Characteristics of Turbulent Transfer during Episodes of Heavy Haze Pollution in Beijing in Winter 2016/17

We analyzed the structure and evolution of turbulent transfer and the wind profile in the atmospheric boundary layer in relation to aerosol concentrations during an episode of heavy haze pollution from 6 December 2016 to 9 January 2017. The turbulence data were recorded at Peking University’s atmospheric science and environment observation station. The results showed a negative correlation between the wind speed and the PM_2.5 concentration. The turbulence kinetic energy was large and showed obvious diurnal variations during unpolluted (clean) weather, but was small during episodes of heavy haze pollution. Under both clean and heavy haze conditions, the relation between the non-dimensional wind components and the stability parameter z/L followed a 1/3 power law, but the normalized standard deviations of the wind speed were smaller during heavy pollution events than during clean periods under near-neutral conditions. Under unstable conditions, the normalized standard deviation of the potential temperature σ _θ /|θ_*| was related to z/L, roughly following a –1/3 power law, and the ratio during pollution days was greater than that during clean days. The three-dimensional turbulence energy spectra satisfied a –2/3 power exponent rate in the high-frequency band. In the low-frequency band, the wind velocity spectrum curve was related to the stability parameters under clear conditions, but was not related to atmospheric stratification under polluted conditions. In the dissipation stage of the heavy pollution episode, the horizontal wind speed first started to increase at high altitudes and then gradually decreased at lower altitudes. The strong upward motion during this stage was an important dynamic factor in the dissipation of the heavy haze.     

Influence of Intermittent Turbulence on Air Pollution and Its Dispersion in Winter 2016/2017 over Beijing,China

Journal of Meteorological Research - With rapid urbanization in recent years, severe air pollution has emerged as a major issue for many regions of China, especially in some metropolises. A...     

Influence of Intermittent Turbulence on Air Pollution and Its Dispersion in Winter 2016/2017 over Beijing,China

With rapid urbanization in recent years, severe air pollution has emerged as a major issue for many regions of China, especially in some metropolises. A persistent pollution case during 6 December 2016–8 January 2017 was selected to investigate the relations between turbulent intermittency and frequent PM_(2.5)(particulate matters with diameter less than 2.5 μm) pollution events over the metropolitan region of Beijing, China. The accumulation of PM_(2.5) near the surface frequently occurred as a combined result of strong inversion layers, stagnant winds, high ambient humidity levels, and stable stratification during this case. Arbitrary-order Hilbert spectral analysis indicated that steep decreases in the PM_(2.5) concentration were simultaneous with the occurrence of intermittent turbulence and strong vertical mixing. A wind profiler observation revealed existence of low-level jets(LLJs) at the end of the polluted periods, suggesting that the upper-level turbulent mixing accompanied by the wind shear of LLJ was transported downward and enhanced the vertical mixing near the surface, which might have caused an abrupt reduction in PM_(2.5) and improvement in air conditions.     

Individual Variations of Winter Surface Air Temperature over Northwest and Northeast China and Their Respective Preceding Factors

Based on monthly mean surface air temperature （SAT） from 71 stations in northern China and NCEP/ NCAR and NOAA-CIRES （Cooperative Institute for Research in Environmental Sciences） twentieth century reanalysis data, the dominant modes of winter SAT over northem China were explored. The results showed that there are two modes that account for a majority of the total variance over northern China. The first mode is unanimously colder （warmer） over the whole of northern China. The second mode is characterized by a dipole structure that is colder （warmer） over Northwest China （NWC） and warmer （colder） over Northeast China （NEC）, accounting for a fairly large proportion of the total variance. The two components constituting the second mode, the individual variations of winter SAT over NWC and NEC and their respective preceding factors, were further investigated. It was found that the autumn SAT anomalies are closely linked to persistent snow cover anomalies over Eurasia, showing the delayed effects on winter climate over northern China. Specifically, the previous autumn SAT anomalies over the Lake Baikal （LB; 50-60°N, 85-120°E） and Mongolian Plateau （MP; 42-52°N, 80-120°E） regions play an important role in adjusting the variations of winter SAT over NWC and NEC, respectively. The previous autumn SAT anomaly over the MP region may exert an influence on the winter SAT over NEC through modulating the strength and location of the East Asian major trough. The previous autumn SAT over the LB region may modulate winter westerlies at the middle and high latitudes of Asia and accordingly affects the invasion of cold air and associated winter SAT over NWC.     

