of the turbulence kinetic energy. Based on this finding, which validates the WRF model suitability for numerical simulations of transient winds in windward areas, this approach can be used in future studies to explore the severe bora upwind of the coastal mountains, which has been studied inadequately thus far. In this context, some of the preliminary results are outlined here.
PubDate: 2022-06-01

• Impacts of Boundary-Layer Structure and Turbulence on the Variations of
PM2.5 During Fog–Haze Episodes

Abstract: Abstract The precise cause of PM2.5 (fine particular matter with a diameter smaller than 2.5 μm) explosive growth and the contribution of intermittent turbulence to the dispersion of PM2.5 are uncertain. Thus, the impact of boundary-layer structure and turbulence on the variations of surface PM2.5 during fog–haze episodes, especially during explosive growth and dispersion episodes, are investigated using turbulence data collected at a 255-m high meteorological tower in Tianjin from 2016 to 2018. Results suggest that the explosive growth of surface PM2.5 during fog–haze episodes is closely related to weak turbulent mixing, nocturnal inversions, or anomalous inversions, and the barrier effect of strong turbulent intermittency. Turbulent intermittency acts as a lid for hindering pollutant dispersion and is favourable for the fast accumulation of surface PM2.5. Apart from the potential causes mentioned above, the persistent moderate south-westerly flow is also a contributing factor for the explosive growth of surface PM2.5 during fog–haze episodes associated with regional transport. In addition, we demonstrate a possible mechanism of how intermittent turbulence affects the dispersion of PM2.5. Results verify that intermittent turbulence induced by the nocturnal low-level jet (LLJ) indeed plays an important role in the dispersion of PM2.5. However, the contribution of intermittent turbulence generated by the nocturnal LLJ to the dispersion of PM2.5 strongly relies on the intensity of the nocturnal LLJ.
PubDate: 2022-06-01

• A Case Study of the Weather Research and Forecasting Model Applied to the
Joint Urban 2003 Tracer Field Experiment. Part III: Boundary-Layer
Parametrizations

Abstract: Abstract Numerical weather prediction is often used to supply the mean wind and turbulence fields for atmospheric transport and dispersion plume models as they provide dense geographic coverage in comparison to typically sparse monitoring networks. Here, the Weather Research and Forecasting (WRF) model 4.0 was run over the month-long period of the Joint Urban 2003 field campaign conducted in Oklahoma City. We compare three different simulations in their ability to reproduce the observations, each using a different boundary-layer parametrization. Specifically, we examine the Mellor–Yamada–Janjic (MYJ), Yonsei University (YSU), and Mellor–Yamada–Nakanishi–Niino (MYNN) boundary-layer parametrizations. All three predict the wind speed well during the day but overpredict it at night. The MYNN parametrization is better than MYJ at predicting the daytime turbulence in the surface layer, but both underpredict the nocturnal turbulence. The MYJ parametrization is best at predicting the reciprocal Obukhov length, while MYNN and YSU both significantly overpredict thermal stability. Reconstructing the reciprocal Obukhov length from other simulated parameters produces more accurate values for both parametrizations. All three models overpredict the boundary-layer height, particularly under convective conditions. The MYJ parametrization overestimates boundary-layer height the most, while YSU and MYNN have comparable performance with MYNN having an advantage in predicting the stable boundary-layer height. Several days were found where the WRF simulations predict significant deviations from the prevailing diurnal pattern in wind direction, which are not found in the observations.
PubDate: 2022-06-01

• A Ship-Based Characterization of Coherent Boundary-Layer Structures Over
the Lifecycle of a Marine Cold-Air Outbreak

