THE TEMPORAL AND SPATIAL CHARACTERISTICS OF MOISTURE BUDGETS OVER ASIAN AND AUSTRALIAN MONSOON REGIONS

Apparent moisture sink and water vapor transport flux are calculated by using NCAR/NCEP reanalyzed daily data for water vapor and wind fields at various levels from 1980 to 1989.With the aid of EOF analysis method,temporal and spatial characteristics of moisture budgets over Asian and Australian monsoon regions are studied.The results show that there is apparent seasonal transition of moistrue sink and water vapor transport between Asian monsoon region and Australian monsoon region.In winter,the Asian monsoon region is a moisture source,in which three cross-equatorial water vapor transport channels in the “continent bridge“,at 80°E and 40°E～50° transport water vapor to the Australian monsoon region and southern Indian Ocean which are moistrue sinks.In summer,Australian Monsoon region anmd southern Indian Ocean are moistrue sources and by the three cross-equatorial transport channels water vapor is transport to the Asian monsoon region which is a moisture sink.In spring and autumn,ITCZ is the main moisture sink and there is no apparent water vapor transport between Asian monsoon region and Australian monsoon region.     

Moisture Sources and Their Contributions to Summer Precipitation in the East of Southwest China

Complex topography, special geographical location and sea-land-air interactions lead to high interannual variability of summer precipitation in the east of Southwest China (ESWC). However, the contributions, influencing factors and mechanisms of remote and local evaporation remain to be further investigated. Using clustering analysis and Hybrid Single-Particle Lagrangian Integrated Trajectory version 5 model, we analyze the contributions of remote moisture transport and local evaporation to summer precipitation in the ESWC and their causes. There are mainly five remote moisture channels in the ESWC, namely the Arabian Sea channel, Bay of Bengal channel, western Pacific channel, Northwest channel 1 and Northwest channel 2. Among the five channels, the western Pacific channel has the largest number of trajectories, while the Bay of Bengal channel has the largest contribution rate of specific humidity (33.33%) and moisture flux (33.14%). The amount of regional average precipitation is close to that of the precipitation caused by remote moisture transport, and both are considerably greater than the rainfall amount caused by local evaporation. However, on interannual time scales, precipitation recirculation rates are negatively correlated to regional average precipitation and precipitation caused by remote moisture transport but are consistent with that caused by local evaporation. An apparent "+ ? +" wave train can be found on the height anomaly field in East Asia, and the sea surface temperature anomalies are positive in the equatorial Middle-East Pacific, the South China Sea, the Bay of Bengal and the Arabian Sea. These phenomena cause southwest-northeast moisture transport with strong updrafts, thereby resulting in more precipitation in the ESWC.     

IMPACT OF ENSO ON THE PRECIPITATION OVER CHINA IN WINTER HALF-YEARS

In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Nio episodes, which are caused by the enhanced warm and humid southwesterlies along the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China, and the convergence of water vapor over southern China increases the precipitable water and specific humidity. In La Nia episodes,although atmospheric elements change reversely, they are not statistically significant as those in El Nio periods. The possible physical mechanism of the different impact of ENSO cycle on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations(ISOs) in El Nio and La Nia winter half-years, respectively. By comparing the characteristics of ISOs in El Nio and La Nia, a physical mechanism is proposed to explain the different responses of the precipitation over China to ENSO in the winter half-year. In El Nio episodes, over western North Pacific(WNP) and South China Sea(SCS) the ISOs are inactive and exert little effect on water vapor transport and convergence, inducing positive precipitation anomalies with statistical significance over southern China in El Nio episodes. In La Nia episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the different responses of precipitation over China to ENSO in the winter half-year are possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Nio and La Nia.     

Effects of Tropical Cyclone Activity on the Boundary Moisture Budget over the Eastern China Monsoon Region

