Revisiting East Asian monsoon change during the Last Glacial Maximum using PMIP4 simulations

利用PMIP4多模式试验数据,本文重新检查了末次冰盛期(距今约21000年)东亚季风变化.结果表明:相对于工业革命前期,所有5个模式一致模拟显示末次冰盛期东亚季风减弱,冬季和夏季减幅分别为1%-18%和2-32%;不同模式中东亚季风环流变化的空间分布存在差异,这主要源于该时期大尺度变冷和海平面气压梯度变化的空间分布不同;由于模式之间的差异和重建记录之间的不确定性,未来有待开展更多模拟和重建工作以更好地理解冰期东亚季风变化.

Evaluation of the interannual variability in the East Asian summer monsoon in AMIP and historical experiments of CAS FGOALS-f3-L

对东亚夏季季风(EASM)模拟的评估可以提高我们对亚洲季风动力和气候模拟的理解.在这项研究中,通过使用中国科学院(CAS)全球海洋-大气-陆地系统(FGOALS-f3-L)模式参加的第六次耦合模式相互比较计划(CMIP6)中的大气模式相互比较计划(AMIP)和历史(historical)试验,明确了EASM的年际变率的模拟能力.通过多变量经验正交函数(MV-EOF)分析发现,观测的EASM的主导模态为西太平洋上的太平洋-日本模态,并伴有局部反气旋异常.主导模态的方差贡献率为24.6%.历史(historical)试验可以基本再现这种空间模态,其方差贡献率较AMIP试验更接近于观测.与AMIP试验相比,历史(historical)试验还能更好地模拟EASM变率的时间频率.然而,由于历史(historical)模拟没有在积分开始时应用初始化过程,而AMIP试验受到海表面温度(SST)的约束,因此主成分(PC1)的位相在历史(historical)试验中没有得到较好地再现.进一步分析发现,印度洋和西太平洋热带地区的海气相互作用对EASM的模拟非常重要,而EASM气候变率的模拟可能与厄尔尼诺-南方涛动(ENSO)的模拟能力有关,这值得进一步分析.

Intensified East Asian summer monsoon and associated precipitation mode shift under the 1.5 ℃ global warming target

In this study, the East Asian summer climate changes under the 1.5 ℃ global warming （1.5 GW） target in 30 simulations derived from 15 coupled models within the Coupled Model Intercomparison Program phase 5 （CMIP5） are examined. Compared with the current summer climate （1975-2005）, both surface air temperature and precipitation increase significantly over the East Asian continent during the 1.5 GW period （average period 2021-2051）. In northeastern China this is particularly pronounced with regional averaged precipitation increases of more than 7.2%, which is greater than that for the whole East Asian continent （approximately 4.2%）. Due to stronger enhancement of precipitation north of 40°N, the leading empirical orthogonal function （EOF） mode of summer precipitation over the East Asian continent changes from tripolar-like mode to dipole mode. As there is stronger surface warming over the East Asian continent than that over surrounding ocean, the land-sea thermal contrast is enhanced during the 1.5 GW period. As a result, the monsoon circulation in the lower troposphere is significantly strengthened, which causes the increased summer precipitation over the East Asian continent. In addition, larger interannual variabilities of East Asian summer monsoon circulation and associated precipitation are also suggested for the 1.5 GW period.

Relationships between intensity of the Kuroshio current in the East China Sea and the East Asian winter monsoon

Based on satellite altimeter and reanalysis data,this paper studies the relationships between the intensity of the Kuroshio current in the East China Sea（ECS） and the East Asian winter monsoon（EAWM）.The mechanisms of their possible interaction are also discussed.Results indicate that adjacent transects show consistent variations,and on an interannual timescale,when the EAWM is anomalously strong（weak）,the downstream Kuroshio in the ECS is suppressed（enhanced） in the following year from February to April.This phenomenon can be attributed to both the dynamic effect（i.e.,Ekman transport） and the thermal effect of the EAWM.When the EAWM strengthens（weakens）,the midstream and downstream Kuroshio in the ECS are also suppressed（intensified） during the following year from October to December.The mechanisms vary for these effects.The EAWM exerts its influence on the Kuroshio＇s intensity in the following year through the tropospheric biennial oscillation（TBO）,and oceanic forcing is dominant during this time.The air-sea interaction is modulated by the relative strength of the EAWM and the Kuroshio in the ECS.The non-equivalence of spatial scales between the monsoon and the Kuroshio determines that their interactions are aided by processes with a smaller spatial scale,i.e.,local wind stress and heating at the sea surface.

