On the onset of the south china sea summer monsoon in 1998

1.IntroductionChinesescientistshavepointedoutsincethe1980sthattheAsiansummermonsooniscomposedoftheSouthAsian(Indian)monsoonsystemandtheEastAsianmonsoonsystem,whichhavetheirparticularcharacteristicsrespectivelybutalsointeractoneachother;andtheAsiansummermonsoonbreaksoutintheSouthChinaSea(SCS)regionatfirst,thenspreadsnorthwestwardandnorthwardrespectively,finallytheSouthAsiansummermonsoonandtheEastAsiansummermonsoonaresetup(TaoandChen,1987;JinandChen,1985;Zhuetal.,1986).Muchattentionhasbe…     

中国华南春季季风及其与大尺度环流特征的关系

定义了中国华南春季季风，并用NCEP／NCAR再分析资料研究了春季风的气候特征以及春季风降水和大尺度环流在年际变化上的关系。结果表明，从降水和大气环流的变化来看，华南春季风在气候上发生于4月和5月；与华南春季风相联系的大气环流特征与夏季风和冬季风所对应的大气环流特征完全不同。华南春季风降水的年际变化主要与太平洋北部的异常环流相关联，而这种异常环流又与亚洲北部的西风急流和极地涡旋有联系；华南春季风降水的年际变化还与太平洋的海表温度异常有关；而亚洲热带大气环流的年际变化与华南春季风降水的变化关系不大。     

Peculiar temporal structure of the south china sea summer monsoon

Beijing located at the junction of four major components of the Asian-Australia monsoon system (the Indian, the western North Pacific, the East Asian subtropical, and the Indonesian-Australian monsoons), the monsoon cli-mate over the South China Sea (SCS) exhibits some unique features. Evidences are presented in this paper to reveal and document the following distinctive features in the temporal structure of the SCS summer monsoon:(1) pronounced monsoon singularities in the lower tropospheric monsoon flows which include the pre-onset and withdrawal easterly surges and the southwesterly monsoon bursts at Julian pentad 34-35 (June 15-24) and pentad 46-47 (August 14-23);(2) four prominent subseasonal cycles (alternative occurrences of climatological active and break monsoons);(3) considerably larger year-to-year variations in convective activity on intraseasonal time scale compared to those over the Bay of Bengal and the Philippine Sea;(4) the redness of the climatological mean spectrum of precipitation / deep convection on synoptic to intraseasona] time scales in the central SCS;(5) a remarkable asymmetry in the seasonal transitions between summer and winter monsoons and an extremely abrupt mid-May transition (the outburst of monsoon rain and the sudden switch in tie lower troposphere winds from an easterly to a westerly regime);(6) the bi-modal interannual variation of summer monsoon onset (normal and delayed modes).In addition, the monsoon rainfall displays enormous east-west gradient over the central SCS. Possible causes for these features are discussed. A number of specific science questions concerning some of the peculiar features are raised for the forthcoming SCS monsoon experiment to address     

Observational Study on the Onset of the South China Sea Southwest Monsoon

ＯｂｓｅｒｖａｔｉｏｎａｌＳｔｕｄｙｏｎｔｈｅＯｎｓｅｔｏｆｔｈｅＳｏｕｔｈＣｈｉｎａＳｅａＳｏｕｔｈｗｅｓｔＭｏｎｓｏｏｎＹａｎＪｕｎｙｕｅ（阎俊岳）ＮａｔｉｏｎａｌＣｌｉｍａｔｅＣｅｎｔｅｒ，Ｂｅｉｊｉｎｇ１０００８１ＲｅｃｅｉｖｅｄＮｏｖｅｍｂ...     

