雅安市一次暖区强降水过程中多普勒雷达回波特征分析

针对2018年7月14日雅安市发生的一次暖区强降水过程,该文利用多普勒天气雷达、常规观测和加密自动站观测资料,对此次过程发生的环境条件和雷达回波的发展传播机制进行分析。结果表明:①回波的发展及维持主要是由于上游对流系统的移入以及对流系统内部的再触发机制;②当回波走向与环境平均风较一致时,可判断未来回波将沿环境平均风方向发展传播。③通过分析地面气象要素气压和气温的变化可判断冷池是否形成,气压陡升和气温骤降表明地面冷池已经形成,而两者变化趋势重叠的时间段表明冷池持续出现。此时若雷达低层风场显示不断有暖湿气流输送过来,有利于对流系统内部不断触发新的对流单体,这种对流系统内部的再触发机制有利于强回波的长时间维持。     

山东极端强降雨风暴传播类型及流场结构特征

根据雷达反射率因子和径向速度产品演变特征,结合天气实况,对山东短时极端强降水反射率因子和流场结构进行了综合分析。结果表明,山东极端对流性强降水单体演变特征有4种类型:后向传播型、前向传播型、准静止型和再生型。后向传播型的主体降水回波产生的下沉气流与一侧的低层环境气流产生辐合上升运动,激发新的对流单体;前向传播型的主体回波后部下沉气流在地面附近辐散形成低层前沿的阵风锋,而低层暖湿人流经过阵风锋抬升进入到回波前沿的对流塔成为上升气流;准静止型回波常与中低层长时间维持的γ尺度气旋性涡旋有关;再生型回波的再生区内总是有新的单体不断生成,常与稳定少动的局地辐合区相对应。在大范围的强降水过程中,包含两种或以上演变方式。     

不同天气形势下首都机场雷雨的发展演变规律

对2013年首都机场不同天气形势下32个雷雨日的雷达回波进行分型研究、对比分析,发现不同类型雷雨的雷达回波有不同的发生、发展和演变特征。高空槽过境雷雨、冷涡前部雷雨、锋面雷雨均有明显冷空气入侵,雷雨回波为大片强对流回波带,自西北向东南(或自西向东)过境,雷雨多持续1~2 h,有时伴有雷雨大风、冰雹等强对流天气;冷涡底部雷雨、冷涡后部雷雨为零散的片状或块状对流单体或多单体雷暴云团有组织移动,并在移动中发展合并,逐渐形成较大的线状或带状多单体雷暴群,沿高空引导气流向南或向东南移动,其中各组成单体或多单体雷暴生成、发展及衰减十分迅速,能造成一段或多段雷雨过程;副高边缘雷雨、切变线雷雨均发生在低层高温、高湿及偏南或偏东气流中,大气中储存有大量不稳定能量,微小的触发抬升条件就会激发出新的对流单体或多单体,此类雷雨回波多突发产生,生消演变频繁,一次过程可造成多段雷雨。     

2017年5月7日广州特大暴雨微物理特征及其触发维持机制分析

2017年5月7日,广州经历了一次罕见的局地特大暴雨事件,刷新了多个雨量历史纪录,造成了严重的国民财产损失。本文利用双偏振雷达、二维雨滴谱仪、微波辐射计和风廓线雷达等多种新型探测资料,分析这次短时暴雨的演变过程和降水特征,并通过大气环境诊断和双多普勒雷达风场反演方法研究其维持机制。结果表明,此次降水过程发生在弱天气系统强迫条件下,大气层结表现为弱对流抑制、低抬升凝结高度、中等对流有效位能、较厚的暖云层,低层受暖湿气流影响但无明显急流。强降水是由中尺度对流系统直接产生的。午夜至凌晨的初始对流主要由偏南暖湿气流与地形相互作用产生,对流单体不断在后部触发并逐渐形成准静止的对流雨带;黎明至早晨,新生对流单体沿着成熟的强降水风暴出流与低层偏南暖湿气流的交界不断激发,后向传播过程更为显著,形成回波列车效应;此后降水以组织化的对流雨带不断南移。此次暴雨过程中的对流云团为典型的低质心降水云团,降水雨滴谱在高湿环境中表现为暖性降水的特征(小雨滴浓度非常高),但同时存在部分大粒子,从而导致更高的降水效率和局地强降水。不断加强的低层偏南暖湿气流对于对流系统的发展和维持具有重要作用。     

