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Tethered-sonde measurements of atmospheric profiles were performed at Urumuqi, capital of the Xinjiang Uyghur Autonomous Region of China, from 29 December 2008 to 14 January 2009. The data were used to examine the boundary layer structure during this severe air pollution period. Diurnal evolution of local wind flow near Urumqi was simulated using t...
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... top boundary of the model was 100 hPa. The parameterization schemes used in this study are summarized in Table 1. The top boundary of the model was 100 hPa. ...
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... Relatively high 129 I concentrations are observed in Zone 2, with the highest 129 I level at site C49 ( Figure S3). The uplifted Altay and Tarbagatai mountains and low-elevation Irtysh River valley form a trumpet-shaped narrow channel that promotes the air masses of the westerlies flowing to Northern Xinjiang, 48,49 which encounter the strong northeastward air current through a similar topography comprised by high mountains and low valleys in the southwest of the Tarbagatai Mountains, 48,49 forming an air convergence zone (Zone 2) that diminishes horizontal transport of air masses and facilitates air convection, 50 finally resulting in high deposition of 129 I carried by westerlies ( Figure S3). It has been reported that air masses converged at low and middle altitudes could quickly remove air particles deposited in the local area. ...
Anthropogenic 129I, as a long-lived fission product and volatile radionuclide, can be used to investigate dispersion of air masses and the deposition of atmospheric pollution. Surface soil and soil core samples were collected from Northern Xinjiang and analyzed for 127I and 129I. The results show that 129I/127I atomic ratios in surface soil are inhomogeneous with a range of (2.07-106) × 10-9, and the maximum values in each soil core occurred at surface-subsurface layers (0-15 cm) at undisturbed sites. The dominant source of 129I in Northern Xinjiang is European nuclear fuel reprocessing plant (NFRP) releases, accounting for at least 70% of the total inventory; less than 20% of 129I originates from the global fallout of atmospheric nuclear weapons tests; less than 10% comes from the regional deposition of nuclear weapons tests at the Semipalatinsk site; and the regional deposition from the nuclear weapons tests at the Lop Nor site is insignificant. The European NFRP-derived 129I was transported to Northern Xinjiang via long-distance atmospheric dispersion with the westerlies through Northern Eurasia. The distribution of 129I in the surface soil in Northern Xinjiang is mainly controlled by topography, wind fields, land utilization, and vegetation coverage.
... Moreover, low wind speed and lesser turbulence during winter do not favour the dispersion of anthropogenic emissions build-up, leading to severe air pollution events(Nair, Madhusoodanan, and Mehajan 2018;. Several reports have shown heightened air pollution levels during winters due to the above-mentioned reasons (X.Li et al. 2012;Regmi et al., 2019;Dumka et al. 2019;. ...
Atmospheric Boundary Layer (ABL) characteristics are investigated using a Ceilometer Lidar over Ahmedabad, a semi-arid region in western India. Strong diurnal variations of ABL are observed during 2019, the observation period. There is a stark winter-summer difference in ABL, with summer Boundary Layer Height (BLH) exceeding winter BLH by 1-1.5 km. ABL usually collapses during monsoon and is equivocal due to the presence of thick clouds on top of ABL. The ABL is thicker during the onset of monsoon in contrast to active monsoon, rises again during the withdrawal of monsoon. Lidar observed ABL have been compared with satellite, radiosonde, and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) dataset. ERA5 shows good agreement with differences within 500 m; radiosonde observations have under-estimated ground-based measurements, especially during summer. Satellite observations highly overestimated BLH. This comparative study reveals the importance of ground-based lidars in continuous monitoring of ABL at high resolution because radiosonde, satellite, and reanalysis datasets have coarser resolutions and sparse observations. Such quantitative evaluation of ABL is formerly unavailable over this region, which can now be used to improve the representation in numerical models and thereby estimates of radiative and climate effects due to ABL.
... black carbon (Zhou et al., 2020) or organic PM 10 tracers like levoglucosan (Marynowski et al., 2020). Numerous studies indicate that an important factor that affects the pollution profile is the wind profile (Li and Han, 2016;Zhou et al., 2020), occurrence of low-level jets (Li et al., 2012 or downward flows of pollutants (Han et al., 2018) which may strongly modify the diurnal cycle of a pollutant concentration in the lowest part of the troposphere. ...
... Similar situations with significant wind direction change in the vertical profile and weak wind speed were presented e.g. in Vergeiner (2004) and Li et al. (2012Li et al. ( , 2015 for mountain valleys, during hydraulic jump occurrence. In the upper layer, wind direction is constant, while wind speed increases with height. ...
