低空暖式切变线引发局地特大暴雨成因分析

利用常规观测、加密自动站降水及NCEP 1°×1°再分析资料,结合铜仁多普勒雷达观测资料对2015年7月14日夜间发生在贵州省松桃县的一次局地特大暴雨进行分析,结果发现:此次局地特大暴雨是发生在中层500 h Pa中低纬"ω"环流型稳定形势下;低层高湿高能环境为暴雨提供了充足的水汽和能量;地面弱冷空气入侵激发了对流的产生,是产生强降水的触发条件;梵净山地形对气流既有抬升又有增强气流辐合的作用,对流单体不断在其迎风坡产生;雷达回波显示对流回波单体沿着地面中尺度辐合线生成、发展、合并、移动和消亡,出现了明显的列车效应,地面辐合线对对流单体起着组织、加强和引导作用;暴雨区位于850 h Pa暖式切变线南侧、地面冷锋前部、地面中尺度辐合线北侧,而地面中尺度辐合线北侧1~1.5个纬距内是强降水的主要落区。     

2005年6月华南特大连续性暴雨的环境条件和中尺度扰动分析

利用常规观测站、地面加密站资料、卫星红外云图TBB和NCEP再分析资料,对2005年6月19-24日发生在广东的特大连续性暴雨过程进行了分析.天气分析表明:高空南亚高压前部的强辐散场,500 hPa河套阻塞高压以及低层低涡切变线横卧在江淮一带、低空急流源源不断地向华南输送暖湿气流的这种大尺度环流形势和相应的大范围动力热力及水汽条件,决定了暴雨的多发时期和持续性;区域暴雨多发期内5次强降水的具体发生和间歇,则与暴雨区大气动力、热力及水汽条件的5个α中尺度时间变化与震荡密切联系并受其影响;暴雨区动力条件的α中尺度时间变化与特定的大尺度环流背景下高低空急流的演变有密切的关系.降水的中尺度特征分析表明:暴雨过程中5场暴雨的发展和间歇对应5个α中尺度系统的发展和减弱,暴雨是由19个β中尺度系统直接造成19个β中尺度大雨团形成.进一步分析表明:强降水主要发生在地面静止锋和锋前暖区的中尺度切变线(或中尺度辐合线)和中尺度涡旋或中尺度辐合中心附近,中尺度涡旋内的降水是由飑线上γ中尺度对流单体形成的"列车效应"产生的,而中尺度切变线附近的降水则是飑线的发展合并加强产生的.发生在冷式切变线附近的强降水移动速度较快,发生在暖式切变线附近的强降水移动缓慢,发生在辐合中心的强降水在原地发展达最强后随辐合中心转为切变线减弱或直接在原地减弱消失而结束.     

“8.13”黄淮北部暴雨云团的组织结构和触发机制

利用FY-2E卫星资料、多普勒雷达监测及4Dvar反演资料、区域自动站和常规观测资料、NCEP分析资料,对2010年8月13日黄淮北部暴雨云团的组织结构、发展演变及形成机制进行研究。结果表明:暴雨云团形成发展于低涡切变形势下,低涡切变线、西南急流及边界层扩散南下弱冷空气是主要影响系统;高的对流不稳定能量、强的低层垂直风切变和持续发展的水汽条件是主要环境特征。不同区域云团的形成机制有差别,发展北上的西南急流促使MβCS旺盛发展。随着低涡发展,MβCS发展合并形成圆形MαCS,强暖湿气流强迫、弱冷空气扩散及地面辐合线是圆形MαCS形成发展的重要机制。γ或β中尺度气旋及辐合线在对流初生阶段起动力触发作用,辐合加强及辐合区的向后延伸导致对流云团的自身发展和后向发展;成熟阶段对流单体后部的强出流促使对流单体分裂,气旋式环流外围西南和偏南气流合并造成对流单体合并。MαCS成熟和衰亡期雷达上出现的线状对流系统具有明显强降水特征。     

“8·16”辽宁特大暴雨多尺度特征分析

利用常规观测资料和区域自动气象站、多普勒雷达、风廓线雷达、地基GPS水汽观测仪等非常规观测资料以及NCEP(1°×1°)再分析资料,对辽宁省清原县2013年8月16日特大暴雨过程的多尺度对流系统特征进行分析。结果表明:低涡切变线和东北低压是本次暴雨过程的主要影响系统。700 h Pa与地面之间假相当位温差达43 K,表明大气强烈的对流性不稳定结构。850 h Pa辽宁大部分地区比湿达14 g·kg~(-1),比湿大值区存在明显的水汽通量辐合,沈阳站监测到的大气可降水量达55 mm,可见本次过程水汽充沛。5次雷达回波依次经过清原地区形成"列车效应",导致该地区特大暴雨。地面辐合线触发的对流单体受其两侧风场的强弱影响,中低层西南风的加强有利于加大新生单体的垂直风切变和水汽条件。短时强降水导致的冷池与其周边暖气流交汇可能触发新的对流单体。在地形影响下,中-β尺度云团和α云系合并过程中的微物理作用可能是导致强降水的主要原因之一。     

