Short-term climatic impacts of afforestation in the East Asian monsoon region

The influence of changes in vegetation cover on short-term climate over the East Asian monsoon region is simulated using the Community Climate System Model Version 3.5.The results show the annual mean surface air temperature significantly decreases by 0.93°C in response to afforestation over the East Asian monsoon region.Also,surface air temperature decreases by 1.46 and 0.40°C in summer and winter,respectively.The cooling is caused by enhanced evapotranspiration(ET) produced by increased forest cover.Evapotranspiration is greater in summer than in winter,so summer cooling is greater than winter cooling.The annual mean precipitation increases in response to afforestation,with a maximum of 7% in April.Water vapor increases significantly because of greater latent heat flux release.Meanwhile,afforestation leads to higher surface roughness,which decreases surface wind speed and induces an ascending air motion.These factors can produce more clouds and precipitation.Moreover,the surface albedo and the reflective solar radiation are reduced in response to afforestation.     

Sensitivity experiments of impacts of large-scale urbanization in East China on East Asian winter monsoon

By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was investigated via idealized numerical experiments.Results suggest that large-scale urbanization can cause a significant warming effect in both surface temperature and air temperature near the surface over most areas of East China.Meanwhile,large-scale urbanization also alters the surface energy balance,causing evident increases in net surface long-wave radiation and sensible heat flux as well as intensified surface thermal heating to the atmosphere.Forced by the surface thermal heating anomalies induced by the large-scale urban expansion,East Asian winter monsoon circulation exhibits distinct changes.Overall,the extensive urbanization over East China will weaken East Asian winter monsoon,but intensify winter monsoon in northeast China.     

Anomalous activity of East Asian winter monsoon and the tropical Pacific SSTA

The relationship between the anomalous East Asian winter monsoon (EAWM) activity and the tropical Pacific SST anomalies has been identified using the results of 40-year integration of the IAP CGCM1 model and 10-year observational data. In the strong EAWM year, the western and central Pacific are dominated by positive SST anomalies while the eastern Pacific is negative ones. In the weak EAWM year, the SSTA pattern is quite different and shows El Nino-like SST anomalies. The strong EAWM activity tends to create extra easterly flow to the east and extra westerly flow to the west of the warm SSTA region over the equatorial western and central Pacific, thus leading to the enhancement of convergence and convection of the flow in this region and favorable to the maintenance and development of such an SSTA pattern. On the other hand, the warm SST anomaly over the western and central Pacific, as a forcing, may lead to a specific pattern of the northern extratropical atmosphere, which is favorable to the strong EAWM activity. The tropical Pacific SSTA pattern related closely to the strong EAWM activity differs significantly from that of the La Nina year.     

锶同位素研究在古季风演化研究中的应用研究

自从Rb—Sr同位素体系被应用于地质年龄以来，随着Rb—Sr同位素地球化学理论和测试分析技术的逐步发展和完善，其应用越来越广泛。主要介绍了锶同位素的基本地球化学特征，分析了锶同位素研究进行全球对比的可能性，探讨了锶同位素研究在我国黄土季风演化研究中的应用。众多研究显示Rb／Sr和^87Sr／^86Sr的比值变化受控于风化成壤作用的强弱，与降雨量、磁化率变化有很好的线性相关关系。通过曲线的分析、对比发现Rb／Sr和^87Sr／^86Sr曲线所蕴含的气候信息比磁化率曲线更为丰富和详细，与SPECMAP δ^18O曲线具有同步变化特征和更好的对应关系。这些研究表明Rb／Sr和^87Sr／^86Sr比值极可能是一种东亚夏季风演化更为灵敏的替代性指标，在古气候重建中有着广阔的应用前景。     

锶同位素研究在古季风演化研究中的应用研究

自从Rb-Sr同位素体系被应用于地质年龄以来,随着Rb-Sr同位素地球化学理论和测试分析技术的逐步发展和完善,其应用越来越广泛。主要介绍了锶同位素的基本地球化学特征,分析了锶同位素研究进行全球对比的可能性,探讨了锶同位素研究在我国黄土季风演化研究中的应用。众多研究显示Rb/Sr和87Sr/86Sr的比值变化受控于风化成壤作用的强弱,与降雨量、磁化率变化有很好的线性相关关系。通过曲线的分析、对比发现Rb/Sr和87Sr/86Sr曲线所蕴含的气候信息比磁化率曲线更为丰富和详细,与SPECMAP     

The East Asian winter monsoon: re-amplification in the mid-2000s

Based on several reanalysis and observational datasets,this study demonstrates that the East Asian winter monsoon(EAWM)recovered from its weak epoch and reamplified in the mid-2000s.Accordingly,East Asia has experienced more cold winters and significant negative surface air temperature anomalies during the recent strong EAWM epoch spanning the period 2004–2012.The associated cooling was mainly located over inland northern East Asia with a west–east orientation.The cooling generally coincided with negative winter temperature trends in eastern Eurasia in the last two decades,possibly contributing to the observed regional cooling trend when the global mean temperature is still trending up.Enhanced wintertime blocking activity around the Ural mountain region and diminished Arctic sea ice concentration in the previous September are suggested to be the responsible internal atmospheric process and external driver for the recent re-amplification of the EAWM,respectively.     

