江淮流域夏季降水异常及与全球中低纬海温异常关系的诊断研究

对1951－1999年中国夏季江淮流域降水异常与海温异常关系的分析表明,前期及同期各季节三大洋海表温度异常（SSTA）与长江流域降水异常的关系是非常显著的,而对淮河流域降水异常总体上的影响较小,前期冬季SSTA的影响显著区主要有：热带印度洋、黑潮、热带中东太平洋和大西洋,各关键区海温异常对亚洲夏季风的影响特征为：当前期冬季赤道印度洋、黑潮、赤道大西洋和热带东太平洋海表温度异常升高（降低）,当年夏季印度西南季风和东亚热带辐合带减弱（加强）,副热带高压位置偏南（北）,副热带辐合带加强（减弱）,长江流域易发生洪涝（干旱）,相关显著性分析表明,前冬赤道印度洋和黑潮区的海温异常对中国夏季降水的影响更为显著。     

热带海温对纵向岭谷区5月降水年际变化的影响研究

 利用主成分分析和典型相关分析方法,研究了纵向岭谷区76个站点5月份降水场与其前期(12~4月)和同期(5月份)热带海温距平场之间的相关关系.其中,资料选用了1961~2001年共41 a的数据资料.研究结果表明,纵向岭谷区5月降水与热带海温距平场以同期相关为最好,而前期热带海温距平场除12月、3月和4月外,其它月份即1月、2月均有很好的相关.通过对热带海温距平场及降水场典型特征向量的分布作分析,太平洋暖池区热带海温与纵向岭谷区5月降水有正相关关系,赤道东太平洋海温与纵向岭谷区5月降水有负相关关系.当太平洋Walker环流增强时,纵向岭谷区5月降水增多;当Walker环流减弱时,纵向岭谷区5月降水减少.     

热带西太平洋和东印度洋对ENSO发展的影响

分析了从1955～1998年44a热带西太平洋次表层海温距平资料,指出在这一期间共发生了11次E1 Nino事件,这些事件的初始海温正距平无一例外地都在 "暖池"次表层160 m附近生成,发展到一定强度,到西太平洋出现异常的持续西风距平后,暖的海温距平沿着气候的温跃层向东向海表传播,经过1 a左右的时间,传播到赤道东太平洋海表的E1 Nino 3或1、2海域形成通常认为的El Nino事件.进一步分析1960～1999年的850 hPa风场指出,在热带西太平洋西风距平爆发前,赤道东印度洋已经有距平西风持续维持了2 a左右(西南季风),然后距平西风快速地向东发展产生热带西太平洋的距平西风,或真正的强西风,致使西太平洋出现E1 Nino爆发不可缺少的条件之一,在这40 a中,这一过程对所有的El Nino事件无一例外.同样的分析方法也用到这44 a中的La Nina事件,冷的海温距平也都首先在"暖池"的次表层形成,然后沿着温跃层向东向表层传播,在热带西太平洋出现东风前,印度洋也早已是持续的东风.     

粤东暴雨中心前汛期降水异常的环流特征及前兆性信号分析

研究了1967～2018年粤东暴雨中心前汛期降水的年际变化,以及降水异常对应的环流异常特征,并对降水异常的前兆性信号特征进行分析。研究结果表明:1990年以后粤东暴雨中心前汛期降水年际变率增强,2005年以后降水偏多年异常增多。降水异常年的环流特征差异显著,偏多年对流层中上层高空急流增强,副热带高压范围偏大西脊点偏西,东亚大槽偏深,江南地区偏南风减弱,有利于粤东辐合增强;偏少年高空急流减弱位置偏北,副热带高压范围偏小,大陆高压增强,底层我国东部地区偏南风一致减弱,不利于粤东辐合。降水偏多(偏少)年的前兆性信号主要表现为极地海冰偏少(偏多)以及赤道东太平洋暖(冷)海温异常。进一步研究表明,高空急流以及东亚大槽和前期极地海冰异常有关,而副热带高压和前期赤道东太平洋海温有关。     

