江淮梅雨锋暴雨过程Q矢量分析及落区预报

应用Ｑ矢量分析方法对２０次伴有暴雨的江淮梅雨锋过程进行分析，揭露了梅雨锋暴雨期对流层低层Ｑ矢量散度场的分布特征以及中、低空主要天气系统和暴雨带之间的时空配置关系，指出了Ｑ矢量散度场对江淮梅雨暴雨的落区有较好的预报意义。     

1991年江淮特大暴雨的降水性质与对流活动

从计算大尺度热源和分析ＴＢＢ资料两个方面，阐述了１９９１年江淮梅雨期间降水性质与对流活动的季节性演变特征。结果表明：梅雨期间江淮上空３个强上升运动时段分别形成了３场暴雨，由暴雨释放的热量使江淮大气出现了３个时段的强加热；３场暴雨的降水性质呈显著的季节性演变，由第１场暴雨以锋面性降水为主发展到第３场暴雨异常强的对流性降水。文中详细分析了热源和水汽汇的时空分布特征，并从大气运动场和热力结构讨论了盛夏强对流降水期间积云对流以涡动形式对热量和水汽的强铅直输送作用。江淮地区ＴＢＢ值能很好地反映降水状况，雨期一致地对应于ＴＢＢ低于２５０Ｋ的时段。梅雨中后期东亚地区对流活动季节性地增强，带状对流区（特别是ＴＢＢ高负距平区）与雨带位置相符。对流带位置及对流活动强弱与西南暖湿气流活动密切相关，它很好地表征了东亚地区的低空急流（给积云输送热带对流大气）。梅雨期间对流带主要出现在江淮流域，但可在东亚范围内飘移，它落在江淮与否则决定了江淮暴雨的维持与中断     

梅雨前后亚洲季风区平均散度风环流和水汽输送的研究

分析了１９８３年江淮流域梅雨期及其前后亚洲季风区平均散度风环流和垂直积分水汽输送的辐散分量。在入梅前强水汽辐合中心位于华南，出梅后则位于印度季风区，梅雨期这两地区都存在着强水汽辐合中心，并且强水汽辐合区和中国东部雨带的位置变化及热源分布有着密切关系。同时指出，江谁流域梅雨与大尺度辐散环流的变化、热源的配置及水汽辐合的位置有着较好的对应关系。     

“07.7”重庆暴雨的数值模拟分析

针对2007年7月17日发生在重庆地区的一次暴雨过程,利用AREM模式进行了数值模拟。结果显示,AREM模式较好地模拟了这次暴雨过程的雨带及雨带上双极值中心的分布。利用模式输出的高时空分辨率结果,对暴雨过程的中尺度特征进行了诊断分析,得到的主要结论有:24h累积降水的双中心峰值发生在不同时段;暴雨中心的动力场结构随时间的演变与降水量在中尺度特征值上有很好的对应关系,两个降水中心对应高低层的流场配置不同;暴雨是在西南涡及低空西南急流的直接作用下发生发展,低涡和急流的维持为降水中心的低层辐合及与之伴随的上升气流的发展提供了有利条件;对流层高层高压脊的变化和中尺度辐散区发展也是造成此次降水的重要因素,辐散区的移动造成强上升运动区的移动,这是引起降水中心移动的原因之一。     

梅雨雨带北跳过程研究

利用1979～2007年逐日再分析资料和高分辨率逐日降水资料,通过定义确定了每年梅雨雨带北跳的日期,对梅雨雨带的北跳过程及其可能的物理机制进行了研究。分析结果表明:梅雨雨带北跳日期存在明显的年际变化,本文合成得到的雨带北跳过程与前人的工作相一致。水汽输送的变化和对流层中层的垂直运动是影响梅雨雨带位置分布的关键因素。Omega方程诊断结果表明,在梅雨雨带北跳前期,对流层高层的环流异常导致江淮流域出现异常下沉运动,不利于梅雨雨带的北跳;而涡度方程的诊断结果表明,江淮流域的异常下沉运动导致的非绝热冷却在中国东部的对流层低层引起异常反气旋涡度倾向,有利于副热带高压西伸,从而有利于梅雨雨带的北跳。因此,当对流层高层环流发生变化（主要受纬向涡度平流影响）,使得江淮流域的异常下沉运动转变为异常上升运动时,高低层相互配合,造成了梅雨雨带的突然北跳。     

2003年江淮梅雨期一次特大暴雨的研究——中尺度对流和水汽条件分析

本文对2003年7月4日-5日江淮梅雨期间的一次特大暴雨过程进行了多尺度的详细分析.环流背景、中尺度对流云团和水汽条件分析表明,这次特大暴雨是在典型梅雨的有利环境背景形势下,由梅雨锋上的中尺度对流系统造成的,地面低压、低层切变线及西南低空急流与这次特大暴雨过程有着密切的关系.强降水中心与中尺度对流云团的关系十分密切,中β尺度云团的生成合并增强,和其中中γ降水系统的存在,导致了降水强度的局地性差异.江淮流域主要表现为经向水汽通量的辐合区,强水汽通量舌与低层高θse的舌区一致,暴雨过程中水汽的快速集中主要是通过风场散度项造成的,局地风场的辐合在水汽快速集中起主要作用.低层充沛的水汽则通过气旋性涡度柱中的强上升气流输送到对流层的中高层.     

