Stable Atmospheric Conditions Research Articles

Evaluation of wind farm parameterizations in the WRF model under different atmospheric stability conditions with high-resolution wake simulations

Abstract. Wind farm parameterizations (WFPs) are used in mesoscale models for predicting wind farm power production and its impact on wind resources while considering the variability of the regional wind climate. However, the performance of WFPs is influenced by various factors including atmospheric stability. In this study, we compared two widely used WFPs in the Weather Research and Forecasting (WRF) model to large-eddy simulations (LES) of turbine wakes performed with the same model. The Fitch WFP and the explicit wake parameterization were evaluated for their ability to represent wind speed and turbulent kinetic energy (TKE) in a two-turbine wind farm layout under neutral, unstable, and stable atmospheric stability conditions. To ensure a fair comparison, the inflow conditions were kept as close as possible between the LES and mesoscale simulations for each type of stability condition, and the LES results were spatially aggregated to align with the mesoscale grid spacing. Our findings indicate that the performance of WFPs varies depending on the specific variable (wind speed or TKE) and the area of interest downwind of the turbine when compared to the LES reference. The WFPs can accurately depict the vertical profiles of the wind speed deficit for either the grid cell containing the wind turbines or the grid cells in the far wake, but not both simultaneously. The WFPs with an explicit source of TKE overestimate TKE values at the first grid cell containing the wind turbine; however, for downwind grid cells, agreement improves. On the other hand, WFPs without a TKE source underestimate TKE in all downwind grid cells. These agreement patterns between the WFPs and the LES reference are consistent under the three atmospheric stability conditions. However, the WFPs resemble less the wind speed and TKE from the LES reference under stable conditions than that under neutral or unstable conditions.

The Relationship between Indoor and Outdoor Fine Particulate Matter in a High-Rise Building in Chicago Monitored by PurpleAir Sensors.

In urban areas like Chicago, daily life extends above ground level due to the prevalence of high-rise buildings where residents and commuters live and work. This study examines the variation in fine particulate matter (PM2.5) concentrations across building stories. PM2.5 levels were measured using PurpleAir sensors, installed between 8 April and 7 May 2023, on floors one, four, six, and nine of an office building in Chicago. Additionally, data were collected from a public outdoor PurpleAir sensor on the fourteenth floor of a condominium located 800 m away. The results show that outdoor PM2.5 concentrations peak at 14 m height, and then decline by 0.11 μg/m3 per meter elevation, especially noticeable from midnight to 8 a.m. under stable atmospheric conditions. Indoor PM2.5 concentrations increase steadily by 0.02 μg/m3 per meter elevation, particularly during peak work hours, likely caused by greater infiltration rates at higher floors. Both outdoor and indoor concentrations peak around noon. We find that indoor and outdoor PM2.5 are positively correlated, with indoor levels consistently remaining lower than outside levels. These findings align with previous research suggesting decreasing outdoor air pollution concentrations with increasing height. The study informs decision-making by community members and policymakers regarding air pollution exposure in urban settings.

Turbulent Fluxes and Evaporation/Sublimation Rates on Earth, Mars, Titan, and Exoplanets

AbstractTurbulent fluxes of heat, momentum, and humidity in the atmospheric boundary layer are pivotal to the evolution of geology, weather and climate, and the possibility of life. Here we extend recent advances in calculating these near‐surface turbulent fluxes in the Earth's atmospheric boundary layer to any terrestrial planetary body with an atmosphere. These improvements include: (a) incorporating Monin‐Obukhov similarity functions that encompass the entire range of atmospheric stability expected on terrestrial planetary bodies, (b) accounting for the additional shear associated with buoyant plumes under unstable conditions, (c) using surface renewal theory to calculate transfer rates within the interfacial layer adjacent to the surface, and (d) explicitly accounting for key humidity effects that become especially important when a volatile is more buoyant than the ambient gas (e.g., on Mars where H2O is lighter than CO2). We tested and validated our model using in situ data collected on Earth, Mars, and Titan under a wide range of atmospheric stability, pressure, and surface roughness conditions. The model shows up to 71% better agreement with measurements compared to methods commonly used on Mars for evaporation/sublimation. Compared to previous estimates for H2O ice on Mars, our model predicts up to 1.5–190x lower latent heat fluxes under stable atmospheric conditions (depending on the wind speed) and 1.78x higher latent heat fluxes under unstable conditions. Our results provide improved constraints on the stability of ice on Mars and will help determine whether ice can melt under present‐day conditions.

