NUMERICAL EXPERIMENT OF IMPACT OF SEA SURFACE TEMPERATURE IN SOUTH CHINA SEA AND WARM POOL/WEST PACIFIC ON EAST ASIAN SUMMER MONSOON*

By using the NCAR CCM1 model, we have designed six sensitive experiments, which are increased and decreased SST(sea surface temperature) by 1℃ each in the SCS(South China Sea) and in the West Pacific warm pool, increased and decreased SST by 1℃ in the warm pool with increased SST by 1℃ in the SCS. All experiments are integrated from April to July. Comparing with the control experiment, we have analyzed the anomalies of the wind field at the upper and lower layers, the anomalies of the seasonal variability of the monsoon and precipitation for each experiment. In the result, we have found that the SST anomaly(SSTA) in the SCS greatly affects the seasonal variability of the SCS monsoon and precipitation in China, especially during the cold period of SST in the SCS. The impact of SSTA in the warm pool on SCS monsoon is also found.but is weak as compared to the effect of SST anomaly in the SCS. Besides, its impact on rainfall in China is uncertain.     

How Well does BCC_CSM1.1 Reproduce the 20th Century Climate Change over China?

The historical simulation of phase five of the Coupled Model Intercomparison Project(CMIP5) experiments performed by the Beijing Climate Center climate system model(BCC_CSM1.1) is evaluated regarding the time evolutions of the global and China mean surface air temperature(SAT) and surface climate change over China in recent decades.BCC_CSM1.1 has better capability at reproducing the time evolutions of the global and China mean SAT than BCC_CSM1.0.By the year 2005,the BCC_CSM1.1 model simulates a warming amplitude of approximately 1℃ in China over the 1961-1990 mean,which is consistent with observation.The distributions of the warming trend over China in the four seasons during 1958-2004 are basically reproduced by BCC_CSM1.1,with the warmest occurring in winter.Although the cooling signal of Southwest China in spring is partly reproduced by BCC_CSM1.1,the cooling trend over central eastern China in summer is omitted by the model.For the precipitation change,BCC_CSM1.1 has good performance in spring,with drought in Southeast China.After removing the linear trend,the interannual correlation map between the model and the observation shows that the model has better capability at reproducing the summer SAT over China and spring precipitation over Southeast China.     

South China Sea Monsoon Experiment （SCSMEX） and the East Asian Monsoon

The SCSMEX is a joint atmospheric and oceanic experiment by international efforts, aiming at studying the onset, maintenance, and variability of the South China Sea (SCS) summer monsoon, thus improving the monsoon prediction in Southeast and East Asian regions. The field experiment carried out in May-August 1998 was fully successful, with a large amount of meteorological and oceanographic data acquired that have been used in four dimensional data assimilations by several countries, in order to improve their numerical simulations and prediction. These datasets are also widely used in the follow-up SCS and East Asian monsoon study. The present paper has summarized the main research results obtained by Chinese meteorologists which cover six aspects: (1) onset processes and mechanism of the SCS summer monsoon; (2) development of convection and mesoscale convective systems (MCSs) during the onset phase and their interaction with large-scale circulation; (3) low-frequency oscillation and teleconnection effect; (4) measurements of surface fluxes over the SCS and their relationship with the monsoon activity; (5) oceanic thermodynamic structures, circulation, and mesoscale eddies in the SCS during the summer monsoon and their relationship with ENSO events; and (6) numerical simulations of the SCS and East Asian monsoon.     

THE CLIMATE FEATURES OF THE SOUTH CHINA SEA WARM POOL

There exists a warm pool in the South China Sea (SCS). The temporal and spatial distribution and evolution of SCS warm pool is investigated using water temperatures at a depth of 20 min the sea. The formation of the warm pool is discussed by combining water temperatures with geostrophic currents and simulated oceanic circulation. It is found that there are significant seasonal and interannual changes in the warm pool and in association with the general circulation of the atmosphere. The development of SCS warm pool is also closely related to the gyre activities in the sea and imported warm water from Indian Ocean (Java Sea) besides radiative warming.     

