INFLUENCES OF LOW-FREQUENCY MOISTURE TRANSPORTATION ON LOW FREQUENCY PRECIPITATION ANOMALIES IN THE ANNUALLY FIRST RAINY SEASON OF SOUTH CHINA IN 2010

85-station daily precipitation data from 1961-2010 provided by the National Meteorological Information Center and the NCEP/NCAR 2010 daily reanalysis data are used to investigate the low-frequency variability on the precipitation of the first rain season and its relationships with moisture transport in South China,and channels of low-frequency water vapor transport and sources of low-frequency precipitation are revealed.The annually first raining season precipitation in 2010 is mainly controlled by 10-20 d and 30-60 d oscillation.The rainfall is more(interrupted) when the two low-frequency components are in the same peak(valley) phase,and the rainfall is less when they are superposed in the inverse phase.The 10-20 d low-frequency component of the moisture transport is more active than the 30-60 d.The10-20 d water vapor sources lie in the South India Ocean near 30° S,the area between Sumatra and Kalimantan Island(the southwest source),and the equatorial middle Pacific region(the southeast source),and there are corresponding southwest and southeast moisture transport channels.By using the characteristics of 10-20 d water vapor transport anomalous circulation,the corresponding low-frequency precipitation can be predicted 6 d ahead.

Impacts of SST and SST Anomalies on Low-Frequency Oscillation in the Tropical Atmosphere

Considering the multiscale character of LFO effects of SST on LFO in the tropical atmosphere （low-frequency oscillation） in the tropical atmosphere, the are discussed by using an absolute ageostrophic, baroclinic model. Here, SST effects include sea surface heating and forcing of SST anomalies （SSTAs）. Studies of the influences of sea surface heating on LFO frequency and stability show that sea surface heating can slow the speed of waves and lower their frequency when SST is comparatively low; while higher SST leads to unstable waves and less periods of LFO. Since the impact of a SSTA on ultra-long waves is more evident than that on kilometer-scale waves, long-wave approximation is used when we continue to study the effect of SSTAs. Results indicate that SSTAs can lead to a longer period of LFO, and make waves unstable. In other words, positive （negative） SSTAs can make waves decay （grow）.

THE STRONG DRAGON BOAT RACE PRECIPITATION OF GUANGDONG IN 2008 AND QUASI-10-DAY OSCILLATION

Guangdong suffered from the most serious precipitation of its corresponding time during the dragon-boat race of 2008 since 1951.The relationship between the strong dragon-boat precipitation in 2008 and atmospheric low-frequency oscillation was analyzed with the methods of wavelet analysis,correlation and Lanczos filter.Results showed that the daily rainfall exhibits a significant 7 to 12-day quasi-periodic oscillation(namely quasi-10-day oscillation) during the precipitation,the daily 500 hPa height over Guangdong exhibits a significant 8 to 13-day quasi-periodic oscillation,and the daily 850 hPa zonal wind averaged over the north of the South China Sea presents a significant quasi-12-day periodic oscillation.The Guangdong rainfall during the annually first rainy season is most closely correlated with monsoon over the north of South China Sea,and less closely with an upper-level trough at 500 hPa affecting Guangdong.Strong monsoon surges induced two heavy rainfall processes in 2008.The monsoon surges joined with a westward-propagating quasi-10-day oscillation that originated from the central Pacific and was enhanced in a strong convective region east of the Philippines and a northward-propagating monsoon that originated from the southern South China Sea was enhanced.With composite analysis of typical phases,the common evolution characteristics of atmospheric circulation of the two heavy rainfall processes were analyzed for different phases.These features can be used as reference for medium prediction of heavy rainfall processes in Guangdong.

