Winter Wind Research Articles

Characteristics of large-scale atmospheric circulation patterns conducive to severe spring and winter wind events over beijing in china based on a machine learning categorizing method

Severe wind events which occur in the metropolis of Beijing in China bring major catastrophes. Characteristics of severe winter and spring wind events over Beijing during the past 40 years have been analyzed. An artificial intelligence-based method is adopted to categorize the favorable large-scale circulation patterns and dominant weather systems. Four categories are concluded and compared to each other in terms of distributions of geopotential height at 500 hPa, temperature at 500 hPa, sea level pressure and their corresponding anomalies in 1979–2019. It is found that the first category (T1) which is dominated by strong cold trough at upper levels with strong cold-core high locating at surface is the most conducive circulation pattern, while the fourth category (T4) which is controlled by weak trough and strong ridge with strong low cyclone at surface is the least one. The second and third categories, represented by T2 and T3, are under the control of strong cold trough and warm ridge at upper levels with weak high at surface, and of weak trough and strong ridge with strong low cyclone at surface, respectively. Characteristics and differences under different backgrounds of global temperatures are analyzed by separating the past 40years into two distinct periods. The decreasing trends of intensities of the trough and ridge, the temperature at 500hPa, together with the surface systems, are found to be responsible for the decrease in severe wind events in T1, T2 and T3 in the last 20 years, while T4 is distinct to the other three categories with little change in its circulation pattern, and thus continues contributing to the severe wind events over Beijing. The results found in this study with the usage of an AI-based algorithm will benefit for the operational forecasting for extreme wind events over Beijing.

Recent expansion and intensification of hypoxia in the Arabian Gulf and its drivers

The Arabian Gulf (also known as Persian Gulf, hereafter Gulf) is a shallow semi-enclosed subtropical sea known for its extreme physical environment. Recent observations suggest a decline in oxygen concentrations in the Gulf over the past few decades accompanied by an expansion of seasonal near-bottom hypoxia. Here, we reconstruct the evolution of dissolved oxygen in the Gulf from 1982 through 2010 and explore its controlling factors. To this end, we use an eddy-resolving hindcast simulation forced with winds and heat and freshwater fluxes from an atmospheric reanalysis. We show that seasonal near-bottom hypoxia (O2< 60 mmol m-3) emerges in the deeper part of the Gulf over summer and peaks in autumn in response to enhanced vertical stratification inhibiting mixing and O2 replenishment at depth. We also find a significant deoxygenation in the Gulf over the study period, with the Gulf O2 content dropping by nearly 1% per decade and near-bottom O2 decreasing by between 10 and 30 mmol m-3 in the deeper part of the Gulf between the early 1980s and the late 2000s. These changes result in the horizontal expansion of seasonal bottom hypoxia with the hypoxia-prone seafloor area increasing from less than 20,000 km2 in the 1980s to around 30,000 km2 in the 2000s. The expansion of hypoxia is also accompanied by a lengthening of the hypoxic season with hypoxia emerging locally 1 to 2 months earlier in the late 2000s relative to the early 1980s. Furthermore, declining near-bottom O2 levels result in the expansion of suboxic conditions (O2< 4 mmol m-3) and the emergence and amplification of denitrification there. An analysis of the Gulf oxygen budget demonstrates that deoxygenation is essentially caused by reduced oxygen solubility near the surface and enhanced respiration near the bottom. While reduced solubility results from the warming of the Gulf waters, enhanced respiration is mostly driven by an increased supply of nutrients imported from the Arabian Sea due to the weakening of winter Shamal winds over the study period. Our findings suggest that recent changes in local climate are not only altering the Gulf physical environment but are also having a strong impact on the Gulf biogeochemistry with profound potential implications for the ecosystems and the fisheries of the region.