亚澳季风区内水汽汇的准两年振荡及其与大气环流的关系

利用1950-2000年大气视水汽汇资料,分析了亚澳季风区内水汽汇准两年振荡的变化特征及其与大气环流的关系.亚澳季风区内水汽汇有显著的准两年振荡,其关键区位于西太平洋暖池、孟加拉湾、东南印度洋和西南印度洋,它们对应3种遥相关型.当暖池水汽汇偏强时,我国华南为偏北风距平,东亚季风区水汽汇偏弱;印度洋水汽汇距平呈现为偶极子分布,东南印度洋附近水汽汇偏强时,东南印度洋至赤道西印度洋为偏西风距平,赤道西印度洋水汽汇偏弱;孟加拉湾水汽汇偏强时,孟加拉湾至西南印度洋为偏南风距平,西南印度洋的水汽汇偏弱.反之亦然.     

热带印度洋和太平洋海气相互作用事件间的联系

在次表层海温距平极值面上海温距平的分布和变化表明,热带西、东印度洋的海温距平呈偶极子模态,即当西印度洋海温距平为正(负)时,东印度洋海温距平为负(正),偶极子模态的海温距平分布在热带太平洋同样存在,两大洋海温距平的偶极子模态间有密切的联系,在分析它们和850 hPa纬向风距平后指出,不仅这种海温距平偶极子模态的形成、发展是和这两大洋热带上空Walker环流相互作用的结果,同时正是Walker环流异常把两大洋的海温距平变化联系起来.     

华北夏季降水年代际变化与东亚夏季风、大气环流异常

利用华北夏季降水资料和NCEP/NCAR再分析资料,对华北夏季降水、东亚夏季风年代际变化特征及大气环流异常进行研究,发现一些有意义的结果:华北夏季降水变化存在明显的8a、18a周期,东亚夏季风变化18a、28a周期性比较明显,二者年代际变化特征明显,但华北夏季降水变化和东亚夏季风变化的周期不完全一致.华北夏季降水量变化在60年代中期发生了突变,东亚夏季风变化在70年代中期发生了突变.华北夏季降水与东亚夏季风变化存在很好的相关关系,强夏季风年,华北夏季降水一般偏多,弱夏季风年,华北夏季降水一般偏少,但又不完全一致.东亚夏季风减弱是造成华北夏季降水减少的一个重要因素,但不是唯一因素,华北夏季降水减少还与环流异常密切相关.在地面上,青臧高原地区、华北地区气温下降造成华北低压系统活动减少,不利于降水.在850 hPa层上,东亚中纬度的西南季风和副热带高压南部的偏东风、西北部的西南风异常减弱,使得西南气流输送水汽很多难以到达30°N以北的地区,而副热带高压西部外围偏东南、偏南气流输送到华北地区的水汽也大量减少,水汽不足造成华北夏季降水偏少.在500 hPa高度场上,80年代欧亚遥相关型表现与50年代相反,变为欧洲( )、乌拉尔山(-)、中亚( )形势,这种环流使得乌拉尔山高压脊减弱,贝加尔湖至青藏高原高空槽变浅,纬向环流表现突出,不利于冷暖空气南北交换.同时在500 hPa气温场上,80年代,西伯利亚至青藏高原西北部的冷槽明显东移南压到蒙古至华北地区,锋区位于华北以东以南位置,使得华北地区冷暖空气交汇减少,降水也因此减少.华北夏季降水减少是由于东亚夏季风减弱和大气环流异常造成的.     

南亚高压和云南雨季降水关系的初步探讨

南亚高压是夏季南亚上空对流层上部的一个强大而稳定的行星尺度环流系统。它的季节性变化规律、东西振荡机理,它的周期性、整体性、持续性、超前性以及与众多的天气尺度和大、中尺度的天气系统的相互联系,为南亚地区某些重要的天气过程的发生、发展和消亡提供了一个环流背景,与我国降水过程存在着显著相关。笔者运用1980～1982年的资料对南亚高压的强度、云南雨季降水和季风环流圈作动率谱和交叉谱分析,对不同系统和不同年份的情况进行了讨论,结果表明:南亚变压通过季风环流圈对云南降水产生影响,云南降水受东亚季风环流系统和印度环流系统、热带和副热带天气系统的综合影响,具有较显著的准一周和准双周的中期振荡周期。     