Fe-bearing minerals and implications for gold mineralization for the Wangu deposit in Central Jiangnan Orogen

Hydrothermal alteration with bleaching of host rocks is the most important prospecting indicator for gold deposits in the Jiangnan Orogen Belt.The alteration has been identified as pre-ore carbonate(siderite)-sericitization and the Fe of siderite in the alteration zone is derived from the host rocks rather than fluids.In addition,such alteration decreases in intensity and width with depth and gold mineralization also occur in the non-bleached rocks,casting doubt on the reliability of the prospecting indicator.Detailed petrographic work and SEM analysis on the Wangu deposit indicate that there are two types of siderites,i.e.,Sd1 and Sd2.Among them,Sd1 grains are relatively small and distributed along the planes of unaltered host rocks,while Sd2 grains,only occurring in the altered slates,are commonly larger.Both types of siderites were altered by auriferous fluids,producing porous cores and minerals such as pyrite,quartz,and ankerite.Compared with unaltered parts,the altered parts have lower Fe,but higher U,Pb,and REE.In addition,Sd1 and Sd2 are similar in Mn,Na,V,and Sr concentrations but different in Fe and Mg.The occurrence and geochemical compositions of both siderites indicate that Sd1 could be transformed into Sd2 by pre-mineralization alteration through dissolution-reprecipitation.Chlorite is another important Fe-bearing mineral in the host rocks,and EPMA analysis suggests that it is ripidolite with relatively high Fe contents.Consequently,chlorite can also provide Fe to form the pre-ore carbonate(siderite)-sericitization.Geochemical modeling demonstrates that both ripidolite and siderite can result in sulfidation and therefore gold precipitation.As a result,this study demonstrates that pre-ore alteration with characterized bleaching is not a prerequisite for gold mineralization despite of its prominent features.Due to the presence of Fe-bearing Sd1 and chlorite,gold mineralization could still occur through sulfidation in the unaltered rocks.

江东金矿床黄铁矿矿物学和微量元素特征对成矿过程的指示

江东金矿床位于湘东北地区万古金矿田,赋存于新元古代冷家溪群浅变质岩中,矿体受NW向断裂控制,金资源量约12.9 t,成矿规模大,能有效代表万古金矿田的成矿特征。目前,对于该矿床细致的矿相学、元素地球化学以及金的富集机制研究相对较少,限制了对其成矿过程的理解。本文在野外地质工作的基础上,对江东金矿床的成矿阶段进行了划分,通过背散射图像和LA-ICP-MS微区原位分析,获得江东金矿床不同世代黄铁矿的微量元素特征。研究表明,江东金矿床成矿阶段划分为:石英-白钨矿阶段(Ⅰ)、石英-黄铁矿阶段(Ⅱ)、石英-多金属硫化物-金阶段(Ⅲ)和石英-方解石阶段(Ⅳ)。根据黄铁矿的结构和微量元素特征,识别出4种类型的黄铁矿:第Ⅱ阶段的粗颗粒自形的Py1a(贫Co、Ni、As、Au)和多孔Py1b(富Co、Ni,贫As、Au);第Ⅲ阶段的Py2a(蚀变围岩中,富As、Au)以及Py2b(烟灰色石英脉中,富As、Au)。不可见金主要以固溶体金(Au~+)的形式赋存于黄铁矿晶格中,且其富集和As关系密切。结合前人研究,推断溶解-再沉淀、围岩硫化作用是江东金矿床主要的金沉淀机制。