Inter-decadal Analysis on the Intensity of Summer Monsoon in Northeast China

In this paper,the intensity index of East Asian summer monsoon in northeast China was defined objectively by using NCEP/NCAR daily reanalysis data and national precipitation data from 1961 to 2004.In the inter-decadal time scales,the correlations between sea-level pressure field,850 hPa flow field,500 hPa geopotential height,sea surface temperature,Arctic sea ice concentration,a variety of oscillation indexes and intensity index of East Asian summer monsoon in northeast China were analyzed.The analysis showed that the great value area of correlations was consistent between sea-level pressure field,500 hPa geopotential height field and intensity index of East Asian summer monsoon in northeast China in pre-winter or summer,and the correlation was much better in summer than in pre-winter.The correlation was poor between the sea surface temperature and intensity index of East Asian summer monsoon in northeast China,but the correlation was good between the Arctic sea ice concentration and intensity index of East Asian summer monsoon in northeast China.The correlation was better between the NPO index and intensity index of East Asian summer monsoon in northeast China than other indexes.

Variation of East Asian Summer Monsoon and Its Relationship with Precipitation of China in Recent 111 Years

Based on the monthly average SLP data in the northern hemisphere from 1899 to 2009, East Asian summer monsoon intensity index in recent 111 years was calculated, and the interdecadal and interannual variation characteristics of East Asian summer monsoon were analyzed. The results showed that East Asian summer monsoon in the 1920s was the strongest. The intensity of East Asian summer monsoon after the middle period of the 1980s presented weakened trend. It was the weakest in the early 21st century. Morlet wavelet analysis found that the interdecadal and interannual variations of East Asian summer monsoon had quasi-10-year and quasi-2-year significance periods. The interannual variation of precipitation in the east of China closely related to intensity variation of East Asian summer monsoon. In strong （weak） East Asian summer monsoon year, the rainfall in the middle and low reaches of Yangtze River was less （more） than that in common year, while the rainfall in North China was more （less） than that in common year. The weakening of East Asian summer monsoon was an important reason for that it was rainless （drought） in North China and rainy （flood） in the middle and low reaches of the Yangtze River after the middle period of the 1980s.

Impact of intensity variability of the Asian summer monsoon anticyclone on the chemical distribution in the upper troposphere and lower stratosphere

During the Asian summer monsoon(ASM)season,the process of stratosphere-troposphere exchange significantly affects the concentration and spatial distribution of chemical constituents in the upper troposphere and lower stratosphere(UTLS).However,the effect of the intensity of the Asian summer monsoon anticyclone(ASMA)on the horizontal distribution of chemical species within and around the ASMA,especially on the daily time scale,remains unclear.Here,the authors use the MERRA-2 reanalysis dataset and Aura Microwave Limb Sounder observations to study the impact of ASMA intensity on chemical distributions at 100 hPa during the ASM season.The intraseasonal variation of ASMA is classified into a strong period(SP)and weak period(WP),which refer to the periods when the intensity of ASMA remains strong and weak,respectively.The relatively low ozone(O_(3))region is found to be larger at 100 hPa during SPs,while its mixing ratio is lower than during WPs in summer.In June,analysis shows that the O_(3) horizontal distribution is mainly related to the intensity of AMSA,especially during SPs in June,while deep convections also impact the O_(3) horizontal distribution in July and August.These results indicate that the intraseasonal variation of the ASMA intensity coupled to deep convection can significantly affect the chemical distribution in the UTLS region during the ASM season.

The Interannual Variability of East Asian Winter Monsoon and Its Relation to the Summer Monsoon

Based on the NCEP/ NCAR reanalysis data the interannual variability of the East Asian winter mon-soon (EAWM) is studied with a newly defined EAWM intensity index. The marked features for a strong (weak) winter monsoon include strong (weak) northerly winds along coastal East Asia, cold (warm) East Asian continent and surrounding sea and warm (cold) ocean from the subtropical central Pacific to the trop-ical western Pacific, high (low) pressure in East Asian continent and low (high) pressure in the adjacent ocean and deep (weak) East Asian trough at 500 hPa. These interannual variations are shown to be closely connected to the SST anomaly in the tropical Pacific, both in the western and eastern Pacific. The results suggest that the strength of the EAWM is mainly influenced by the processes associated with the SST anom-aly over the tropical Pacific. The EAWM generally becomes weak when there is a positive SST anomaly in the tropical eastern Pacific (El Ni?o), and it becomes strong when there is a negative SST anomaly (La Ni?a). Moreover, the SST anomaly in the South China Sea is found to be closely related to the EAWM and may persist to the following summer. Both the circulation at 850 hPa and the rainfall in China confirm the connection between the EAWM and the following East Asian summer monsoon. The possible reason for the recent 1998 summer flood in China is briefly discussed too. Key words East Asian winter monsoon - Interannual variability - SST - Summer monsoon This study was supported by “ National Key Programme for Developing Basic Sciences” G1998040900 part 1, and by key project (KZ 952-S1-404) of Chinese Academy of Sciences.