Abstract: Abstract Convective coherent structures shape the atmospheric boundary layer over the lifecycle of marine cold-air outbreaks (CAOs). Aircraft measurements have been used to characterize such structures in past CAOs. Yet, aircraft case studies are limited to snapshots of a few hours and do not capture how coherent structures, and the associated boundary-layer characteristics, change over the CAO time scale, which can be on the order of several days. We present a novel ship-based approach to determine the evolution of the coherent-structure characteristics, based on profiling lidar observations. Over the lifecycle of a multi-day CAO we show how these structures interact with boundary-layer characteristics, simultaneously obtained by a multi-sensor set-up. Observations are taken during the Iceland Greenland Seas Project’s wintertime cruise in February and March 2018. For the evaluated CAO event, we successfully identify cellular coherent structures of varying size in the order of 4  $$\times$$  10 $$^2$$  m to 10 $$^4$$  m and velocity amplitudes of up to 0.5 m  $$\hbox {s}^{-1}$$ in the vertical and 1 m  $$\hbox {s}^{-1}$$ in the horizontal. The structures’ characteristics are sensitive to the near-surface stability and the Richardson number. We observe the largest coherent structures most frequently for conditions when turbulence generation is weakly buoyancy dominated. Structures of increasing size contribute efficiently to the overturning of the boundary layer and are linked to the growth of the convective boundary-layer depth. The new approach provides robust statistics for organized convection, which would be easy to extend by additional observations during convective events from vessels of opportunity operating in relevant areas.
PubDate: 2022-06-01

• An Iterative Method for Calculation of Wind Profiles at the Mesoscale and
Microscale

Abstract: Abstract This paper presents the variational diagnostic model and iterative procedure, which enables the wind field in subdomains to be adjusted. Diagnostic models are not time dependent. Consideration of more complex features of the thermodynamic structure requires models with high resolution, which require large calculation times. The model presented applies the variational approach and enables topographical complexity of the terrain to be considered. The problem of adjusting the wind field is solved in two steps. The first step adjusts the initial wind field by means of experimental measurements or a prognosis in the larger domain, which includes smaller domains. Then the results obtained are used as the initial wind field when the grid refinement in the smaller domain is performed. This allows more precise mapping of the terrain and its architecture. Nevertheless the algorithm proposed ensures a considerable reduction in calculation time. This approach also allows us to eliminate the problem of the lack of initial data when the number of meteorological stations in the smaller domain is insufficient. The algorithm is described and validated, and numerical simulations for pollutant dispersion for a chosen town are described, followed by discussion of the iterative procedure.
PubDate: 2022-06-01

• Hysteresis and Surface Shear Stresses During Snow-Particle Aeolian
Transportation

Abstract: Abstract Surface shear stresses produced by wind and particle collision play a key role in aerodynamic entrainment and splash processes. The fluid shear stress at the surface during aeolian transport has been researched for decades; however, the equilibrium property reported in the literature, numerical simulations, and experiments is inconsistent. To discuss this discrepancy, this study investigates fluid and particle shear stresses at the surface during the aeolian transport of snow particles using a two-dimensional random-flight model of drifting snow. The simulations are performed for various friction velocities on a loose snow bed. By varying the wind conditions in stages, the transport hysteresis is confirmed, and the impact threshold is estimated from the particle transport rate ( $$0.206\,\hbox {m\,s}^{-1}$$ ). The friction velocity at the surface during transport decreases marginally with an increase in wind speed caused by the impact threshold, revealing that our results do not contradict Owen’s second hypothesis. The total shear stress, which is calculated by summing the fluid and particle shear stresses, is vertically uniform in the equilibrium state; thus, the increase in the particle shear stress decreases the fluid shear stress at the surface. The equilibrium property of the fluid shear stress near the surface changes significantly with height (from a decreasing trend to an increasing trend) because the particle shear stress decreases rapidly in the height range of 1–10 mm. Our findings suggest that it is difficult to accurately measure the fluid shear stress in the surface vicinity using anemometers, and a new methodology is needed.
PubDate: 2022-06-01

• Modelling Fractal Turbulent Velocity Spectra: Application to a Dispersion

Abstract: Abstract The present work develops a model for the turbulent velocity spectra that considers the anomalous behaviour of the turbulent flow. The $$\beta$$ -model assumes that the standard Kolmogorov phenomenology is valid only in active turbulence regions, and it proposes an expression for the turbulent velocity spectra in the inertial subrange that is a function of the Hausdorff fractal dimension. From this idea, expressions are obtained for the components of the turbulent velocity spectra that describe the turbulence that exists in geophysical turbulence above the ocean and in very stable situations in the planetary boundary layer where intermittent turbulence occurs. With these spectra, the main parameters used in dispersion models are obtained, that is, the eddy diffusivity and the Lagrangian time scale. The eddy diffusivity is used in an Eulerian dispersion model to estimate the concentration of contaminants in the stable boundary layer. The results obtained are compared with experimental data and other models in the literature.
PubDate: 2022-06-01