热带气旋“桑美”和“碧利斯”降水特征的对比分析

为了分析"桑美"和"碧利斯"云系中的对流发展特征,利用NCEP(the national centers for environ-mental prediction),对TBB(Temperature of brightness blackbody)高分辨率资料进行2次过程输送通道的对比分析并计算了垂直积分的水汽通量矢量.结果表明:2006年夏季发生在前后不超过一个月的2个热带气旋过程"碧利斯"和"桑美"的特征有着十分显著的差异,"碧利斯"主要受异常活跃西南季风和南海季风的影响,水汽输送强度大,产生了持久的、大范围强降水."桑美"主要受东亚副热带季风的影响,水汽输送强度仅为"碧利斯"的一半,其登陆后东亚副热带季风明显减弱,造成了降水集中、持续时间短的特点.     

热带海洋海表温度和西太平洋副高西伸脊点的关系研究

 应用谱分析的方法,讨论了热带太平洋、印度洋和大西洋海温对西太平洋副高西伸脊点的影响,得出热带太平洋、印度洋、大西洋海温变化对西伸脊点有影响的最佳落后时间长度.分别找出三大洋在上述落后时间长度下对西伸脊点东退和西伸有影响的关键区域.它可以作为西伸脊点东退或西伸的强信号因子,并对上述区域进行比较分析.西太平洋副高西伸脊点可以作为衡量东亚季风的一个指数,而东亚季风对处于低纬高原的云南的天气和气候有很大的影响.     

东亚夏季风异常的研究

本文运用经验正交函数分析方法,对10～65°N,90°E～175°W范围内近30年逐年7月和8月平均海平面气压场进行了分析研究.结果表明,第一、第三特征向量与东亚季风异常有关,第二特征向量与西风环流异常有关.讨论了东亚季风异常与大气环流的关系,以及季风异常对华北东部地区降水时空分布的影响.     

Tropospheric biennial oscillation of the western Pacific subtropical high and its relationships with the tropical SST and atmospheric circulation anomalies

There is the significant period of tropospheric biennial Oscillation(TBO)over East Asian monsoon region at the interannual timescales,which has the important influences on East China climate.Based on a set of reconstructed indices which describes the western Pacific subtropical high(WPSH)objectively,this paper focuses on the TBO component of WPSH,one of the key members of the East Asian Monsoon system,and its relationships with the tropical SST and atmospheric circulation anomalies.It is found that(1)As an important interannual component of WPSH,the time series of TBO has the obvious transition in the late1970s,and the variability of the WPSH’s TBO component is more significant after the late 1970s.(2)The time-lag correlations between the WPSH’s TBO and the tropical sea surface temperature(SST)anomalies in several key ocean regions are more significant and have longer correlation duration than the raw data.The response of the western boundary index to ENSO is earlier than the intensity index,and the time-lag correlations of them are up to maximum when lagging ENSO by 3–5 months and 5–6months,respectively.(3)In the course of the WPSH’s TBO cycle,the occurrence of the El Ni o-like anomaly in the tropical central-eastern Pacific in winter is always coupled with the weak East Asian winter monsoon,with the most significant enhancing phase of the WPSH’TBO.In contrast,the La Ni a-like anomaly in the central-eastern Pacific in winter is coupled with the strong East Asian winter monsoon,with the most weakening phase of the WPSH’s TBO.(4)The distribution of the tropical SST and atmospheric circulations anomalies are asymmetric in the TBO cycle.The WPSH’s TBO is more significant in the period of the developing El Ni o-like anomaly in central-eastern Pacific than in the period of the developing La Ni a-like anomaly.Therefore,during the period of developing El Ni o-like anomaly,more attention should be paid to the interannual component of TBO signal in the short-term climate prediction.     