The study on the interannual variation and the mechanism of the south china sea monsoon

l.Intr0ductionTheonset0ftheSouthChinaSea(SCS)monsoonisasignofthecomingoftheAsianmonsoon.Inaverage,theonsetoftheSCSmonsoonisinthemiddleofMay,butitsstrengthandtheonsetdatediffergreatlyfromoneyeartoanother.TheanomaliesoftheSCSmon-soonhighlydePendonnotonIytheprecipitationinSCS,butalsotheanomaliesofthecircu-lationintheworld.WhyisthemonsoononsetearliestinSCS?Whatisthemechanismoftheonsetanditsvariation?Thisisascientificproblemthatisinterestedinbymeteorologistsbothathomeandabroad.TaoandChen…     

南海夏季风爆发前后大气环流的演变

利用1958-1997年的NCEP/NCAR再分析资料,以南海夏季风爆发日为临界日,分析了季风爆发前后全球平均环流和扰动环流的演变.结果显示,季风爆发前后气候平均场的环流形势是完全不同的,且这一变化是全球性的.从扰动场的演变看,伴随季风的爆发,扰动环流的变化不仅是全球的,而且具有突发性.分析还指出了南海西南季风的来源和三支越赤道气流的作用,特别是南半球环流的变化以及其对南海夏季风爆发的影响.     

Diagnostic study of apparent heat sources and moisture sinks in the south china sea and its adjacent areas during the onset of 1998 SCS monsoon

1.IntroductionItiswellknownthattheSouthChinaSea(SCS)monsoonisnotonlyamajormemberoftheEastAsianmonsoon,butalsohasanimportantfunctionontheweatherandclimateintheSouthChinaSea,theneighboringareasandtheworld.Manyscholarsathomeandabroadhavedonevariousresearchesaboutit.Jinngetal.(1993a,1993b)foundthatthetroposphericheatingincreasesabruptly,andtheheatsourcesandthemoisturesinksbecomestrongobviouslyinthesoutheasternTibetanPlateauandtheeastplainofChinawhentheSouthChinaSeamonsoononsets.Additionally…     

南方涛动年际变化与夏季亚澳季风环流及海洋性大陆区域气候异常的联系

利用美国NOAA卫星观测的SOI(Southern Oscillation Index,南方涛动指数)资料以及NCEP/NCAR、CMAP月平均资料,采用相关分析等方法,研究了南方涛动年际变化与夏季亚澳季风环流及海洋性大陆区域气候异常的联系。结果表明:南方涛动具有显著的年际变化特征,这种年际变化对夏季亚澳季风区及海洋性大陆区域的环流、降水及温度异常有重要影响。当SOI正位相时,赤道以南的澳大利亚东部地区以及西北太平洋海域高层为气旋,低层为反气旋,赤道地区的东部太平洋低层为辐散中心,高层为辐合中心,有利于下沉运动维持;加里曼丹岛附近低层辐合,高层辐散,有利于上升运动维持;海洋性大陆地区降水为显著的正异常,东亚地区降水存在较弱的正异常;海洋性大陆地区以及我国青藏高原到东海一带温度为正异常,孟加拉湾及印度半岛区域温度为负异常。     

中南半岛地区热力特征对南海季风爆发的可能影响及机理

利用1998年5月1日－8月31日南海季风试验(SCSMX)产1980年1月－1995年12月NCEP／NCAR候平均再分析资料，分析1998年和多年平均情况下南海夏季风爆发期间中南半岛地区热力特征，揭示该地区热状况的异常与南海夏季风爆发之间的可能联系，从而讨论引起南海夏季风爆发的可能机制。结果发现，南海季风爆发前中南半岛附近地区存在较强的持续地面感知加热并具有显的低频振荡特征，低层大气在中南半岛地区出现较强的暖中心，由此导致局地强的水平温度梯度和位势高度梯度，有利于加强该地区的西南风。南海季风爆发前中南半岛地区低层出现较强的辐合风，高层出现较强的辐散风，这种低层强的辐合，高层强的辐射散配置有利于垂直运动的发展，降水的加强，进而触发南海季风的爆发。对多年平均资料的分析也证实了1998年南海季风爆发过程中所具有的特征，并进一步发现南海季风爆发前中南半岛地区850hPa温度是逐渐增加的，且增温幅度大于南海地区上空，由此加强了中南半岛与南海之间的温差。另外，比纬圈温度偏差和位势高度偏差的分析中发现，南海季风爆发期间南海和中南半岛地区的副高东撤与中南半岛地区的增温和孟加拉湾低槽的向东扩展有关。     