• Gradient-Based Turbulence Estimates from Multicopter Profiles in the
Arctic Stable Boundary Layer

Abstract: Abstract We explore the potential of a new method for the estimation of profiles of turbulence statistics in the stable boundary layer (SBL). By applying gradient-based scaling to multicopter unoccupied aircraft system (UAS) profiles of temperature and wind, sampled over sea-ice during the 2018 Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer (ISOBAR18) field campaign, turbulence profiles can be derived. We first validate this method by scaling turbulence observations from three levels on a 10-m mast with the corresponding scaling parameters, and compare the resulting non-dimensional parameters to the semi-empirical similarity functions proposed for this scaling scheme. The scaled data of turbulent fluxes and variances from the three levels collapse to their corresponding similarity functions. After the successful validation, we estimate turbulence statistics from UAS profiles by computing profiles of the gradient Richardson number to which we then apply the similarity functions. These UAS profiles are processed from raw time-series data by applying low-pass filters, time-response corrections, altitude corrections, and temporal averaging across successive flights. We present three case studies covering a broad range of SBL conditions to demonstrate the validity of this approach. Comparisons against turbulence statistics from the 10-m mast and a sodar indicate the broad agreement and physically meaningful results of the method. Successful implementation of the method thus offers a powerful diagnostic tool that requires only a multicopter UAS with a simple thermodynamic sensor payload.
PubDate: 2022-06-01

• Integrated Quadrant Analysis: A New Method for Analyzing Turbulent
Coherent Structures

Abstract: Abstract Integrated quadrant analysis is a novel technique to identify and to characterize the trajectory and strength of turbulent coherent structures in the atmospheric surface layer. By integrating the three-dimensional velocity field characterized by traditional quadrant analysis with respect to time, the trajectory history of individual coherent structures can be preserved with Eulerian turbulence measurements. We develop a method to identify the ejection phase of coherent structures based on turbulence kinetic energy (TKE). Identifying coherent structures within a time series using TKE performs better than identifying them with the streamwise and vertical velocity components because some coherent structures are dominated by the cross-stream velocity component as they pass the sensor. By combining this identification method with the integrated quadrant analysis, one can animate or plot the trajectory of individual coherent structures from high-frequency velocity measurements. This procedure links a coherent ejection with the subsequent sweep and quiescent period in time to visualize and quantify the strength and the duration of a coherent structure. We develop and verify the method of integrated quadrant analysis with data from two field studies: the Eclipse Boundary Layer Experiment (EBLE) in Corvallis, Oregon in August 2017 (grass field) and the Vertical Cherry Array Experiment (VACE) in Linden, California in November 2019 (cherry orchard). The combined TKE identification method and integrated quadrant analysis are promising additions to conditional sampling techniques and coherent structure characterization because the identify coherent structures and couple the sweep and ejection components in space. In an orchard (VACE), integrated quadrant analysis verifies each coherent structure is dominated by a sweep. Conversely, above the roughness sublayer (EBLE), each coherent structure is dominated by an ejection.
PubDate: 2022-05-14

• Effects of Measurement Height and Low-Pass-Filtering Corrections on
Eddy-Covariance Flux Measurements Over a Forest Clearing with Complex
Vegetation

Abstract: Abstract Flux measurements over heterogeneous surfaces with growing vegetation and a limited fetch are a difficult task, as measurement heights that are too high or too low above the canopy adversely affect results. The aim of this study is to assess implications from measurement height in regard to low-pass filtering, footprint representativeness, and energy balance closure for a clear-cut site with regrowing vegetation of varying height. For this, measurements from two open-path eddy-covariance systems at different heights are compared over the course of one growing season. Particular attention is paid to low-pass-filtering corrections, for which five different methods are compared. Results indicate significant differences between fluxes from the upper and lower systems, which likely result from footprint differences and an insufficient spectral correction for the lower system. Different low-pass-filtering corrections add an uncertainty of 3.4% (7.0%) to CO2 fluxes and 1.4% (3.0%) to H2O fluxes for the upper (lower) system, also leading to considerable differences in cumulative fluxes. Despite limitations in the analysis, which include the difficulty of applying a footprint model at this study site and the likely influence of advection on the total exchange, the analysis confirms that information about the choice of spectral correction method and measurement-height changes are critical for interpreting data at complex sites.
PubDate: 2022-05-11