In summer, water vapor over the eastern China monsoon region(ECMR) comes mainly from low latitudes and is modulated by tropical cyclone(TC) activity in East Asia(EA). This study examines the variability of water vapor transport over the ECMR, especially of the moisture inflow via the southern and eastern boundaries. The results of composite and correlation analyses, using data from 1979 to 2010, reveal significant differences in moisture budgets along the boundaries between TC days and non-TC days. Almost 80% of the water vapor transport via the eastern boundary occurs during TC days, while at the southern boundary most inflow occurs on non-TC days. The ratio of the total water vapor transport between TC and non-TC days is about 4:6. In addition, the El Nio–Southern Oscillation(ENSO) exhibits a remarkable influence on moisture transport over EA and the contributions of moisture inflow on TC days increase(reduce) in El Nio(La Nia) years. Moreover,different types of TCs, based on their tracks, have different effects on the moisture budgets along the southern and eastern boundaries. When TCs enter EA(but not the ECMR), they favor the moisture inflow via the eastern boundary and hinder the moisture inflow via the southern boundary. After TCs enter the ECMR, the inhibition of moisture inflow via the southern boundary will be weakened, and more water vapor can be brought into the ECMR. For some recurving TCs with an increase in TC activity in the midlatitudes, the influence is uncertain in different cases. The results herein suggest that TC activity is an important factor that influences the boundary moisture budgets in the ECMR.     

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. The 10–20 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.     

The impacts of moisture transport of East Asian monsoon on summer precipitation in Northeast China

By using the ECMWF reanalysis daily data and daily precipitation data of 80 stations in Northeast China from 1961 to 2002, the impacts of moisture transport of East Asian summer monsoon on the summer precipitation anomaly in Northeast China, and the relationship between the variation of moisture budget and the establishment of East Asian summer monsoon in this region are studied. The results demonstrate that the moisture of summer precipitation in Northeast China mainly originates from subtropical, South China Sea, and South Asia monsoon areas. East China and its near coastal area are the convergent region of the monsoonal moisture currents and the transfer station for the currents continually moving northward. The monsoonal moisture transport, as an important link or bridge, connects the interaction between middle and low latitude systems. In summer half year, there is a moisture sink in Northeast China where the moisture influx is greater than outflux. The advance transport and accumulation of moisture are of special importance to pentad time scale summer precipitation. The onset, retreat, and intensity change of the monsoonal rainy season over Northeast China are mainly signified by the moisture input condition along the southern border of this area. The establishment of East Asian summer monsoon in this area ranges from about 10 July to 20 August and the onset in the west is earlier than that in the east. The latitude that the monsoon can reach is gradually northward from west to east, reaching 50°N within longitude 120°-135°E. In summer, the difference of air mass transport between summers with high and low rainfall mainly lies in whether more air masses originating from lower latitudes move northward through East China and its coastal areas, consequently transporting large amounts of hot and humid air into Northeast China.     

STABILITY AND POTENTIAL PREDICTABILITY OF ANNUAL PERCIPITATION OVER CHINA

The precipitation is a primary element which directly affects the agricultural production of thecountry with one fifth of the world population.With the economic development the water resourcestress is getting greater.In this paper,based on the data at 162 stations selected evenly over Chinafrom 1960 to 1991 the stability and potential predictability of annual precipitation have been stud-ied.The eastern and southern parts of the country having abundant precipitation enjoy more stableprecipitation.The north and northwest parts of the country where the precipitations are deficienthave unstable precipitations.The potential predictability approximates to the ratio of the estimatedinterannual variance to the climatic noise.Generally the annual precipitation over China is poten-tially predictable.In the area between the Huanghe River and Changjiang River and the east ofnortheastern China the potential predictability is the lowest in the country.In the north and north-west of the country the potential predictability is greater.The southeastern coast has relatively lowvalues of potential predictability.Also,the method of estimating climatic noise of annual precipita-tion has been discussed from the idea of Yamamoto et al.(1985)in order to estimate the potentialpredictability.     

THE CORRELATIONS BETWEEN SST AND SUMMER PRECIPITATION OVER EASTERN CHINA AND THE EFFECT OF THE SST ANOMALY IN THE SOUTH CHINA SEA ON THE SUMMER MONSOON AND PRECIPITATION

By use of the method of empirical orthogonal function resolution a study is made of the distributionpatterns of summer rainfall percentage anomalies over eastern China with the result that such anomalies areable to reflect the relative amount of local precipitation.Then the correlations are obtained through calcula-tion between the patterns and the January and June global SST,indicating key regions in association withChina's summer rainfall.On this basis,an 11-layer atmospheric circulation model by the U.K.Meteorol-ogical Office is used to simulate the effect of a weak SST anomaly of the South China Sea upon the summermonsoon circulation in China's mainland.Results show that‘attraction’is available for the Indian monsoonwith a warm anomaly of the SST and‘repelling’with a cold,representing one of the reasons for the anti-phase between the monsoons over the South China Sea and India.Such functions of SST anomalies have asignificant influence on summer rainfall over eastern China.     