我国东北地区冬季气温变化的东亚冬季风背景

利用中国气象局国家气象信息中心1961—2011年我国东北地区72个气象站月平均气温资料及NCEP/NCAR月平均海平面气压、500 hPa高度场及200 hPa与850 hPa风场再分析资料,对东亚冬季风强度与我国东北地区冬季气温序列经去除线性趋势处理后的变化特征进行对比分析。结果表明:去除线性趋势后,东亚冬季风强度与我国东北地区冬季气温序列的相关系数为-0.69,较原始序列更为显著;两者变化的阶段性较为同步,我国东北地区冬季气温于2004年已转入低温阶段,这与东亚冬季风同时转为偏强阶段关系密切;两者均存在20年左右的长周期,同样存在相近的阶段性短周期;我国东北地区冬季气温的增温变化趋势在1986年前后的增暖性气候突变中起重要作用。东亚冬季风强度与我国东北地区冬季气温年代际信号的相关系数达-0.86,较原始序列年代际相关更为显著;两者的年代际变化存在21.5年左右的共同准周期。东亚冬季风强度与我国东北地区冬季气温的年际变化序列存在4年左右的共同准周期。我国东北地区冬季气温的年际和年代际异常存在与东亚冬季风相关联的200 hPa东亚急流、500 hPa东亚大槽、乌拉尔高压、850 hPa风场、地面西伯利亚高压等的异常背景。     

东北地区冬季气温与北极涛动年代际关系研究

利用中国160站气温资料、北极涛动指数资料及关国NCEP／NCAR再分析资料中月平均海平面气压场、高度场、风场资料，分析了东北地区冬季气温、冬季北极涛动的年代际特征及其关系。结果表明：在年代际时间尺度上，两者之间存在显著正相关。冬季北极涛动处于低（高）指数期，东北冬季气温为持续冷冬（暖冬）期。可能影响机制是：在地面，冬季北极涛动处于低（高）指数期时，西伯利亚高压增强（减弱），亚洲大陆偏北冬季风增强（减弱），东北为持续冷冬（暖冬）期；在对流层中层，冬季北极涛动处于低（高）指数期时，东亚大槽加深（减弱），贝加尔湖以西以北脊增强（减弱），环流呈经向（纬向）型发展，东北对流层中层偏北风增强（减弱），东北为持续冷冬（暖冬）期。     

Influence of October Eurasian Snow on Winter Temperature over Northeast China

This paper addresses the interannual variation of winter air temperature over Northeast China and its connection to preceding Eurasian snow cover.The results show that there is a significant negative correlation between October Eurasian snow cover and following-winter air temperature over Northeast China.The snow cover located in eastern Siberia and to the northeast of Lake Baikal plays an important role in the winter air temperature anomaly.More(less)eastern Siberia snow in October can cause an atmospheric circulation anomaly pattern in which the atmospheric pressure is higher(lower)than normal in the polar region and lower(higher)in the northern mid-high latitudes.Due to the persistence of the eastern Siberia snow from October to the following winter,the winter atmospheric anomaly is favorable(unfavorable)to the widespread movement of cold air masses from the polar region toward the northern mid-high latitudes and,hence,lower(higher)temperature over Northeast China.Simultaneously,when the October snow cover is more(less),the SST in the northwestern Pacific is continuously lower(higher)as a whole; then,the Aleutian low and the East Asia trough are reinforced(weakened),favoring the lower(higher)temperature over Northeast China.     