南海夏季风强弱年环流形势与热带对流特点对比分析

利用NCEP/NCAR(美国国家环境预报中心/国家大气研究中心)再分析资料,对南海强夏季风年和弱夏季风年进行合成分析,结果表明,无论是在夏季风爆发前的1月份或是夏季风盛行的7月份,强弱夏季风年的平均经圈环流和平均纬圈环流都有明显差异。在强夏季风年,1月份的哈特莱环流、7月份的瓦克环流和季风经圈环流都比弱夏季风年同期的明显。强夏季风年的西太平洋副热带高压比弱夏季风年明显偏弱。利用OLR资料分析强夏季风年(1981年)和弱夏季风年(1983)4～9月份赤道东印度洋和南海对流活动的季节内振荡,发现在南海强夏季风年,季节内振荡的次数偏少而强度偏强,在弱夏季风年,季节内振荡的次数偏多而强度偏弱。相比之下,在南海强夏季风年,赤道东印度洋的季节内振荡比南海的更具典型性。     

Regional and synoptic-scale features associated with inactive periods of the summer monsoon over south china(1)

This paper presents an observational study of the physical processes responsible for the inactive period (break) of the summer monsoon over South China (SC). The break of the monsoon is defined by using the rainfall data over Hong Kong Meteorological parameters provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the period 1985-1990 are examined. Daily values of each parameter for the six years are then composited each day for the period of 5 days before to 1 day after the break. It is found that several days before the break, changes opposite to those occurred during the onset and active periods begin to take place. This suggests that a feedback mechanism is present which tends to restore the atmosphere to a more stable state. This mechanism may be initiated by the formation of convective clouds during the onset and active periods. These clouds then reduce the solar radiation to the ground, leading to a gradual drop in the temperature. This drop, together with the cooling of the atmosphere due to the large amounts of rainfall, causes the pressure over the SC region to become higher, which in turn induces a westward extension of the subtropical ridge. The decrease in temperature over SC may also shift the location of the heat source to the west, which leads to a concomitant westward shift of the convergence of the southerlies and results in less moisture-laden air reaching the SC region. The atmosphere then becomes unfavourable for heavy convection and therefore a break starts.     

强弱南海夏季风活动及大气季节内振荡

应用ＮＣＥＰ再分析资料和中国降水资料，分析研究了对应南海强、弱夏季风的环流形势及其与之相应的中国东部的降水异常。其结果表明，由强、弱夏季风所引起的中国气候异常是完全不同（甚至反相）的。分析大气季节内振荡（ＩＳＯ）的活动还表明，对应大气强（弱）南海夏季风，南海地区 ８５０ ｈＰａ也有强（弱）大气 ＩＳＯ；而强、弱南海夏季风环流（２００ ｈＰａ和 ８５０ ｈＰａ）主要由异常的大气ＩＳＯ所激发。本研究还揭示了南海地区大气ＩＳＯ的变化往往与江淮地区大气ＩＳＯ的变化反相，例如南海地区的强（弱）大气ＩＳＯ常与江淮流域的弱（强）大气ＩＳＯ相对应。对于大气ＩＳＯ的强度，一般多表现出局地激发特征，经向传播相对较弱。     

A regional climate model simulation of summer monsoon over east asia: a case study of 1991 flood in yangtze-huai river valley

Ｉ．ＩＮＴＲＯＤＵＣＴＩＯＮＥａｓｔＡｓｉａｉｓｓｉｔｕａｔｅｄｉｎｔｈｅｅａｓｔｅｒｎｐａｒｔｏｆｔｈｅＥｕｒａｓｉａｎｃｏｎｔｉｎｅｎｔｗｈｅｒｅｔｈｅｈｕｇｅＴｉｂｅｔａｎＰｌａｔｅａｕｅｘｉｓｔｓ．Ｆａｃｉｎｇｅａｓｔａｎｄｓｏｕｔｈｅａｓｔ...     