• Pollutant Concentration Changes During the COVID-19 Lockdown in Barcelona
and Surrounding Regions: Modification of Diurnal Cycles and Limited Role
of Meteorological Conditions

Abstract: Abstract One of the consequences of the COVID-19 lockdowns has been the modification of the air quality in many cities around the world. This study focuses on the variations in pollutant concentrations and how important meteorological conditions were for those variations in Barcelona and the surrounding area during the 2020 lockdown. Boundary-layer height, wind speed, and precipitation were compared between mid-March and April 2016–2019 (pre-lockdown) and the same period in 2020 (during lockdown). The results show the limited influence of meteorological factors on horizontal and vertical dispersion conditions. Compared with the pre-lockdown period, during lockdown the boundary-layer height slightly increased by between 5% and 9%, mean wind speed was very similar, and the fraction of days with rainfall increased only marginally, from 0.33 to 0.34, even though April 2020 was extremely wet in the study area. Variations in nitrogen dioxide ( $$\hbox {NO}_{{2}}$$ ), particulate matter with a diameter less than 10 $${\mu }$$ m (PM10), and ozone ( $$\hbox {O}_{{3}}$$ ) concentrations over a 10-year period showed a 66% reduction in $$\hbox {NO}_{{2}}$$ , 37% reduction in PM10, and 27% increase in $$\hbox {O}_{{3}}$$ at a traffic station in Barcelona. The differences in the daily concentration cycle between weekends and weekdays were heavily smoothed for all pollutants considered. The afternoon $$\hbox {NO}_{{2}}$$ peak at the traffic station was suppressed compared with the average daily cycle. The analysis of ozone was extended to the regional scale, revealing lower concentrations at rural sites and higher ones in urban zones, especially in Barcelona and the surrounding area. The results presented not only complement previous air quality COVID-19 lockdown studies but also provide insights into the effects of road-traffic reduction.
PubDate: 2022-05-01

• The Strength of the Evening Wind

Abstract: Abstract When cooling curves of 10-m wind speed versus temperature are measured at different sites, some show the wind speed falling to near-zero as the evening progresses while at other sites the wind speed declines to a fairly constant value of over a half of the daytime value. A theory of the stable boundary layer after Nieuwstadt is used to determine what equilibrium wind speed might be expected at a site in flat terrain later in the evening and hence which sites are influenced by forces not included in the basic theory.
PubDate: 2022-05-01

• Interactions Between the Nocturnal Low-Level Jets and the Urban Boundary
Layer: A Case Study over London

Abstract: Abstract Understanding the physical processes that affect the turbulent structure of the nocturnal urban boundary layer (UBL) is essential for improving forecasts of air quality and the air temperature in urban areas. Low-level jets (LLJs) have been shown to affect turbulence in the nocturnal UBL. We investigate the interaction of a mesoscale LLJ with the UBL during a 60-h case study. We use observations from two Doppler lidars and results from two high-resolution numerical-weather-prediction models (Weather Research and Forecasting model, and the Met Office Unified Model for limited-area forecasts for the U.K.) to study differences in the occurrence frequency, height, wind speed, and fall-off of LLJs between an urban (London, U.K.) and a rural (Chilbolton, U.K.) site. The LLJs are elevated ( $$\approx$$ 70 m) over London, due to the deeper UBL, while the wind speed and fall-off are slightly reduced with respect to the rural LLJ. Utilizing two idealized experiments in the WRF model, we find that topography strongly affects LLJ characteristics, but there is still a substantial urban influence. Finally, we find that the increase in wind shear under the LLJ enhances the shear production of turbulent kinetic energy and helps to maintain the vertical mixing in the nocturnal UBL.
PubDate: 2022-05-01

• The Heat-Flux Imbalance: The Role of Advection and Dispersive Fluxes on
Heat Transport Over Thermally Heterogeneous Terrain

