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Barchan dunes do not often coexist with grasslands. However, in Gonghe Basin, north‐eastern part in Qinghai‐Tibetan Plateau (QTP), China, many barchan dunes are distributed on the grassland at high altitude. Identifying celerity and morphodynamics of barchan dunes and exploring the interaction between barchans and grassland landscape can help us better understand aeolian system sand mitigate damages. In this work, we tracked dune celerity and observed three‐dimensional changes of symmetrical and asymmetrical barchan dunes in Ertala based on high‐resolution UAV‐SfM reconstruction in short‐term monitoring and discussed the factors influencing dune celerity and deformation at high altitude. The results revealed that the barchan dunes are highly mobile with an average celerity of 0.85 m/M for the whole study area. Based on observations of dune morphology and dynamics, we found the following: (1) The dune deformation degree in a short time is not large but is widespread, especially in the elongated arm of asymmetric dune. The deformation of symmetric dune is symmetrical, whereas that of dune with extended horn is asymmetrical; (2) the sand supply, vegetation and airflow at low air density all influence the celerity and deformation degree in the development of barchan dunes; (3) the asymmetric airflow and sediment supply are important cause of dune asymmetry. The above results help us understand the deformation of barchan dune from the three‐dimensional, especially the difference reflected by the symmetry of barchan dune at high altitude. [ABSTRACT FROM AUTHOR]

Formaldehyde (HCHO) is a widespread air pollutant in the indoor environment. Previous studies have shown that some bacteria have potential application to remove indoor HCHO. The purpose of this study is to evaluate the effectiveness of Methylobacterium sp. strain R1 (S-R1) in removing formaldehyde (HCHO) from indoor air using biofilters. Three experiments confirmed S-R1's ability to degrade HCHO in the air, with 13C-NMR analysis revealing its involvement in the metabolic process. Optimal biofilter parameters, including 35 sponge layers, 30% humidity, and 9.50 m3/min air flow, resulted in a removal efficiency of up to 90% and an elimination capability of 24111-27000 μg/(m3 ∗ h) during a 60-minute test period. Long-term (31-day) operation of the biofilter with the optimal parameters effectively reduced HCHO levels from 1.60 mg/m3 to 0.02-0.03 mg/m3, below China's national standard, and maintained this level. Fluorescence microscope observation and downstream gas detection revealed stable S-R1 cell numbers and no bacterial leakage, respectively. Two conclusions can be drawn: (1) S-R1 is effective in removing HCHO in polluted air and (2) with optimum parameters, the S-R1 biofilter is engineering effective in purifying the indoor air environment. [ABSTRACT FROM AUTHOR]

Fruit tree frost, an agricultural meteorological disaster primarily occurring in spring, severely impacts the growth and development of trees and fruit set. Therefore, exploring the temperature change rules of fruit trees during frost events is of considerable importance. This study used a T40 unmanned aerial vehicle (UAV) as the test vehicle based on the air disturbance frost prevention principle. The airflow field change pattern of the UAV was explored using the computational fluid dynamics simulation method, and the reliability of the multi-rotor UAV in frost prevention was verified using field tests. Setting the UAV height at 6.0 m above the ground and the rotor speed at 1000 r min−1, it was found that under the conditions of the inverse temperature phenomenon, the temperatures of different altitude layers will eventually converge to a stable value when the UAV down-rotating airflow is disturbed, which could be completed rapidly within 20 s. The results of the field test also showed that when the fruit trees reached the critical temperature of frost at the flowering stage, UAV intervention could have a substantial effect on the warming of the near-surface layers, whose warming amplitude was in the range of 2.5 °C–3 °C. This study provides a reliable method for mitigating frost, which serves as an important theoretical and guiding basis for improving agricultural frost disasters in China. • A multi-rotor UAV is used to test frost protection performance on fruit trees. • The temperature field characterizations are obtained. • The anti-frost effectiveness of UAV intervention is confirmed. [ABSTRACT FROM AUTHOR]

With the development of civil aviation in China, airspace congestion has become more and more serious and has gradually spread from airport terminal areas to en route networks. Traditionally, most prediction methods that obtain traffic flow data are based on the number of aircraft passing through an en route sector and require flight data to meet strict assumptions and conditions. While these methods are normally used in the actual operation of air traffic flow management departments in China, the results are not satisfactory due to the nonlinearity of traffic demand along en route sectors and the change in high-frequency noise. In order to refine aircraft control in airspace, it is necessary to predict traffic flow accurately. Thus, this paper proposes the quantile regression neural network and kernel density estimation method to obtain some quantiles of continuous traffic demand data in the future, which combines the strong nonlinear adaptive ability of neural networks with the ability of quantile regression to describe explanatory variables. By using these continuous conditional quantiles, we obtain the probability density function and probability density curve of the continuous traffic demand in the future using the kernel density estimation method. In this way, we can obtain not only a specific point prediction value and its change interval but also the probability of each value in the prediction change interval of traffic demand in the en route sector as well as a more accurate point prediction value for a specific day. [ABSTRACT FROM AUTHOR]

Air Traffic Flow Management (ATFM) delay can quantitatively reflect the congestion caused by the imbalance between capacity and demand in an airspace network. Furthermore, it is an important parameter for the ex-post analysis of airspace congestion and the effectiveness of ATFM strategy implementation. If ATFM delays can be predicted in advance, the predictability and effectiveness of ATFM strategies can be improved. In this paper, a short-term ATFM delay regression prediction method is proposed for the characteristics of the multiple sources, high dimension, and complexity of ATFM delay prediction data. The method firstly constructs an ATFM delay prediction network model, specifies the prediction object, and proposes an ATFM delay prediction index system by integrating common flow control information. Secondly, an ATFM delay prediction method based on feature extraction modules (including CNN, TCN, and attention modules), a heuristic optimization algorithm (sparrow search algorithm (SSA)), and a prediction model (LSTM) are proposed. The method constructs a CNN-LSTM-ATT model based on SSA optimization and a TCN-LSTM-ATT model based on SSA optimization. Finally, four busy airports and their major waypoints in East China are selected as the ATFM delay prediction network nodes for example validation. The experimental results show that the MAEs of the two models proposed in this paper for ATFM delay regression prediction are 4.25 min and 4.38 min, respectively. Compared with the CNN-LSTM model, the errors are reduced by 2.71 min and 2.59 min, respectively. Compared with the TCN-LSTM model, the times are 3.68 min and 3.55 min, respectively. In this paper, two improved LSTM models are constructed to improve the prediction accuracy of ATFM delay duration so as to provide support for the establishment of an ATFM delay early warning mechanism, further improve ATFM delay management, and enhance resource allocation efficiency. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has emphasized the crucial role of ventilation systems in mitigating cross-infections, especially in infectious-disease hospitals. This study introduces a dual-design operation ventilation system that can operate under two sets of ventilation conditions for normal and epidemic times. A challenge is optimizing duct diameters for required airflow while maintaining hydraulic balance. We designed an improved genetic algorithm with an adaptive penalty factor and velocity constraint, as well as the improved crossover probability and mutation probability. The improved genetic algorithm is suitable for ventilation system networks, which can find a better combination of air duct diameters to improve the hydraulic balance rate and reduce the usage of air valves, resulting in efficient hydraulic balancing commissioning. A supply air ventilation system of an actual hospital in China was selected as a case study, and the number of imbalanced air ducts was reduced from 14 to 4. Compared with the traditional genetic algorithm, it has a faster search speed and a better global search ability, which is effective for the optimal design of ventilation system networks. [ABSTRACT FROM AUTHOR]

The tropical cyclones (TCs) often cause intense rain and destructive winds. While these catastrophic weather conditions capture our attention, the less-known impact of TCs remains overlooked. This study reveals that TCs have a notable suppressive effect on monsoonal rainfall in southern China when they traverse the South China Sea. This phenomenon can be attributed to the influence of these mesoscale disturbances on the quasi-stationary, large-scale monsoonal circulation, which alters the moisture pathway. Furthermore, the case-by-case analysis indicates that ~76% of TCs correspond to rainfall reduction, whereas the other 24% correspond to rainfall increase. The latter is due to the concurrent occurrence of another independent influencing factor: extratropical cyclonic anomalies that promote enhanced rainfall through favoring lower-tropospheric moisture convergence. This study suggests that TCs, as mesoscale disturbances, can change the moisture channel that is usually controlled by quasi-stationary and large-scale monsoonal airflows, and suppress the adjacent land rainfall over China. [ABSTRACT FROM AUTHOR]