The paper shows wind shear impact on PM10 vertical profiles in Kraków, southern Poland. The data used consist of background data for two cold seasons (September 2018 to April 2019 and September 2019 to April 2020) and data for several case studies from November 2019 to March 2020. The data are composed of PM10 measurements, model data, and wind speed and direction data. The background model data come from operational forecast results of the AROME model. PM10 concentration in the vertical profile was measured with a sightseeing balloon. Significant spatial variability of the wind field was found. The case studies represent the conditions with much lower wind speed and a much higher PM10 level than the seasonal average. The inversions were much more frequent than on average too. Wind shear turned out to be the important factor in terms of PM10 vertical profile modification. It is generated due to the relief impact, i.e. the presence of a large valley, blocked on one side with the hills. The analysis of PM10 profiles from all flights allows us to distinguish three vertical zones of potential air pollution hazards within the valley (about 100 m deep) and the city of Kraków: (1) up to about 60 m a.g.l. – the zone where during periods of low wind speed, air pollution is potentially the highest and the duration of such high levels is the longest, i.e. the zone with the worst aerosanitary conditions; (2) about 60–100 m a.g.l. – transitional zone where the large decrease in PM10 levels with height is observed; (3) above 100–120 m a.g.l. – the zone where air quality is significantly better than in zone 1, either due to the increase in the wind speed or due to the wind direction change and advection of different, clean air masses.
... Orographic forcings are confirmed to be a key factor in producing these windstorms by enhancing the low-level pressure gradient (Ding et al., 2019), inducing gravity waves (Lu et al., 2014), causing downslope winds (Zhang et al., 2018) and applying a narrow pipe effect (Wang et al., 2011). Thus far, most previous studies are applied to windstorms in Northern Xinjiang (Tang et al., 2011;Wang et al., 2011;Li et al., 2012;Lu et al., 2014;Zhang et al., 2018;Ding et al., 2019). For Southern Xinjiang, where the geographical features are remarkably different from those of Northern Xinjiang, mechanisms accounting for the development of windstorms still remain vague. ...
Abstract Based on the European Centre for Medium‐Range Weather Forecasts (ECMWF) ERA5 reanalysis data, in this study, formation mechanisms of a severe windstorm that caused successive trippings of the transmission lines in Southern Xinjiang were investigated. The strong windstorm occurred within a lower‐tropospheric warm region due to adiabatic heating of the descending motions ahead of a shortwave trough in the westerly wind (the blocking effects of high mountain was a key reason for the strong descending motions). The kinetic energy (KE) budget indicates two typically different stages appeared in the variation of the windstorm. The former stage showed a rapid wind KE enhancement in the lower troposphere. The KE increase was mainly governed by the downward stretching of high KE (i.e., downward momentum transportation) from the middle troposphere (rather than from the upper‐level jet) and the KE production due to the work on rotational wind by the pressure gradient force. The latter stage showed a rapid KE decrease mainly due to the transport of KE by the rotational wind and the pressure gradient force's negative work on the rotational wind. In contrast, the vertical advection of KE still acted as transporting high KE from middle troposphere to lower troposphere, which resisted the KE reduce at the lower levels.
... Much attention has been paid to GBSEGs in Xinjiang because they can cause a significant amount of damage to urban infrastructure and transportation (Zhang et al., 1986;Meng et al., 1995Meng et al., , 1996. However, the formation of ESEGs and their potential impacts have been largely neglected, despite that this kind of foehn flows can significantly change the local boundary layer structure and thereby greatly influence air quality (Li, 2013;Li et al., 2012Li et al., , 2015. Studies have linked the occurrence of foehn to poor air quality. ...
The climatology of shallow foehn, also known locally as elevated south-easterly gales (ESEGs), on the northern lee side of the central Tianshan Mountains is analysed using radiosonde data recorded over a period of 10 years at Urumqi, the capital of Xinjiang Uygur Autonomous Region in north-western China. ESEGs are a frequent weather phenomenon in the region, occurring on average 128.5 days/yr and most often in winter (47.0 days), particularly January (17.5 days), and least in summer (18 days). The vertical ESEG structures also undergo seasonal variations, with the height of the maximum ESEG wind and the base and top of the ESEG layer more elevated in the warm half (late spring through early fall) of the year than the cold half. However, the monthly mean maximum wind speeds, which vary around 10 m/s, appear to be independent of season. A typical synoptic pattern accompanying ESEGs is characterized by opposite air masses to the east (cold) and west (warm) of Xinjiang. A strong low-level west-east pressure gradient helps push cold air to enter Xinjiang from the east, which subsequently induces a north-south pressure gradient across the Tianshan Mountains. This regional pressure gradient combined with terrain channelling leads to the development of ESEGs. A comparison of boundary layer structure between days with/without ESEGs in winter shows that the ESEG days are accompanied by deeper (average of 900 m) and more intense (average 6 °C) inversion, but there is little difference in the cold air pool Froude Number between the two types of days.