云南2009—2012年4年连旱的气候成因研究

利用云南124个气象站逐月降水资料、NCEP/NCAR大气环流再分析资料、全球海表面温度(SST)资料以及向外长波辐射(OLR)资料,分析了云南2009—2012年连续4年干旱的气候特征,并从异常大气环流、海温、局地对流等方面分析了4年连续夏季干旱发生的成因.结果表明:①云南2009—2012年干旱是一次持续时间长,跨越春、夏、秋、冬四季、影响范围广的全省性严重干旱,最严重的区域主要是滇中及滇东南.并且是发生在云南降水减少的气候背景下.②2009—2012年夏季500 hPa欧亚地区高、中、低纬度的高度场分布不是很相似,但4年的环流配置形势表明东亚冷空气路径偏东,影响中国西南地区的冷空气偏弱,不利于冷空气南下影响云南.另外2009年和2010年副高位置偏西偏强,云南在其控制之下,不利于降水;而2011年和2012年副高位置偏北偏东,其外围的水汽不易输送到云南.③2009—2012年云南大部地区及其南侧的孟加拉湾地区高度场持续偏高,孟加拉湾附近的印缅槽不活跃或偏弱,也不利于南方水汽向云南界内输送.④El Nino事件发展期、La Nina事件衰弱期以及印度洋海温偏暖时都有利于云南干旱的发生和发展.⑤2009—2012年夏季云南局地及其以南大部地区基本维持低层辐散、高层辐合的垂直散度场配置,不利于上升运动的生成和发展.孟加拉湾及南海一带基本为西北或偏东气流控制,向北输送的水汽较常年偏弱,是造成云南连续4年夏季干旱少雨异常气候的直接原因之一.⑥2009—2012年连续4年夏季云南局地对流相对常年偏弱,这也是云南降水偏少的重要因素之一.     

East Asian monsoon change for the 21st century: Results of CMIP3 and CMIP5 models

Forty-two climate models participating in the Coupled Model Intercomparison Project Phases 3 and 5 were first evaluated in terms of their ability to simulate the present climatology of the East Asian winter (December-February) and summer (June-August) monsoons. The East Asian winter and summer monsoon changes over the 21st century were then projected using the results of 31 and 29 reliable climate models under the Special Report on Emissions Scenarios (SRES) mid-range A1B scenario or the Representative Concentration Pathways (RCP) mid-low-range RCP4.5 scenario, respectively. Results showed that the East Asian winter monsoon changes little over time as a whole relative to the reference period 1980-1999. Regionally, it weakens (strengthens) north (south) of about 25°N in East Asia, which results from atmospheric circulation changes over the western North Pacific and Northeast Asia owing to the weakening and northward shift of the Aleutian Low, and from decreased north- west-southeast thermal and sea level pressure differences across Northeast Asia. In summer, monsoon strengthens slightly in East China over the 21st century as a consequence of an increased land-sea thermal contrast between the East Asian continent and the adjacent western North Pacific and South China Sea.     

黄、东海沿岸海表温度变化与厄尔尼诺的关系

利用黄、东海沿岸8个长期水文观测站多年海表温度资料,分析黄、东海沿岸海表温度的季节和年际变化特征,重点分析在1982—1983年和1997—1998年两次厄尔尼诺年期间的异常变化,以及ENSO影响黄、东海沿岸海表温度的可能机制。结果表明,在厄尔尼诺发生年,夏季风较弱,鄂霍次克海高压加强,西太平洋副高位置偏南,强度偏强,江淮流域及长江中下游降水偏多,黄、东海沿岸海表温度偏低。黄、东海沿岸海表温度受到ENSO和PDO(太平洋年代际振荡)的影响和调制,在厄尔尼诺发生的前冬半年及当年,黄、东海沿岸海表温度偏低;在厄尔尼诺发生次年,黄、东海沿岸海表温度偏高。厄尔尼诺对黄、东海沿岸海表温度变化的影响通过海洋和大气2个通道,1982—1983年海表温度异常以负异常为主,1997—1998年海表温度异常以正异常为主;ENSO期间,北赤道流减弱,黑潮流量减少,海表温度降低。海表温度受局地气温影响显著,如果ENSO期间东亚气温升高,则黄、东海沿岸海表温度偏高。     

重庆汛期降水与西太平洋副热带高压的关系

 利用近47a(1960～2006年)完整而系统的副高特征指数资料和重庆34个站点的汛期(6～8月)降水量资料进行相关普查,得出副高脊线、北界位置与重庆汛期降水之间都存在很高的正相关关系.当西太平洋副高偏北时,重庆汛期降水将会偏少;而当副高偏南时,该地区的降水将偏多.因此,重点讨论副高南北位置的变化与重庆汛期降水的关系.研究表明副高南北位置的异常对应着欧亚地区特别是东亚地区大气环流的异常变化,从而影响重庆乃至中国的汛期降水.     