Chemical release risk assessment in earthquake: Natech event scenario

IntroductionIn recent decades, an increase in natural disasters has led to the Natech events occurrence, which are technological accidents triggered by natural hazards. This study aims to assess the risk of chemical release of the H2S toxic gas following an earthquake from the refinery. MethodThe Natech risk assessment was carried out in potential earthquake risk scenarios via a semi-quantitative method using Rapid-N software. The reference scenario was obtained using the Australian SMUG Model, which has presented precise prioritization. FindingsThe Natech risk assessment has shown 40 possible earthquake risk scenarios from 5 enclosing Faults in Tehran (North Tehran, Mosha, North Ray, South Ray, and Kahrizak) with an extension of more than 15 km. The earthquake moment magnitudes of 7.5, 7.1, 6.5, and 5.9 were obtained on the Richter scale and at two Focal depths of 5 and 10 km. The South-Ray Fault (HSR-1) was selected as the reference scenario with a moment magnitude of 7.5 on the Richter scale at a Focal depth of 5 km and a distance of 5.5 km from the earthquake epicenter. The highest probability of Natech risk has shown the release of H2S toxic gas in an area with a radius of 6.59 km from the studied vessel in atmospheric stability conditions. ConclusionLegislation in line with risk reduction, planning for the transfer of potentially dangerous industries to outside urban areas, monitoring land use laws, and promoting coordination between the government, industries, and people in the management of risks caused by industries containing hazardous substances and processes, assessing the risk of Natech events and their consequences, strengthening risk communication and the installation of early warning systems, and public education to adopt personal and socially safe behaviors when facing natural disasters are recommended.

Evolution of Getter Technology in Electronic Hermetic Packaging

Hermetic packaging is a well-established technology used for sealing electronic and optoelectronic devices. A reliable and enabling way to preserve the proper stable atmosphere conditions in hermetic packages is the integration of engineered getter solutions, specifically designed for the characteristics of different packaged systems. Getter solutions may vary from sintered, compressed or sputtered metallic alloys for vacuum sealed packages to dispensable hybrid organic-inorganic materials for gas back filled devices. The paper will present the main features of getter materials suitable for different type of packages and will show their efficiency in absorbing detrimental gases in the devices.

Overview of the Alaskan Layered Pollution and Chemical Analysis (ALPACA) Field Experiment.

The Alaskan Layered Pollution And Chemical Analysis (ALPACA) field experiment was a collaborative study designed to improve understanding of pollution sources and chemical processes during winter (cold climate and low-photochemical activity), to investigate indoor pollution, and to study dispersion of pollution as affected by frequent temperature inversions. A number of the research goals were motivated by questions raised by residents of Fairbanks, Alaska, where the study was held. This paper describes the measurement strategies and the conditions encountered during the January and February 2022 field experiment, and reports early examples of how the measurements addressed research goals, particularly those of interest to the residents. Outdoor air measurements showed high concentrations of particulate matter and pollutant gases including volatile organic carbon species. During pollution events, low winds and extremely stable atmospheric conditions trapped pollution below 73 m, an extremely shallow vertical scale. Tethered-balloon-based measurements intercepted plumes aloft, which were associated with power plant point sources through transport modeling. Because cold climate residents spend much of their time indoors, the study included an indoor air quality component, where measurements were made inside and outside a house to study infiltration and indoor sources. In the absence of indoor activities such as cooking and/or heating with a pellet stove, indoor particulate matter concentrations were lower than outdoors; however, cooking and pellet stove burns often caused higher indoor particulate matter concentrations than outdoors. The mass-normalized particulate matter oxidative potential, a health-relevant property measured here by the reactivity with dithiothreiol, of indoor particles varied by source, with cooking particles having less oxidative potential per mass than pellet stove particles.