An Index Measuring the Interannual Variation of the East Asian Summer Monsoon-The EAP Index

Based on the EAP (East Asia/Pacific) teleconnection in the summer circulation anomalies over the Northern Hemisphere, an index measuring the strength of the East Asian summer monsoon, i.e., the so-called EAP index, is defined in this paper. From the analyses of observed data, it is clearly shown that the EAP index defined in this study can well describe the interannual variability of summer rainfall and surface air temperature in East Asia, especially in the Yangtze River valley and the Huaihe River valley, Korea, and Japan. Moreover, this index can also reflect the interannual variability of the East Asian summer monsoon system including the monsoon horizontal circulation and the vertical-meridional circulation cell over East Asia. From the composite analyses of climate and monsoon circulation anomalies for high EAP index and for low EAP index, respectively, it is well demonstrated that the EAP index proposed in this study can well measure the strength of the East Asian summer monsoon.

The Instability of the East Asian Summer Monsoon-ENSO Relations

The instability in the relation between the East Asian summer monsoon and the ENSO cycle in the long-term variation is found through this research. By instability, we mean that high inter-relation exists in some periods but low inter-relation may appear in some other periods. It is reveals that the interannual variation of the summer atmospheric circulation during the ' high correlation' periods (HCP) is significantly different from that during the ' low correlation' periods (LCP). Larger interannual variability is found during HCP for trade wind over the tropical eastern Pacific of the Southern Hemisphere, the low-level air temperature over the tropical Pacific, the subtropical high pressure systems in the two hemispheres, and so on. The correlation between summer rainfall over China and ENSO is as well different between HCP and LCP.

Natural and human-induced changes in summer climate over the East Asian monsoon region in the last half century: A review

In the last half century,a significant warming trend occurred in summer over eastern China in the East Asian monsoon region.However,there were no consistent trends with respect to the intensity of the East Asian summer monsoon(EASM) or the amount of summer rainfall averaged over eastern China.Both of the EASM and summer rainfall exhibited clear decadal variations.Obvious decadal shifts of EASM occurred around the mid- and late 1970 s,the late 1980 s and the early 1990 s,and the late 1990 s and early 2000 s,respectively.Summer rainfall over eastern China exhibited a change in spatial distribution in the decadal timescale,in response to the decadal shifts of EASM.From the mid- and late 1970 s to the late 1980 s and the early 1990 s,there was a meridional tri-polar rainfall distribution anomaly with more rainfall over the Yangtze River valley and less rainfall in North and South China; but in the period from the early 1990 s to the late 1990 s and the early 2000 s the tri-polar distribution changed to a dipolar one,with more rainfall appearing over southern China south to the Yangtze River valley and less rainfall in North China.However,from the early 2000 s to the late 2000 s,the Yangtze River valley received less rainfall.The decadal changes in EASM and summer rainfall over eastern China in the last half century are closely related to natural internal forcing factors such as Eurasian snow cover,Arctic sea ice,sea surface temperatures in tropical Pacific and Indian Ocean,oceaneatmospheric coupled systems of the Pacific Decadal Oscillation(PDO) and AsianePacific Oscillation(APO),and uneven thermal forcing over the Asian continent.Up to now,the roles of anthropogenic factors,such as greenhouse gases,aerosols,and land usage/cover changes,on existing decadal variations of EASM and summer rainfall in this region remain uncertain.

Interdecadal Variability of the East Asian Summer Monsoon and Associated Atmospheric Circulations

Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.

Interdecadal Variability of the East Asian Summer Monsoon in an AGCM

It is well known that significant interdecadal variation of the East Asian summer monsoon （EASM） occurred around the end of the 1970s. Whether these variations can be attributed to the evolution of global sea surface temperature （SST） and sea ice concentration distribution is investigated with an atmospheric general circulation model （AGCM）. The model is forced with observed monthly global SST and sea ice evolution through 1958-1999. A total of four integrations starting from different initial conditions are carried out. It is found that only one of these reproduces the observed interdecadal changes of the EASM after the 1970s, including weakened low-level meridional wind, decreased surface air temperature and increased sea level pressure in central China, as well as the southwestward shift of the western Pacific subtropical high ridge and the strengthened 200-hPa westerlies. This discrepancy among these simulated results suggests that the interdecadal variation of the EASM cannot be accounted for by historical global SST and sea ice evolution. Thus, the possibility that the interdecadal timescale change of monsoon is a natural variability of the coupled climate system evolution cannot be excluded.