To understand why convection initiation and heavy rain sometimes occur ahead of fronts over South China in the presummer rainy season but sometimes do not, a climatology of 137 fronts is constructed, in which 34% of the fronts exhibit no prefrontal convection initiation (NoPCI), 31% of the fronts exhibit prefrontal convection initiation (PCI), and 35% of the fronts exhibit prefrontal convection initiation and heavy rain (PCI+HR). An anticyclonically curved upper-level jet streak and midtropospheric QG forcing produce synoptic-scale descent for the prefrontal region in NoPCI events, whereas the right-entrance region of a straight upper-level jet streak and forcing for ascent dominate the prefrontal region in PCI and PCI+HR events. Whether prefrontal convection and heavy rain occur is also related to the character of low-level flows. NoPCI features anticyclonic southerly winds, with an environment having low dewpoint throughout the troposphere, unfavorable for convection initiation. However, synoptic circulation of PCI and PCI+HR events favors a broad prefrontal surface low, which determines the greater cyclonic character of airflows in PCI+HR events, in contrast with that of the PCI events. Convective available potential energy is useful in distinguishing NoPCI and PCI events, and the three events have statistically significant differences in precipitable water. Moreover, larger magnitudes of precipitable water and bulk wind shear in PCI+HR events are conducive for prefrontal convection to produce heavy rain compared to those of PCI events. These results indicate the importance of the upper-level forcing on the prefrontal convection initiation, and heavy rain is sensitive to the changes in prefrontal airflow and moisture. Significance Statement: Convection and heavy rain sometimes occur a few hundred kilometers ahead of fronts in the warm air over South China in early summer. To understand atmospheric conditions favoring or inhibiting convection and heavy rain ahead of fronts, we examine 46 fronts without prefrontal convection, 43 fronts with prefrontal convection, and 48 fronts with prefrontal convection and heavy rain. These scenarios have similarities in environmental behaviors but different large-scale conditions that favor or inhibit ascent in the prefrontal area. Specifically, prefrontal heavy rain tends to occur in a very moist environment with a prefrontal surface low. These findings help researchers and operational forecasters better discriminate the subtle conditions that favor or inhibit prefrontal convection and heavy rain over South China. [ABSTRACT FROM AUTHOR]

Plant protection drones are fast and efficient application machines that are characterised by high application efficiency and no damage to crops. They are particularly suitable for small areas of farmland and mountainous terrain in regions such as Asia and are currently the dominant insecticide application technology in China. The presence of wind is a prerequisite for the spread and dissemination of airborne diseases and it can directly influence the distance and height of ascent of pathogenic spores. This paper investigates the effect of downwash airflow generated by the flight altitude of a plant protection drone on the horizontal distribution, vertical distribution and ground distribution of powdery mildew spores in wheat. Monitoring the changing dynamics of airborne powdery mildew conidia using spore traps. The test results show that: the number of powdery mildew pathogenic spores is related to various factors such as weather, relative humidity and wind speed; the release of spores is greatly influenced by airflow disturbances but has little effect at the early stages of sporulation; the disease is caused by the accumulation process of pathogenic spores and in the control of powdery mildew in wheat, preventive spraying should be carried out within 2–3 days of the germination of pathogenic spores. The study lays the foundation for further in-depth research on the spread of powdery mildew spores and improved pest control, and provides a basis for scientific and rational spraying and control by agricultural drones. [ABSTRACT FROM AUTHOR]

The opposed wall-fired boiler has been widely employed in power plants in China due to its adaptability. However, the airflow in the same layer burners from the large air box is uneven, affecting the combustion characteristics of pulverized coal and causing the corrosion and slagging of the water-cooled wall. In this study, the numerical simulation is performed on a 600 MW wall-fired boiler to investigate the air distribution and flow characteristics of each burner and the secondary air duct under variable boiler loads (100%, 75%, 50%, and 30%), which would provide the basis for optimization of the secondary air box. The effectiveness of the modified burner, over-fire air (OFA) nozzle, and secondary air duct is demonstrated through the numerical simulation. The results indicate that the burner and OFA nozzle exhibit distinct flow deviation characteristics within the original air box. Specifically, the burner demonstrates a flow deviation ranging from 2% to 4%, whereas the OFA nozzle exhibits a flow deviation ranging from 10% to 35%. Integrating poly air rings into the burners and OFA nozzles on the sidewall separately addresses the issue of non-uniform flow distribution of the OFA nozzle while concurrently improving the air flow rate on both sides of the burners and OFA nozzles. The main air duct could be divided into three smaller air ducts by installing two deflectors at the corner of the secondary air duct. This scheme effectively decreases the pressure drops at the corner interface from 337.4 to 254.3 Pa. The findings of this study could have the potential to offer scientific insights into and recommendations for the optimal functioning of the boiler system. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Northwest A & F University - Natural Science Edition is the property of Editorial Department of Journal of Northwest A&F University (Natural Science Edition) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the steady increase of air traffic column, an auxiliary decision tool is required to compensate the operation redundancy deficiency of more sectors of air traffic control. To solve the problem of nonconflict high-density departure and arrival traffic flow, this method is expected to rapidly establish and maintain safe separation with more flexible changing strategies for aircraft heading and speed. This paper proposes an improved reinforcement learning framework to achieve conflict detection and resolution. The proposed framework includes the first development of an air traffic flow model based on a multiagent Markov decision process. The goal reward function was then maximized by improved Monte-Carlo tree search combined with an upper confidence bound tree. Three simulation scenarios were designed for illustrating the improvements of the proposed algorithm, with the results indicating that the algorithm could establish and maintain safe separation between 20 agents in the simplified hexagon-shaped airspace of Huadong, China. Furthermore, the proposed method was demonstrated to reduce the number of conflicts between aircraft agents by up to 26.32% compared to previous research. [ABSTRACT FROM AUTHOR]

Rainstorms always occur in the southeast and northeast quadrants of the Northeast China Cold Vortex (NCCV), resulting in significant flooding. This study investigated water vapor and trigger mechanisms for rainstorms within these two regions of an NCCV event during 11–14 June 2022 in terms of Lagrangian backward tracking, stratification stability, and upward motion using the ERA5 reanalysis. In the mid-troposphere, a quasi-stationary "ridge-NCCV-ridge" pattern resided over northeastern China, with an "anticyclonic-cyclonic-anticyclonic" airflow in the lower troposphere. As a result, water vapor originated from the Yellow Sea and was transported in an "L" shape toward both two regions. The southeast region was influenced by southwesterly and northwesterly airflows, resulting in the convergence of moist air from the Yangtze River and Lake Baikal and significant vertical shear of positive vorticity advection. This dynamic created deep and pronounced upward currents in the southeast of the NCCV, leading to the development of intensive and extensive rainstorms in situ. In contrast, the northeast region of the NCCV was dominated by southerly airflow. The moist air converged against the lee side of the Great Khingan Mountains and generated shallow, unstable stratification. The upward motion in this area was relatively weaker and thus induced regional rainstorms. [ABSTRACT FROM AUTHOR]