江南5月降水与热带印-太海温及对流的联系

本文将1980-2021年江南5月降水作为研究对象,采用美国国家气候预测中心(Climate Prediction Center,CPC)降水、美国环境预测中心(National Center for Environmental Prediction,NCEP)大气环流以及英国气象局哈德莱中心(Met Office Hadley Centre)海表面温度等资料,对江南5月降水年际变化特征及其与热带印度洋、太平洋的海表面温度异常(Sea surface temperature anomaly,SSTA)以及对流异常的可能联系进行了分析。结果表明,偏涝年通常伴随有自年前秋季开始发展的热带印度洋暖SSTA,5月同期对流层850 hPa在热带东印度洋至中国南海一带出现东风异常,同时热带印度洋上空对流活动旺盛,通过Hadley环流增强了在西北太平洋的下沉气流,共同增强了西北太平洋异常反气旋(Northwest Pacific anomaly anticyclone,WNPAC),促进了水汽向江南地区输送。热带印度洋中东部的冷SSTA自偏旱年前的冬季开始不断发展,在5月同期的热带印度洋异常冷洋面上空表现为对流抑制,与偏涝年相反的异常Hadley环流促使副高减弱东退,撤出南海,不利于水汽向江南地区输送。除热带印度洋外,热带太平洋和海洋性大陆地区的SSTA及其上空的对流活动异常与WNPAC和江南5月降水异常在一些年份也存在一定的关系,但较热带印度洋复杂。

近20年北大西洋中纬度海温与江南5月降水关系增强的可能原因

本文以1980—2021年江南5月降水为研究对象,利用美国国家气候预测中心(Climate Prediction Center, CPC)降水资料、美国环境预测中心(National Centers for Environment Prediction, NCEP)大气环流和Hadley中心的海表面温度资料,分析了江南5月降水极端性的变化及其与大气环流、北大西洋海温的联系。结果表明,自2004年江南5月降水年际差异显著增大以来,200 hPa上的Rossby波能量从北大西洋向下游传播,一部分能量沿副热带西风急流传播,形成南支波列;另一部分沿不列颠群岛向西伯利亚地区传播,上述两支波列在旱涝年的不同配置一方面可以通过影响江南地区高空200 hPa附近的辐合辐散影响江南地区的垂直运动;另一方面波列下游的中国东南沿海200 hPa的异常气旋或反气旋具有准正压结构,对应于对流层中下层西北太平洋异常气旋或反气旋在孟加拉湾、中南半岛和南海上空位置和强弱变化,影响水汽向江南地区的输送。在偏涝年形成正位相的欧亚遥相关波列,利于冷空气在贝加尔湖附近积累并向江南地区输送,它和低纬暖湿气流在江南地区附近相遇,形成降水。2004年以来,欧亚大陆上空与5月不列颠群岛附近海温异常有关的波列分布发生了改变,影响了江南地区高空200 hPa的辐合辐散。上述遥相关波列增强了和西北太平洋异常反气旋的关系,进一步与江南5月降水建立起紧密联系。2004年以来自江南5月偏涝年前的冬季开始,北大西洋中纬度通常出现冷海温异常并随时间东移,于5月降水同期东移到不列颠群岛附近,偏旱年反之,这对江南5月降水具有一定的预报意义。

Low-Frequency Oscillations of the East Asia-Pacific Teleconnection Pattern and Their Impacts on Persistent Heavy Precipitation in the Yangtze-Huai River Valley

Based on the daily reanalysis data from NCEP NCAR and daily precipitation data from the China National Meteorological Information Center,an ensemble empirical mode decomposition method is employed to extract the predominant oscillation modes of the East Asia Pacific（EAP） teleconnection pattern.The influences of these low-frequency modes on persistent heavy precipitation in the Yangtze Huai River（YHR）valley are investigated.The results indicate that the EAP pattern and rainfall in YHR valley both exhibit remarkable 10 30- and 30 60-day oscillations.The impacts of the EAP pattern on the YHR persistent heavy precipitation can be found on both the 10 30- and 30 60-day timescales the 10 30-day scale for most cases.Composite analysis indicates that,on the 10 30-day timescale,formation of the EAP pattern in the lower and middle troposphere is determined by convective systems near the tropical western Pacific;whereas in the middle troposphere,the phase transition is jointly contributed by both the dispersion of zonal wave energies at higher latitudes and convective systems over the South China Sea.In the context of the10 30-day EAP pattern,the anomalously abundant moisture is transported by an anomalous subtropical anticyclone system,and strong moisture convergence results from that anomalous anticyclone system and a cyclonic system in the midlatitude East Asia.Such a combination of systems persists for at least three days,contributing to the formation of persistent heavy precipitation in the YHR valley.