Small Cultural Forests: Landscape Role and Ecosystem Services in a Japanese Cultural Landscape

Small woods, linear tree formations, or scattered trees in agricultural areas are receiving increasing attention for their multifunctional role, especially if associated to cultural landscapes. Osaki Kodo’s Traditional Water Management System for Sustainable Paddy Agriculture represents one of the most important cultural landscapes (satoyama) of Japan, also included by the FAO in the GIAHS (Globally Important Agricultural Heritage Systems) Programme. Here, local farmers surrounded their farmhouses with small woods, called igune, as a protection from the cold winter wind, creating a peculiar landscape characterized by an intensively cultivated plain dotted with small wood patches. The research aims at deepening the knowledge of igune, evaluating the landscape role and monitoring their changes in the last 20 years, through multitemporal and spatial analyses. In addition, a literature review has been performed to assess other Ecosystem Services (ESs) provided by igune within the study area. Despite the limited overall surface, 1737 igune and small woods currently characterize the area, with 72% of them having a surface smaller than 0.5 hectares. The multitemporal and spatial analyses show that their number, distribution, and spatial pattern remained almost completely unchanged in the last 20 years, testifying their key role in characterizing the local cultural landscape. Least-Cost Path analysis highlighted a crucial role in connecting the two forest nodes of the region, as 90% of the path passes inside more than 70 different igune and small woods. Literature review demonstrated that igune and other small woods still provide various ESs, including ecological network, habitat for various flora and fauna species, firewood, and byproducts, as well as cultural services. This maintenance of the traditional management in cultural forests is crucial not only to retain their landscape role, but mostly for the preservation of the related ESs, as changes in the management can lead to changes in horizontal and vertical structures, and in species composition.

Thermal Environment Analysis and Thermal Comfort Evaluation of Huizhou Folk Dwelling Houses Guided by Auxiliary Interior Space Layout

The Huizhou folk dwelling houses are important carriers of the traditional Huizhou cultural and architectural heritage in China. However, such dwelling houses have obvious shortcomings such as damp, dark, insufficient lighting, and inability to cope with cold weather. Existing studies on Huizhou folk dwelling houses haven’t considered factors such high humidity or low temperature that can lead to poor indoor thermal environment in winter, and few have concerned about the theoretical analysis on the formation mechanism of the indoor thermal environment. Therefore, to fill in this research blank, this paper aims to give thermal environment analysis and thermal comfort evaluation on the Huizhou folk dwelling houses under the guidance of auxiliary interior space layout. At first, this paper took the first courtyard of the typical “series-courtyard” structure of the Huizhou folk dwelling houses as the subject, and analyzed the thermal environment of the second courtyard, including the outer wall, door, roof, patio, and ground, and the amount of heat transfer, the amount of radiant heat, and the amount of heat exchange of ventilation were tested. Then, based on the location selection, layout, and architectural morphology of the Huizhou folk dwelling houses, this paper studied the relationship between the thermal comfort of Huizhou folk dwelling houses and the wind and heat environment in winter, the specific test items were indoor temperature, comfort degree, wall temperature, and air tightness, and the test results could provide basis and direction for the renovation of indoor thermal environment of Huizhou folk dwelling houses. At last, this paper gave the analysis results of an actual example, and verified the effectiveness of the analysis and evaluation methods in this paper.

Assessment of future wind speed and wind power changes over South Greenland using the Modèle Atmosphérique Régional regional climate model

AbstractWind is an infinitely renewable energy source that is not evenly distributed in space and time. The interconnection of energy‐demanding and energy‐resourceful (yet remote) regions would help prevent energy scarcity in a world where fossil fuels are no longer used. Previous studies have shown that South Greenland and West Europe have complementary wind regimes. In particular, the southern tip of Greenland, Cape Farewell, has gained growing interest for wind farm development as it is one of the windiest places on Earth. In order to gain new insights about future wind speed variations over South Greenland, the Modèle Atmosphérique Régional (MAR), validated against in situ observations over the tundra where wind turbines are most likely to be installed, is used to build climate projections under the emission scenario SSP5‐8.5 by downscaling an ensemble of CMIP6 Earth System Models (ESMs). It appeared that between 1981 and 2100, the wind speed is projected to decrease by ~−0.8 m·s−1 at 100 m a.g.l. over the tundra surrounding Cape Farewell. This decrease is particularly marked in winter while in summer, a wind speed acceleration is projected along the ice sheet margins. An analysis of two‐dimensional wind speed changes at different vertical levels indicates that the winter decrease is likely due to a large‐scale circulation change while in summer, the katabatic winds flowing down the ice sheet are expected to increase due to an enhanced temperature contrast between the ice sheet and the surroundings. As for the mean annual maximum wind power a turbine can yield, a decrease of ~−178.1 W is projected at 100 m a.g.l. Again, the decrease is especially pronounced in winter. Considering the very high winter wind speeds occurring in South Greenland which can cut off wind turbines if too intense, the projected wind speed decrease might be beneficial for the establishment of wind farms near Cape Farewell.