Preliminary assessment of volatile organic compounds and hazardous gases dispersion at low winds: case study of Mellitah Gas Complex, Libya

Air pollution from industrial areas has become really worrying especially for city dwellers. The plume dispersion emitted from industrial sources is subject to several factors: temperature and emission rate velocity, wind speed and direction, source height, and atmospheric stability. This study aimed to evaluate the applicability of the dispersion coefficients correlated within a Gaussian plume approach to an industrial source in Libya (Mellitah Gas Complex) under low and moderate wind speeds. To this end, we have developed a specific code based on the Gaussian method to study the dispersion of (1) Volatile Organic Compounds (VOCs) from oil storage tanks and condensate storage tanks, and (2) sulfur oxides (SOx) and nitrogen oxides (NOx) emitted by the flaring process through three stacks of 80 m height. The emissions from multisource points and their dispersion have been predicted at calm wind conditions and the flammability and danger-prone toxic zones have been delimited around the studied site. The obtained results reveal that the emissions, particularly generated at low and moderate wind speeds, induce a dispersion with high concentration levels in the area surrounding the industrial site. The VOCs critical concentration region indicates a real risk of flammability at low-speed wind and stable atmospheric condition, from a height of 5 m above the ground. In fact, the VOCs concentration reach the Flammability Inferior Limit value of 0.018 m3 VOCs/m3 and these concentrations, appearing in the form of a plume, extend downstream to approximately 1000 m. The dispersion of NOx and SOx emissions downwind from the stacks are enhanced by wind speed; nevertheless, at 2 m height from the ground, the levels could exceed the limit value of 0.125 mg/m3, especially under the condition of unstable and very unstable atmospheric classes. From our findings, we recommend continuous monitoring campaigns inside and around the complex of Mellitah to ensure an environmentally secure zone that respects safety and health guidelines. Furthermore, enhanced simulations based on hourly weather conditions for extended area would be of great interest to accurately assess the air quality index in the region.

Lost life expectancy following a hypothetical urban radiological incident

The consequences of mass radiological events, particularly those involving the activation of a radiological dispersion device (RDD), have been extensively studied by scientific groups. However, the critical initial period of such an event, usually spanning the first 100 h, can be characterized by a scarcity of information, potentially leading to delays in mitigating strategies. In response, a research group utilized computer simulations to generate solid, conservative analytical details that can aid decision-making and guide the prioritization of initial care based on variables such as age, sex, location, and local atmospheric stability conditions. The study estimates the Lost Life Expectancy (LLE) and provides relevant information to increase support for decision-making and allow evaluation of data closer to the lay public. The research team behind the study has been granted funding by the Brazilian National Council for Scientific and Technological Development (CNPq), and further simulations will be conducted utilizing codes that implement numerical models, specifically in atmospheric data forecasting. The methodology used to evaluate the LLE can be applied to any location, provided that the relevant variables are updated accordingly. Overall, this study offers critical insights into the impact of mass radiological events and enhances simulations' predictive capacity and precision.

The Response of Precipitation to Initial Soil Moisture over the Tibetan Plateau: Respective Effects of Boundary Layer Vertical Heat and Vapor Diffusions

Abstract This study investigates the influences of initial soil moisture over the Tibetan Plateau (TP) on precipitation simulation, and the respective effects of boundary layer vertical diffusion for heat (Kh) and vapor (Kq). Results indicate that the responses of boundary layer vertical diffusion to soil moisture are obvious mainly in the daytime. Wetter land surface corresponds to weaker vertical diffusion, which could strengthen thermal forcing and dynamic lifting in the lower atmosphere, and encourage water vapor saturation near the top of boundary layer to prevent the environmental dry air entrainment/invasion, which would be beneficial to more convection and precipitation. Wetter land surface over the TP could enhance the contrast between the cold in the northwestern TP and the warm in the southeastern TP, which would be conducive to the southeastward propagation of precipitation. The simulation of heat and moisture in the boundary layer could be improved by perturbing the relative intensity of Kh and Kq. From the perspective of heat and moisture, Kh affects atmospheric stability, while Kq affects moisture and its vertical transport in the boundary layer. The Kh and Kq have competitive effects on precipitation intensity by influencing the relative importance of moisture and atmospheric stability conditions in the boundary layer. Adjusting the relative intensity of Kh and Kq would deactivate the competitive effects. Stronger Kh but weaker Kq would alleviate the overestimated precipitation by inhibiting vertical transport of moisture to the top of boundary layer and attenuating convective instability in the boundary layer. Significance Statement The purpose of this study is to better understand the effects of boundary layer vertical heat and moisture diffusion in the response of precipitation to soil moisture. This is important because boundary layer vertical diffusion is a crucial factor influencing the relation between soil moisture and precipitation. Our results reveal the competitive effects of boundary layer vertical diffusion for heat and vapor on the simulation of precipitation. These results point a potential way toward better understanding the response of precipitation to soil moisture.