Since the 12th Five-Year Plan, large-scale and long-term haze pollution has become a major bottleneck restricting China ’s high-quality development and ecological civilization construction. Facing the pressures of economic development and environmental governance, innovation, and technological progress is a win-win choice for China to achieve economic growth and improve air quality. Based on patent stock and PM2.5 concentration data of 282 prefecture-level cities from 2004 to 2019, this paper constructed two instrumental variables, namely, administrative protection of intellectual property rights and public innovation environment and analyzed the effects and mechanisms of innovation on haze pollution by the two-stage least square method. The study found that the use of air flow coefficient, temperature inversion days, and rainfall could effectively control the spatial diffusion of haze, and both green innovation and non-green innovation can significantly reduce haze pollution. It was found that, after adding instrumental variables, the invention patent and utility-model patent were the most effective in haze treatment, and the haze control effect of non-green patents exceeded that of green patents. Heterogeneity analysis showed that the haze control effect of the patent stock in the eastern and central cities was relatively strong, and the effect of innovation to curb haze was strengthened after 2012. Furthermore, in cities with abundant human capital and a high degree of marketization, innovation was more conducive to reducing PM2.5. The test on the intermediate mechanism showed that green patents could achieve haze management front-end prevention and end treatment through industrial green transformation and energy efficiency improvement, while non-green patents could play a role through allot efficiency improvement mechanisms. The above conclusions are still valid after a series of robustness tests, such as changing indicators and considering the spatial spillover effect of haze pollution. Based on the empirical results, this paper puts forward the following policy recommendations: local governments should strengthen the intellectual property protection system, promote more investment and incentive policies for green technology innovation, encourage high-quality innovation output at the ecological level, and improve urban air quality. [ABSTRACT FROM AUTHOR]

Copyright of Wool Textile Journal is the property of National Wool Textile Science & Technology Information Center and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A multilayer network approach to model and analyze air traffic networks is proposed. These networks are viewed as complex systems with interactions between airports, airspaces, procedures, and air traffic flows (ATFs). A topology-based airport-airspace network and a flight trajectory network are developed to represent critical physical and operational characteristics. A multilayer traffic flow network and an interrelated traffic congestion propagation network are also formulated to represent the ATF connection and congestion propagation dynamics, respectively. Furthermore, a set of analytical metrics, including those of airport surface (AS), terminal controlled airspace (TCA), and area-controlled airspace (ACA), is introduced and applied to a case study in central and south-eastern China. The empirical results show the existence of a fundamental diagram of the airport, terminal, and intersections of air routes. Moreover, the dynamics and underlying mechanisms of congestion propagation through the AS-TCA-ACA network are revealed and interpreted using the classical susceptible-infectious-removed model in a hierarchical network. Finally, a high propagation probability among adjacent terminals and a high recovery probability are identified at the network system level. This study provides analytical tools for comprehending the complex interactions among air traffic systems and identifies future developments and automation of layered coupled air traffic management systems. [ABSTRACT FROM AUTHOR]

The spring sensible heating (SSH) over the Tibetan Plateau (TP), which can significantly affect the precipitation in China, has experienced three different stages of change, showing significant increasing (1961–1979, Stage I), decreasing (1980–2002, Stage II), and increasing (2003–2014, Stage III) trends. In this study, the impact of these different trends in TP SSH on spring precipitation (SPR) in China and their possible mechanisms are investigated, based on observations and the reanalysis product. In Stage I, the SPR represents a contrasting north-south pattern associated with the increasing TP SSH, showing increasing trends over southern China and decreasing trends over central and northern China. Further, the spatial distribution of SPR trends shows a contrasting east-west pattern in Stage II. That is, persistent weakening TP SSH plays a more crucial role in increasing and decreasing SPR over southwestern and southern China, respectively. However, compared with the significant trend in SPR in Stage III, the regulation of TP SSH on SPR weakens significantly. Dynamically, the increasing TP SSH in Stage I can strengthen the subtropical westerly jet in the upper layer, simultaneously configured with an anomalous cyclone in northeastern China, which deepens the East Asian trough. Thus, anomalous convergence in the upper layer occurs over central and northern China, favoring the downdraft. It then causes more cold and dry air to move southward in the lower troposphere, which then encounters the warm and wet southwest airflows, boosting the updraft over southern China. In Stage II, regression analysis shows that if the TP SSH increases, an anomalous cyclone in the middle and upper troposphere occurs over the western TP, causing the downdraft and less precipitation over southwestern China, while a cyclone in the lower troposphere occurs over the western North Pacific and extends to southern China, promoting the ascending motions and more precipitation in southern China. However, in this stage, TP SSH actually weakens, thus contributing to more precipitation over southwestern China and less precipitation over southern China. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Under the large-scale application of hydrogen energy and the acceleration of utility tunnel construction in China, the hydrogen pipeline would enter the utility tunnel soon. The explosion-prevention strategy is of important to hydrogen transportation in utility tunnel. Thus, a series of comparative studies were carried out in the present study, to explore the high efficiency dilution methods for unexpected hydrogen leak scenarios. (1) Effects of source type and domain extension were further validated based on our previous numerical model. The small-hole model was found to be simple and feasible for pipe release simulation, and has the same high accuracy like the notional nozzle model. The influence of unexpanded domain is acceptable. (2) Investigation of the explosion-prevention strategies was performed based on the finding of the worst leakage case, and hydrogen leaks at the middle of the upwind tunnel with upward leak direction was found to be the worst leakage case for the normal utility tunnel. (3) Compared with the layouts of lateral vents and the single horizontal air distributor, the middle exhaust vent was found to be the optimal airflow controlling strategy. (4) Furtherly, compared to the optimal airflow controlling strategy, closed-inerting was validated to be the most efficient dilution method. In the closed-inerting cases, the peak value of the flammable gas volume which is only ∼40% of the unimproved case appears. After that, the flammable cloud volume decays gradually, while the value increases steadily in the initial unimproved case. No obvious difference was found between the N 2 and CO 2 injection cases. • The hydrogen explosion-prevention strategies in utility tunnel were explored. • The effects of source model and extension domain were clarified. • The worst leakage case of leak location and leak direction was found. • The airflow controlling and closed-inerting methods were studied. [ABSTRACT FROM AUTHOR]

Stable isotopes (18O/16O and 2H/1H) are fingerprints of water molecules and thus can be used to gain insight on water circulation. Especially, the factors controlling the isotopic composition of precipitation should be identified because they act as baseline determinants of the isotopic variations of surface water and groundwater. Here, using the HYSPLIT model, we attribute observed isotope variations to different moisture sources and characterize the isotopic composition of meteoric precipitation in Northwest China. Results show that the westerlies play a dominant role across the region throughout the year, while other moisture sources only affect some parts of the region during a specific season, i.e., Arctic airflow only affects the Altay Mountains as far as the Middle Tianshan Mountains; the East Asia Monsoon only affects the region east of 100° E longitude during the summer; and summer rainfall of local origin may contribute to the precipitation budget of basin areas. Given the different moisture sources across Northwest China, a local meteoric water line (NWMWL) of δ2H = 6.8δ18O − 1.6 is observed. Our findings not only can provide valuable insights into the mechanism of precipitation isotope fractionation in Northwest China but also can contribute to a better understanding of regional climate and hydrological studies. [ABSTRACT FROM AUTHOR]

This study identifies causal links between a high-PM2.5 episode in Korea and air pollutants originating from China during a high-PM2.5 episode that occurred in Korea between February 23 and March 12, 2019. Datasets on ground-based PM2.5 levels in Korea and China, airflows from the back-trajectory models, and satellite images were investigated, and long-range transboundary transport (LRTT) effects were statistically analyzed using spatial panel-data models. The findings are: 1) visual presentations of the observed PM2.5 concentration in China and Korea, back-trajectory air flows, and satellite images from the Moderate Resolution Imaging Spectroradiometer Aerosol Optical Depth and the Copernicus Atmosphere Monitoring Service clearly show that transboundary air pollutants from China affect PM2.5 concentration in Korea; 2) the effect of LRTT from China is likely to intensify under certain meteorological conditions, such as westerly winds from China to Korea, the formation of high pressure in China and low pressure in Korea, relatively high temperature, and stagnant air flow in Korea; 3) the results from the spatial panel-data models provide statistical evidence of the positive effect of LRTT from China on increasing local PM2.5 concentration in Korea. The nationwide average LRTT contributions to PM2.5 concentration in Korea are 38.4%, while regional contributions are 41.3% for the Seoul Metropolitan Area, 38.6% for the northwest region, and 27.5% for the southeast regions in Korea, indicating the greatest impact on the Seoul Metropolitan Area. [ABSTRACT FROM AUTHOR]