青藏高原积雪异常对亚洲夏季风气候的影响

为了研究青藏高原积雪异常对亚洲夏季风气候的影响,从季风环流和季风降水等方面综合分析了高原积雪异常对气候的影响,并利用IAP 9L AGCM模式,对高原雪量进行了增加和减少的数值试验。从而提出高原多(少)雪年南亚夏季风偏弱(强),东亚夏季风反而偏强(弱)的新观点。高原积雪异常会导致高原上空大气垂直运动的扰动,扰动传播到下游致使我国长江流域和西太副高所在区域大气对流运动发生变化。高原多(少)雪,夏季我国南方的偏南风增强(减弱),有利于水汽从孟加拉湾和南海向我国大陆输送,但到长江流域时,由于偏南风存在较强(弱)的辐合,江淮流域偏涝(旱)。     

Asian-Pacific Oscillation index and variation of East Asian summer monsoon over the past millennium

To study the long-term variation of the East Asian summer monsoon （EASM）, the Asian-Pacific Oscillation index （IAPO）, representing a zonal thermal contrast between Asia and the North Pacific, is reconstructed over the past millennium. During the Little Ice Age （LIA）, the variability of the reconstructed IAPO is closely linked to dry-wet anomalies in eastern China on the centennial scale. This correlation pattern is consistent with the observation during the current period, which suggests that the reconstructed IAPO may generally represent the centennial-scale variation of the EASM and rainfall anomalies over eastern China during the LIA.     

Millennial- and orbital-scale changes in the East Asian monsoon over the past 224,000 years

High-resolution speleothem records from China have provided insights into the factors that control the strength of the East Asian monsoon. Our understanding of these factors remains incomplete, however, owing to gaps in the record of monsoon history over the past two interglacial-glacial cycles. In particular, missing sections have hampered our ability to test ideas about orbital-scale controls on the monsoon, the causes of millennial-scale events and relationships between changes in the monsoon and climate in other regions. Here we present an absolute-dated oxygen isotope record from Sanbao cave, central China, that completes a Chinese-cave-based record of the strength of the East Asian monsoon that covers the past 224,000 years. The record is dominated by 23,000-year-long cycles that are synchronous within dating errors with summer insolation at 65 degrees N (ref. 10), supporting the idea that tropical/subtropical monsoons respond dominantly and directly to changes in Northern Hemisphere summer insolation on orbital timescales. The cycles are punctuated by millennial-scale strong-summer-monsoon events (Chinese interstadials), and the new record allows us to identify the complete series of these events over the past two interglacial-glacial cycles. Their duration decreases and their frequency increases during glacial build-up in both the last and penultimate glacial periods, indicating that ice sheet size affects their character and pacing. The ages of the events are exceptionally well constrained and may thus serve as benchmarks for correlating and calibrating climate records.     

Natural interdecadal weakening of East Asian summer monsoon in the late 20th century

Based on the reanalysis data throughout 1948-2002 as derived from the United States National Centers for Environmental Prediction and National Center for Atmospheric Research, it is revealed that East Asian summer monsoon （EASM） intensity weakens on an interdecadal timescale since the mid-1960s, and twice interdecadal jumps are recorded in the EASM intensity index series in the late 20th century, respectively occurring in the mid-1960s and mid- to late 1970s. Six globally coupled atmosphere-ocean models＇ outputs under the SRES A2 greenhouse gas and aerosol emission scenario, provided by the IPCC Data Distribution Center and the Hadley Center for Climate Prediction and Research, are then systematically examined. It follows that the above EASM weakening is not closely related to synchro- nizing anthropogenic global warming, and, therefore, it should be qualitatively natural change process. Over the 21st century, the EASM intensity is likely increased slightly by continually intensified greenhouse effect relative to the late 20th century.     

Seasonal cycle of the zonal land-sea thermal contrast and East Asian subtropical monsoon circulation

Based on analysis of the climatic temperature latitudinal deviation on middle troposphere, its seasonal cycle suggests that due to the rapid warming from eastern China continent to the east of Tibetan Plateau and the heating of Tibetan Plateau in spring, seasonal transition of the thermal difference between East Asia continent and West Pacific first takes place in the subtropical region with greatest intensity. On the accompanying low troposphere, the prevailing wind turns from northerly in winter to southerly in summer with the convection precipitation occurring at the same time. This maybe indicates the onset of the East Asian subtropical summer monsoon. Consequently, we advice that the seasonal cycle formed by the zonal thermal contrast between Asian continent and West Pacific may be an independent driving force of East Asian subtropical monsoon.     