Abstract: Abstract Data from the Idealized Planar-Array experiment for Quantifying Spatial heterogeneity are used to perform a control volume analysis (400 $$\times$$ 400 $$\times$$ 2 m $$^3$$ ) on the total derivative of the temperature tendency equation. Analysis of the heat-flux imbalance, which is defined as the ratio of the sum of advective, dispersive, and turbulence-flux terms to the turbulence-flux term, are presented. Results are divided amongst free-convective and forced-convective days, as well as high-wind-speed and quiescent nocturnal periods. Findings show that the median flux imbalance is greater on forced-convective days (a 168% turbulence-flux overestimation, or relative importance of the advection to dispersive flux to the turbulence flux) when compared to free-convective periods (79% turbulence-flux overestimation). During nocturnal periods, a median turbulence-flux underestimation of 146% exists for quiescent nights and a 43% underestimation of the flux for high-wind-speed nights. These results support the existing literature, suggesting that mean air-temperature heterogeneities lead to strong bulk advection and dispersive fluxes. A discussion of the impact of the flux imbalance on the surface energy balance and numerical-weather-prediction modelling is presented.
PubDate: 2022-05-01

• A Single-Column Comparison of Model-Error Representations for Ensemble
Prediction

Abstract: Abstract Various perturbation approaches have been proposed for representing model error in convection-permitting ensemble prediction. Their evaluation usually relies on time-averaged ensemble prediction statistics and on complex case studies. In this work, their detailed physical behaviour is studied in order to understand their differences, and to help their optimization. A process-level intercomparison framework is used to investigate the widely used SPPT (stochastic perturbations of physics tendencies), independent SPPT, and random-parameters model-perturbation approaches. Ensemble predictions with the single-column version of the Arome numerical-weather-prediction model are evaluated on three different boundary-layer regimes: cumulus convection, stratocumulus-topped boundary layer, and radiation fog. The independent SPPT approach is found to produce more dispersion than the SPPT approach, particularly when several physics parametrizations are in near equilibrium. It also appears to be more numerically stable near the surface. The random parameters approach perturbations are structurally very different from the other approaches, particularly regarding cloud structure. The independent SPPT and random parameters approaches have very different sensitivities to the atmospheric conditions, which suggests that intercomparisons of ensemble-model-error approaches should carefully account for situation dependency. Substantial forecast biases are produced by random parameters with respect to the unperturbed model. These results suggest that the independent SPPT approach can bring major improvements over the SPPT approach with minimal effort, that there is some complementarity between the independent SPPT and random parameters approaches, but that implementing random-parameters-type approaches in operational applications may require careful tuning to avoid creating forecast biases.
PubDate: 2022-05-01

• Using Commercial Aircraft Meteorological Data to Assess the Heat Budget of
the Convective Boundary Layer Over the Santiago Valley in Central Chile

Abstract: Abstract The World Meteorological Organization Aircraft Meteorological Data Relay (AMDAR) programme refers to meteorological data gathered by commercial aircraft and made available to weather services. It has become a major source of upper-air observations whose assimilation into global models has greatly improved their performance. Near busy airports, AMDAR data generate semi-continuous vertical profiles of temperature and winds, which have been utilized to produce climatologies of atmospheric-boundary-layer (ABL) heights and general characterizations of specific cases. We analyze 2017–2019 AMDAR data for Santiago airport, located in the centre of a $$40\times 100$$  km $$^2$$ subtropical semi-arid valley in central Chile, at the foothills of the Andes. Profiles derived from AMDAR data are characterized and validated against occasional radiosondes launched in the valley and compared with routine operational radiosondes and with reanalysis data. The cold-season climatology of AMDAR temperatures reveals a deep nocturnal inversion reaching up to 700 m above ground level (a.g.l.) and daytime warming extending up to 1000 m a.g.l. Convective-boundary-layer (CBL) heights are estimated based on AMDAR profiles and the daytime heat budget of the CBL is assessed. The CBL warming variability is well explained by the surface sensible heat flux estimated with sonic anemometer measurements at one site, provided advection of the cool coastal ABL existing to the west is included. However, the CBL warming accounts for just half of the mean daytime warming of the lower troposphere, suggesting that rather intense climatological diurnal subsidence affects the dynamics of the daytime valley ABL. Possible sources of this subsidence are discussed.
PubDate: 2022-05-01

• Logarithmic-Linear Law of the Streamwise Velocity Variance in Stably
Stratified Boundary Layers

Abstract: Abstract We exploit Monin–Obukhov similarity theory and Townsend’s attached-eddy hypothesis and arrive at a logarithmic-linear law for the streamwise velocity variance in the surface layer of stably stratified boundary layers. To test the logarithmic-linear law, we conduct large-eddy simulations (LES) of stably stratified turbulent boundary layers at various stratification conditions. The LES results give strong support to the scaling, and the logarithmic-linear law is found to be valid in the wake layer (i.e., outside the surface layer) of strongly stratified boundary layers. A detailed analysis shows that this is because stable thermal stratification suppresses the large-scale detached eddies in the wake layer.
PubDate: 2022-05-01