Transition of the annual cycle of precipitation from double-peak mode to single-peak mode in South China

Previous studies revealed the double-peak mode (DPM) in South China precipitation, corresponding to the two stages in the rainy season, i.e. the first rainy stage (FRS) and the second rainy stage (SRS). But observations in recent two decades show that the DPM has changed to a single-peak mode (SPM). Both the precipitation amount and the heavy rainfall event frequency enhanced significantly in the gap between the FRS and the SRS in 1991–2010, compared to those in 1961-1990. This change can be linked to the effects of the global warming. During the warmer period, the July sea surface temperature over the western Pacific has greater increases than that over the central and eastern Pacific, especially west of 140°E. It may generate more tropical cyclones (TCs) in the inshore areas and then more typhoon rainfall over South China. On the other hand, the increments of the air temperature over the East Asian continent are greater than those of the SST over the western Pacific under the global warming, which enlarges the land-ocean temperature/pressure contrast and leads to a trend of the earlier onset dates of the Asian summer monsoon (ASM) in recent two decades. Then, the earlier ASM will facilitate the western Pacific subtropical high (WPSH) to retreat earlier from the South China Sea and enhance the convective precipitation in South China between the FRS and the SRS. Also, due to the warmer ocean, the WPSH locates more westward in July, and more moisture will be transported to South China from the southwest side to the WPSTH. All these influences favor a remarkably increasing precipitation in the gap in the warmer period and changes the seasonal cycle from double-peak mode to single-peak mode.     

Precursory influence of the Antarctic Oscillation on the onset of Asian summer monsoon

The Asian summer monsoon(ASM) begins firstly over the Indo-China Peninsula in early May and over the South China Sea(SCS) in mid-May.The different monsoon onset dates can exert distinct effects on the summer rainfall in Asia.Statistical results indicate that the Antarctic Oscillation(AAO) in the boreal winter has a significant precursory influence on the ASM onset dates.In stronger AAO years,both the Mascarene high and the Australia high in March are stronger owing to the "see-saw" structure of atmospheric circulation over the subtropics and higher latitudes in the Southern Hemisphere,and the tropical intertropical convergence zone(ITCZ) is deeper.Thus,the pressure gradient between the subtropical and tropical regions increases in spring.As a result,the Somalia cross-equatorial flow(SCEF) occurs earlier,strengthens,and enhances the westerlies over the tropical Indian Ocean.The enhanced westerlies impel an eastward withdrawal of the western Pacific subtropical high and intensify the convergence and rising motion at the lower troposphere,accelerating the burst of ASM.Differently,weaker AAO weakens the pressure gradient between the tropical and subtropical regions and delays the establishment of SCEF,resulting in a delayed onset of ASM.This study extends the leading time of seasonal forecast of ASM onset from the previous spring to winter and provides useful information about precursory signals in climate prediction operation.     

Interannual variability of Mascarene high and Australian high and their influences on summer rainfall over East Asia

Based on the reanalysis data from NCEP/NCAR and other observational data,interannual variability of Mascarene high(MH) and Australian high(AH) from 1970 to 1999 is examined.It is shown that interannual variability of MH is dominated by the Antarctic oscillation(AAO),when the circumpolar low in the high southern latitudes deepens,the intensity of MH will be intensified.On the other hand,AH is correlated by AAO as well as EI Nino and South Oscillation(ENSO),the intensity of AH will be intensified when EI Nino occurs.Both correlation analysis and case study demonstrate that summer rainfall over East Asia is closely related to MH and AH.When MH intensifies from boreal spring to summer (i.e.from austral autumn to winter),there is more rainfall over regions from the Yangtze River valley to Japan,in contrast,less rainfall is found over southern China and western Pacific to the east of Taiwan,and most of regions in mid-latitudes of East Asia.Compared with MH,the effect of AH on summer rainfall in East Asia is limited to localized regions,there is more rainfall over southern China with the intensification of AH.The results in this study show that AAO is a strong signal on interannual timescale,which plays an important role in summer rainfall over East Asia.This discovery is of real importance to revealingt the physical mechanism of interannual variability of East Asian summer monsoon and prediction of summer precipitation in China.