New insights for origin of fine-grained sediments from the early neogene Qaidam Basin: Wind and fluvial–lacustrine source-to-sink processes

Fine-grained sediment deposition is widely distributed in lacustrine and marine facies and significant for petroleum geology. However, the causes of fine-grained sediment deposition remain controversial. In this study, we examine the cause of fine-grained sedimentation in the Neogene saline lacustrine Qaidam Basin, and propose a new insight into the sedimentary process for fine-grained sediments. Various sedimentary structures identified from the fine-grained sediments such as erosional structures with lag deposits, hummocky cross-stratification (HCS)-like structures, asymmetrical ripples, or sandy ball-and-pillow structures, are generated by winter storms. These winter storms are related to the winter winds that cause eolian sedimentation in Asia. Abundant detrital material may be rapidly transported into lakes by winter storms, favoring extensive terrigenous detrital deposition in the lacustrine basin, hardly controlled by the division of sedimentary facies and topographical differentiation. The genetic features and shallow-water origin with wind and fluvial–lacustrine source-to-sink processes, may be the main reason for the poor hydrocarbon potential of the Neogene fine-grained sediments in the Qaidam Basin.

Sufficient conditions for rapid range expansion of a boreal conifer

Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra1, thereby reducing albedo2–4, altering carbon cycling4 and further changing climate1–4, yet the patterns and processes of this biome shift remain unclear5. Climate warming, required for previous boreal advances6–17, is not sufficient by itself for modern range expansion of conifers forming forest–tundra ecotones5,12–15,17–20. No high-latitude population of conifers, the dominant North American Arctic treeline taxon, has previously been documented5 advancing at rates following the last glacial maximum (LGM)6–8. Here we describe a population of white spruce (Picea glauca) advancing at post-LGM rates7 across an Arctic basin distant from established treelines and provide evidence of mechanisms sustaining the advance. The population doubles each decade, with exponential radial growth in the main stems of individual trees correlating positively with July air temperature. Lateral branches in adults and terminal leaders in large juveniles grow almost twice as fast as those at established treelines. We conclude that surpassing temperature thresholds1,6–17, together with winter winds facilitating long-distance dispersal, deeper snowpack and increased soil nutrient availability promoting recruitment and growth, provides sufficient conditions for boreal forest advance. These observations enable forecast modelling with important insights into the environmental conditions converting tundra into forest.

Surface-area development of foredune trough blowouts and associated parabolic dunes quantified from time series of satellite imagery

• Blowout surface area quantified from medium-scale satellite imagery. • Blowouts grow, stabilize and decay with a life time exceeding multiple decades. • Seasonal variation in blowout area increases with latitude. • Foredune erosion results in episodic, yet temporary increase in blowout surface area. Foredune trough blowouts are elongated wind-eroded depressions in the most seaward dune and their adjoining depositional lobes. Despite their importance to the sand budget and floral diversity of coastal dunes, the spatiotemporal evolution of trough blowouts is not well understood. We designed an automated workflow in the Google Earth Engine platform to produce time series of blowout surface area from medium-resolution satellite imagery available since the mid-1980s and applied it to a blowout system in the Netherlands, Denmark and the USA. Blowout surface areas were found to vary on multi-annual, seasonal and episodic time scales. Multi-annual change reflects successive development through stages of growth, stabilization and decay. The transition from growth to stabilization appears to be related to a change in blowout shape (width-to-length ratio). The decay phase starts with vegetation obstructing the blowout connection to the beach; the lobe can still migrate inland and develop into a parabolic dune before also becoming fully vegetated. The seasonal variations in blowout area increase with latitude; the observed larger areas in winter at the Dutch and Danish site presumably reflect seasonal plant development and the effect of stronger winds in winter. Episodic increases in blowout area, observed during winter at the Danish site only, are associated with pronounced foredune erosion. None of the episodic events changed blowouts into a different stage or persistently affected seasonal dynamics. Future work should focus on the combined analysis of changes in blowout area and sand volume to improve our understanding of sand-vegetation interactions driving blowout dynamics.