... Whiteman et al. (1999) noted that the temperature inversion in wintertime, once formed in the basin, can persist for a multiday period and that the stable basin atmosphere tends to be isolated from the atmosphere aloft with relatively strong prevailing winds. The persistent temperature inversion often results in poor air quality in cities located in complex terrain (e.g., Malek et al., 2006;Olofson et al., 2009;Jung et al., 2010;Li et al., 2012). ...
Temperature inversions are frequently observed in mountainous urban areas and can cause severe air pollution problems especially in wintertime. This study investigates wintertime winds in and around the Ulaanbaatar, the capital of Mongolia, metropolitan area in the presence of a temperature inversion using the Weather Research and Forecasting (WRF) model coupled with the Seoul National University Urban Canopy Model (SNUUCM). Ulaanbaatar is located in complex terrain and in a nearly east-west-oriented valley. A wintertime scenario with clear skies, weak synoptic winds, and a temperature inversion under the influence of a Siberian high-pressure system is selected. Local winds are weak in the presence of the temperature inversion. In the daytime, weak mountain upslope winds develop, up-valley winds appear to be stronger in the urban area than in the surrounding areas, and channeling winds are produced in the main valley. The bottom of the temperature inversion layer rises up in the urban area, and winds below the bottom of the temperature inversion layer strengthen. In the nighttime, mountain downslope winds and down-valley winds develop. Urban effects in the presence of the temperature inversion are examined by comparing the results of simulations with and without the city. It is shown that in the daytime the urban area acts to elevate the bottom of the temperature inversion layer and weaken the strength of the temperature inversion layer. Winds east of the city weaken in the afternoon and down-valley winds develop later in the simulation with the city.
The composition of air pollutants and features of the near–ground layer were investigated from four 100 m high towers during a heavy pollution event in 2013 in Urumqi, northwest China. The PM2.5, PM10, SO2, NO2, and CO concentrations increased rapidly during the heavy pollution event, with the exact amounts dependent on air pollutant emissions and meteorological conditions. Ozone concentrations increased in northern rural areas, and were affected by the emission and conversion of primary pollutants from urban areas. The maximal mixing layer was slightly lower than 1000 m. A strong temperature inversion intensity of 6.8, 2.5, 4.2, and 4.7 °C/100 m in suburban, urban, northern suburban, and rural sites, respectively, occurred during the heavy pollution event. A significant mountain–valley wind in the urban and northern suburbs was an important factor affecting the heavy pollution. During heavy pollution days, the wind was almost always from the south and east, and the wind speed was mostly over 7 m·s−1 in the southern suburbs. Conversely, it was lower than 2 m s−1 in the urban and northern rural sites, where the wind directions were variable. There was a positive correlation between pollutant concentrations and air temperature, but pollutant concentrations were negatively correlated with relatively humidity. Dynamic and thermal turbulence (friction velocity and vertical kinematic eddy heat flux) favored the diffusion and accumulation of heavy pollution in Urumqi. The friction velocity was strong in the southern suburbs (0.5 m s−1), but was weak at the northern rural (0.11 m s−1) site, which were located on high and low terrain, respectively. The turbulent thermal effect was the main atmospheric condition associated with the formation of heavy pollution events, which had little relationship with the turbulent dynamic effect. A backward trajectory analysis of the atmospheric motion showed that heavy pollution events were more likely to be caused by local pollutant transport.