Why Does Japan’s South Foehn, “Jintsu-Oroshi,” Tend to Onset during the Night?: An Investigation Based on Two Case Studies

Abstract The Jintsu-oroshi refers to Japan’s south foehn, which blows over the Toyama Plain in the Hokuriku region. This region faces the Sea of Japan to the north and the central mountain range to the south. The Jintsu-oroshi occurs more frequently at night than during the day. In this study, we determined the primary factors causing this feature using the Weather Research and Forecasting (WRF) Model. We selected a typical Jintsu-oroshi case in May 2016 for analysis. An extratropical cyclone traversed the Sea of Japan during the event, leading to a temporal change in the synoptic-scale pressure pattern. The observations and numerical simulation results showed that the collapse of the mixed layer over the mountains and the end of the sea breeze are key factors for the nighttime onset of the Jintsu-oroshi. Indeed, mountain waves and their resulting downslope winds did not occur under near-neutral atmospheric stability conditions over the mountains during the daytime. After sunset, the atmospheric stability changed to stable conditions, which caused the downslope winds to blow. However, the downslope winds did not reach the plains because of the sea breeze. After several hours, the sea breeze disappeared, and the downslope winds reached the leeward plains and increased the temperature there. Similar features were confirmed in August 2013 for another typical Jintsu-oroshi case under atmospheric conditions, without temporal changes in the synoptic-scale pressure pattern. We expect the results obtained in this study to advance our understanding of foehn occurrence in regions where mountains adjoin seas, similar to the coastal areas adjacent to the Sea of Japan. Significance Statement The Jintsu-oroshi refers to Japan’s south foehn, which blows over the Toyama Plain in the Hokuriku region. This foehn occurs more frequently at night than during the day. Strong foehns enhance the risk of fire. Nocturnal high temperatures due to foehns can cause sleeplessness in people. Nighttime foehns cause damage to paddy rice. Analyses of observations and numerical simulations for the two typical cases showed that Jintsu-oroshi did not tend to occur during the daytime because the development of a convective boundary layer over the mountains and sea breezes in the leeward plain inhibited the occurrence of the downslope winds. We expect the results obtained in this study to advance our understanding of foehn occurrence in regions where mountains adjoin seas, similar to the coastal areas adjacent to the Sea of Japan.

On the importance of the humidity flux for the surface mass balance in the accumulation zone of the Greenland Ice Sheet

Abstract. It is highly uncertain how the humidity flux between the snow surface and the atmosphere contributes to the surface mass balance (SMB) of the interior Greenland Ice Sheet (GrIS). Due to sparse observations, evaluations of the simulated humidity flux are limited. Model-based estimates of the humidity flux contribution to the SMB are, therefore, unconstrained and even disagree in magnitude and sign. In this study, we evaluate the regional climate model MAR at the EGRIP (East Greenland Ice-Core Project) site in the accumulation zone of the GrIS. We use a combined dataset of continuous one-level bulk estimates of the humidity flux covering the period of May 2016–August 2019 and eddy-resolving eddy-covariance humidity flux measurements from all four summer seasons. In summer, we document a bias of too little sublimation (−1.3 W m−2, −1.65 mm w.e.) caused by a cold bias in both air and surface temperature, leading to a reduced humidity gradient. In winter, MAR overestimates vapor deposition by about 1 order of magnitude. This is a consequence of an overestimated temperature gradient in too stable atmospheric conditions compared to observations. Both systematic errors cause a large discrepancy in the annual net humidity flux between the model and observations of −9 mm w.e. yr−1. Remarkably, the simulated net annual humidity flux contributes positively to the SMB, contrary to observations documenting a net sublimation flux. We correct the systematic errors by applying a simple but effective correction function to the simulated latent heat flux. Using this correction, we find that 5.1 % of the annual mass gain at the EGRIP site sublimates again, and 4.3 % of the total mass gain is deposited vapor from the near-surface air. The estimated net humidity flux contribution to the annual SMB is about −1 % (net sublimation) compared to +5.6 % for the uncorrected simulation. In summer, the corrected MAR simulation shows that vapor deposition accounts for 9.6 % of the total mass gain and that 31 % of the total mass gain at the EGRIP site sublimates again. The net fluxes contribute to −32 % of the summer SMB. These results demonstrate that the humidity flux is a major driver of the summer SMB in the accumulation zone of the GrIS and highlight that even small changes could increase its importance for the annual SMB in a warming climate.