Interannual Variability of the Convective Activities Associated with the East Asian Summer Monsoon Obtained from TBBV ariability

In this paper, the interannual variability of the convective activities associated with the East Asian summer monsoon and its association with the thermal distribution of SST anomalies in the tropical Pacific are analyzed by using the daily TBB (Temperature of Black Body at Cloud Top) dataset from 1980 to 1991. The results of composite and individual analyses of TBB anomalies show that the interannual variability of the convective activities associated with the summer monsoon in East Asia is large and has a close relation to the thermal distribution of SST anomalies in the tropical Pacific, especially in the western Pacific warm pool. In the summer with ENSO-like distribution of SST anomalies in the tropical Pacific, the convective activities are weak around the Philippines, then the convective activities are intensified and the summer monsoon rainfall is strong in the area from the Yangtze River basin and the Huaihe River basin in China to Republic of Korea and Japan. On the contrary, in the summer with anti-ENSO-like distribution of SST anomalies in the tropical Pacific, the convective activities are strong around the Philippines, then the convective activities are weakened and the summer monsoon rainfall is weak in the area from the Yangtze River basin and the Huaihe River basin to Republic of Korea and Japan. It may be also found either from the composite analysis or from the individual analysis of TBB anomalies that the convective activities associated with the summer monsoon in East Asia have a good negative relation to that around the Philippines and a positive relation to that over the equatorial central Pacific.

Influence of Soil Moisture in Eastern China on the East Asian Summer Monsoon

The sensitivity of the East Asian summer monsoon to soil moisture anomalies over China was investigated based on ensembles of seasonal simulations （March-September） using the NCEP GCM coupled with the Simplified Simple Biosphere Model （NCEP GCM/SSiB）. After a control experiment with free-running soil moisture, two ensembles were performed in which the soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China （YRNC） was double and half that in the control, with the maximum less than the field capacity. The simulation results showed significant sensitivity of the East Asian summer monsoon to wet soil in YRNC. The wetter soil was associated with increased surface latent heat flux and reduced surface sensible heat flux. In turn, these changes resulted in a wetter and colder local land surface and reduced land-sea temperature gradients, corresponding to a weakened East Asian monsoon circulation in an anomalous anticyclone over southeastern China, and a strengthened East Asian trough southward over Northeast China. Consequently, less precipitation appeared over southeastern China and North China and more rainfall over Northeast China. The weakened monsoon circulation and strengthened East Asian trough was accompanied by the convergence of abnormal northerly and southerly flow over the Yangtze River valley, resulting in more rainfall in this region. In the drier soil experiments, less precipitation appeared over YRNC. The East Asian monsoon circulation seems to show little sensitivity to dry soil anomalies in NCEP GCM/SSiB.

Regional-scale Surface Air Temperature and East Asian Summer Monsoon Changes during the Last Millennium Simulated by the FGOALS-gl Climate System Model

The spatial patterns and regional-scale surface air temperature （SAT） changes during the last millennium,as well as the variability of the East Asian summer monsoon （EASM） were simulated with a low-resolution version of Flexible Global Ocean-Atmosphere-Land-Sea-ice （FGOALS-gl） model.The model was driven by both natural and anthropogenic forcing agents.Major features of the simulated past millennial Northern Hemisphere （NH） mean SAT variations,including the Medieval Climate Anomaly （MCA）,the Little Ice Age （LIA） and the 20th Century Warming （20CW）,were generally consistent with the reconstructions.The simulated MCA showed a global cooling pattern with reference to the 1961-90 mean conditions,indicating the 20CW to be unprecedented over the last millennium in the simulation.The LIA was characterized by pronounced coldness over the continental extratropical NH in both the reconstruction and the simulation.The simulated global mean SAT difference between the MCA and LIA was 0.14°C,with enhanced warming over high-latitude NH continental regions.Consistencies between the simulation and the reconstruction on regional scales were lower than those on hemispheric scales.The major features agreed well between the simulated and reconstructed SAT variations over the Chinese domain,despite some inconsistency in details among different reconstructions.The EASM circulation during the MCA was stronger than that during the LIA The corresponding rainfall anomalies exhibited excessive rainfall in the north but deficient rainfall in the south.Both the zonal and meridional thermal contrast were enhanced during the MCA.This temperature anomaly pattern favored a stronger monsoon circulation.