东亚夏季风的年际到年代际变化及其与全球大气环流和海表温度的联系

The East Asian summer monsoon (EASM) underwent an interdecadal variation with interannual variations during the period from 1958 to 1997, its index tended to decline from a higher stage in the mid-1960＇s until it reached a lower stage after 1980＇s. Correlation analysis reveals that EASM is closely related with the global atmospheric circulation and sea surface temperature (SST). The differences between the weak and strong stage of EASM shows that, the summer monsoon circulation over East Asia and North Africa is sharply weakened, in the meantime, the westerlies in high latitudes and the trade--wind over the tropical ocean are also changed significantly. Over the most regions south of the northern subtropics, both air temperature in the lower troposphere and SST tended to rise compared with the strong stage of EASM. It is also revealed that the ocean-atmosphere interaction over the western Pacific and Indian Ocean plays a key role in interannual to interdecadal variation of EASM, most probably, the subtropical Indian Ocean is more important. On the other hand, the ENSO event is less related to EASM at least during the concerned period.     

2013年5月华南强降水与中国南海夏季风爆发

利用2013年"华南季风强降水外场试验与研究"的外场试验数据、美国NCEP FNL资料和卫星云顶黑体辐射温度资料,对2013年5月7—17日华南地区出现的两次强降水过程(7—12日和14—17日)中的高低空环流以及相关气象要素场的变化进行了对比分析。中国南海夏季风于5月第3候建立,两次过程分处于夏季风爆发前后。通过对比影响两次强降水过程的主要环流系统如南亚高压、高空副热带西风急流、500 hPa环流型、水汽来源等,指出影响两次强降水过程大尺度环流场之间的显著区别,说明南海季风爆发前后大尺度环流场对暴雨影响的典型差异。7—12日过程主要受北方锋面影响和南方暖湿气流辐合作用,导致华南地区出现南北两条雨带。14—17日过程则由于季风爆发后强的暖湿空气活动致使华南地区对流活跃,从而形成一条位于广东北部的雨带,此次过程强降水比第1次过程集中且对流性更强。两次降水过程的内在物理机制是一个准平衡态的热力适应过程,由于第2次过程降水更强,导致热源作用明显增强,动力向热力的适应过程也更显著。利用探空资料揭示出两次过程暖区暴雨大气热力和动力条件存在显著区别,7—12日南海季风爆发前的暖区暴雨主要受低层强垂直风切变导致的大气斜压不稳定影响;14—17日南海季风爆发后的暖区暴雨主要受高低空急流的强耦合作用影响。     

Overview of the South China sea monsoon experiment

The present paper gives an overview of the key project “ South China Sea Monsoon Experiment(SCSMEX)” operated by the Ministry of Science and Technology of China during the period of 1996-2001. The SCSMEX is a joint atmospheric and oceanic field experiment which aims to better understandthe onset, maintenance, and variability of the summer monsoon over the South China Sea (SCS). It is a large-scale international effort with many participating countries and regions cooperatively involved in this experiment. With the field observation in May-August 1998, a large amount of meteorological and oceanic data was acquired, which provides excellent datasets for the study of the SCS monsoon and the East Asian monsoon and their interaction with the ocean. The preliminary research achievements are as follows. (1) The earliest onset of the Asian monsoon over the SCS and Indo-China Peninsula has been well documented. From the viewpoint of the synoptic process, its onset is closely related to the early rapid development of a twin cyclone to the east of Sri Lanka. The conceptual model of the SCS monsoon onset in 1998 was put forward. The 50-year time series of the SCS monsoon onset date was also made. (2) Two major modes, namely the 30-60-day and 10-20-day oscillations were ascertained. The influences of the abnormal SCS monsoon on the precipitation over eastern China and its modes were identified. A strong(weak) monsoon over the SCS usually leads to less (more) precipitation over the middle and lower reaches of the Yangtze River basin, and more (less) precipitation in North China. (3) During the monsoon onset over the SCS, a wide variety of organized mesoscale convective systems (MCSs) were observed by a Doppler radar array deployed over the northern SCS. The relationship between large-scale circulations and MCSs during the monsoon onset process in 1998 was clearly revealed. It was suggested that there is a kind of positive feedback mechanism between large-scale circulations and MCSs. (4) The SST over the SCS during the early period influences the timing of the monsoon onset date and the monsoon‘s intensity. During the monsoon onset, the ocean undergoes a process of energy release through air-sea interaction. During the break phase of the SCS monsoon, the ocean demonstrates the process of energy re-accumulation. Obvious differences in the air-sea turbulent flux exchange between the southern and northern parts of the SCS due to different characteristic features of the atmosphere and sea structure were observed in those regions.(5) The verification of impact of intensive observations on the predictive performance is made by the use of regional models. The air-sea coupled regional climate model (CRCM) was also developed under the SCSMEX Project . The simulation of the oceanic circulation in 1998 produced with the model was well compared with the observations.     