Comparison of Submicron Particles at a Rural and an Urban Site in the North China Plain during the December 2016 Heavy Pollution Episodes

An extensive field experiment for measurement of physical and chemical properties of aerosols was conducted at an urban site in the Chinese Academy of Meteorological Sciences (CAMS) in Beijing and at a rural site in Gucheng (GC), Hebei Province in December 2016. This paper compares the number size distribution of submicron particle matter (PM1, diameter < 1 μm) between the two sites. The results show that the mean PM1 number concentration at GC was twice that at CAMS, and the mass concentration was three times the amount at CAMS. It is found that the accumulation mode (100–850 nm) particles constituted the largest fraction of PM1 at GC, which was significantly correlated with the local coal combustion, as confirmed by a significant relationship between the accumulation mode and the absorption coefficient of soot particles. The high PM1 concentration at GC prevented the occurrence of new particle formation (NPF) events, while eight such events were observed at CAMS. During the NPF events, the mass fraction of sulfate increased significantly, indicating that sulfate played an important role in NPF. The contribution of regional transport to PM1 mass concentration was approximately 50% at both sites, same as that of the local emission. However, during the red-alert period when emission control took place, the contribution of regional transport was notably higher.     

东北三省冬季气温变化的有关研究进展

 通过简要回顾中国学者有关东北三省冬季气温变化的研究成果,概括分析了近百年或近几十年时间尺度平均气温及最高、最低气温年际、年代际变化的基本特征,综述了与冬季气温年际、年代际变化相关的各类海-气环流因子。近百年来,东北冬季气温上升,1987年前后发生增暖突变;北极涛动、西伯利亚高压、东亚冬季风等是影响东北冬季气温年际变化的主要因子;北极涛动、东亚冬季风、东亚中高纬环流型等的持续性是冬季气温年代际变化的主要因子。对多种变化特征集中出现的20世纪70年代末的气候变化值得深入探讨,也有必要在整个东北三省的范围内,深入开展冬季气温预测方法的系统研究。另外,测站气温序列的非均一性问题也应引起足够重视。     

影响东北的两个罕见气旋发展机制对比

2007年3月3—5日和2016年5月2—3日有两个气旋（简称C304和C502）在江淮流域生成后,以相似路径影响东北地区,但发展强度不同。利用常规观测资料和NCEP FNL分析资料,通过对涡度平流、温度平流、湿位势涡度及锋生函数等物理量进行诊断并结合高、低空环流形势对两个气旋发展动力机制进行对比分析,结果表明：C304低空温度平流在气旋发展初期起主要作用,高空正涡度平流为地面气旋发展提供高空辐散场,地面气旋中心上空垂直上升运动增强,对流层低层斜压性明显,气旋性涡度增加主要在对流层下层,低空斜压强迫是主要发展机制;C502低空温度平流弱,斜压性不明显,高空正涡度平流促使高空闭合环流发展,对流层上层有高湿位涡舌发展下垂并与对流层下层正湿位涡柱耦合贯通,垂直上升运动分布在地面气旋中心两侧,高空位涡下传是主要发展机制。两个气旋发生发展在对流层上层两支急流共存、急流非纬向性反气旋性弯曲环流形势下,对流层低层为气旋式环流背景。     

Chemical Components,Variation, and Source Identification of PM1 during the Heavy Air Pollution Episodes in Beijing in December 2016