Grid-based sand-fixing protection barriers have been widely used to solve linear engineering problems in sandy areas. Their placement directly affects the combined change law of wind speed weakening and sand sediment in the sand barrier. It also affects the cost of sand control and the selected structure of the protection system. Therefore, quantifying the effect of different sand barriers is important. We installed nylon mesh checkerboard sand-fixing barriers of three heights and three sizes on the windward side of the highway in the Ulanbuhe Desert, China. By using anemometer and sand collecting instrument, through comparing and observing air flow changes, windproof efficiency, and sand sediment inside the sand barrier, it is found that height had more influence on the protective benefit of a sand barrier than did the mesh specification. The protective effect at the boundary of a sand barrier resulted from compound superposition. The model for calculating a suitable sand barrier protection width was affected by sand-driving wind speed, open field wind speed, sand barrier unit side length, height, and actual protection demand. Sand barriers of 1 × 1 m (It is the grid size of the mesh.) at 20-cm height, 1 × 1 m and 1.5 × 1.5-m at 30-cm height could be laid over a wide area. Different collocation patterns can be selected according to the dominant wind direction. The results can provide basic data and theoretical support for sand barrier protection system. [ABSTRACT FROM AUTHOR]

The air traffic control (ATC) network's airspace sector is a crucial component of air traffic management. The increasing demand for air transportation services has made limited airspace a significant challenge to sustainable and efficient air transport operations. To address the issue of traffic congestion and flight delays, improving the operational efficiency of ATC has been identified as a key strategy. A clear understanding of the characteristics of airspace sectors, which are the building blocks of ATC, is essential for optimizing air traffic management. In this research, a novel approach using complex network theory was applied to examine the features and invulnerability of the airspace sector network. We developed a model of the airspace sector network by treating air traffic control sectors as network nodes and the flow of air traffic between these sectors as edges. Network characteristics were analyzed using several metrics including degree, intensity, average path length, betweenness centrality, and clustering coefficient. The static invulnerability of the airspace sector network was evaluated through simulation, and the network efficiency and the size of the connected component were used to assess its invulnerability. A study was conducted in North China based on the ATC sector network. The findings of the study revealed that the sector network did not exhibit the traits of a small-world network model, characterized by short average path lengths and high clustering coefficients. The evaluation of network invulnerability showed that the network's invulnerability varied depending on the attack strategy used. It was discovered that attacking sectors with high betweenness resulted in the most significant harm to network invulnerability, and betweenness centrality was considered to be a useful indicator for identifying critical sectors that require optimization. [ABSTRACT FROM AUTHOR]

Through a field experiment on a sandy beach at Pingtan, China, we propose the first model to characterize the variability of apparent von Kármán parameter κa ${\kappa }_{a}$ in the thermally and sedimentologically stratified air flows. The model shows that κa ${\kappa }_{a}$ is negatively correlated to flux Richardson number as well as sediment transport rate. The atmospheric stability can be either from thermal stratification or sedimentological stratification, neglecting either of them can lead to substantial errors in predicting shear velocity and sediment transport rate. Plain Language Summary: In natural conditions, atmospheric boundary layer flows are often non‐neutral due to thermal stratification. However, recent studies indicate sedimentological stratification may also have a similar effect while almost no research was conducted to examine their combined effect on the flows. We present the first model to characterize the apparent von Kármán parameter κa ${\kappa }_{a}$, a parameter representing the scale of flow eddy size, as a function of thermal and sedimentological stabilities. This work provides a feasible means to correct the potentially substantial errors when estimating shear velocity and predicting sediment transport rate for sedimentologically and thermally stratified air flows. Key Points: Apparent von Kármán parameter for thermally and sedimentologically stratified air flows was obtainedApparent von Kármán parameter has a negative, linear relationship with flux Richardson number and sediment transport rateNeglecting thermal and sedimentological stratifications can lead to substantial errors in shear velocity and transport rate estimations [ABSTRACT FROM AUTHOR]

At present, China's high-speed rail is in a period of rapid development. Most of the refrigerants used in Chinese motor train units at this stage are still R134a and R407c, which have an impact on the environment. In response to the environmental protection concept of green travel, it is of great significance to study the air conditioning system of motor train units using CO2 refrigerant. Using CFD simulation analysis technology, the heat transfer performance of the air side of the CO2 finned tube evaporator used in the air conditioning system of the motor train unit is studied. We select the air outlet temperature, pressure drop, heat transfer factor, and resistance factor as the objective function, in addition, monitoring points are set up in the air flow channel to monitor the turbulent flow field and pipe wall pressure. Our research shows that the cooling capacity of the CO2 evaporator can reach up to 29.76 kW, which can meet the heat exchange required in the air conditioning system of the motor train unit. In order to obtain a better structure and the conditions of the heat transfer effect, structural optimization was conducted. The simulation results demonstrate several trends: (i) With the augment of the air inlet velocity, the cooling capacity of the evaporator increases and the heat exchange effect improves; when the air inlet ve > 2.2 m/s, the effect of continuing to augment ve on heat exchange is weak. (ii) Following appropriate reduction of the diameter of the heat exchange tube, the wind resistance is reduced and the cooling capacity of the evaporator is improved. (iii) With the enlargement of the fin spacing, the turbulent motion in the flow channel can be fully developed, there is a peak in the change in the heat exchange tube area optimization factor, and the optimal fin spacing is between 1.6 mm and 1.7 mm; at this time, the average turbulent kinetic energy of the air side is larger and the turbulent dissipation rate is smaller. These results provide a reference for the practical application of CO2 refrigerant in the motor train unit. [ABSTRACT FROM AUTHOR]

The wind environment in residential areas can exert a direct or indirect influence on the spread of epidemics, with some scholars paying particular attention to the epidemic prevention and control of residential areas from the perspective of wind environments. As a result, it is urgent to re-examine the epidemic prevention response of residential spaces. Taking high-rise residential areas in Xi'an as an example, the article defines the air flow field area based on on-site wind environment measurements, crowd behavior annotation, and CFD simulation. Using the double-effect superposition of crowd behavior and risk space, the paper undertook a multiple identification strategy of epidemic prevention space. The identification methods and management and control strategies of epidemic prevention in high-rise residential areas are proposed. Additionally, the living environment of residential areas is optimized, and a healthy residential space is created. The transformation from concept and calls for action to space implementation is made to provide a reference for improving the space management and control capabilities in high-rise residential areas in China. The results of this study can be used as a guideline for future residential planning and design from the perspective of preventing airborne diseases. [ABSTRACT FROM AUTHOR]

The characteristics and causes of a drop in temperature during a cold wave process in the early winter of 2020/2021 were analyzed. The results show that the air temperature at 700 -600 hPa over China was firstly and mostly influenced by the cold wave process, and then the cold air gradually extended to the lower layer, causing the most severe cooling in North China and its nearby areas. During the cold wave, the longitude of the upper-level jet over the Chinese mainland was larger; the Ural blocking high and the East Asian trough were stronger, so that the geopotential height gradient between the two was also significantly larger; the meridional air flow was abnormally strong, which was conducive to the southward transport of cold air from the middle and high latitudes. Results of the diagnostic analysis further show that the outbreak of the cold wave and the negative temperature tendency anomaly in the key area were mainly caused by the meridional temperature horizontal advection anomaly, while the temperature rise accompanied by abnormal air subsidence compensated for the abnormal decrease in temperature, which was conducive to the gradual rise of temperature in the key area. [ABSTRACT FROM AUTHOR]