Abrupt Climate Change around 4 ka BP： Role of the Thermohaline Circulation as Indicated by a GCM Experiment

A great deal of palaeoenvironmental and palaeoclimatic evidence suggests that a predominant tem-perature drop and an aridification occurred at ca. 4.0 ka BP. Palaeoclimate studies in China support thisdedution. The collapse of ancient civilizations at ca. 4.0 ka BP in the Nile Valley and Mesopotamia hasbeen attributed to climate-induced aridification. A widespread alternation of the ancient cultures was alsofound in China at ca. 4.0 ka BP in concert with the collapse of the civilizations in the Old World. Palaeo-climatic studies indicate that the abrupt climate change at 4.0 ka BP is one of the realizations of the coldphase in millennial scale climate oscillations, which may be related to the modulation of the ThermohalineCirculation (THC) over the Atlantic Ocean. Therefore, this study conducts a numerical experiment ofa GCM with SST forcing to simulate the impact of the weakening of the THC. Results show a drop intemperature from North Europe, the northern middle East Asia, and northern East Asia and a significantreduction of precipitation in East Africa, the Middle East, the Indian Peninsula, and the Yellow RiverValley. This seems to support the idea that coldness and aridification at ca. 4.0 ka BP was caused by theweakening of the THC.     

POSSIBLE RELATIONSHIPS AMONG SOUTH CHINA SEA SSTA, SOIL MOISTURE ANOMALIES IN SOUTHWEST CHINA AND SUMMER PRECIPITATION IN EASTERN CHINA

By using 1958-2001 NOAA extended reconstructed sea surface temperature(SST) data, ERA40 reanalysis soil moisture data and precipitation data of 444 stations in China(east of 100°E), the possible relationships among South China Sea(SCS) SST anomaly(SSTA), soil moisture anomalies(SMA) and summer precipitation in eastern China as well as their possible physical processes are investigated. Results show that the SSTA of SCS bears an evidently negative correlation with spring soil moisture in the east part of Southwest China. More(less) precipitation happens in the Yangtze River basin and less(more) in the Southeast China in summer when the SSTA of SCS is higher(lower) than normal and the soil in the east part of Southwest China is dry(wet) in spring. Further analysis shows that when the SSTA of SCS is high(low), the southwesterly wind at low level is weak(strong), decreasing(increasing) the water vapor transport in South China, resulting in reduced(increased) spring precipitation in the east part of Southwest China and more(less) soil moisture in spring. Through the evaporation feedback mechanism, the dry(wet) soil makes the surface temperature higher(lower) in summer, causing the westward extension(eastward retreat) of the West Pacific Subtropical High, eventually leading to the summer precipitation anomalies.     

Comparison of the Double Summer Monsoon Troughs over East Asia

Based on NCEP/NCAR reanalysis data, an investigation has been carried on the comparison of the double summer monsoon troughs over East Asia, which refer to the subtropical summer monsoon trough (subtropical-trough) and the South China Sea summer monsoon trough (SCS trough), respectively. The results show that the SCS trough is stronger than the subtropical-trough either in convergence or convection. The subtropical-trough extends up to higher levels and inclines northward with altitude, while, the SCS trough extends up to a lower level, and its position is seldom changed. The SCS trough establishes early and abruptly with the low level positive relative vorticity appearing suddenly, and retreats slowly, but the subtropical-trough establishes step by step with the positive relative vorticity initially over the Yunnan-Guizhou Plateau and Guangxi areas spreading gradually northeastward, and withdraws rapidly. The onset of SCS trough is obviously indicated by the reverse of the easterly, but the establishment of the subtropical-trough is characteristic of the westerly enhancement. The subtropical-trough has clearly frontal property, yet the SCS trough has not.     

NUMERICAL SIMULATIONS OF OCEANIC ELEMENTS IN THE SCS AND ITS NEIGHBORING SEA REGIONS FROM JANUARY TO AUGUST IN 1998

Studies on oceanic conditions in the South China Sea (SCS) and adjacent waters are helpful for thorough understanding of summer monsoons in East Asia. To have a 3-dimensional picture of how the oceanic currents vary, the oceanic elements in the South China Sea (SCS) and its neighboring sea regions in January～August 1998 have been simulated by using the improved Princeton University Ocean Model (POM) in this paper. The main results are in good agreement with that of ocean investigations and other simulations. The results show that the SCS branch of the Kuroshio Current is an important part in the north SCS from January to August; the SCS warm current is reproduced clearly in all months except in winter; there always exists a large-scale anti-cyclonic vortex on the right of the Kuroshio Current from January to August. In the model domain, the surface currents of the SCS have the closest relations with the monsoon with an apparent seasonal variation. In addition, the developing characteristics of the SST in the SCS and its neighboring sea regions before and after the summer monsoon onset are also well simulated by the improved POM. Those are the foundation for developing a coupled regional ocean-atmospheric model system.     

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.     