Modeling snowpack dynamics and surface energy budget in boreal and subarctic peatlands and forests

Abstract. The snowpack has a major influence on the land surface energy budget. Accurate simulation of the snowpack energy and radiation budget is challenging due to, e.g., effects of vegetation and topography, as well as limitations in the theoretical understanding of turbulent transfer in the stable boundary layer. Studies that evaluate snow, hydrology and land surface models against detailed observations of all surface energy balance components at high latitudes are scarce. In this study, we compared different configurations of the SURFEX land surface model against surface energy flux, snow depth and soil temperature observations from four eddy-covariance stations in Finland. The sites cover two different climate and snow conditions, representing the southern and northern subarctic zones, as well as the contrasting forest and peatland ecosystems typical for the boreal landscape. We tested different turbulent flux parameterizations implemented in the Crocus snowpack model. In addition, we examined common alternative approaches to conceptualize soil and vegetation, and we assessed their performance in simulating surface energy fluxes, snow conditions and soil thermal regime. Our results show that a stability correction function that increases the turbulent exchange under stable atmospheric conditions is imperative to simulate sensible heat fluxes over the peatland snowpacks and that realistic peat soil texture (soil organic content) parameterization greatly improves the soil temperature simulations. For accurate simulations of surface energy fluxes, snow and soil conditions in forests, an explicit vegetation representation is necessary. Moreover, we demonstrate the high sensitivity of surface fluxes to a poorly documented parameter involved in snow cover fraction computation. Although we focused on models within the SURFEX platform, the results have broader implications for choosing suitable turbulent flux parameterization and model structures depending on the potential use cases for high-latitude land surface modeling.

Arctic/North Atlantic atmospheric variability causes Severe PM10 events in South Korea

Severe PM10 (particulate matter with a diameter of <10 μm) events in South Korea are known to be caused by stable atmospheric circulation conditions related to high-pressure anomalies in the upper troposphere. However, research on why these atmospheric circulation patterns occur is unknown. In this study, we propose new large-scale teleconnection pathways that cause severe PM10 events during the midwinter in South Korea. This study investigated instances of extremely high (EH)-PM10 in South Korea during mid-winter and examined the corresponding atmospheric teleconnection patterns to identify the factors contributing to EH-PM10 events. K-means clustering analysis revealed that EH-PM10 instances were associated with two large-scale teleconnection patterns. Cluster 1 exhibited a wave train pattern originating in the North Atlantic that developed from Eurasia to the Korean Peninsula. Cluster 2 was associated with a wave-like teleconnection pattern from the Barents-Kara Sea to the Korean Peninsula. The Rossby waves, triggered by the North Atlantic and the Arctic, propagated and weakened the surface pressure system. This led to a high-pressure anomaly over the Korean Peninsula, reducing atmospheric ventilation and causing a rapid increase in PM10 concentration within a few days. Furthermore, an experiment involving a linear baroclinic model established that atmospheric forcing in upstream regions has the potential to induce large-scale atmospheric teleconnection patterns, resulting in EH-PM10 cases in South Korea. These findings emphasize the ventilation effect and transport of PM10 concentrations modulated by two large-scale teleconnection patterns originating from the Arctic and North Atlantic, leading to EH-PM10 events in South Korea. Understanding this combined phenomenon may assist in the implementation of emission reduction measures based on the results of short-term forecasts of severe PM10 events.

Land use as key element for urban heat island inception in small cities. Case study: Barlad City, Romania