Air pollution is a current global concern. The heavy air pollution episodes(HPEs) in Beijing in December 2016 severely influenced visibility and public health. This study aims to survey the chemical compositions, sources, and formation processes of the HPEs. An aerodyne quadruple aerosol mass spectrometer(Q-AMS) was utilized to measure the non-refractory PM1(NR-PM1) mass concentration and size distributions of the main chemical components including organics, sulfate, nitrate, ammonium, and chloride in situ during 15–23 December 2016. The NR-PM1 mass concentration was found to increase from 6 to 188 μg m–3 within 5 days. During the most serious polluted episode, the PM1 mass concentration was about 2.6 times that during the first pollution stage and even 40 times that of the clean days. The formation rates of PM2.5 in the five pollution stages were 26, 22, 22, 32, and 67 μg m~(–3) h–1, respectively. Organics and nitrate occupied the largest proportion in the polluted episodes, whereas organics and sulfate dominated the submicron aerosol during the clean days. The size distribution of organics is always broader than those of other species, especially in the clean episodes. The peak sizes of the interested species grew gradually during different HPEs. Aqueous reaction might be important in forming sulfate and chloride, and nitrate was formed via oxidization and condensation processes. PMF(positive matrix factorization) analysis on AMS mass spectra was employed to separate the organics into different subtypes. Two types of secondary organic aerosol with different degrees of oxidation consisted of 43% of total organics. By contrast, primary organics from cooking, coal combustion, and traffic emissions comprised 57% of the organic aerosols during the HPEs.     

Roles of Synoptic to Quasi-Monthly Disturbances in Generating Two Pre-Summer Heavy Rainfall Episodes over South China

In this study, power spectral analysis and bandpass filtering of daily meteorological fields are performed to explore the roles of synoptic to quasi-monthly disturbances in influencing the generation of pre-summer heavy rainfall over South China. Two heavy rainfall episodes are selected during the months of April-June 2008-15, which represent the collaboration between the synoptic and quasi-biweekly disturbances and the synoptic and quasi-monthly disturbances,respectively. Results show that the ...     

利用星载和地基激光雷达分析2019年5月东亚沙尘天气过程

2019年5月中旬,中国北方出现大范围沙尘暴天气,此次天气过程持续时间较长,影响范围较大.利用星载激光雷达CALIOP(Cloud-Aerosol Lidar with Orthogonal Polarization)和地基激光雷达AD-NET(Asian Dust and aerosol lidar observat...     

中国东北南部冬季气温异常及其大气环流特征变化

该文在对东北冬季气温异常的时空变化特征进行分析的基础之上，利用NCEP/NCAR再分析资料，探讨了影响其异常的同期因子——该地区上空大尺度环流异常特征。发现:东北冬季气温20世纪80年代中期以前处于冷期，60年代达到低谷，80年代中期以后一直处于暖期，90年代为49年来最暖期，1986年是由冷转暖的明显突变点；气温异常存在3～4年、8～9年的年际周期及16～18年的年代际周期；东北地区冬季气温异常与黄河以北地区一致性非常好，是49年全国增暖最显著的地区之一；冷、暖冬年，欧亚中高纬度大气环流异常存在显著的差异，西伯利亚高压、亚洲极涡、贝加尔湖高压脊、东亚大槽及极锋急流是影响其异常的同期重要因子。     

天津冬季重霾污染过程及气象和边界层特征分析

京津冀大气灰霾污染严重,天津市作为其核心组成之一其污染形势亦严峻。选取2013年2月20~28日天津重霾污染时段7站PM2.5(空气动力学当量直径小于等于2.5μm的颗粒物,即细颗粒物)和气态污染物数据,结合北京污染数据、地面气象要素、能见度、边界层温湿和风廓线、后向轨迹,深入分析重霾污染过程特征及气象和边界层成因。结果显示,研究时段天津PM2.5、SO2、NO2、CO和O3浓度均值为150、87、56、2.4和22μg m-3,气态污染物各站差异显著,但仅有SO2全面超过国家空气质量一级标准(50μg m-3),而PM2.5具有区域同步变化特征,且严重超标,是一级标准(35μg m-3)的2~8倍,最高小时均值高达364μg m-3;高浓度PM2.5是导致低能见度的主因,能见度小于10 km对应PM2.5阈值为50μg m-3。弱风和高湿度导致局地排放累积,PM2.5始增,在高湿度条件下,持续偏南风促使其稳步增加,配合弱北风和弱东风PM2.5震荡上扬,污染高值阶段,南北气流短时迅速切换,区域污染传输叠加污染的循环累积,PM2.5浓度峰值达到最高;除因边界层强东风导致的平流逆温外,高浓度PM2.5与平流逆温密切相关;高污染时段高湿主要集中在500 m以下,且随高度递减幅度较大;位于200~600 m的低空急流一定程度抑制污染上升,尤其持续强东风使PM2.5浓度稳步降低到二级水平,污染迅速有效清除最终依赖整层的强西北风。北京、环绕天津的河北中部和西南部地区对天津重污染有显著贡献。     