Background and objective: The major contributing risk factors to airflow obstruction (AO) in China remain largely unknown. We examined the environmental and lifestyle risk factors of unrecognized AO in the baseline of a population‐based cohort drawn from 115 urban and rural communities across 12 provinces in China. Methods: Amongst 46,285 adults recruited from 2005 to 2009, 3686 were identified with AO on spirometry (defined by the ratio of forced expiratory volume in the first second to forced vital capacity <0.7) and without known chronic lung disease. These cases were age‐ and sex‐matched to 11,129 controls with normal spirometry and no chronic lung disease from the same community. Conditional multivariable adjusted OR and population attributable fraction (PAF) were calculated for each identified risk factor and their combined effect. Results: Compared to controls, smoking initiation age <20 years (OR 1.22 [95% CI 1.01–1.48]), smoking duration ≥40 years (OR 1.82 [1.50–2.22]), low vegetables (OR 1.86 [1.67–2.07]) and fruits (OR 1.14 [1.02–1.29]) intake, cooking with biomass fuels (OR 2.54 [2.32–2.78]) and poor kitchen ventilation (OR 1.37 [1.19–1.58]) were significantly associated with elevated risks of unrecognized AO. The combined effect of these lifestyle factors significantly elevated the odds by 25 fold (18.6–34.3). The addition of prior tuberculosis and low socioeconomic status further increased the odds to 40.1 (28.2–57.0) and the PAF to 66.7% (51.1–78.1). Conclusion: Smoking, unhealthy diet, biomass cooking fuels and low socioeconomic status are strongly associated with AO. Addressing these risk factors could substantially reduce the burden of AO in China. [ABSTRACT FROM AUTHOR]

In order to find potential low-frequency signals and provide new ideas for extended-range forecasting, the intraseasonal oscillation (ISO) characteristics of persistent high temperature events (PHTEs) in the extended summer in Jiangnan area are explored by using daily maximum air temperature (Tmax) data from the China Meteorological Data Network and daily reanalysis data provided by NCEP/DOE. The results show that the low-frequency PHTEs can be classified into three types according to the position variation of the Western Pacific subtropical high (WPSH). For the first two types of PHTEs, a southwestward migrating mid-latitude wave train from the North American coast to the central and eastern China can be clearly seen in the whole troposphere. Whereas the two types of PHTEs show different features in the low-latitude. It is found that a significantly westward extension of the WPSH during the first type of PHTEs, with the low-frequency anticyclone moving westward in the mid-lower troposphere. For the second type of PHTEs, the WPSH is mainly located in the southeastern China with slightly movement. Analysis of the low-frequency vertical circulation and the thermodynamic equation further reveal that the increase of temperature in Jiangnan region is primarily attributed to the descending airflow. [ABSTRACT FROM AUTHOR]

Wet flue gas desulfurization systems (WFGD) are the most popular method to remove the SO 2 from the flue gas in China's power plants. Most WFGD systems contain an oxidation subsystem, which is one of the most important subsystems. In this paper, a hybrid modeling and operating optimization method of oxidation process of WFGD system is proposed, verified and applied on the WFGD system of a typical 1000 MW unit. The influence of important parameters such as the diameter of droplets or bubbles, the liquid-gas ratio or the gas-gas ratio (the ratio of between oxidized air flow rate and flue gas flow rate) and the height of the natural oxidation zone or the slurry level on natural oxidation rate and forced oxidation rate are further explored. The application results show that the above method can significantly reduce the operating energy consumption of the oxidation fan by more than 25 %. Furthermore, field tests are also carried out on the WFGD systems of 130 t/h and 220 t/h circulating fluidized bed (CFB) units. The energy consumption can be reduced by 30.6 % and 37.5 %, respectively. The results will be helpful to reduce the auxiliary power consumption and additional CO 2 emission of WFGD. [Display omitted] • Hybrid modeling method for oxidation process of WFGD system. • Influence of important parameters on natural oxidation rate and forced oxidation rate. • Operating optimization strategy of oxidation process with or without VFD. • Application on typical 1000 MW unit and two circulating fluidized bed (CFB) units. [ABSTRACT FROM AUTHOR]

Air-assisted sprayers are the mainstream orchard plant protection machinery in China. During the usage of sprayers, the pesticide droplets carried by strong air jets from sprayers enter into the target canopy. Therefore, the distribution of airflow field in the canopy has significant influence on the spatial movement of the droplets and the adhesion and penetration of the droplets inside the canopy. To enhance the working performance of sprayers, it is imperative to study their use in tree canopies. Based on computational fluid dynamics (CFD), the k-ε turbulence model, and the SIMPLE algorithm, a 3D simulated model of the spatial distribution of the airflow field in and around the tree canopy was established based on the porous model in this paper. The model was used to simulate and calculate the air field distribution of an air-assisted orchard sprayer under different operating parameters. The results showed that the optimal operation effect was achieved when the driving speed and the air speed of the fan outlet were 1 m/s and 20 m/s, respectively, while the air speed in the canopy was not less than 2 m/s. The 36 points measured in the canopy were compared with the simulated results through field experiments. It showed that average relative error between the measured and simulated values was 13.85%, and the overall goodness-of-fit was 0.97656. The model accurately simulated the airflow distribution in the canopy and provided a basis for optimizing the operating parameters of the air-assisted sprayers in orchards. [ABSTRACT FROM AUTHOR]

The built-in refrigerator has been popular in China in recent years due to users' high requirements for the integration of home appliances and furnishings. However, the built-in configuration will cause a significant performance deterioration, which has been less quantitively studied. The condenser and its refrigerator performance are compared experimentally and numerically between built-in and free-standing configurations. By contrast with the free-standing condition, the built-in condenser has poor performance attributed to two reasons: 28.6% lower condenser air flowrate and 10.72 °C higher condenser inlet air temperature caused by the hot short-circuited airflow. This heat dissipation deterioration increases the condensing temperature and discharge temperature, resulting in a refrigerator cooling capacity loss. Correspondingly, the compressor increases the rotating speed and power to compensate for the loss. The compressor ON-time ratio reduces by 8% but the average power during the compressor-on period increases by 56.9%, finally increasing the energy consumption by 43.4%. This study also provides some guidance for further heat dissipation and airflow field optimization of built-in refrigerators. [ABSTRACT FROM AUTHOR]

The existing knowledge illustrated the role of surrounding mountains in the transportation of dust into a basin, including the blocking of low-layer dust and the allowance of elevated dust intrusion. Taking the Sichuan Basin in southwestern China as an example, we found the impact of clouds on the transportation process of dust in the basin area. If there were low-level clouds on the basin edges, the dust particles could not penetrate the cloud layers, but settled down from upper air into the basin in the cloudless regions. They could be transported beneath clouds in the basin. Considering that the upslope airflow accompanied by dust transportation was conducive to the low-level clouds on the basin edge, this mechanism further reduced the dust intrusion besides the shelter of the surrounding mountains. [ABSTRACT FROM AUTHOR]

On the basis of the Prandtl boundary layer theory and an improved perturbation method, the process of laminar flow bifurcating into the Southwest China vortex (SWV) in the Hengduan Mountains is studied. The results show that the formation of SWV is mainly determined by the speed of incoming airflow in the direction of the main axis of the Hengduan Mountains. The vortex is generated in the leeward area of the Hengduan Mountains when the speed of incoming airflow is greater than the critical velocity. Moreover, it means that the laminar flow bifurcates into a vortex. The formation position of the SWV is mainly determined by the relative position of the incoming airflow in the windward area of the Hengduan Mountains and the main axis of the Hengduan Mountains. The seasonal distribution of SWVs is determined by both the velocity of the incoming airflow and the relative position of the incoming airflow to the main axis of the Hengduan Mountains. These findings are consistent with the SWV observation facts, which not only adequately explain the physical formation mechanisms and processes of SWVs, but also present the formation location and seasonal distribution of SWVs. Meanwhile, a solution from laminar to vortex in circumflow motion is also presented. [ABSTRACT FROM AUTHOR]