A Note on the South China Sea Shallow Interocean Circulation

1. IntroductionThe South China Sea (SCS) has many channelsconnecting with the outer oceans/seas (Fig. 1). Thewidest and deepest channel is the Luzón Strait, whichis the main entrance to the SCS from the WesternPacific Ocean, having a sill depth of about 2500 m.On the north, the Taiwan Strait connects with theEast China Sea, with a sill depth of about 70 m. Inthe vicinity of Mindoro Island, there are a numberof channels connecting the SCS with the Sulu Sea.The main channel is the M…     

基于卫星观测的南海表层温度气候学特征及长期变化

利用高分辨率AVHRR Pathfinder卫星海表温度资料,分析了1982-2012年南海及其毗邻海区海表温度（SST）的变化趋势,并给出了近30年该海域SST的气候学特征。结果表明：南海年平均SST随纬度的增加而降低,且越靠近陆地海温梯度越大,等温线呈西南-东北向分布;南海最高、最低SST分别出现在夏季和冬季;夏季中南半岛和海南岛东侧存在相对低温区,应与西南季风和地转偏向力共同作用引起的深层冷水涌升有关;近30年南海及毗邻海区年平均SST增温趋势为0.100℃/10a,20世纪90年代末到21世纪初年平均SST处于高值期,最高值出现在1998年;南海海区四季均存在变暖趋势,冬季增温趋势最大,为0.194℃/10a,夏、春季次之,分别为0.121℃/10a和0.107℃/10a,秋季最小,为0.086℃/10a;近30年台湾海峡和中国大陆东南沿海增温最显著,最大增温值达到0.7℃/10a以上。     

The NPO/ NAO and interdecadal climate variation in China

This article discusses the interannual variation of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO), its relationship with the interdecadal climate variation in China which is associated with the climate jump in the Northern Hemisphere in the 1960’s, using the data analyses. It is clearly shown that both the amplitudes of the NAO and NPO increase obviously in the 1960’s and the main period of the oscillations changes from 3-4 years before the 1960’s to 8-15 years after the 1960’s. Therefore, interdecadal climate variation in China or the climate jump in the 1960’s is closely related to the anomalies of the NAO and NPO.     

Effects of the Thermal Contrast Between Indo-China Peninsula and South China Sea on the SCS Monsoon Onset

The seasonal and interannual variations of the thermal contrast between Indo-China Peninsula (ICP)and South China Sea (SCS) were analyzed using the pentad mean NCEP/NCAR reanalysis data during 1958-1998 and the pentad mean outgoing long-wave radiation (OLR) data during 1975{1998, along with the effects of such a thermal contrast on the SCS monsoon onset (SCSMO). It is shown that there exists significant seasonal evolution for such a thermal contrast. The surface temperature of ICP is higher than that of SCS from pentad 3 to pentad 25 due to the sensible heating of the ICP. After pentad 25, such a thermal gradient reverses due to the temperature decrease resulted from the convection and rainfall over the ICP from pentad 22 to pentad 23. Furthermore, the above seasonal evolution of the discussed thermal contrast also demonstrates a remarkable interannual change which plays an important role in the SCSMO.On one hand, the reversion happens prior to (or simultaneously with) the SCSMO each year during 1958-1998, thus becoming a precondition for the SCSMO. On the other hand, the earlier (later) the date when the surface temperature of ICP becomes higher (lower) than that of the SCS, the later the SCSMO.     

孟加拉湾西南季风与南海热带季风季节内振荡特征的比较

采用美国国家环境预报中心的向外长波辐射和风场资料及日本气象厅的降水资料,用30-60d滤波后的夏季风指数在孟加拉湾和南海的区域平均值分别代表孟加拉湾西南季风和南海热带季风季节内振荡,对两支季风的季节内振荡特征进行比较分析,发现孟加拉湾西南季风的季节内振荡和南海热带季风的季节内振荡在夏季风期间(5-10月)都有约3次半的波动.夏季风期间,在阿拉伯海-西太平洋纬带上,夏季风的季节内振荡有4次从阿拉伯海的东传和3次从西太平洋的西传,其中7月后东传可直达西太平洋.孟加拉湾和南海在夏季风期间都有4次季节内振荡的经向传播,但孟加拉湾在约15°N以南为季节内振荡从热带东印度洋的北传,在约15°N以北则为副热带季风季节内振荡的南传;而在南海则是4次季节内振荡从热带的北传.在以孟加拉湾西南季风季节内振荡和南海热带季风季节内振荡分别划分的6个位相中,都存在1-3位相和4-6位相中低频对流、环流形势相反的特征,这是由热带东印度洋季节内振荡的东传和北传所致.热带印度洋季节内振荡沿西南-东北向经过约14d传到孟加拉湾,激发了孟加拉湾西南季风季节内振荡的东传,经过约6d到达南海,激发了南海热带季风季节内振荡的北传,经过约25d到达华南,形成热带印度洋季节内振荡向华南的经纬向接力传播(45d).孟加拉湾西南季风季节内振荡所影响的降水主要是在20°N以南的热带雨带随低频对流的东移而东移;而南海热带季风季节内振荡所影响的降水除了这种热带雨带随低频对流的东移外,还有在20°N以北的东亚副热带地区存在雨带随南海低频对流的北移而北移.     