乌鲁木齐冬季浅薄型焚风对扩散条件及污染物浓度的影响

本文针对峡口城市乌鲁木齐市2013-2015年冬季6个环境监测站、逐时的6类污染物浓度数据,气象数据及风廓线雷达资料,分析了浅薄型焚风对扩散条件及污染物浓度的影响。研究发现：冬季乌鲁木齐出现浅薄型焚风的频率为57.3%,平均气流底高约605m,气流顶高约2108m,气流厚度约1502m;乌鲁木齐市冬季焚风日比非焚风日混合层厚度低200m,逆温层厚度厚344m,逆温差大4.4℃,逆温强度强0.01℃/100m,平均风速小0.1m/s;空气质量各污染等级出现频率焚风日都高于非焚风日,3级高18%,5级以上重度污染高7%;污染物浓度日变化呈双峰结构,并表现为焚风日污染浓度＞冬季平均浓度＞非焚风日污染浓度;污染物浓度（除O3外）空间分布特征为焚风日比非焚风日高。     

两类ENSO对我国华南地区冬季降水的不同影响

El Nino Modoki是近年发现的赤道太平洋海温异常分布的新特征,主要表现为热带太平洋海温异常为纬向"三极型"分布,与传统的El Nino的"偶极型"分布显著不同。本文利用1979～2010年冬季降水观测资料以及NCEP/NCAR再分析月平均资料,分析了El Nino和El Nino Modoki对我国华南地区冬季降水的不同影响。结果表明,El Nino年冬季,西太平洋副热带高压偏强偏南,我国华南地区受其西侧异常西南风影响,获得充足的水汽供应。另外,高层抽吸作用增强,上升运动加强,对流发展,降水偏多;而El Nino Modoki年冬季,西太平洋副热带高压位置偏北,我国华南地区受高压脊控制。华南地区高层抽吸作用减弱,上升运动减弱,对流减弱,并且水汽供应不足,导致降水偏少。     

2016年1月我国中东部一次大气污染物传输过程分析

利用常规气象数据和空气质量模式CAMx对2016年1月15—19日一次冷空气影响下郑州、武汉、南京的大气污染物传输过程进行了分析。观测发现,本次过程中武汉和南京在地面锋线到达后出现明显的PM2.5浓度的快速增长。通过分析发现,两地在1000~950 hPa高度层上偏北风的侵入带来上风向的大气污染物,同时在垂直方向上锋区内的稳定性层结抑制了大气污染物的扩散,两种作用共同导致污染物快速增长。在冷空气主体影响下,尤其是950~900 hPa高度层上弱风区消失后,污染物得到清除。大气污染物的传输作用主要发生在1000~950 hPa高度上。模式PM2.5来源示踪模拟结果表明,武汉(17日夜间至18日)和南京(17日夜间)在本次污染物快速增长过程中区域污染物输入的贡献在51%和58%左右。由于模式对PM2.5传输过程的低估,区域输送贡献率仍存在不确定性。但是,与1月15—19日平均相比, PM2.5的本地贡献明显减少,上风区域贡献明显增加。