INVESTIGATIONS ON MOISTURE TRANSPORTS, BUDGETS AND SOURCES RESPONSIBLE FOR THE DECADAL VARIABILITY OF PRECIPITATION IN SOUTHERN CHINA

In the context of global warming, apparent decdal-interdecdal variabilities can be detected in summer precipitation in southern China. Especially around the 1990s, precipitation in South China experienced a phase transition from a deficiency regime to an abundance regime in the early 1990s, while the Yangtze River Valley witnessed a phase shift of summer precipitation from abundance to deficiency in the late 1990s. Pertinent analyses reveal a close relationship between such decadal precipitation shifts and moisture budgets, which is mainly modulated by the meridional component. This relationship can be attributed to large-scale moisture transport anomalies. Further, the HYSPLIT model is utilized to quantitatively evaluate relative moisture contributions from diverse sources during different regimes. It can be found that during the period with abundant precipitation in South China, the moisture contribution from the source of Indochina Peninsula-South China Sea increased significantly, while during the deficient precipitation regime in the Yangtze River Valley, moisture from local source, western Pacific and Indochina Peninsula-South China Sea contributed less to precipitation. It means some new features of relative moisture contributions from diverse sources to precipitation anomaly in southern China took shape after 1990s.     

WATER VAPOR CONTENT AND MEAN TRANSFER IN THE ATMOSPHERE OVER NORTHWEST CHINA

The interannual and intermonthly climatic features of the water vapor content(hereafterWVC)and its mean transfer in the atmosphere over Northwest China(hereafter NWC)arecalculated and analyzed by using the NCEP/NCAR global reanalysis grid data(2.5°×2.5°Lat/Lon)for 40 years(1958—1997).The results show that the WVC in the total air column over NWC infour seasons of the year is mainly concentrated on eastern and western NWC respectively.On theaverage,the WVC over eastern NWC decreases obviously during recent forty years except forwinter.while it decreases over western NWC in the whole year.But the WVC over NWC has beenincreasing since late 1980s in summer.The water vapor comes from the southwestern warm andwet air current along the Yarlung Zangbo River Valley and the Bay of Bengal.and from mid-western Tibetan Plateau and also from the Qinling Mountains at southern Shaanxi Province.Theyearly water vapor divergence appears over the middle of NWC to northern Xinjiang andsoutheastern Shaanxi Province.The yearly water vapor convergence appears over the Tarim Basinand the Tibetan Plateau as well as western Sichuan and southern Gansu.     

2004年南海夏季风的爆发及中南半岛陆面过程的可能影响 I： 诊断分析

南海夏季风的爆发受高原、海洋(海气相互作用)、冷空气和陆地(陆面过程或陆气相互作用)等多种因素的影响,其中中南半岛由于是连接南海夏季风和印度、孟加拉湾季风的关键区,而且孟加拉湾不仅是亚洲最早爆发夏季风的地区,又是副热带高压最早断裂的地区。因此它的陆面过程对南海夏季风的影响是不可忽视的。文章从2004年南海夏季风爆发前后的环流和降水分析其活动特征,并进一步研究中南半岛陆面过程对南海夏季风的爆发日期和强度的影响。2004年南海夏季风于5月19日爆发,利用NCEP再分析资料及地面站点降水资料对这次季风爆发前后的环流形势和降水分布进行分析,结果表明:强对流活动由孟加拉湾移到中南半岛,引起中南半岛的降水增大,导致陆面过程发生改变(包含土壤湿度,感热、潜热通量,向上长波辐射),最终使得中南半岛—南海之间的低层气温差出现符号逆转,为南海夏季风的爆发提供了必要的条件。此外,中南半岛—南海低层气温差同南海夏季风的活跃程度有密切的联系。通常负的温差出现后不久,南海夏季风即进入活跃期或非活跃期,正的温差出现之后则常常是南海夏季风的中断期。     