The study investigates the thermal characteristics of the urban area of Bârlad city, Romania, in relation with urban land use (LU) and land cover (LC). This was done using Land Surface Temperature (LST) data provided by Moderate Resolution Imaging Spectroradiometer (MODIS) and mobile measurements conducted during stable atmospheric conditions. To identify important factors that influence Surface Urban Heat Island (SUHI) and Canopy Layer Urban Heat Island (CLUHI) two types of LU/LC classifications were used. At the annual level, during the day, the highest LST values are observed in the most densely built-up areas of the city, with values exceeding 18°C. The lowest LST instead are observed in the northern area of the city, with prevailing natural areas, where LST values reach 17.4°C. During the night, the urban area maintains constantly high LST above 4°C, while the lowest LST values are observed in the forested area in the eastern part of the city, where mean LST drops close to 3°C. The results of this study highlight the significant impact that LU/LC has on the inception of SUHI in small cities. Generally, built-up surfaces from Urban Atlas (UA) and Local Climate Zones (LCZ) classifications, are warmer than natural land cover types, both during day and night, with at least 0.5 to 1.5°C, which is enough to outline a clearly delimited SUHI especially during summer days. During stable atmospheric conditions the CLUHI exhibits large intensities emphasized by local cooling processes manifested especially during thermal inversion conditions.

Investigation of wind veer characteristics on complex terrain using ground-based lidar

The wind direction shift with height significantly influences wind turbine performance, particularly in relation to terrain conditions. In this work, wind conditions at 12 measurement heights ranging from 40 m to 200 m using a ground lidar, Windcube V2, installed on a 16 m tall building were analysed to examine the characteristics of wind veer angles in complex terrain. The measurement campaign was carried out from January 1st to December 31st, 2022, in the southeastern part of South Korea. The terrain complexity around the ground lidar system was evaluated using the ruggedness index (RIX), whose result was 14.06 percent corresponding to complex terrain. The ground lidar measurements were compared with mesoscale data, EMD-WRF South Korea, for the data accuracy check. Wind veer frequencies and wind roses were derived to identify directional shifts with height. Furthermore, diurnal, monthly, and seasonal variations of wind veer characteristics were analysed. Wind shear exponent factor (WSE) and turbulence kinetic energy (TKE) were calculated, and wind veer profiles were constructed based on these parameters. The relative errors of wind speeds were analysed for rotor equivalent wind speed (REWS) and hub height wind speed (HHWS), with REWS with wind veer correction, REWSveer, as a reference. Additionally, atmospheric stability conditions were classified using WSE and TKE, and the vertical changes in wind veering were analysed according to the stability conditions. The findings reveal lower wind speeds exhibited larger wind veer values and fluctuations. The relative errors for the REWS and the HHWS were 0.04 % and 0.20 % on average, respectively. The study demonstrates that terrain conditions significantly impacted wind veer angles at heights below 100 m, whereas the influence diminished with increasing height above 100 m. The results could be helpful for wind farm developers to make decisions on the siting as well as the hub height of wind turbines on complex terrain

Spatial and temporal variation of three Eddy-Covariance flux footprints in a Tropical Dry Forest

Tropical Dry Forest (TDF) is a distinctive ecosystem characterized by distinct seasonal changes, primarily composed of deciduous trees adapted to endure prolonged drought periods. Obtaining ecosystem-scale flux measurements using the Eddy Covariance (EC) technique is crucial for comprehending the spatiotemporal dynamics of interactions between the land and the atmosphere. It is imperative to have information about the variability in the contribution source area of the Flux Footprint Area (FFA) to assess the impact of changing microclimate variables on the EC FFA. In this study, we describe and evaluate the influence of various phases of the El Niño Southern Oscillation (ENSO) on the spatial and temporal climatology of FFA at three EC sites within the TDF of the Santa Rosa National Park-Environmental Super Site (SRNP-EMSS). Our analysis covered the period from 2014 to 2021 on a seasonal scale and employed a 2D model. Our findings indicate that: a) seasonal climatology FFAs exhibit variation across locations and over time due to factors such as forest canopy height, site topography, wind direction, and atmospheric stability conditions; b) FFAs are smaller during dry seasons compared to wet seasons; and c) multiple ENSO phases (cold, neutral, and warm) significantly affect the seasonal climatology of FFAs. Notably, during the moderate La Niña phase (2020/2021), the mean FFA size was 4.20 km2, which was 23.80% larger than the mean FFA during the intense El Niño phase (2015/2016) at 3.20 km2. Additionally, during La Niña phases, FFAs were more asymmetrically distributed around the EC tower compared to El Niño phases, with mean symmetric indices of 0.35 and 0.29, respectively. Finally, the overlap among the three EC climatology FFAs during La Niña phases was 35% greater than that during the El Niño phases. Our study highlights how variations in FFAs can significantly impact intra-annual flux estimates.