The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China, is very serious in winter. Of particular importance is the influence of terrain-induced shallow foehn, known locally as elevated southeasterly gale (ESEG). It usually modulates atmospheric boundary layer structure and wind field patterns and produces favorable meteorological conditions conducive to hazardous air pollution. During 2013–17, Urumqi had an average of 50 d yr−1 of heavy pollution (daily average PM2.5 concentration >150 µg m−3), of which 41 days were in winter. The majority (71.4%) of heavy pollution processes were associated with the shallow foehn. Based on microwave radiometer, wind profiler, and surface observations, the surface meteorological fields and boundary layer evolution during the worst pollution episode in Urumqi during 16–23 February 2013 are investigated. The results illustrate the significant role of shallow foehn in the building, strengthening, and collapsing of temperature inversions. There were four wind field patterns corresponding to four different phases during the whole pollution event. The most serious pollution phase featured shallow foehn activity in the south of Urumqi city and the appearance of an intense inversion layer below 600 m. Intense convergence caused by foehn and mountain-valley winds was sustained during most of the phase, resulting in pollutants sinking downward to the lower boundary layer and accumulating around urban area. The key indicators of such events identified in this study are highly correlated to particulate matter concentrations and could be used to predict heavy pollution episodes in the feature.
The paper shows wind shear impact on PM10 vertical profiles, in Kraków, southern Poland. The data used consist of background data for two cold seasons (Sep. 2018 to Apr. 2019, and Sep. 2019 to Apr. 2020), and data for several case studies from November 2019 to March 2020. The data is composed of PM10 measurements, model data, and wind speed and direction data. The background model data come from operational forecast results of AROME model. PM10 concentration in the vertical profile was measured with a sightseeing balloon. Significant spatial variability of wind field was found. The case studies represent the conditions with much lower wind speed and a much higher PM10 levels than the seasonal average. The inversions were much more frequent than on average, too. Wind shear turned out to be the most important factor in terms of PM10 vertical profile modification. It is generated due to the relief impact, i.e. the presence of a large valley, blocked on one side with the hills. The analysis of PM10 profiles from all flights allows to distinguish three vertical zones of potential air pollution hazard within the valley (about 100 m deep) and the city of Kraków: 1. up to about 60 m a.g.l. – the zone where during periods of low wind speed, air pollution is potentially the highest and the duration of such high levels is the longest, i.e. the zone with the worst aerosanitary conditions; 2. about 60–100 m a.g.l. – transitional zone where the large decrease of PM10 levels with height is observed; 3. above 100–120 m a.g.l. – the zone where air quality is significantly better than in the zone 1, either due to the increase of the wind speed, or due to the wind direction change and advection of different, clean air masses.
Influenced by strong winds associated with a southeastward-moving Mongolian cyclone, a severe transmission line galloping occurred in Baiyin City, Gansu Province, on 14 April 2020. This caused a tripping incident of the transmission line in this region. Based on the hourly, 0.5° × 0.5°, ECMWF ERA5 reanalysis data, this study investigated the formation mechanisms of the Mongolian cyclone and its associated strong winds. Results from the vorticity budget indicate that the convergence-related vertical stretching and the upward transport of cyclonic vorticity governed formation of the Mongolian cyclone in this event; whereas, tilting and export of cyclonic vorticity from the central region of the cyclone mainly decelerated the cyclone's formation. The kinetic energy (KE) budget shows that the wind associated with the Mongolian cyclone was mainly enhanced by the positive work of the pressure gradient force. Unlike some typical strong wind events in Northwest China, during this event, no significant downward momentum transportation from the upper troposphere was found. The vertical transport of KE exerted a slightly favorable effect on the KE increase around the location where the transmission line galloping trip appeared. In contrast, the horizontal transport mainly caused an export of KE from this region, which applied an overall negative effect on the wind enhancement associated with the Mongolian cyclone.
摘要
受一次向东南方向移动蒙古气旋强风的影响, 2020年4月18日甘肃省白银市的高压输电线路出现了严重的舞动, 这造成了该地区的输电线路跳闸事故.基于0.5度逐小时分辨率的ERA5再分析数据, 本文研究了这次蒙古气旋及其强风的形成机理.涡度收支的结果表明, 辐合相关的垂直伸展以及垂直运动向上的正涡度输送是本次蒙古气旋形成的主因, 而倾斜项的负涡度制造以及从气旋中心区域向外的正涡度输送在一定程度上不利于蒙古气旋的形成.动能收支的结果表明, 蒙古气旋所伴随的风场主要由于气压梯度力的做功而迅速增强.与我国西北部其它的典型强风事件不同的是在本次事件中, 未发现显著的来自于对流层高层的动量下传现象, 垂直的动能输送在本次事件中仅对强风的形成有些许的促进作用.此外, 水平风场对动能的输送作用使得蒙古气旋大风区的动能存在向外的净输出, 这对蒙古气旋强风的生成有一定的延缓作用.