局部大暴雨形成的机理与中尺度分析

利用常规气象观测资料、区域自动站加密观测资料、NCEP逐6 h的1°×1°的再分析资料和FY-2C卫星逐时TBB资料、多普勒雷达探测资料,对2012年7月7-8日河南商丘地区大暴雨天气过程形成机理和中尺度系统活动特征进行了研究.结果表明:500 hPa低槽与低层东西向切变线和低空急流相互配合、共同作用是此次大暴雨形成的大尺度环境条件。中尺度分析显示:多个中尺度雨团的活动形成了4个大暴雨中心,中尺度雨团与MαCS相伴,而MαCS是由多个MγCS和MβCS合并、加强的结果。这些MγCS和MβCS是由地面中尺度辐合线或辐合中心触发产生并发展,MαCS覆盖区下强降水回波的移动和发展与地面中度辐合系统对应较好,大暴雨出现在地面辐合系统形成后的1~2 h内;而暖平流导致的局地升温,是地面中尺度辐合系统形成的主要原因。TBB梯度与降水强度成正比,当▽TBB/0.5°E≥34℃,并且TBB≤-63℃时,将产生30mm·h~(-1)的强降水;当MCS发展成熟时强降水发生在中尺度对流云团TBB低值中心附近,当TBB在1 h内降低31℃以上时,1~2 h后该地将出现雨强为50 mm的短时强降水。因此,地面热力不均匀导致的局地升温是此次地面中尺度辐合系统生成的主要原因,而地面中尺度辐合系统的发生发展触发了中小尺度对流系统的发生发展,导致了局部大暴雨的产生。根据中小尺度对流云团的TBB强度及变幅,可提前1~2 h预报短时强降水。     

豫西南一次局地大暴雨中尺度对流系统的结构特征分析

利用FY静止卫星资料、多普勒雷达监测及四维变分(4DVAR)反演产品、区域自动站和常规观测资料、NCEP分析资料,对2011年8月16日淮河上游副热带高压(简称副高)边缘MCS的结构、演变规律及形成原因进行研究。结果表明:卫星监测的中尺度对流系统(Mesoscale convective system,简称MCS)形成于副高边缘切变线附近,扩散南下冷空气触发高对流不稳定能量释放是系统形成发展的主要机制。对流系统的发展演变可分为四个时期:对流系统初生期、β中尺度对流系统(简称MβCS)合并发展期、圆形α中尺度对流系统(简称MαCS)旺盛期和减弱衰亡期,前三个阶段是产生强降水的主要时期。卫星监测的MCS初生期在雷达上表现为单体和多单体风暴,后三个时期则多表现为β和α中尺度对流系统,成熟期在雷达上表现为带状对系统。对流系统在低层辐合线附近发展,辐合区合并造成对流系统合并,进而造成MCS爆发性发展和降水强度的增加,边界层气旋式旋转气流使冷云罩具有圆形特征。对流系统的垂直辐合辐散层及正负涡度层均呈交替分布特征,高层辐散和垂直上升运动相对弱。低层辐合区的宽度与系统的水平尺度有关。地面冷暖气流交汇及地形辐合线具有重要的对流触发作用,地面气流汇合和豫西中尺度地形对降水落区和中心强度均有影响。     

天津一次局地大暴雨中尺度对流系统组织化特征与成因

应用常规观测资料与地面加密自动站、卫星云图、多普勒雷达等多种非常规观测资料以及雷达变分同化分析系统(VDRAS)分析场资料,对2013年7月1日天津南部大暴雨中尺度对流系统的结构、演变特征及其成因进行了分析。结果表明:(1)大暴雨发生在副热带高压边缘暖湿气流、低空700—850 h Pa暖性切变线、高低空急流有利配置的背景下,属暖区暴雨。(2)大暴雨由若干β中尺度对流云团合并加强后的α中尺度对流云团造成,对应雷达,强降雨是由西南方向不断移入天津南部的γ中尺度对流单体发展加强,并先后组织成若干东—西向带状β中尺度对流系统先东北后偏东方向移动造成的,在大港南部有列车效应,具有典型的热带型降水回波特征。(3)逆风区的出现、中空急流向低层伸展,低空急流、超低空急流先后形成并加强,是降水强度加强的重要原因。(4)地面中尺度切变线的维持、加强和中尺度低压倒槽东移、发展、入海加强为中尺度气旋,是先后造成对流单体发展加强并组织成带状中尺度对流系统的两个中尺度系统。(5)近地层中尺度切变线是地面中尺度切变线形成的原因,对流单体前侧的偏南冷性水平出流的叠加,一方面增强了沿切变线的辐合,一方面也加大了低层的水汽输送;带状对流系统后侧的偏北冷性水平出流与东南气流形成的中尺度切变线是地面中尺度气旋形成的原因。     