• Modification of a Wavelet-Based Method for Detecting Ebullitive Methane
Fluxes in Eddy-Covariance Observations: Application at Two Rice Fields

Abstract: Abstract Ebullition, the release of gas bubbles, is an important pathway of methane emission in many ecosystems, yet its high spatio–temporal variability makes it challenging to quantify. In this work, a methane-flux partitioning method based on scalar similarity in the wavelet domain is applied to eddy-covariance data collected at two flooded rice fields. Inspection of initial results indicates that several modifications are needed for robust ebullition detection. With these modifications, our objectives are to compare the original and modified methods, conduct a sensitivity analysis of the program’s empirical parameters, characterize the importance of ebullition in rice across growth stages, and identify the primary drivers of ebullition. The modified method’s ebullitive fluxes are significantly lower and show lower variance than those from the original method. Furthermore, the two methods produce distinct patterns of diel variation. While partitioning estimates show non-trivial sensitivity to the program parameters, this sensitivity is lower in magnitude than the random error in the ebullitive flux estimates. Ebullitive fluxes make up 9% of the total flux on average, with ebullition increasing in importance as plants develop. Ebullitive fluxes are best predicted by wind speed (negative effect), ecosystem respiration (positive effect), and sensible heat flux (positive effect), suggesting an indirect effect of plant-mediated transport, a link with temperature and methane production, and a potential effect of water column turnover, respectively. In addition to validating the method with independent ebullition observations, we recommend its application at more natural and managed wetlands to improve understanding of this highly variable transport pathway.
PubDate: 2022-04-30

• Large-Eddy Simulation of the Atmospheric Boundary Layer with Near-Wall
Resolved Turbulence

Abstract: Abstract In this study, a large-eddy simulation (LES) code with the one-dimensional turbulence (ODT) wall model is tested for the simulation of the atmospheric boundary layer under neutral, stable, unstable and free-convection conditions. The ODT model provides a vertically refined flow field near the wall, which has small-scale fluctuations from the ODT stochastic turbulence model and an extension of the LES large-scale coherent structures. From this additional field, the lower boundary conditions needed by LES can be extracted. Results are compared to the LES using the classical algebraic wall model based on the Monin–Obukhov similarity theory (MOST), showing similar results in most of the domain with improvements in horizontal velocity and temperature spectra in the near-wall region for simulations of the neutral/stable/unstable cases. For the free-convection test, spectra from the ODT part of the flow were directly compared to spectra generated by LES-MOST at the same height, showing similar behaviour despite some degradation. Furthermore, the additional flow field improved the near-wall vertical velocity skewness for the unstable/free-convection cases. The tool is demonstrated to provide adequate results without the need of any case-specific parameter tuning. Future studies involving complex physicochemical processes at the surface (such as the presence of vertically distributed sources and sinks of matter and energy) within a large domain are likely to benefit from this tool.
PubDate: 2022-04-26

• A Methodology for Providing Surface-Cover-Corrected Net Radiation at
Heterogeneous Eddy-Covariance Sites

Abstract: Abstract A one-point measurement of net radiation is typically not representative of radiative energy available for the turbulent exchange of latent and sensible heat at eddy-covariance sites with heterogeneous surface cover. We propose a methodology for providing surface-cover-corrected net radiation matching the footprint of turbulent fluxes at a heterogenous eddy-covariance site. This is demonstrated at a complex sub-alpine site in southern central Norway over a week. The methodology is assessed by comparing the energy balance closure calculated with the regular one-point net radiation measurement at the flux tower against the surface-cover-corrected net radiation. The assessment indicates a decrease in the energy imbalance by 8% when assessed with the energy balance ratio, but no improvement is revealed when assessed with regression methods. However, only a small dataset serves as basis for this demonstration, and the findings therefore cannot necessarily be generalized. Further testing and application of the methodology is required to understand the full effect of surface-cover-correcting mismatching footprints of turbulent fluxes and net radiation at heterogeneous eddy-covariance sites.
PubDate: 2022-04-23

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