CFD simulation of pollutant dispersion using anisotropic models: Application to an urban like environment under neutral and stable atmospheric conditions

Modeling the atmospheric dispersion of pollutants emitted from different types of sources under various atmospheric conditions is an essential prerequisite for risk assessment studies and emergency preparedness. In this study, we evaluate the performance of different turbulence models and velocity-scalar correlation models implemented in the Code_Saturne. The evaluation is done with observations of four trial cases of the Mock Urban Setting Test (MUST) campaign in an urban type environment and in neutral and stable atmospheric conditions. For all of the trials studied, the CFD model with a first-order closure model (k−ɛ) predicts 61.1% of the concentrations within a factor of two of the observations, which is higher than the percentage of predicted points (58.8%) when a second-order closure model (Rij−ɛ) is used. Overall, the CFD model underestimates observed concentrations, regardless of the turbulence model used. For the trial with slightly stable conditions, the results show that the k−ɛ model combined with an algebraic SGDH model predicts 75% concentrations within a factor of two of the observations. The performance of the k−ɛ model is compared to that of the Rij−ɛ model when used with the algebraic SGDH, GGDH models and with the scalar flux transport equation (DFM model). Under slightly stable atmospheric conditions, the DFM model predicts 69% of concentrations within a factor of two of observations, showing promise for modeling under these conditions, despite its relatively high computational cost.

Constant stress layer characteristics in simulated stratified air flows: Implications for aeolian transport

Varying thermal atmospheric stability conditions and their effects on shearing flows has long been a subject of interest for researchers working in atmospheric science. The development of new instrument technologies now offers an opportunity to study flows with high spatial and temporal resolutions in wind tunnel atmospheric boundary layers. In the presented study, we use a laser Doppler anemometer within the Trent Environmental Wind Tunnel Laboratory to investigate the influence of thermal stratification on the constant stress layer. Analyses of the thermal stratification represented by the gradient Richardson number and the apparent von Kármán parameter, shear velocity, and the slope of the streamwise velocity profiles reveal strong linear relationships. An exponential relationship between thermal stability and the apparent roughness length is also revealed. Profiles of the streamwise and vertical velocity and turbulence intensity, as well as the dimensionless Reynolds stress, are influenced by the gradient Richardson number. These findings have implications for producing accurate models of sediment entrainment and transport by wind in non-neutral conditions.

Experimental study on outdoor sound propagation under various meteorological conditions

From the winter of 2018 through the spring of 2021, outdoor sound propagation experiments were repeatedly conducted three times a day on weekdays at a glider airfield in Hokkaido, Japan. In each experiment, impulse responses at the points of 155 m and 300 m from sound sources were measured. The ground surface condition of the experimental field was grass-covered in summer and snow-covered in winter. The monthly averages of sound pressure levels under upwind, downwind, and calm conditions were calculated every month. The data show that the seasonal variation depends on wind conditions, propagation distance, and frequencies. At the point of 300 m from sound sources, the seasonal variations are small under downwind conditions, whereas the range of variations is about 10 dB at high frequencies under upwind conditions and calm conditions. The relationship between vector wind speed and excess attenuation is discussed focusing on differences in atmospheric stability, snowfall, and snow cover conditions, respectively. We also introduce trial calculation results assuming the logarithmic-liner effective sound speed profiles and the parameters of turbulence proposed in previous studies.

Doppler LiDAR Observation of Subsidence in Synoptic Scale and Performance of a Global Numerical Weather Prediction Model in Capturing the Subsidence

The vertical velocity data from a Doppler LiDAR situated at the centre of Hong Kong were examined to look for signature of subsidence within the atmospheric boundary layer against a synoptic background. Two case studies were performed, namely, stable atmospheric conditions in foggy weather and possible “subsidence heating” at the periphery of the outer circulation of an intense tropical cyclone. The LiDAR’s Doppler velocity data were found to provide insights into the vertical motion of the air on the synoptic scale. They appear to confirm subsidence in foggy weather but provide new information about the mechanism for the occurrence of extremely hot weather. The data were also compared with vertical velocity forecasts from a numerical weather prediction model to assess the quality of the forecast. The Doppler LiDAR’s vertical velocity data were found to be useful in the verification of omega forecasts from the global numerical weather prediction model. They were found to provide further insights into the subsidence of the troposphere, particularly the atmospheric boundary layer, in certain synoptic patterns.