青藏高原东北部一次罕见强对流天气的中小尺度系统特征分析

2016年8月17-18日青藏高原东北部出现了罕见的大冰雹、短时暴雨、雷暴大风等强对流天气。运用常规观测资料、NCEP再分析资料、葵花静止气象卫星、多普勒天气雷达等观测资料分析了此次强对流过程的大气环境场和中小尺度对流系统的发生发展和对流传播机制。结果表明:西太平洋副热带高压北抬明显,属于低层暖平流强迫型。水汽输送主要来自南海。维持较长时间的弱冷锋是强对流的地面触发机制;对流云团逐渐演变为MCC,对流传播整体具有沿着河谷往层结不稳定区的正向和往低层入流风的反向传播的特征。河谷地形是影响对流移动和传播路径的关键;强对流风暴单体生命史均较长,强降雹单体为类超级单体和普通多单体,强降水回波属于多单体线状对流。降雹单体整体比降水单体发展得更强,变化幅度更大,尤其是垂直累积液态水含量的变化更剧烈。强对流开始前单体垂直累积液态水含量均是先增后降;几处局地雷暴大风是由雷暴云团内弱降水在较厚的环境干层蒸发而显著降温所产生的较大负浮力或由线状对流中强降水拖曳导致的强下沉辐散气流造成,雷达回波具有质心急剧下降或中层径向速度辐合特征。     

阵风锋、海风锋和冷锋等触发局地强对流风暴实例分析

利用CINRAD/SA雷达探测资料,结合地面实况和探空资料,对7次典型中尺度辐合线触发强对流风暴的特征进行了分析。结果表明：阵风锋、海风锋和冷锋等边界层辐合线在一定条件下雷达低层反射率因子产品上表现为清晰的窄带回波,某些辐合线在反射率因子产品上不能得到任何有用信息,但在低层径向速度上可识别出线性径向速度辐合;识别出窄带回波或清晰的径向辐合线约1 h后,是雷暴首次触发的主要时间段;对于干型强对流风暴产生的阵风锋,其右侧往往是雷暴触发的主要区域,导致风暴右向传播;湿型强对流风暴产生的阵风锋,激发雷暴的方向与雷暴平均移动方向基本相反,导致风暴呈后向传播特征;海风锋向内陆推进速度快的区域是雷暴触发的主要区域,后继雷暴具有两侧传播特征;单纯的线性低层径向速度辐合在合适的环境条件下触发强对流,主要特征是对流风暴移动缓慢,可造成局地灾害性强降雨天气。     

2014年7月14日新乡强对流过程成因分析

利用常规和区域自动站观测资料、卫星和多普勒雷达监测产品及NCEP再分析资料,对2014年7月14日新乡强对流过程进行了综合分析。结果表明：高空东移冷槽与低层暖脊叠加使新乡上空形成明显的不稳定层结,而中低层暖湿空气在午后表现出明显的北抬和向高空扩展的趋势,使大气对流不稳定度进一步加强,有利于雷暴大风和冰雹强对流天气的出现;同时,强对流天气发生前0—6 km垂直风切变达到中等偏强程度,有利于对流系统的形成和维持。地面中尺度辐合线起对流触发作用,辐合线尾部前侧的对流云团发展更强更快。云团合并导致对流云团迅猛加强,对流单体合并有利于对流回波的暴发性发展及回波顶快速抬升。过程中雷暴外流边界也是强对流的重要触发机制,太行山脉东侧的雷暴外流边界受地形抬升作用,触发大范围分散的对流单体,导致了局地短时强降水天气。风灾主要是由多单体风暴中的下击暴流和雷暴外流边界造成的,下击暴流造成的大风比由雷暴外流边界导致的大风更强。此外,强回波中心强度增强、质心高度迅速升高,回波顶高和VIL值跃增等对强对流过程中局地冰雹预报有较好的指示意义。     