江淮流域梅雨锋暴雨南北雨带干冷空气侵入作用的对比研究

对2007—2011年梅雨期江淮流域降水进行统计分析,确认此时段降水频次与降水量空间分布在淮河与长江中下游,形成两个分离的多降雨区。长江与淮河两分离雨带在盛行中尺度系统、空间结构、梅雨锋位置、水汽输送通道、暴雨落区、干冷气团入侵以及干冷动量南移等方面,均有各自特征。在主导高空环流下,更多低涡暴雨(77%)位于长江流域,更多辐合线暴雨(86%)发生在淮河流域,这些盛行的浅薄降水系统,造成梅雨暴雨雨强大、风速小的特征。长江流域低涡环流引导水汽输送来自南海与东海两地,因而暴雨范围更大,雨带更宽,而淮河流域辐合线主要水汽来源仅为南海。假相当位温表现的梅雨锋作为干冷空气的前缘,在淮河流域因辐合线结构垂直剖面陡峭,在长江流域因低涡环流,形成干冷和暖湿气团的层次叠加混合。在梅雨锋北侧,干冷空气从对流层中高层向下侵入,在淮河流域位置较长江流域偏高且狭窄。湿位涡垂直分布显示,暴雨区与湿位涡斜压项大于0的正涡度发展区对应。干冷动量中心的下传与湿位涡斜压项小于0对应,下传时向南移,其前缘对暴雨雨带位置有指示性;其南下速度,因纬度与密度差异,在淮河流域移速小于长江流域。     

基于WRF模式的雅安暴雨数值模拟研究

利用WRF模式对2010年8月21日发生在雅安地区的一次暴雨过程进行了数值模拟。对比分析模拟和实况发现,WRF模式较好的模拟了此次降水过程的时空分布,人而利用模式输出的高时空分辨率模拟资料对此次暴雨进行诊断分析。结果表明,青藏高原地形的阻挡作用使副热带高压西南缘的暖湿气流持续向四川盆地输送,在雅安地区上空700 hPa形成气旋性环流中心;主要降水时段内强降水中心从低层到高层均出现了强烈的上升运动,以及暴雨中心上空维持着高层辐散、低层辐合,高空为负涡度、低空为正涡度,且随暴雨过程发展对流层正涡度的加强作用为暴雨的生成和维持提供了有利的动力条件;对流层中低层接近饱和的空气、强烈的水汽输送以及水汽通量散度高低层的配置,为本次暴雨提供了充足的水汽条件;对流层低层大气存在明显的不稳定层结,中层为中性层结,这种对流性不稳定的维持为暴雨天气的发生提供了热力条件,有利于强降水过程的形成。     

非地转湿Q矢量在台风暴雨预报中的应用试验

利用NCEP/NCAR全球格点资料和TRMM卫星资料,采用改进后的非地转湿Q矢量,对0908号台风＂莫拉克＂引起的台湾南部特大暴雨过程进行预报应用试验。试验结果表明：（1）850 hPa高度层的非地转湿Q矢量散度及水汽通量散度分布可以预报未来24 h暴雨的落区及其雨带的分布,暴雨发生在Q矢量散度梯度大值区靠近辐合区域,同时该区域要有水汽辐合中心,雨带分布与该梯度大值区分布基本一致。（2）Q矢量辐合区的倾斜式发展很好地描述了暴雨中心强对流系统垂直结构,强对流系统发展旺盛期出现在暴雨发生前的18 h,具有一定预报意义。（3）台风暴雨发生在次级环流的上升支附近,最强次级环流上升支出现在暴雨发生时期;次级环流中的上升气流从低层到高层的倾斜方向较好地描述了雨带的移动,次级环流的调整比雨带移动提前了24 h,具有较好的预报应用价值。     

重庆2次西南涡暴雨过程的类比分析

基于AREM模式分别对2010年夏季发生在重庆的两次西南涡暴雨过程进行数值模拟,并利用模拟结果对暴雨过程的动力和热力场演变以及涡度收支变化进行分析。结果表明:1)西南涡造成的降水落区位于低涡中心附近,整个降水过程雨带分布与低涡移动路径相一致;2)整层水汽通量辐合极值出现时间超前于最大降水出现时间,降水增强阶段,整层水汽呈增长趋势,说明存在稳定的水汽输送;3)最强辐合出现时间略早于最大正涡度出现的时间,说明大气辐合能够促进涡度的发展,辐合中心比正涡度中心位置低;4)涡度辐合辐散项对低涡的发展加强起最主要的作用;涡度平流项和涡度辐合辐散项的作用集中体现在中低层大气中,而垂直对流项和扭转项的作用则在中高层更为明显;降水的强弱与涡度变率的大小及伸展高度相对应。     

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.     

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.     

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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正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.SUBMISSIONAll submitted     

A Brief Introduction to Marine Meteorological Science Experiment Base at Bohe Town,Maoming City,Guangdong Province

<正>With the support of specialized funds for national science institutions,the Guangzhou Institute of Tropical and Marine Meteorology,China Meteorological Administration set up in October 2008 an experiment base for marine meteorology and a number of observation systems for the coastal boundary layer,air-sea flux,marine environmental elements,and basic meteorological elements at Bohe town,Maoming city,Guangdong province,in the northern part of the South China Sea.     

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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.