东亚太平洋地区近地面臭氧的季节和年际变化特征及其与东亚季风的关系

利用东亚清洁背景站近地面臭氧观测资料,结合风场和降水资料,分析东亚各地区臭氧的多年季节变化特征,并探讨东亚太平洋地区臭氧的季节和年际变化与季风的关系以及影响近地层臭氧的主要因子。结果表明：东亚大部分地区与北半球背景站观测一致,近地层臭氧季节变化表现为春季最高、夏季最低的特征;但在东亚中纬度33～43°N,臭氧表现为夏季最高,而在东亚20°N以南地区臭氧则表现为冬末、春初最高。东亚太平洋沿岸近地面臭氧的季节变化主要受东亚冬、夏季风环流的季节变化控制。该地区不同纬度上春季峰值出现时间的差异与亚洲大陆春季不同时期污染物输送路径的差异有关。对东亚太平洋沿岸对流层顶附近位势涡度、高空急流和垂直环流季节变化的分析表明,冬春季可能是平流层向对流层输送的最强期,对近地面臭氧贡献最大。初夏至秋季（5-11月）,平流层向对流层输送较弱,对近地面臭氧贡献较小。东亚太平洋地区夏季风爆发的时间和强度以及季风环流型的年际差异是导致该地区春、夏季臭氧年际变化的主要原因;而季风降水和云带位置以及平流层一对流层交换是造成臭氧年际变化的其他原因。     

Numerical simulation of the regional ocean circulation in the coastal areas of china

The regional ocean circulation in the coastal areas or China (including a part of the western Pacific Ocean, the South China Sea and the Bay of Bengal el al.) is simulated by using the improved Princeton Uni-versity ocean circulation model (POM). Compared with the modeling results obtained by the large-scale ocean general circulation model (OGCM), the basic ocean circulation features simulated by the regional ocean circulation model are in good agreement with that simulated by OGCM and some detailed character-istics such as the regional ocean circulation, sea temperature, salinity and free sea surface height have also been obtained which are in good accord with the observations. These results indicate that the regional ocean circulation model has good capability to produce the regional ocean circulation characteristics and it can be used to develop coupled regional ocean-atmospheric model systems.     

Atmospheric circulation characteristics associated with the onset of Asian summer monsoon

The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer monsoon is found to occur first over the southwestern part of the South China Sea (SCS) and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump (from 25–28N to around 30N) occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere (500–200 hPa) and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet.     

1998 SCSMEX期间亚洲30－60天低频振荡特征的分析

对１９９８年 ５－８月南海季风试验（ＳＣＳＭＥＸ）期间东亚地区 ８５０ ｈＰａ中低纬环流指数、东亚季风指数和长江中下游降水进行了Ｍｏｒｌｅｔ 小波分析,结果表明在此期间这些要素均有明显的３０－６０天周期低频振荡。在此基础上对 ５－８月每隔 ５天的 ８５０ ｈＰａ低频流场进行分析,结果表明：（１）１００°－１５０°Ｅ间东亚从中国东中部大陆经南海和西太平洋的南北半球中明显的存在一个以３０－６０天低频荡为特征的东亚季风低频环流系统,东亚季风活动主要受东亚季风系统中低频活动影响;（２）５月第５候南海热带季风爆发、６月中旬长江中下游人梅及产生大暴雨以及７月中旬以后的该地区大暴雨均与低频气旋带在该地区活动有关,而８月长江上游大暴雨则与低频反气旋伸人到大陆有关;（３）ＳＣＳＭＥＸ期间东亚低频振荡系统的源地有二个,即南海赤道和北半球中太平洋中高纬。南海低频系统向北传播,而中高纬低频系统自东北向西南传播为主。长江中下游６、７月二次大暴雨均与上述二个低频气旋系统自热带向北和中高纬向西南传播并于长江中下游汇合有关;（４）５－８月间东亚季风系统中有二次低频气旋带和二次低频反气旋带活动,这些低频环流系统的活动与印度季风低频环流系统活动并无明