Xinjiang Climatic Center

Urunchi, China

Xinjiang Climatic Center

Urunchi, China
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Li X.,Institute of Desert Meteorology | Xia X.,CAS Institute of Atmospheric Physics | Xia X.,Nanjing University of Information Science and Technology | Wang L.,Urumqi Meteorological Bureau | And 5 more authors.
Journal of Geophysical Research D: Atmospheres | Year: 2015

The impact of sandwich foehn on air pollution in Urumqi, a gap town located on the northern lee side of the Tianshan Mountains of China, is analyzed. The results show that during days with high pollution, the boundary layer over the city and the down-valley area can be divided into a three-layer structure, with the southeasterly foehn sandwiched between the northwesterly winds on top and the cold air surface pool beneath. The southeasterly foehn at heights between 480 and 2100 m results in a very stable boundary layer structure. In combination with the decoupling between the foehn flow and cold air pool, such boundary layer structure prevents vertical mixing of atmospheric pollutants. In the up-valley area from the northern lee side flank to the southern urban area, the ground-based foehn confronts the thermally driven valley breeze and forms a "minifront," which moves northward in the morning and retreats southward in the afternoon. Although the minifront disappears in the early evening, the wind shear of the mountain breeze between the southern suburb and downtown areas is still remarkable, which is favorable for a convergence line to persist around the city all day long. In this case, air pollutants emitted from the up-valley and down-valley areas are transported toward the urban area. Therefore, the air pollutants accumulate daily, leading to the frequent occurrence of heavy pollution events in Urumqi. This indicates that the sandwich foehn plays a critical role in the formation of heavy air pollution events in Urumqi. Key Points The winter boundary layer is characterized by the presence of a sandwich foehn The boundary layer with a sandwich foehn is very stable on HPDs in winter The interaction between cold air pool and foehn causes the convergence in town. © 2015 American Geophysical Union. All Rights Reserved.

Li X.,Institute of Desert Meteorology | Guo Y.-H.,Xinjiang Environmental Monitor Center | Lu X.-Y.,Xinjiang Meteorological Observatory | Gulgina H.,Xinjiang Meteorological Information Center | And 7 more authors.
Zhongguo Huanjing Kexue/China Environmental Science | Year: 2016

Measures mainly based on the Coal to Gas Engineering (CTGE) for heating between 2012 and 2013 were taken to improve the air quality in Urumqi. In this paper, a comprehensive study was conducted to evaluate the effects of these measures on atmospheric environment in Urumqi by using the data of the concentrations of major air pollutants during wintertime of 2009~2014, the direct radiation, visibility, hazy days between 1993~2014. The results show that the concentrations of PM10, SO2 and NO2 in Urumqi during the wintertime of 2013~2014 decline by 26.1%, 80.2% and 11.6% respectively compared to those in the wintertime of 2009~2011 which represent the concentrations before CTGE. The ratio of total water-soluble matter to PM2.5 also decreases by 20.57%. The top three ions' concentrations in PM2.5 are SO4 2, NH4 + and NO3 -before and after the CTGE. However, there is 50% decrease of the mass fractions of SO4 2-and NH4 + in PM2.5 after the CTGE, and the mass fraction of NO3 -in PM2.5 remains unchanged. In the view of atmospheric physics, the total direct radiations during the wintertime in Urumqi increase after the CTGE and the value of 2013~2014 reaches up to the second peak for the past 23 years. There is a 5.7 km increase for the wintertime visibility of 2013~2014 which is the maximum value since 1997. At the same time, there are 15days less for the wintertime hazy days of 2012~2013 compared to that of previous year which is a decrease of 50%. The results and analysis indicate that the CTGE for heating improved the atmospheric environment in Urumqi to a certain extent. © 2016, Chinese Society for Environmental Sciences. All right reserved.

Jiang Y.-A.,Xinjiang Climatic Center | Chen Y.,Xinjiang Climatic Center | Zhao Y.-Z.,Urumqi Meteorological Bureau | Chen P.-X.,Xinjiang Climatic Center | And 3 more authors.
Advances in Climate Change Research | Year: 2014

By using the observation data from 89 weather stations in Xinjiang during 1961-2010, this paper analyzed the basic climatic elements including temperature, precipitation, wind speed, sunshine duration, water vapor pressure, and dust storm in the entire Xinjiang and the sub areas: North Xinjiang, Tianshan Mountains, and South Xinjiang. The results indicate that from 1961 to 2010 the annual and seasonal mean temperatures in the entire Xinjiang show an increasing trend with the increasing rate rising from south to north. The increasing rate of annual mean minimum temperature is over twice more than that of the annual mean maximum temperature, contributing much to the increase in the annual averages. The magnitude of the decrease rate of low-temperature days is larger than the increase rate of high-temperature days. The increase of warm days and warm nights and the decrease of cold days and cold nights further reveal that the temperature increasing in Xinjiang is higher. In addition, annual and seasonal rainfalls have been increasing. South Xinjiang experiences higher increase in rainfall amounts than North Xinjiang and Tianshan Mountains. Annual rainy days, longest consecutive rainy days, the daily maximum precipitation and extreme precipitation events, annual torrential rain days and amount, annual blizzard days and amount, all show an increasing trend, corresponding to the increasing in annual mean water vapor pressure. This result shows that the humidity has increased with temperature increasing in the past 50 years. The decrease in annual mean wind speed and gale days lessen the impact of dust storm, sandstorm, and floating dust events. The increase in annual rainy days is the cause of the decrease in annual sunshine duration, while the increase in spring sunshine duration corresponds with the decrease in dust weather. Therefore, the increase in precipitation indicators, the decrease in gales and dust weather, and the increasing in sunshine duration in spring will be beneficial to crops growth.

Li X.,Institute of Desert Meteorology | Li X.,CAS Institute of Atmospheric Physics | Xia X.,CAS Institute of Atmospheric Physics | Xin Y.,Xinjiang Climatic Center | And 3 more authors.
Journal of the Air and Waste Management Association | Year: 2012

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 the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). Measurements from operational radiosonde data showed that a southeasterly elevated low-level jet often intruded upon Urumqi through the middle Tianshan Mountain pass to the south of the city. The tethered-sonde measurements showed that calm and northwesterly winds prevailed near the surface in Urumqi, whereas the southeasterly winds of relatively higher speed were dominant above ~400 m. Both temperature inversion and humidity inversion frequently occured during day and nighttime. Temperature inversion intensity could sharply rise as the stronger elevated southeasterly gale (ESEG) happened. Model simulations showed that the winds near the surface around Urumqi remained calm during nighttime and developed toward the mountains during daytime. As cool air flow in the basin confronted the southeasterly winds from the pass in the lower layer, they formed a convergence line around Urumqi city, which was not favor for dilution of air pollutants. Implications: There is little knowledge about the relationship between air pollution and the local gap wind (well known as the southeasterly gale [SEG]) in Urumqi during winter. On the basis of tethered-sonde measurements and model simulations, the authors showed that the SEG, if only occurring above ~400 m (called the elevated SEG [ESEG] in this study), did alter the urban boundary-layer structure and favor formation of a convergence zone near the surface, which was beneficial for occurrence of severe air pollution episode. Therefore, it needs to further study how the ESEG maintains and impacts on atmospheric environment. © 2012 Copyright 2012 A&WMA.

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