The study of particle nucleation and growth within clouds forms the fundamental microphysical component of cloud precipitation physics. Thus, we can establish cloud and fog precipitation development theories, providing a foundation for understanding weather, climate, and environmental changes. This case study, we observed ice cloud particles and meteorological elements using aircraft instruments over the North China Plain region on February 18, 2019. Focusing on aerosol–cloud interactions, we categorized clouds using altitude, vertical airflow, and cloud droplet concentration. The average number concentrations of cloud droplets (Nc), ice (Ni), and aerosols (Na) were 1.06 cm−3, 5.30 L−1, and 1.63 × 10 3 cm−3, respectively. The ice water content (IWC) in clouds was two orders of magnitude higher than the liquid water content (LWC). The differences in Nc at different heights were primarily caused by the presence of small droplets (smaller than 15 μm). Droplet concentrations were higher at 1–2 km and at the top of the clouds (5–6 km). Ice formation and growth was nonuniform in all zones, concentrated in the smallest and largest particle size ranges, with peaks at 125 and 1500 μm. Updraft significantly impacted cloud droplets, promoting their development and growth through water vapor condensation. Vertical airflow exerted a minor impact on aerosols. The Wegener–Bergeron–Findeisen process, driven by ice supersaturation and cloud liquid water subsaturation, led to a decrease in cloud droplet concentration and an increase in ice crystal concentration within the updraft region. In regions with different cloud droplet enrichment levels, the distribution of particles varied within the clouds. Zone with no vertical movement exhibited higher Nc than zone with downdraft airflow. The dense cloud droplet zone with downdraft airflow indicated narrower spectrum. Nc ranged from 2.5 to 19 μm, Ni ranged from 125 to 1350 μm, and Na ranged from 0.1 to 1 μm (no particles between 0.4 and 1 μm were observed). Ice formation and growth varied in each zone, possibly due to ice fragmentation. [Display omitted] • The sizes of ice cloud particles are predominantly found at 125 and 1500 μm. • Cloud drops in the updraft region were prone to form ice through the WBF process. • Formation and growth of ice were non-uniform due to ice fragmentation. • The dense cloud droplets zone with downdraft airflow had a narrower spectrum. [ABSTRACT FROM AUTHOR]

Aiming at the current problem of the high rate of impurity and loss in the cleaning device of corn seed harvesters in China, this paper took the cleaning device of 4YZL-6 self-propelled corn seed harvester as a sample and analyzed the movement law of the material on the sieve. Box-Behnken response surface experimental design theory was used for the orthogonal tests. Wind inlet angle, airflow velocity, and crank angular velocity were selected as influencing factors, and the impurity rate and loss rate as the evaluation index of operation quality. A regression mathematical model between each influencing factor and indicator was established, and the model was also integrated and optimized. The optimal parameter combination was obtained as follows: the wind inlet angle was 37.95o, the airflow velocity was 11.3 m/s, and the crank angular velocity was 4.1 r/s. The corresponding impurity rate was 0.87% and the loss rate was 0.34%. Verification tests were conducted on the optimization results, and the test results showed that under the optimal combination of parameters, the impurity rate was 0.89% and the loss rate was 0.35%. The relative errors of each evaluation index and its model prediction were 2.29% and 2.94%, respectively. [ABSTRACT FROM AUTHOR]

Extreme torrential rainfall events are low‐probability events. A "China‐Record Extremely Heavy Rainfall" (CREHR) event with rain rate of 201.9 mm/hr occurred on 20 July in Zhengzhou in North China. Using high‐density meteorological observations, ERA5 reanalysis data, remote sensing data from China's FY‐4A satellite, and numerical simulation, we revealed that sufficient warm–humid airflows were continuously transported to the Zhengzhou area via multiple pathways that were mainly modulated by the large‐scale western Pacific subtropical high to the north along with the anomalies of the westerly belt and a meso‐scale binary typhoon system. At the local scale, under the combined action of the vertical circulation that caused low‐level convergence and high‐level divergence, and the rapid uplift of water vapor related to the blocking by mountainous terrain, this CREHR event was eventually triggered. Particularly, our present work shows the roles of both typhoon Cempaka and meso‐scale convective systems to south of Henan province can not be ignored, producing a strong super‐thick water vapor transport layer. The existence of the binary typhoon raises the level of uncertainty involved in the water vapor transport of this CREHR event. Plain Language Summary: Extreme torrential rainfall events are low‐probability events. The rainfall from 16:00 to 17:00 Beijing time on 20 July in Zhengzhou in North China reached 201.9 mm, which was a record in mainland China—a so‐called "China‐Record Extremely Heavy Rainfall" (CREHR) event. By using high‐density meteorological observations, ERA5 reanalysis data, remote sensing data from China's FY‐4A satellite, and numerical simulation, we found that sufficient warm–humid airflows were continuously transported to the Zhengzhou area via multiple pathways that were mainly modulated by the large‐scale western Pacific subtropical high to the north along with the anomalies of the westerly belt and a meso‐scale binary typhoon system. At the local scale, under the combined action of the vertical circulation that caused low‐level convergence and high‐level divergence, and the rapid uplift of water vapor related to the blocking by mountainous terrain, this CREHR event was eventually triggered over northern mainland China. Our findings reveal that the existence of the binary typhoon circulation raises the level of uncertainty involved in the water vapor transport of this CREHR event, which has implications for improving our ability to predict and provide early warnings for severe rainstorms and related disasters in cities with such a complex context. Key Points: Sufficient warm‐humid airflows were continuously transported to the Zhengzhou area via multiple water vapor pathwaysMultiple pathways were mainly modulated by the large‐scale western Pacific subtropical high, the westerly belt and mesoscale binary typhoonsNorthward movement of multiple meso‐scale convective systems caused a strong super‐thick water vapor transport layer [ABSTRACT FROM AUTHOR]

Rice fertilizer application is often disturbed by the moisture or mud and water in the field, particularly, in the rainy and humid southern region of China. The complicated working environment can result in fertilizer clogging or leakage in the fertilizer application machinery. The photoelectric and capacitive sensors are often developed to monitor the fertilizer application blockage at present. However, the traditional sensors are susceptible to fertilizer dust during operation, resulting in reduced sensitivity and even monitoring failure, which cannot meet the actual production needs. In this study, an airflow anti-clogging and monitoring system was proposed for fertilizer application in the rice direct seeding machine. The agronomic requirements were combined with the fertilizer application in the direct seeding of southern rice. The smoothness of the fertilizer application pipeline was effectively improved to prevent fertilizer clogging. Once the fertilizer clogging occurred, the alarm alerts were run in the system simultaneously. Firstly, the working principle of the fertilizer application system was determined to design the key components, such as the airflow diversion duct and the airflow change feedback device. At the same time, the structural parameters were optimized for the key components of devices. A parameter calibration test was carried out to determine the air pressure value (P1) of less than 1 000 Pa at the inlet of the airflow diversion duct. Secondly, a coupled simulation was carried out using Fluent and Rocky software. An experiment was then conducted to calculate the motion state of fertilizer particles with or without applied airflow in the airflow diversion duct of the key component. The test results showed that the velocity of fertilizer granules increased significantly under the action of airflow. The kinetic energy of the fertilizer granules increased by about 39.7%, compared with no airflow. It infers that the airflow effectively improved the smoothness of the fertilizer application pipeline. Finally, the prototype test was performed on the blockage monitoring and alarm performance of the device. The air pressure pre-test demonstrated that the air pressure of the air inlet should be taken as 600-800 Pa in the static test of the prototype. A combination of inlet air pressure, pipe inner diameter, and device fertilization rate was then tested to determine the optimal operating parameters of the device. The test protocol was designed by the Box-Behnken response surface method. After that, the regression model and the variation of the response surface were used to determine the inner diameter of the airflow diversion pipe of 28 mm, the air pressure value of 700 Pa at the air inlet, and the fertilizer application rate of 20 g/s, as the better working parameters of the device. The optimal combination of parameters was selected for the test in the field trials. Consequently, the accuracy of alarm monitoring was above 90.0%, and the highest accuracy was 96.7%. The better performance of the device was achieved in the stability, which fully met the requirement of clogging monitoring accuracy of the rice fertilizer device. The finding can provide an important reference for fertilizer application in the anti-blocking and blockage monitoring for rice production. [ABSTRACT FROM AUTHOR]