Cloud and precipitation interference by strong low-frequency sound wave

Acoustic interference of atmosphere has been an attractive research area because of its potential effect on environment,water resources,ecology,agriculture,and other areas.However,it is also a controversial topic because of the difficulty of quantitative assessment and high operating costs.In this study,a novel acoustic interference technology is proposed that uses strong lowfrequency sound waves.There is no chemical pollution or dependence on airborne vehicles,and it can be remotely controlled at low cost.A complete equipment system for acoustic atmospheric interference technology is established,based on which a series of experimental studies on cloud and precipitation response under acoustic action are performed,mainly including the radar echo intensity,cloud microphysical characteristics and the spatial distribution of ground rainfall intensity.The trigger and periodic effect of the acoustic waves on the cloud are proposed to be the key responses of acoustic atmospheric interference.This study is important to further research on atmosphere interference technology based on low frequency strong sound waves.

2021年5月江南持续强降水的准双周振荡及可能成因

2021年5月江南地区降水量是近40年最多的,达到常年的2倍,严重影响了人民的生产和生活。基于逐日的降水和NCEP再分析资料,本文对2021年5月江南地区的异常降水事件进行分析,并重点分析了降水的准双周振荡特征及可能机制。结果表明,乌拉尔山阻塞和异常偏西、偏北的西北太平洋副热带高压(简称为副高)为持续性强降水提供了稳定的大气环流形势。来自北大西洋的Rossby波的能量向欧亚大陆频散,维持欧亚遥相关(Eurasian teleconnection,EU)稳定的正位相,使冷空气不断南下影响江南地区。异常偏西、偏北的副高有利于来自孟加拉湾、南海和西北太平洋的暖湿空气输送至江南地区。来自热带的暖湿气流与高纬度南下的冷空气在长江流域及其以南地区形成锋面,产生降水。副高脊线和西伸脊点的准双周振荡引起江南地区降水的南北摆动,造成降水量和降水落区的准双周振荡。此外,海洋大陆(Maritime continent,MC)附近对流活动也具有显著的准双周振荡特征,可能通过激发东亚遥相关波列影响副高位置和强度的准双周振荡,进而造成江南降水的准双周振荡。

Effect of minor Sc and Zr addition on microstructure and properties of ultra-high strength aluminum alloy

The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys （x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%）, produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al3（Sc,Zr） particles formed during solidification as heterogeneous nuclei. Secondary Al3（Sc,Zr） precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al-Zn-Mg-Cu-Zr alloy with 0.05%Sc and 0.15%Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.

江汉和江南西部春玉米涝渍指标及风险评估

以江汉和江南西部地区春玉米为研究对象,利用研究区域内57个气象站1961—2012年的逐日降水量资料、春玉米生育期资料和春玉米涝渍灾情资料,筛选春玉米不同生育时期的涝渍灾害样本。采用多元线性回归分析方法,定量分析当前过程降水量和前期降水量对春玉米涝渍灾害的影响,并据此构建当量降水量。基于正态分布的Lilliefors检验和t-分布区间估计方法,计算不同生育时期、不同等级涝渍灾害的当量降水量指标阈值,由此构建该区域春玉米不同生育时期的涝渍灾害等级指标并进行独立样本验证。在此基础上,利用信息扩散理论风险评估方法,计算各站点的春玉米涝渍致灾风险指数。结果表明:当前过程降水量和前2旬降水量对该区域春玉米涝渍灾害有显著性影响;构建的区域春玉米涝渍等级指标能够较好地反映实际受灾情况,指标验证结果与历史记录有较高一致性;出苗-拔节期和拔节-抽雄期发生春玉米涝渍灾害的风险相对较低,抽雄-成熟期为春玉米涝渍灾害的高风险时期,高风险区域主要位于湖北省恩施市、宜昌市西南部、荆州市西南部以及湖南省张家界市北部。