雅安一次极端强降水的超级单体风暴特征及成因分析

2020年8月10日-11日雅安市出现了一次区域大暴雨天气过程,其中芦山县出现了特大暴雨,此次特大暴雨天气过程,持续时间长,最大累积降水量、最大小时雨强较大,均突破了历史极值,具有较强的极端性。通过分析雷达回波可知,此次极端强降水由强降水超级单体风暴的稳定少动造成,本文根据雅安市365个区域自动站雨量数据、micaps实况资料、雷达以及NCEP 1°×1°再分析资料等资料,分析其产生的原因：（1）行星尺度和天气尺度系统稳定少动,低层夜间低层急流发展,输送暖湿平流,有利于对流不稳定层结的建立,为强降水超级单体风暴的发生提供了有利的环流条件。（2）地面到低层的假相当位温异常偏高,有利于对流不稳定的进一步发展,在强对流风暴附近还存在中尺度的假相当位温的密集区,锋区的动力强迫生成的次级环流有利于低层不稳定能量和水汽向高层输送,同时也触发不稳定能量的释放,产生较强的上升运动。（3）强的垂直风切变以及大的对流有效位能有利于强降水超级单体风暴的发生和维持其有组织的程度。（4）水汽条件异常也是此次强降水超级单体风暴的重要原因。（5）极端的高能高湿的大气状态下,边界层的中尺度辐合线是触发此次强降水超级单体风暴的直接原因,并且受地形的阻挡作用,强降水超级单体稳定少动,造成了此次极端强降水的发生。     

一次槽后型大暴雨伴冰雹的形成机制和雷达观测分析

利用常规气象观测资料、新一代天气雷达、自动站、NCEP再分析资料等对西北气流形势下一次局地大暴雨伴多次降雹的强对流天气形成机制和对流系统结构进行了精细化分析。结果表明:(1)局地大暴雨伴冰雹发生在西北气流控制和大气层结极不稳定的形势下,14:00(北京时,下同)CAPE较08:00显著增大,为大暴雨和冰雹提供了不稳定能量;对流层低层的水汽含量大值中心为后向和前向传播新生单体的不断生成提供了充分的水汽条件;地面局地加热不均匀,午后地面温度达到对流温度临界值使地面暖气团自由上升,从而产生初始对流回波。在达到热力对流的条件下,地面中尺度辐合线和露点锋对局地大暴雨伴多次冰雹天气的发生有加强触发作用,地面中尺度低压是辐合维持和水汽集中的重要原因。(2)雷达图上,初始回波在周口附近生成、加强并向东南方向移动的过程中,其后侧和右后侧不断有中γ尺度对流单体生成,新生单体经历了积云生成加强、成熟合并、减弱消散阶段,其传播方向和移动方向近于相反,使周口附近强回波呈准静止动态平衡状态而持续存在。随后,在许昌到太康近东西向带状回波的前侧不断有中γ尺度新对流单体生成,并与周口附近后向传播的对流单体相接,排列成西北—东南向的线状多单体回波带,前向传播和后向传播分别经历了后侧减弱和前侧减弱阶段,中间回波在周口附近发展最旺盛。向前和向后两种传播形式多单体结构中的中γ尺度对流单体形成显著的"列车效应"使周口、西华出现局地大暴雨和多次降雹。在平均径向速度图上有中尺度涡旋,西北—东南向线状对流回波带在中低层有辐合—辐散—辐合相间的结构特征,在高层则与中低层相反,线状雷暴系统的形成和演变与强雷暴下沉气流抬升暖湿空气有较大关系,对流单体生成于低层辐合、高层辐散处。     