南海季风爆发的年代际转折与东亚副热带夏季降水的关系

利用1979—2016年NCEP再分析资料, 分析了南海季风爆发的年代际转折与东亚副热带夏季降水的关系。结果表明:南海夏季风爆发时间在1993/1994年出现年代际转变, 1979—1993年爆发时间相对偏晚, 夏季华南降水偏少, 长江中下游至日本南部降水偏多; 1994—2016年爆发时间偏早, 夏季华南降水偏多, 长江中下游到日本南部降水偏少。南海季风爆发时间年代际转折与夏季东亚副热带降水关系可能受到菲律宾越赤道气流强度的调控, 季风爆发时间与菲律宾越赤道气流有显著正相关, 且均在1993/1994年间存在年代际转变。在1994—2016(1979—1993)年南海夏季风爆发偏早(晚), 菲律宾越赤道气流偏弱(强), 澳大利亚北部有偏北(南)风异常, 将暖池的热量往赤道输送, 使得赤道对流增强(减弱), 产生异常上升(下沉)运动汇入Hadley环流上升支, 增强(减弱)的Hadley环流导致下沉主体偏北(南), 促使副高脊线偏北(南), 从西北太平洋(孟加拉湾)往华南地区(江淮到日本南部)输送水汽增强, 所以华南(江淮到日本南部)夏季降水偏多。      

南海、孟加拉湾不对称环流变化对2009年西南特大秋旱的影响

利用NCEP再分析资料及我国160站降水资料,分析了2009年秋季东亚中、低纬环流特征和水汽输送特征及其对西南干旱的影响。同时讨论了秋季不同ENSO状态下东亚地区水汽输送差异,并与2009年进行比较。结果表明:孟加拉湾(简称孟湾)和南海之间环流形势在2009年秋季发生不对称变化,造成两地上空气压梯度减小,孟湾和南海上空分别出现一个反气旋式和气旋式距平环流中心,我国西南至中南半岛处于两距平环流中心之间偏北距平风控制之下,使得进入我国的西南气流异常减弱。水汽输送随之出现变化,南海南部季风低压水汽环流圈异常偏强,孟湾和南海水汽主体经中南半岛重回南海而未进入我国,最终造成我国西南降水异常偏少,出现干旱。这段时间内,西南地区上空出现异常下沉运动,对流活动受到抑制,加剧了干旱程度。在El Ni o年,我国西南及江南地区秋季水汽通量比La Ni a年明显增大,西北及华北则减少。2009年秋季我国的降水分布及南海一带水汽输送特征与普通El Ni o年特征不符,甚至出现相反状态,经对2009年秋季东亚El Ni o影响特征作简单模拟还原和分析,认为上述差异可能与El Ni o反气旋环流影响位置偏北有关。     

2007 年南海夏季风季节内振荡的北传及影响因子

利用2007年全球降水气候计划GPCP(the Global Precipitation Climatology Project)卫星红外窗口导出的全球降水指数GPI(the Global Precipitation Index)的日降水资料及频率-波数分析方法,分析2007年南海夏季风季节内振荡(Intraseasonal Oscillation,ISO)的传播特征,并使用美国国家环境预报中心(NCEP)/美国大气研究中心(NCAR)再分析的逐日资料,探讨影响其传播的主要因子.结果表明,南海夏季风ISO有明显的北传趋势,并且明显比南传分量占优.影响南海夏季风ISO北传的主要因子是平均纬向风垂直切变和平均经向风对异常水汽的输送.之所以异常经向风对平均水汽的输送及海-气相可作用的影响在南海地区不重要,而在印度季风区有一定的贡献,是因为平均水汽和纬向风分布在两个地区的差异.     

华南前汛期典型涝年低频降水特征及其与低频水汽输送的关系

利用1961—2013年国家气象信息中心提供的全国753站逐日降水资料、NCEP/NCAR逐日再分析风场和比湿资料,以及NOAA的HYSPLIT模式同期驱动资料,分析了华南前汛期9个典型涝年的低频降水特征及其与低频水汽输送的关系,探讨了低频水汽输送通道及源地。结果表明,华南前汛期9个典型涝年降水存在显著的10~20 d低频振荡周期,闽赣地区30~60 d低频周期也显著。华南前汛期850 hPa纬向、经向水汽通量都存在10~20 d的显著低频周期。影响华南前汛期典型涝年10~20 d低频降水的四个低频水汽输送通道及源地为:以马达加斯加岛北部印度洋、赤道中印度洋为参考源地的西南水汽通道;以日本群岛东南洋面和赤道中太平洋为源地的东南水汽通道;以里海北部和贝加尔湖东南侧为参考源地的西北冷空气通道;以白令海为参考源地的东北冷湿水汽通道。对广东佛冈站和江西广昌站的典型涝年进行水汽后向轨迹模拟验证了上述四个水汽通道,模拟源地均位于水汽通道关键区域。水汽信号参考源地和模拟源地,可作为华南前汛期提前2~6 d延伸期预报时重点考察地区。      