江南地区汛期降水与热带海温关系的SVD分析

江南汛期降水异常的分析指出,6月是江南最易发生降水异常的一个月。从空间分布看,降水异常最易发生在江南的中部地区。用SVD方法分析发现,与江南汛期降水异常相关的海温异常分布型是"翘翘板"型,关键区恰好位于相关最显著的部位,前一年5～7月为海温的关键影响时段,且与汛期中4～5月的降水有最好的负相关关系。在该海温异常型影响下,次年中国东部4～6月的降水异常表现为长江南北的反位相变化特征,而江南地区位于该雨型相关显著的部位,江南中部为其影响最显著的区域。

中高纬度与热带大气的共同作用对江南4-6月低频降水的影响

基于中国国家气象观测站的逐日降水资料、NOAA(National Oceanic and Atmospheric Administration)提供的逐日向外长波辐射资料和NCEP(National Centers for Environmental Prediction)/NCAR(National Center for Atmospheric Research)逐日全球再分析资料,采用非滤波法提取10—30 d低频降水及低频环流因子,分析了1979—2013年江南地区4—6月低频降水及其关联的大气环流特征,着重讨论了中高纬度与热带共同作用对低频降水的影响及可能机理。结果表明:(1)江南4—6月降水的第1模态呈现全区一致的变化趋势,其10—30 d低频降水方差贡献率在江南南部较大,部分区域可达20%。(2)降水的低频异常不仅与热带对流有关,还与中高纬度大气环流的变化显著相关。当东印度洋及印度尼西亚一带对流旺盛,中国上游欧洲至西伯利亚地区高纬度位势高度表现为显著的正异常,江南上空为负异常时,有利于江南低频降水。(3)中高纬度大气环流与热带对流共同作用影响江南4—6月低频降水:当热带对流旺盛区(抑制区)位于东印度洋及印度尼西亚海洋性大陆一带时,热带热源的非绝热加热引起显著的上升(下沉)运动,并激发经向罗斯贝波北传;同时高纬度欧洲至西伯利亚地区的位势高度负异常(正异常)向东向南传播,两者在江南上游叠加,低压(高压)底前部的西南风(东北风)有利于孟加拉湾对江南的水汽输送加强(减弱),对应江南地区整层水汽通量辐合(辐散),低频降水偏多(偏少)。

江南造山带万古金矿床含金硫化物组构与金沉淀机制

万古金矿床位于江南造山带中部,赋存于新元古界冷家溪群浅变质岩系中,受NNE-NE向长沙-平江断裂带和近EW向九岭-清水韧性剪切带联合控制,金资源量约85t。其主要矿石类型为毒砂-黄铁绢英岩型和石英-硫化物脉型,其次为构造角砾岩型。毒砂和黄铁矿为该矿床主要的载金矿物,分布广泛。金成矿作用可分为四个阶段,I为乳白色石英-绢云母-白钨矿阶段;Ⅱ为烟灰色石英-绢云母-毒砂-黄铁矿-金阶段;Ⅲ为烟灰色石英-绢云母-黄铁矿-毒砂-多金属硫化物-金阶段;IV为乳白色石英-方解石阶段。其中,Ⅱ、Ⅲ为成矿主阶段。根据成矿主阶段毒砂电子探针分析结果,Ⅱ阶段毒砂中As的含量在42.19%~44.84%之间,均值为43.42%(n=56),Ⅲ阶段毒砂中As的含量在40.08%~43.36%之间,均值为42.08%(n=19)。通过毒砂温度计相图估算出Ⅱ、Ⅲ阶段的形成温度和硫逸度分别为364±21℃、319±22℃和10^(-9.7)~10^(-7)、10^(-11.5)~10_(-8.6)。电子探针数据揭示的载金毒砂和黄铁矿中不可见金含量分别为0.01%~0.66%和0.01%~0.11%。黄铁矿Au-As元素投点分布于金溶解度曲线两侧,说明其内金主要以纳米级颗粒和固溶体金或晶格金的形式赋存;其中Ⅱ阶段黄铁矿纳米级金颗粒占比为73.33%,多于Ⅲ阶段黄铁矿(67.80%)。以上数据说明在水岩反应过程中,围岩中的含铁矿物与成矿流体中的H;S发生反应,生成毒砂和黄铁矿。伴随着强烈的水岩反应,成矿温度和硫逸度降低,成矿Ⅱ阶段至Ⅲ阶段主要载金硫化物由毒砂转变为黄铁矿,强烈的硫化作用导致金-硫络合物失稳并释放金,金以置换的方式进入硫化物晶格或以显微-超显微金颗粒的形式沉淀,形成含金硫化物;即硫化作用是导致万古矿床不可见金沉淀的主导机制。