The Huaihe River basin (HRB) is an important economically developed and grain production region in China, which is severely affected by rainfall anomalies, especially extreme rainfall events (EREs). It is crucial to the features of interdecadal change in EREs and the contribution of EREs to summer-mean total rainfall amount (TRA) over the HRB. Using the observational 24-h ac-cumulated rainfall and the reanalysis products from the European Center for Medium-Range Weather Forecast (ECMWF), as well as the methods of composite analysis and Mann–Kendal and running t tests, we revealed that the EREs experienced a significant interdecadal increase from the period 1990–1999 to the period 2000–2009. The EREs, particularly long persistent extreme rainfall events (LPEREs), occurred more frequently over the HRB during the latter period and dominated the interdecadal increase in the summer mean TRA. An anomalous high-pressure ridge and associated anomalous anticyclone appeared around Lake Baikal during the latter period, which led to anomalous northeasterlies along the eastern flank of the anomalous anticyclone, inducing the southward intrusion of cold air flow from higher latitudes and associated anomalous ascent and more active convection over the HRB. As such, more EREs and LPEREs occurred during the latter period. The higher pseudo-equivalent temperatures also support more active convective ascent and relevant more EREs. The results may shed light on further understanding the effect of large-scale atmospheric circulation on the interdecadal variability of EREs over the HRB, helping mitigate the disastrous impacts of EREs on local ecosystems, agriculture, soil erosion, and societies. [ABSTRACT FROM AUTHOR]

The highest concentration of PM2.5 in cold rural dwellings of Northeast China is often generated by using mini stoves for cooking and heating, which can directly influence human health. As of yet, little is known about the impact of different daily life behavior on PM2.5 diffusion and residents' exposure in rural dwellings. In this study, the characteristics of indoor PM2.5 variation and diffusion in rural dwellings was described by measuring some rural dwellings and establishing a multi-zone network model. The calculated results indicated that the relative errors between theoretical calculated results and experimental measured results are within 10%. PM2.5 diffusion in a rural dwelling can be predicted. Furthermore, the impacts of daily life behavior on PM2.5 diffusion and exposure assessment can be analyzed. Through discussion, heating behavior is the most important factor causing high concentrations of PM2.5 in each room, followed by cooking, smoking, and cleaning. Door opening time can lead to different interzonal airflows and PM2.5 diffusion rates. By reducing the inner door opening time to less than 1 min, PM2.5 could decrease to 300 μg/m3. Door closing behavior could decrease risk that PM2.5 diffuses to bedrooms by more than 50%, and exposure of residents in bedrooms could reduce to 100 (μg·h)/m3 effectively. [ABSTRACT FROM AUTHOR]

With the increase in orchard areas and the transfer of rural labor, various air-assisted sprayers have been widely used in China. However, the problem of off-target drift still exists, which has caused pesticide waste and environmental pollution. In order to improve the droplet deposition in the canopy of fruit trees, a V-shaped anti-drift spray device with multi-airflow synergy was designed in this paper. A droplet spatial motion model was constructed, and the anti-drift mechanism of multi-airflow synergy was clarified based on particle dynamics analysis. The influences of spray pressure and V-shaped wind speed on droplet movement were investigated by Matlab, and the experimental results showed that the machine's anti-drift effect was better when the V-shaped wind speed ranged from 15 m/s to 25 m/s. According to modern orchards with low root stock in a high-density planting, a simulation model of the flow field between the spray device and the fruit trees canopy was established by the method of computational fluid mechanics (CFD). By considering crosswind speed, V-shaped wind speed, and spray pressure, three-level simulation experiments of droplet deposition were designed for each factor using a partial multivariate orthogonal regression method. The influence of V-shaped wind speed on the droplets' spatial distribution was analyzed, and the prediction model of the drift distance of the droplets' deposition center was established. The simulation results showed that the three factors had a significant influence on the droplets' deposition characteristics, and the degree from big to small was V-shaped wind speed, crosswind speed, and spray pressure. The fitting degree of the prediction model was high, and the correlation coefficient was 0.998. The anti-drift experiments of the machine were carried out, and the results showed that when the crosswind speed, the spray pressure, and V-shaped wind speed were 2.2 m/s, 0.52 MPa, and 20.8 m/s, respectively, the droplet drift rate was 29.2% lower than that of single-airflow. The drift distance of the droplets deposition center was 5.0 cm, which was consistent with the prediction model. The research can provide a basis for the design and parameters optimization of the similar sprayers used in modern orchards with low root stock in a high-density planting. [ABSTRACT FROM AUTHOR]

Large-scale open burning of straw residues causes seasonal and severe atmospheric pollution in Northeast China. Previous studies focused on the causes or assessment of atmospheric pollution in a single city. However, studies conducted on the interaction range, degree and policy control of pollutant transport on a large scale are still to be performed. In this study, we propose combined control of straw burning by dividing region the straw burning in Northeast China in recent 20 years, determining the transport routes between main cities, and analyzing the interaction characteristics of straw burning under different scenarios. The fire point data suggest that the most intense straw burning years in Northeast China in the past 20 years occurred in the range from 2014 to 2017, mainly after the autumn harvest (October–November) and before spring cultivation (March–April). The burning areas were concentrated in the belt of Shenyang-Changchun-Harbin, the border of the three provinces and Eastern-Inner Mongolia, and the surrounding area of Hegang and Jiamusi City. The lower number of fire points before 2013 indicates that high-intensity burning has not always been the case, while the sharp decline after 2018 is mainly due to scientific control of straw burning and increased comprehensive utilization of straw. Compared with S2, the PM2.5 concentrations increased by 6.2% in S3 and 18.7% in S4, indicating that burning in three or four provinces at the same time will significantly increase air pollution and exert a regional transmission effect. Straw burning in Northeast China is divided into six main regions based on correlation analysis and satellite fire monitoring. Under typical S3, the case analysis results indicate that there is regional transmission interaction between different cities and provinces, focusing on multi-province border cities, and it is affected by Northwest long airflow, and Southeast and Northeast short airflow. These results provide scientific and technological support for implementing the joint prevention and control plan for straw incineration in Northeast China. [ABSTRACT FROM AUTHOR]

The extreme rainfall from 19 to 21 July 2021, which caused massive flooding and loss of life, is the second heaviest rainfall that has occurred in Henan province, central China. To identify the key factors controlling this rainfall event, we conducted an ensemble‐based analysis using ECMWF operational global ensemble forecasts. The forecasts of extreme rainfall had a relatively large spread and there was a large bias in the ensemble mean precipitation, indicating uncertainties in the forecast. The extreme rainfall was closely related to the Huang‐Huai cyclone and the southerly and southeasterly flows. Although they had little influence on the southeasterly flow, the uncertainty and predictability of typhoons In‐fa and Cempaka probably caused the variation in the southerly flow and the maintenance of the Huang‐Huai cyclone, which determined the amount of precipitation for this extreme event in the ensemble forecast model. When typhoon In‐fa was located further northwest, the northeasterly airflow generated by the binary interaction between typhoons In‐fa and Cempaka weakened the intensity of the southerly flow, reduced the transport of water vapor to the rainstorm area and weakened the Huang‐Huai cyclone, thus reducing precipitation in the control area. The results of this study indicate that ensemble‐based analysis can improve our understanding and forecasting of extreme precipitation events under the influence of multiple remote tropical cyclones. Plain Language Summary: Extreme rainfall events are expected to become more intense and frequent in the future under a warming climate, but forecasting such events is challenging. Extreme precipitation events in China are often influenced by distant typhoons. The basic idea is that a typhoon air flow can increase the transport of water vapor and interact with remote weather systems, triggering more intense rainfall. When multiple typhoons are present, forecasting extreme precipitation is further complicated because it is difficult to simulate multiple typhoons in global models. The second heaviest extreme rainfall event ever recorded in the province occurred in Henan, central China from 19 to 21 July 2021. We analyzed the response of this event to the evolution of typhoons In‐fa and Cempaka using operational global ensemble forecasts. The relative location between the binary typhoons affected the key weather systems of the extreme rainfall event, suggesting that the binary interaction between typhoons In‐fa and Cempaka may be a crucial factor in this event. This study suggests that ensemble‐based analysis, which can be automated and updated in real time, could be a useful tool for the analysis of the distant effects of multiple typhoons. Key Points: The Henan extreme rainfall from July 19 to 21, 2021 was closely related to the Huang‐Huai cyclone and southerly and southeasterly flowsThis extreme rainfall event may not be a typical tropical cyclone remote precipitation eventThe interaction of typhoons In‐fa and Cempaka may affect the uncertainty in the southerly flow and maintenance of the Huang‐Huai cyclone [ABSTRACT FROM AUTHOR]