一次槽后型大暴雨伴冰雹的形成机制和雷达观测分析北大核心CSCD

利用常规气象观测资料、新一代天气雷达、自动站、NCEP再分析资料等对西北气流形势下一次局地大暴雨伴多次降雹的强对流天气形成机制和对流系统结构进行了精细化分析。结果表明:(1)局地大暴雨伴冰雹发生在西北气流控制和大气层结极不稳定的形势下,14:00(北京时,下同)CAPE较08:00显著增大,为大暴雨和冰雹提供了不稳定能量;对流层低层的水汽含量大值中心为后向和前向传播新生单体的不断生成提供了充分的水汽条件;地面局地加热不均匀,午后地面温度达到对流温度临界值使地面暖气团自由上升,从而产生初始对流回波。在达到热力对流的条件下,地面中尺度辐合线和露点锋对局地大暴雨伴多次冰雹天气的发生有加强触发作用,地面中尺度低压是辐合维持和水汽集中的重要原因。(2)雷达图上,初始回波在周口附近生成、加强并向东南方向移动的过程中,其后侧和右后侧不断有中γ尺度对流单体生成,新生单体经历了积云生成加强、成熟合并、减弱消散阶段,其传播方向和移动方向近于相反,使周口附近强回波呈准静止动态平衡状态而持续存在。随后,在许昌到太康近东西向带状回波的前侧不断有中γ尺度新对流单体生成,并与周口附近后向传播的对流单体相接,排列成西北—东南向的线状多单体回波带,前向传播和后向传播分别经历了后侧减弱和前侧减弱阶段,中间回波在周口附近发展最旺盛。向前和向后两种传播形式多单体结构中的中γ尺度对流单体形成显著的"列车效应"使周口、西华出现局地大暴雨和多次降雹。在平均径向速度图上有中尺度涡旋,西北—东南向线状对流回波带在中低层有辐合—辐散—辐合相间的结构特征,在高层则与中低层相反,线状雷暴系统的形成和演变与强雷暴下沉气流抬升暖湿空气有较大关系,对流单体生成于低层辐合、高层辐散处。     

COMPARATIVE ANALYSIS OF VARIOUS DATA OF AIR–SEA TEMPERATURE DIFFERENCE AND ITS VARIATION ACROSS SOUTH CHINA SEA IN THE PAST 35 YEARS

Using the International Comprehensive Ocean-Atmosphere Data Set(ICOADS) and ERA-Interim data, spatial distributions of air-sea temperature difference(ASTD) in the South China Sea(SCS) for the past 35 years are compared,and variations of spatial and temporal distributions of ASTD in this region are addressed using empirical orthogonal function decomposition and wavelet analysis methods. The results indicate that both ICOADS and ERA-Interim data can reflect actual distribution characteristics of ASTD in the SCS, but values of ASTD from the ERA-Interim data are smaller than those of the ICOADS data in the same region. In addition, the ASTD characteristics from the ERA-Interim data are not obvious inshore. A seesaw-type, north-south distribution of ASTD is dominant in the SCS; i.e., a positive peak in the south is associated with a negative peak in the north in November, and a negative peak in the south is accompanied by a positive peak in the north during April and May. Interannual ASTD variations in summer or autumn are decreasing. There is a seesaw-type distribution of ASTD between Beibu Bay and most of the SCS in summer, and the center of large values is in the Nansha Islands area in autumn. The ASTD in the SCS has a strong quasi-3a oscillation period in all seasons, and a quasi-11 a period in winter and spring. The ASTD is positively correlated with the Nio3.4 index in summer and autumn but negatively correlated in spring and winter.     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

IMPACT OF ATMOSPHERIC LOW-FREQUENCY OSCILLATION ON THE IMMIGRATION OF NILAPARVATA LUGENS(STL) IN HUNAN AND JIANGXI PROVINCES