江南造山带曲溪金矿床载金黄铁矿地球化学特征

湘东北曲溪金矿床位于江南造山带中段黄金洞金矿田,其赋存于新元古界冷家溪群浅变质岩系中,受NNE-NE向长平断裂及其次级断裂控制;主要发育石英–硫化物型、破碎蚀变角砾岩型和蚀变岩型三种矿化。金属矿物主要为自然金、黄铁矿、毒砂、黄铜矿、方铅矿和闪锌矿等;非金属矿物主要为石英、方解石、绿泥石与绢云母等。金以自然金和不可见金两种形式产出,其中不可见金主要为赋存于金属硫化物中的“固溶体金”和“纳米级自然金”。根据脉体穿插关系和矿物共生组合,将曲溪金矿床成矿作用划分为:I. 石英–毒砂–黄铁矿–绢云母阶段;II. 石英–金–多金属硫化物–绢云母阶段;III. 石英–绿泥石–方解石阶段。电子探针分析表明,曲溪金矿床黄铁矿中As含量达0.008~2.92 wt%,为含砷黄铁矿。砷与硫具有一定负相关关系,表明少量砷取代硫进入黄铁矿晶格,这增加了Au进入黄铁矿的机率。除此以外,铜与金具有较弱的正相关性,银含量偏低。热液黄铁矿中钴、镍含量及其比值波动较大,部分Co/Ni比值小于1,说明在热液运输或沉淀过程中,流体与沉积地层发生了强烈的物质交换。曲溪金矿床地质、硫化物组构特征以及元素地球化学数据指示:硫化作用导致流体中硫氢络合物分解是不可见金的主要沉淀机制;流体压力波动导致的流体不混溶是可见金的主要形成机制。

江南地区两类区域性极端降水的特征对比分析

基于中国气象局1961~2018年地面降水日值格点(0.5°×0.5°)数据集(V2.0)及位势高度、风速、比湿等NCEP/NCAR逐日再分析资料,采用百分位阈值法确认江南区域性极端降水事件,并对其天气图进行综合分析提取锋面型和气旋型极端降水,并对两类极端降水的时空分布及环流演变特征进行了对比。结果表明:(1)锋面型极端降水事件主要分布在春季,而气旋型主要分布在夏季,并且锋面型极端降水事件发生频率约为气旋型的3倍;(2)锋面型极端降水主要分布于武夷山脉、南岭等地势较高地区,而气旋型则位于东南沿岸地区,福建等地受两类极端降水影响都较大;(3)锋面型和气旋型极端降水发生前两天至当天,气流垂直上升速度均增大,副高西移,锋面型极端降水的最大水汽辐合中心由江南地区850 hPa等压面降至地表,而气旋型的水汽辐合中心位于地表由南向北移至江南地区;(4)锋面型极端降水形成所需的水汽主要来源于西太平洋、印度洋和孟加拉湾,汇合于江南地区,而气旋型水汽主要来源于印度洋,并呈涡旋型随时间西移。