Wind simulation using different parameters in a weather research and forecasting model

A study designed different parameter schemes for a weather research and forecasting model to simulate hourly winter and summer wind speed and direction at a wind-farm tower in China. The schemes were found to reproduce the local wind conditions accurately and simulate wind direction very well. The results showed that one scheme performed better for the wind speed and wind direction simulation at 10 and 90 m height in the winter, while another performed better for simulation at 10 m height in the summer. The results for these schemes showed that the correlation coefficients of wind speed and wind direction were 0.75 and 0.62 in winter and 0.55 and 0.44 in summer, respectively. Overall, the parameterised model exhibited better simulation of the wind speed than wind direction, and was better in winter than in summer.

Analysis of Synergistic Effects of Cold Source and East Asian Winter Wind on Air Pollution in Typical Regions of China in Winter

This paper collects and analyzes the 1954–2017 monthly average reanalysis data from the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), the 1954–2017 haze days observation data from the National Meteorological Information Center/China Meteorological Administration (NMIC/CMA) and the PM2.5 daily average mass concentration data in 2013–2017 from the China Air Quality Online Monitoring Platform. The atmospheric apparent heat source Q1 (negative Q1 means cold source in winter) over the Tibetan Plateau in December of 1954–2017 is estimated based on thermodynamic equations, and the East Asian winter monsoon index (EAWMI) is calculated. In addition, the discrepancies of the air quality among China’s five typical regions (Beijing–Tianjin–Hebei, Fen-Wei Plain, Yangtze River Delta, Pearl River Delta and Sichuan-Chongqing regions) under the joint influence of the Q1 and EAWMI are studied. Results show that when it is a strong cold source year, abnormal downdrafts and “temperature inversion covers” occur in areas far from the high terrain, resulting in increased pollution, while the opposite is true in weak cold source years. In strong EAWMI years, there is an abnormal northerly sinking cold flow in the lower layers of mid-high latitudes, which increases the pollution in the area south of 30° N, and the opposite is true in weak EAWMI years. Affected by the combined activities of the Q1 and the EAWMI, the meteorological conditions of the five typical regions are different, and thus present different air pollution characteristics.

Linking moisture and near-surface wind with winter temperature to reveal the Holocene climate evolution in arid Xinjiang region of China

An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle- to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds; and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally, we develop a conceptual model to explain the pattern of Holocene climate changes in this region. From the early to the late Holocene, the increasing atmospheric CO2 content and winter insolation, and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system, which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.

A statistical downscaling prediction model for winter temperature over Xinjiang based on the CFSv2 and sea ice forcing

AbstractBased on a year‐to‐year increment approach, a statistical downscaling model is developed for winter temperature prediction over Xinjiang of northwest China by using the predicted 200‐hPa westerly wind in winter over the Ural Mountains from the Climate Forecast System version 2 (CFSv2) as well as the observed sea ice over the Barents Sea–Laptev Sea in the preceding September. The statistical downscaling hindcasts on the 1983–2018 winter temperature over Xinjiang show that the statistical downscaling method has significantly improved the prediction capability compared with the original CFSv2. Specifically, the temporal correlation coefficients increase from negative to positive in most of Xinjiang, with the values passing the significance test at 90% confidence level at 81% of the stations. The regional averaged root‐mean‐square error reduces by more than 20%. In addition, the anomaly correlation coefficient increases from 0.08 to 0.26, passing the significance test at 95% confidence level. For two typical cases of the extreme cold winter in 2011 and the extreme warm winter in 2016, the spatial distribution characteristics of temperature anomaly are well reproduced, which are generally consistent with the observations. Overall, the statistical downscaling model based on the year‐to‐year increment strategy is a relatively effective method for predicting the winter temperature in Xinjiang.

Short-term wind speed forecasting using neural network models for Taiwan Strait

In recent years, renewable energy has received rapidly growing attention due to its eco-friendly and sustainable properties. Taiwan as an island nation that is planning to develop offshore wind power to reduce the dependence on imported energy. Due to the intermittent and variable nature of wind, a study on wind characteristics and forecasting will make it possible to obtain valuable information on local wind conditions and enhance local forecasting abilities. In this study, wind data from 2017 to 2019, obtained from the Taipower Meteorological Mast in the Taiwan Strait, was used to develop a short-term multistep wind forecasting model. This model was based on a combination of an artificial neural network and a Long Short-Term Memory (LSTM) models. The results revealed that the northeast winds in winter and autumn were steadier, in terms of both speed and direction, than those in spring and summer. The prediction accuracies of this three-step forecasting model reached 0.991, 0.981, and 0.970, respectively. These findings will greatly improve our ability to forecast this important Taiwan Strait wind resource.