Various features of the atmospheric environment affect the number of migratory insects, besides their initial population. However, little is known about the impact of atmospheric low-frequency oscillation(10 to 90 days) on insect migration. A case study was conducted to ascertain the influence of low-frequency atmospheric oscillation on the immigration of brown planthopper, Nilaparvata lugens(Stl), in Hunan and Jiangxi provinces. The results showed the following:(1) The number of immigrating N. lugens from April to June of 2007 through 2016 mainly exhibited a periodic oscillation of 10 to 20 days.(2) The 10-20 d low-frequency number of immigrating N. lugens was significantly correlated with a low-frequency wind field and a geopotential height field at 850 h Pa.(3) During the peak phase of immigration, southwest or south winds served as a driving force and carried N. lugens populations northward, and when in the back of the trough and the front of the ridge, the downward airflow created a favorable condition for N. lugens to land in the study area. In conclusion, the northward migration of N. lugens was influenced by a low-frequency atmospheric circulation based on the analysis of dynamics. This study was the first research connecting atmospheric low-frequency oscillation to insect migration.     

A COMPARATIVE ANALYSIS OF ATMOSPHERIC AND OCEANIC CONDITIONS BEFORE THE OCCURRENCE OF TWO TYPES OF EL NIO EVENTS

The atmospheric and oceanic conditions before the onset of EP El Ni?o and CP El Ni?o in nearly 30 years are compared and analyzed by using 850 hPa wind, 20℃ isotherm depth, sea surface temperature and the Wheeler and Hendon index. The results are as follows: In the western equatorial Pacific, the occurrence of the anomalously strong westerly winds of the EP El Ni?o is earlier than that of the CP El Ni?o. Its intensity is far stronger than that of the CP El Ni?o. Two months before the El Ni?o, the anomaly westerly winds of the EP El Ni?o have extended to the eastern Pacific region, while the westerly wind anomaly of the CP El Ni?o can only extend to the west of the dateline three months before the El Ni?o and later stay there. Unlike the EP El Ni?o, the CP El Ni?o is always associated with easterly wind anomaly in the eastern equatorial Pacific before its onset. The thermocline depth anomaly of the EP El Ni?o can significantly move eastward and deepen. In addition, we also find that the evolution of thermocline is ahead of the development of the sea surface temperature for the EP El Ni?o. The strong MJO activity of the EP El Ni?o in the western and central Pacific is earlier than that of the CP El Ni?o. Measured by the standard deviation of the zonal wind square, the intensity of MJO activity of the EP El Ni?o is significantly greater than that of the CP El Ni?o before the onset of El Ni?o.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

Could the Recent Taal Volcano Eruption Trigger an El Ni?o and Lead to Eurasian Warming?

正The Taal Volcano in Luzon is one of the most active and dangerous volcanoes of the Philippines. A recent eruption occurred on 12 January 2020(Fig. 1a), and this volcano is still active with the occurrence of volcanic earthquakes. The eruption has become a deep concern worldwide, not only for its damage on local society, but also for potential hazardous consequences on the Earth's climate and environment.     

VARIABILITY OF INTER-ANNUAL RELATIONSHIP BETWEEN INDIAN OCEAN DIPOLE AND HUAXI REGION’S AUTUMN PRECIPITATION

The moving-window correlation analysis was applied to investigate the relationship between autumn Indian Ocean Dipole (IOD) events and the synchronous autumn precipitation in Huaxi region, based on the daily precipitation, sea surface temperature (SST) and atmospheric circulation data from 1960 to 2012. The correlation curves of IOD and the early modulation of Huaxi region’s autumn precipitation indicated a mutational site appeared in the 1970s. During 1960 to 1979, when the IOD was in positive phase in autumn, the circulations changed from a “W” shape to an ”M” shape at 500 hPa in Asia middle-high latitude region. Cold flux got into the Sichuan province with Northwest flow, the positive anomaly of the water vapor flux transported from Western Pacific to Huaxi region strengthened, caused precipitation increase in east Huaxi region. During 1980 to 1999, when the IOD in autumn was positive phase, the atmospheric circulation presented a “W” shape at 500 hPa, the positive anomaly of the water vapor flux transported from Bay of Bengal to Huaxi region strengthened, caused precipitation ascend in west Huaxi region. In summary, the Indian Ocean changed from cold phase to warm phase since the 1970s, caused the instability of the inter-annual relationship between the IOD and the autumn rainfall in Huaxi region.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on