QBO 与南海夏季风爆发的关系

利用1979—2001 年ECMWF 再分析资料和NOAA 海温资料,通过相关分析和合成分析等统计方法,分析了平流层准两年周期振荡(QBO)与南海夏季风建立时间的关系。结果表明,QBO 位相与南海夏季风爆发时间有显著的相关关系:超前南海夏季风爆发约18 个月的QBO 西(东)风位相对应着季风爆发时间偏早(晚)。QBO 与南海夏季风爆发的联系要比ENSO 与南海夏季风爆发的联系更密切。      

热带印度洋-西太平洋水汽输送异常对中国东部夏季降水的影响

利用1979~2015年NCEP/NCAR发布的月平均全球再分析资料,分析了热带印度洋-西太平洋水汽输送异常对中国东部夏季降水的影响及其形成机理。研究结果表明:热带印度洋-西太平洋地区（10°S~30°N,60°~140°E）夏季异常水汽输送主要包括两个模态,他们可以解释总的水汽输送异常34%的方差。其中,第一模态（EOF1）表现为异常水汽沿反气旋从热带西太平洋经过南海及孟加拉湾输送到中国东部上空,对应南海、孟加拉湾水汽路径输送均偏多,此时西太平洋副热带高压显著偏强,异常水汽在长江中下游地区辐合并伴随显著上升运动,有利于长江中下游降水偏多;第二模态（EOF2）表现为异常水汽从热带印度洋沿阿拉伯海、印度半岛、中南半岛等呈反气旋式输送,华南上空相应出现气旋式水汽输送异常,并对应异常水汽辐合和上升运动,有利于华南降水偏多。就可能的外部成因而言,EOF1与ENSO关系密切,表现为前冬热带中东太平洋显著偏暖,夏季同期热带北印度洋、南海上空显著偏暖,造成西太平洋副热带高压显著偏强,异常水汽主要来源于热带西太平洋和南海;EOF2与同期热带印度洋偶极子（TIOD）异常有关,TIOD为正位相时热带印度洋上空出现异常东风,华南上空出现异常气旋并伴随水汽异常辐合,异常水汽主要来源于热带南印度洋。     

华南一次暴雨过程热力和动力特征的诊断分析

2015年5月19—20日广东省强降水过程具有降水集中、强度大和局地性强的特点,利用广东省自动气象站观测资料、ECMWF_FINE再分析资料,对此次强降水过程进行分析发现:华南地区受低槽东移影响,强降水发生在切变线南侧偏南暖湿流场中,粤北降水属于锋面降水,粤东降水属于锋前暖区降水,两者在水汽输送和动力机制上有显著区别。孟加拉湾和南海输送的水汽在这次强降水过程中占主导地位,南边界和东边界为水汽的流入边界,整体水汽输送以经向输入为主。暖区降水区域处于较强的水汽平流环境中,具有更大的水汽净输送量,造成粤东地区的降水量更大。对流层高层辐散比中低层辐合更为重要,是粤东暖区降水重要的动力属性,且暖区中低层流场的旋转效应弱,有区别于典型的梅雨锋降水。利用绝热无摩擦湿位涡守恒进行诊断发现对流不稳定是此次强降水发展的主要机制,暴雨发生区域对应湿位涡垂直分量为负值,水平分量为正值,底层MPV1＜0和MPV2＞0综合反映了大气对流不稳定和斜压不稳定的增强过程。降水区对流层低层受负湿位涡控制,低层湿位涡负值区与强降水落区有较好的对应关系。      

利用大尺度环流确定2006年南海夏季风爆发日期

南海夏季风爆发最显著的特征就是南海地区西南风的突然增强和降水的明显增多,往往采用南海地区低层平均风场和(或)对流强度来判别南海夏季风的爆发日期。这种方法在大多数的年份是适用的,但是2006年由于0601号台风“珍珠”的介入,利用南海地区的区域指标来确定南海夏季风的爆发日期就略显不足。要解决以上的问题,必须从更大尺度上去想办法。利用经圈和纬圈环流可以较好地确定2006年南海夏季风的爆发日期。分析结果表明2006年南海夏季风爆发于5月16日(第4候)。