The Variability of Stable Water Isotopes and the Young Water Fraction in a Mountainous Catchment

AbstractSoil water movement is an important component in water cycle, which is also closely correlated with the transport of nutrients and contaminants in the catchment. Although there have been many studies in quantifying the water residence in soil, the understanding of the controlling factors is limited and could be controversial. Here, stable isotopes of water to explore the water age distribution in a mountainous catchment in the southwest China are used. The results are consistent with the regional climate pattern that the water vapor of the study catchment is brought by monsoons from Pacific Ocean in summer and prevailing westerly winds in winter. The estimated young water fraction is found to be strongly correlated with topographic gradient but presents no significant correlation with drainage area or vegetation coverage. Comparison between the difference in young water fraction of two adjacent sub‐catchments suggests that soil water in the steeper sub‐catchment tends to favor deep vertical infiltration, resulting in longer flow path, longer mean residence time, and smaller young water fraction. This difference between the soil water movement and the hydrological response revealed in this study has impacts on the biogeochemical cycles in the catchment.

Trends in the Climatology of Winter Wind Wave Heights in a Back-Barrier Bay in Western North Atlantic Ocean

Trends in the Climatology of Winter Wind Wave Heights in a Back-Barrier Bay in Western North Atlantic Ocean

Environmental influences on breeding biology and pup production in Australian fur seals.

Knowledge of factors affecting a species' breeding biology is crucial to understanding how environmental variability impacts population trajectories and enables predictions on how species may respond to global change. The Australian fur seal (Arctocephalus pusillus doriferus, AUFS) represents the largest marine predator biomass in southeastern Australia, an oceanic region experiencing rapid warming that will impact the abundance and distribution of prey. The present study (1997–2020) investigated breeding phenology and pup production in AUFS on Kanowna Island, northern Bass Strait. The pupping period varied by 11 days and the median pupping date by 8 days and were negatively correlated to 1- and 2-year lagged winter zonal winds, respectively, within Bass Strait. While there was no temporal trend over the study period, annual pup production (1386–2574 pups) was negatively correlated to 1-year lagged summer zonal winds in the Bonney Upwelling region and positively correlated to the current-year Southern Oscillation Index (SOI). In addition, a fecundity index (ratio of new-born pups to adult females at the median pupping date) was positively correlated with current-year Southern Annular Mode (SAM) conditions. Periods of positive SOI and positive SAM conditions are forecast to increase in coming decades, suggesting advantageous conditions for the Kanowna Island AUFS population.

Overturning Instabilities Across a Warm Core Ring From Glider Observations

AbstractThis work presents new evidence for conducive conditions for the existence of overturning instabilities in the mixed layer across a mesoscale anticyclonic Loop Current Eddy (LCE) and surrounding cyclonic eddies in the Gulf of Mexico (GoM). The LCE was intensively sampled using four gliders during 12 months. The LCE is characterized by a strong anomaly of fresh and warm water in the center and strong strain at the periphery. Mixed layers prone to overturning instabilities are diagnosed from the gradients of buoyancy. In the GoM, the reduction of potential vorticity (PV) in the mixed layer is driven by surface cooling by year‐round persistent negative turbulent heat fluxes, eventually reaching −700 W m−2 during extreme winter wind events. Lateral buoyancy gradients associated with submesoscale filaments and fronts at the periphery of the LCE enhance the frictional torque supplied by the wind stress when aligned with the geostrophic jet current. Negative PV in the mixed layer occurs simultaneously with negative turbulent heat fluxes and events of Ekman buoyancy fluxes that reduce the stratification. These regions are susceptible to mixed‐layer gravitational‐symmetric instability preferentially in winter. Extreme Ekman equivalent heat flux (≤−10,000 W m−2) associated with wind stress of 1.2 N m−2 coincides with the development of inertial‐symmetric instability across anticyclonic vorticity. These observations might have several implications for the restratification processes, kinetic energy budget, and biogeochemical cycles inside LCEs and can contribute to the formation of low‐PV waters that could feed mode water formation inside the GoM.