基于自然的气候变化解决方案

基于自然的解决方案(NbS)是近10年提出的人类社会应对一系列环境和社会挑战的成本有效的方式,但直到近期才在国际社会引起重视。针对气候变化,NbS指通过对生态系统的保护、恢复和可持续管理减缓气候变化,同时利用生态系统及其服务功能帮助人类和野生生物适应气候变化带来的影响和挑战。这些生态系统包括森林、农田、草地、湿地（海岸带）生态系统,人工的或天然的。NbS能够为实现《巴黎协定》目标贡献30%左右的减排潜力,同时带来巨大的环境和社会经济的协同效益。但是,在过去的气候变化政策和行动中,包括国家自主贡献（INDC）,NbS尚未得到充分的重视,流入NbS相关的气候资金明显不足。为充分发挥NbS的潜力,建议开展中国NbS减排潜力及其协同效应研究,识别成本有效的中国NbS优先领域,梳理国际国内NbS成功案例,制定推动NbS主流化相关激励政策,推动多领域NbS协同治理。     

Determination of onset date of the South China Sea summer monsoon in 2006 using large-scale circulations

Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset.The methods can be used successfully in most of the years but not in 2006.Due to the intrusion of Typhoon Chanchu(0601)that year,the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date.In order to solve the problem,larger-scale situations have to be taken into account.Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006.The result indicates that its onset date is May 16.Moreover,similar onset dates for other years can be obtained using various methods,implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.     

IPCC AR6报告解读：短寿命气候强迫因子的气候及环境效应

影响气候变化的大气成分,依据其在大气中存留的时间,分为长寿命的温室气体和短寿命的气候强迫因子（SLCFs)。考虑到SLCFs在气候变化和大气环境中的重要作用,IPCC第六次评估报告（AR6）首次有了专门针对SLCFs的章节（第六章)。本文解读IPCC报告关于SLCFs的主要结论,特别强调AR5以来的最新结论,包括：SLCFs的定义、SLCFs排放和大气含量的变化特征及其对辐射强迫和全球气候的影响、不同共享社会经济路径（SSP）情景下SLCFs对未来气候变化和空气质量可能的影响,以及COVID-19疫情期间减排对气候变化的影响。文末也讨论了结论的不确定性以及结论对我国的启示。     

Temporal Variations of the Spring Persistent Rains and South China Sea Sub-high and Their Correlations to the Circulation and Precipitation of the East Asian Summer Monsoon

National Meteorological Information Center （NMIC） rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains （SPR） and the decay-pentad time index of the South China Sea （SCS） sub-high. These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon （EASM）. Results show that, the summer rainfall over southeastern China decreases when SPR onset is late. For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau （TP） strengthens, which makes abnormal anti-cyclonic circulation （cyclonic convergent circulation weakens） appear over southeastern China. When the decay of SCS sub-high delays, abnormal flood prevails over the middle and lower reaches of the Yangtze River （MLYR） and to the south. That is mainly caused by EASM weakening while SCS sub-high strengthening, then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley. The two indexes have high correlations with multivariate ENSO index （MEI） in March, indicating that the climate abnormity in East Asia is related to global climate abnormity tightly. The two time indexes are independent of each other, which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM. From this point of view, we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.     

RELATIONSHIP BETWEEN TROPICAL ISO AND TROPICAL CYCLONE ACTIVITY OVER THE SOUTH CHINA SEA

The relationship between the tropical intra-seasonal oscillation (ISO) and tropical cyclones (TCs) activities over the South China Sea (SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009. The main conclusions are: (1) A new ISO index is designed to describe the tropical ISO activity over the SCS, which can simply express ISO for SCS. After examining the applicability of the index constructed by the Climate Prediction Center (CPC), we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories. Consequently, the CPC index can’t replace the function of the new ISO index; (2) The eastward spread process of tropical ISO is divided into eight phases using the new ISO index, the phase variation of which corresponds well with the TCs activities over the SCS. TCs generation and landing are significantly reduced during inactive period (phase 4-6) relative to that during active period (phase 7-3); (3) The composite analyses indicate distinct TCs activities over the SCS, which is consistent with the concomitant propagation of the ISO convective activity. During ISO active period, the weather situations are favorable for TCs development over the SCS, e.g., strong convection, cyclonic shear and weak subtropical high, and vice versa; (4) The condensation heating centers, strong convection and water vapor flux divergence are well collocated with each other during ISO active period. In addition, the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period, and vice versa. Thus, the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.