Extreme short-term hourly rainfall accumulations are shown to be commonly attendant with rotation-featured mesovortices. This study aims to document the detailed aspects of mesovortex-related extreme rain rates in a record-breaking event that occurred over South China on 7 May 2017 through high-resolution observations, and to reveal how the mesoscale storm contributes to the extreme rain rates, with special attention given to the minute rain-rate enhancement episode (MREE). The event accumulation possesses highly local distribution, with a spatial rainfall core. Extreme rain rates are dictated by a meso-γ-scale storm, and it is found that the observed rain rate is well correlated to storm-related maximum reflectivity in the lowest 2 km above ground level (AGL) as well as its reflectivity centroid (i.e., reflectivity factor exceeding 50 dBZ) depth. The cross section reveals that the storm structure evolves progressively into a single centroid, which subsequently descends to the near surface, resulting in the rain-rate peak (4.8 mm min−1). Extremely weak environmental mean flow interacts with the near-opposite storm propagation that determines the slow storm movement, prolonging local rainfall. Rainfall-induced cold outflow surges ahead unevenly, leading to an inhomogeneous mesoscale outflow boundary (IMOB) at low levels. A mesovortex subsequently develops along the IMOB in the lowest ∼5.5 km AGL, with a horizontal radius of 1.5–3 km. A mesoscale low-level jet observed over the upstream of the storm increases the low-level shear despite short duration, which provide potential dynamics for the storm and mesovortex development. These results help us better understand the generation of extreme rain rates in small spatiotemporal scale. Significance Statement: Despite many extreme short-duration rainfall events linking to low-level rotation phenomenon, we are still exploring how these rotations develop within extreme-rainfall-producing storms. While past studies have found that these low-level rotations within such storms are conducive to enhancing rainfall, rotation characteristics are less understood. In this study, we examine how the rotations develop during an episode of observed-rainfall rise. The results reveal that the cold airflows resulted from the storm-inducing rainfall impinge unevenly on warm moist southerly wind, leading to such low-level rotation. The rainfall observed per minute is found to associate well with low-level rotation that develops upward. These results further motivate exploration of extreme short-duration rainfall and storm-related rotation. [ABSTRACT FROM AUTHOR]

Among food crops, rice has the largest planting area, the highest yield per unit area and the largest total yield in China. However, cleaning performance is reduced by the high moisture content of rice during the harvesting process. In order to decrease the adhesion among wet rice threshed mixtures and improve the cleaning performance, the method of hot airflow cleaning was proposed. Firstly, the fluidization characteristics of wet sticky rice under the action of hot air were compared with those of dry particles. In this work, the minimum suspension velocity and the fastest suspension time were used and quantified to characterize the fluidization characteristics. It was found that the minimum suspension velocity and the fastest suspension time of the wet rice threshed mixture are both higher than those of dry particles due to the liquid bridge force. Moreover, the dispersion degree of the wet rice threshed mixture can be improved by the hot airflow due to the decrease in the surface water content of impurities. Secondly, the influence of the temperature and vibration frequency in the air-and-screen cleaning device on the dispersion characteristics of the wet rice threshed mixture were investigated. The accumulation mass was measured to quantify the dispersion degree. It was found that the increase in vibration frequency has little effect on the dispersion of the wet rice threshed mixture. The accumulation mass on the front of the sieve decreases slightly with the increase in the gas temperature range from ambient temperature to 30 °C. Then, the dispersion degree increases rapidly when the temperature exceeds 40 °C. The dispersion effect is the best when the temperature is 50 °C and the vibration frequency is 5 Hz. These results provide a basis for the cleaning of the wet rice threshed mixture in a combine harvester. [ABSTRACT FROM AUTHOR]

Extremely persistent heavy rainfall (EPHR) events frequently occur in southern China. The mechanisms underlying their generation and development are not well understood, and this leads to difficulties in accurately forecasting these events. In this paper, hourly precipitation grid data and ERA‐5 reanalysis data are used to examine the relationships between precipitation, ageostrophic winds, and low‐level jets (LLJ). The results suggest that ageostrophic winds in the boundary layer mainly exhibit confrontational and asymptotic convergence, with the former being accompanied by double LLJ, which transport more vapor and provide favorable uplift conditions, thus producing stronger precipitation and wider rainbands. The different cooperated relationships between LLJ and ageostrophic winds play an important role in the development of EPHR events, and greater account needs to be taken of these relationships when forecasting. Plain Language Summary: Coastal extremely persistent heavy rainfall (EPHR), long‐duration heavy rainfall in local coastal area, occurs frequently in Southern China, and this kind of rainfall is usually accompanied by southwesterly in the lower atmosphere, which we call as the southwest low‐level jet. Generally, the occurrence and development of rainfall is accompanied by the convergence of the lower air flow. Since the divergence of the geostrophic wind component of the wind field is zero, the convergence situation is characterized by the ageostrophic wind component, which doesn't satisfy the geostrophic balance. In this type of coastal EPHR accompanied by the Southwest Jet, the ageostrophic wind is mainly manifested in two different convergence situations. One is that the ageostrophic wind presents several opposite branches of directions presenting a confrontational pattern around the rainfall area, and the other is an asymptotic convergence in which two similar wind directions, such as northeasterly and southeasterly, gradually converge to the rain area. The former has stronger lower‐level uplift, greater precipitation and wider rain bands, while the latter is relatively weak. This is an interesting phenomenon, of which the specific mechanisms need to be further studied. Key Points: About 74% of extremely persistent heavy rainfall cases along the coast of southern China are accompanied by southwest jets in the marine boundary layerAgeostrophic winds mainly exhibit confrontational and asymptotic convergence, and the former is accompanied by double low‐level jetsCases of ageostrophic winds with confrontational convergence have stronger precipitation and wider rainband [ABSTRACT FROM AUTHOR]

Natural ventilation can cool down the indoor environment and improve the air quality of buildings without consuming energy. The configuration of an inner corridor with double-sided classrooms is widely used in school buildings because of advantages such as space-saving and compactness. However, the inner doors or windows on the corridor side of these classrooms are often closed due to the dispersion of pollution and noise between classrooms. To introduce more fresh air from the outside, this study proposes a novel design to set up a horizontal airflow channel through the building to provide cross-ventilation for classrooms on both sides. A computational fluid dynamics (CFD) model was verified using experimental data and was employed to predict the airflow rate of the air channel by investigating different, sizes of air channels, wind directions, wind velocities and climate data, to assess the potential of the technology. The implementation of a channel area-to-floor area ratio of 2% (1.8 m2) provided an average increase in the ventilation rate of 215% on an annualized basis when applied and simulated in typical conditions from 10 different cities in China. This technology could be used to improve natural airflow rates in other buildings which use interior corridors in their design. [ABSTRACT FROM AUTHOR]

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Indoor moisture is a crucial aspect of the environment in naturally ventilated underground shelters that remain unattended for long periods of time. The objective of this study was to investigate the impact of natural ventilation on the indoor temperature and humidity of underground shelters using a multi-zone airflow simulation and thereby evaluate the ability of natural ventilation to maintain the indoor environment of shelters in various climates in China. Firstly, a multi-zone airflow model was coupled with the dynamic heat transfer in an underground shelter to simulate the natural ventilation rate and indoor environment. The accuracy of this coupled simulation was subsequently validated using the data measured at an actual shelter. Next, the verified simulation method was applied to analyse the seasonal fluctuations in the natural ventilation rate of underground shelters in the various climates in China; these results were applied to determine the corresponding annual variations in the indoor temperature and humidity. The analysed results show that the relationship between the ventilation rate and indoor humidity level is dependent on both season and climate, and that the influence of the ventilation rate can be negative during summer, especially in wet climate zone. Finally, these findings were evaluated to provide guidelines for regulating natural ventilation according to climate, informing the management of unattended shelters in China. [ABSTRACT FROM AUTHOR]