Investigation into spatiotemporal characteristics of coastal winds around the Taiwan Island

Temporal and spatial variation characteristics of winds and their relationship with terrain environment in the Taiwan Island were investigated in this research. Based on the empirical orthogonal function (EOF) analysis, the monthly-averaged wind speed and direction at eight observation stations around Taiwan island from 1980 to 2015 were analyzed. Then the temporal and spatial variation characteristics of wind direction and wind speed as well as the abrupt change characteristics of wind speed were studied. Main results are: (1) The first EOF modal variance contribution rate of wind speed reaches 43%, and its spatial distribution numerical center shows that the positive value center is at S10, and the negative value center is at S1. The value at other areas does not change significantly. The contribution rate of the second EOF mode is 22%, which is also reflected in the positive center at S10, and the variance contribution rate of the third EOF mode is 16%. At the same time, the analysis of the wind direction EOF results shows that the first EOF modal variance contribution rate is 35%, which is lower than that of wind speed. Only stations S1 and S12 are positive but have small values, while S5 and S8 have the maximum negative value. In combination with the local terrain, it shows that wind speeds are significantly affected by topography. The wind speed is stable, but the wind direction is unstable near the plain along the Taiwan Strait. Additionally, the wind speed is less stable and the wind direction is more stable at the north and south of Taiwan Island due to the influence of the central mountains. (2) Analysis on the main contribution modal time coefficient of wind speed EOF indicate that the value is mostly negative in winter and positive in summer, which shows that the wind speed around Taiwan Island has significant variation at a seasonal scale, with a strong northeast wind in winter significantly affected by the northeast monsoon and a weak southwest wind in summer affected by the southwest monsoon.

Development and application of a street-level meteorology and pollutant tracking system (S-TRACK)

Abstract. A multi-model simulation system for street-level circulation and pollutant tracking (S-TRACK) has been developed by integrating the Weather Research and Forecasting (WRF), the STAR-CCM+ (computational fluid dynamics model – CFD), and the Flexible Particle (FLEXPART) models. The winter wind environmental characteristics and the potential contribution of traffic sources to nearby receptor sites in a city district of China are analysed with the system for January 2019. It is found that complex building layouts change the structure of the wind field and thus have an impact on the transport of pollutants. The wind speed inside the building block is lower than the background wind speed due to the dragging effect of dense buildings. Ventilation is better when the dominant airflow is in the same direction as the building layout. Influenced by the building layout, the local circulations show that the windward side of the building is mostly the divergence zone, and the leeward side is mostly the convergence zone, which is more obvious for high buildings. With the hypothesis that the traffic sources are uniformly distributed on each road and with identical traffic intensity, the potential contribution ratios (PCRs) of four traffic sources to certain specific sites under the influence of the street-level circulations are estimated with the method of residence time analysis. It is found that the contribution ratio varies with the height of the receptor site. As a result of the generally upward motion in the airflow, the position with the greatest PCR from the four road traffic sources is located at a certain height which is commonly influenced by the distance of this location from the traffic source and the background wind field (about 15 m in this study). The potential contribution of a road to one of the receptor sites is also investigated under different wind directions. The established system and the results can be used to understand the characteristics of urban wind environment and to help the air pollution control planning in urban areas.

Long‐Term Moored Current and Temperature Measurements of the Atlantic Inflow Into the Nordic Seas in the Norwegian Atlantic Current; 1995–2020

AbstractInterannual variability of the Atlantic inflow (AI) into the Nordic Seas is studied using moored current and temperature measurements in the Norwegian Atlantic Current during the 25‐year period 1995–2020. We show that the properties of the AI are strongly connected to the dynamics of the Northern Atlantic and demonstrate the robustness of the average winter wind field in driving the variability with 3‐month winter maxima in the range of (40–50) cms−1. In that sense, the zero‐wind‐stress‐curl (ZWSC)‐lines aligned northeastward are crucial. Occasional events with slowdown of winter‐maxima are connected to a meridional and zonal shift of the ZWSC‐lines, and not the strength of the wind. This is manifested in a correlation of 0.3 versus the North Atlantic Oscillation (NAO) winter‐index, demonstrating that the NAO‐index is insufficient to explain the AI‐variability. The records show no long‐term‐trend over the 25‐year period 1995–2020, regarding volume flux, temperature, nor temperature flux.