Interference of the East Asian Winter Monsoon in the Impact of ENSO on the East Asian Summer Monsoon in Decaying Phases

The variability of the East Asian winter monsoon （EAWM） can be divided into an ENSO-related part （EAWMEN） and an ENSO-unrelated part （EAWMres）.The influence of EAWMres on the ENSO-East Asian summer monsoon （EASM） relationship in the decaying stages of ENSO is investigated in the present study.To achieve this,ENSO is divided into four groups based on the EAWMres：（1） weak EAWMres-E1Ni（n）o （WEAWMres-EN）; （2） strong EAWMres-E1Ni（n）o （SEAWMresEN）; （3） weak EAWMres-La Ni（n）a （WEAWMres-LN）; （4） strong EAWMres-La Ni（n）a （SEAWMres-LN）.Composite results demonstrate that the EAWMres may enhance the atmospheric responses over East Asia to ENSO for WEAWMres-EN and SEAWMres-LN.The corresponding low-level anticyclonic （cyclonic） anomalies over the western North Pacific （WNP） associated with El Ni（n）o （La Ni（n）a） tend to be strong.Importantly,this feature may persist into the following summer,causing abundant rainfall in northern China for WEAWMres-EN cases and in southwestern China for SEAWMres-LN cases.In contrast,for the SEAWMres-EN and WEAWMres-LN groups,the EAWMres tends to weaken the atmospheric circulation anomalies associated with E1 Ni（n）o or La Ni（n）a.In these cases,the anomalous WNP anticyclone or cyclone tend to be reduced and confined to lower latitudes,which results in deficient summer rainfall in northern China for SEAWMres-EN and in southwestern China for WEAWMres-LN.Further study suggests that anomalous EAWMres may have an effect on the extra-tropical sea surface temperature anomaly,which persists into the ensuing summer and may interfere with the influences of ENSO.

Interannual to Interdecadal Variation of East Asian Summer Monsoon and its Association with the Global Atmospheric Circulation and Sea Surface Temperature

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.

Relationship Between East Asian Winter Monsoon and Summer Monsoon

Using National Centers for Environmental Prediction/National Centre for Atmospheric Research（NCEP/NCAR） reanalysis data and monthly Hadley Center sea surface temperature（SST） data,and selecting a representative East Asian winter monsoon（EAWM） index,this study investigated the relationship between EAWM and East Asian summer monsoon（EASM） using statistical analyses and numerical simulations.Some possible mechanisms regarding this relationship were also explored.Results indicate a close relationship between EAWM and EASM：a strong EAWM led to a strong EASM in the following summer,and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in the tropical Indian Ocean and the South China Sea,and on the equatorial atmospheric thermal anomalies at both lower and upper levels.Through these impacts,the EAWM influences the land-sea thermal contrast in summer and the low-level atmospheric divergence and convergence over the Indo-Pacific region.It further affects the meridional monsoon circulation and other features of the EASM.Numerical simulations support the results of diagnostic analysis.The study provides useful information for predicting the EASM by analyzing the variations of preceding EAWM and tropical SST.

Simulating the Intraseasonal Variation of the East Asian Summer Monsoon by IAP AGCM4.0

ABSTRACT This study focuses on the intraseasonal variation of the East Asian summer monsoon （EASM） simulated by IAP AGCM 4.0, the fourth-generation atmospheric general circulation model recently developed at the Institute of Atmospheric Physics, Chinese Academy of Sciences. In general, the model simulates the intraseasonal evolution of the EASM and the related rain belt. Besides, the model also simulates the two northward jumps of the westem Pacific subtropical high （WPSH）, which are closely related to the convective activities in the warm pool region and Rossby wave activities in high latitudes. Nevertheless, some evident biases in the model were found to exist. Due to a stronger WPSH, the model fails to simulate the rain belt in southern China during May and June. Besides, the model simulates a later retreat of the EASM, which is attributed to the overestimated land-sea thermal contrast in August. In particular, the timing of the two northward jumps of the WPSH in the model is not coincident with the observation, with a later jump by two pentads for the first jump and an earlier jump by one pentad for the second, i.e., the interval between the two jumps is shorter than the observation. This bias is mainly ascribed to a shorter oscillating periodicity of convection in the tropical northwestern Pacific.