云南哀牢山东侧一次突发性暴雨过程诊断分析

利用加密自动站资料、NCEP每6 h再分析资料和FY-2C红外TBB等资料,对2012年6月15日发生在哀牢山东侧突发性暴雨进行诊断分析。结果表明:700hPa切变线移到哀牢山后受滇缅脊和地形阻挡形成与山脉同向的切变线.地面冷锋移到哀山东侧后形成静止锋,受不断南下冷空气补充.形成冷空气下沉,暖湿气流上升,出现强烈的上升运动。切变线附近辐合云带内形成的中尺度对流云团在高空西北气流引导下产生的"列车效应"导致了突发性暴雨发生。来自东海和孟加拉湾水汽在切变线附近交汇,受切变线两侧风向辐合产生强烈的水汽辐合,并在哀牢山附近形成深厚的水汽辐合层,是本次突发性暴雨天气的主要水汽特征。逐小时地面自动站海平面气压场和对流有效位能在哀牢山沿线突发性暴雨发生前有明显变化,强降水主要发生在地面中尺度暖低压附近和对流有效位能高值区,此分析对此类短时强降水预报和预警具有一定指示意义。     

“0374”南京特大暴雨中尺度对流系统分析

采用常规观测、地面加密降水资料、逐时云顶亮温TBB资料以及高分辨率模式输出资料,对2003年7月4~5日南京特大暴雨过程中尺度对流系统的发生发展、结构特征及成因进行了综合分析。结果表明:①此次暴雨是由两个中β尺度云团合并而成的MαCS产生,期间有2个强降雨时段,每个时段持续5 h左右;②MαCS发生在低层切变线南侧的中尺度辐合线(或辐合中心)上,并在减弱阶段演变为明显的低涡结构;③在其发展强盛期,MαCS垂直倾斜的上升气流显示出对流风暴云特点,并在对流层中高层具有一定的暖心结构;④低空急流脉动引起急流左侧出口区非地转风辐合的急剧增强以及凝结潜热释放和边界层干冷空气的侵入,导致了MαCS的发生发展。     

2011年7月3日山东局地大暴雨过程的观测分析

应用常规气象资料、FY-2E红外TBB资料、地面加密自动站观测资料和NCEP再分析资料,对2011年7月3日山东中部地区出现的大暴雨过程进行了分析。结果表明：该过程在有利的天气形势下发生,其降水具有中尺度强对流系统特征;强降水落区位于地面自动站风场辐合中心偏冷锋前位置;一个MαCS和一个MβCS是该暴雨过程的直接影响系统;强降水出现在中尺度对流系统（MCS）发展强盛到成熟阶段,降水区最初位于TBB梯度最大处,再沿TBB梯度最大处向下风方移动,并始终处于强冷云顶区后侧;自高纬度向暴雨区低空锲入的东北气流对降水过程起触发作用;强降水区位于低层切变线南侧与水汽通量舌区左侧等值线密集带上,并与假相当位温陡立面密集区位置对应。     

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.     

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.     

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.     

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     

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AIMS AND SCOPE
Atmospheric and Oceanic Science Letters （AOSL） publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.     

Information for Authors

AIMS AND SCOPE Atmospheric and Oceanic Science Letters （AOSL） pub- lishes short research letters on all disciplines of the atmos- phere sciences and physical oceanography. Contributions from all over the world are welcome.     

INFORMATION FOR AUTHORS

正Aims Scope Advances in Atmospheric Sciences(AAS)is an international journal on the dynamics,physics,and chemistry of the atmosphere and ocean with papers across the full range of the atmospheric sciences,co-published bimonthly by Science Press and Springer.The journal includes Articles,Note and Correspondence,and Letters.Contributions from all over the world are welcome.     

Editorial

As we will soon celebrate the 90th anniversary of the founding of the Chinese Meteorological Society （CMS）,Acta Meteorologica Sinica （AMS）,which was originally named as Bulletin of the Chinese Meteorological Society,has gone through 89 years of development and excitement since her first issue in July 1925.According to archived documents （CMS Editorial Committee,1925）,AMS was founded to report the research findings of Chinese meteorologists,record their recommendations for improving meteorological services,and share their common meteorological interests in order to promote the growth of AMS such that more members could be inspired to conduct atmospheric research and meteorological knowledge would be better disseminated to and benefit the general public.By upholding and carrying forward this purpose,AMS has published many highly valuable scientific papers.Some could be treated as classical articles,which have produced important influences on both domestic and international meteorological communities and the related fields.