The East Asian summer monsoon circulation anomaly index and its interannual variations

Based on the concept of East Asia-Pacific (EAP) teleconnection which influences East Asian summer monsoon, an index for East Asian summer monsoon circulation anomaly was defined and it was pointed out that this index can describle the interannual variation character of summer climate in East Asia, especially in the Yangtze River and Huaihe River Valley.     

Response of the East Asian summer monsoon to large volcanic eruptions during the last millennium

The responses of the East Asian summer monsoon （EASM） to large volcanic eruptions were analyzed using a millennial simulation with the FGOALS-gl climate system model. The model was driven by both natural （solar irradiance, volcanic eruptions） and anthro- pogenic （greenhouse gases, sulfate aerosols） forcing agents. The results showed cooling anomalies after large volcanic eruptions almost on a global scale. The cooling over the continental region is stronger than that over the ocean. The precipitation generally decreases in the tropical and subtropical regions in the first summer after large volcanic eruptions. Cooling with amplitudes up to -0.3 ℃ is seen over eastern China in the first summer after large volcanic eruptions. The East Asian continent is dominated by northeasterly wind anomalies and the corresponding summer rainfall exhibits a coherent reduction over the whole of eastern China. An analysis of the surface heat flux suggested the reduction in summer precipitation over eastern China can be attributed to a decrease of moisture vapor over the tropical oceans, and the weakening of the EASM may be attributed to the reduced land-sea thermal contrast after large volcanic eruptions.     

Records of the East Asian winter monsoon from the mud area on the inner shelf of the East China Sea since the mid-Holocene

AMS¹⁴C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 μm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ¹⁸O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300–6300 a BP, strong and unstable; 6300–3800 a BP, strong but stable; 3800–1400 a BP, weak and unstable; after 1400 a BP, weak but stable.     

ENSO对东亚夏季风和我国夏季降水的影响研究进展

回顾了最近几年我国学者在ENSO对东亚夏季风和我国夏季降水影响方面的研究成果,通过夏季风时降水的影响分析ENSO对夏季降水的作用,结合1997-1998年的ENSO现象,对前人的理论和统计结果进行了讨论,指出除了ENSO发生的时间、区域、强度外,其增长和衰减率在这一问题的研究中也值得关注。     

Weakening relationship between East Asian winter monsoon and ENSO after mid-1970s

The East Asian winter monsoon(EAWM) is characterized by the frequent cold surges and associated closely with the Siberia High,East Asian Trough,and high-level westerly jet stream.The ENSO cycle can modulate the EAWM since it has co-variability with the sea surface temperature over the Indo-Western-Pacific which can tune the land-sea thermal contrast for the EAWM.This paper,by analyzing the EAWM,ENSO,and associated atmosphere-ocean variability,documents the weakening of the EAWMENSO relationship after the 1970s.The significant out-of-phase inter-relationship is found to be diminished after the 1970s.Further study in this work suggests that the weakened co-variability of the tropical Indo-Western-Pacific climate associated with ENSO after the 1970s is partly responsible for the weakened inter-relationship.Meanwhile,the reduced EAWM interannual variability and northward retreat of the EAWM-associated climate variability are favorable to the weakened ENSO-EAWM connection.     

Relationship between East Asian winter monsoon, warm pool situation and ENSO cycle

Based on the observational data analyses and numerical simulations with the air-sea coupled model (CGCM), a new perspective on the occurrence mechanism of ENSO is advanced in this paper. The continuous strong (weak) East Asian winter monsoon will lead to continuous westerly (easterly) wind anomalies over the equatorial western Pacific region. The anomalous equatorial westerly (easterly) winds can cause eastward propagation of the subsurface ocean temperature anomalies (SOTA) in the warm pool region, the positive (negative) SOTA have been in the warm pool region for quite a long time. The eastward propagating of positive (negative) SOTA along the thermocline will lead to positive (negative) SSTA in the equatorial eastern Pacific and the occurrence of El Niño (La Niña) event. After the occurrence of ENSO, the winter monsoon in East Asia will be weak (strong) due to the influence of El Niño (La Niña).     

Global and China temperature changes associated with the inter-decadal variations of East Asian summer monsoon advances

The modern atmospheric observation and literatural historical drought-flood records were used to extract the inter-decadal signals of dry-wet modes in eastern China and reveal the possible relationship of global and China temperature changes associated with the East Asian summer monsoon advances.A climate pattern of "wet-north and dry-south" in eastern China and cool period in China and globe are associated with the strong summer monsoon that can advance further to the northernmost part in the East Asian monsoon region.On the contrary,a climate pattern of "dry-north and wet-south" in eastern China and a warm period in China and globe are associated with the weaker summer monsoon that only reaches the southern part in the region.An interdecadal oscillation with the timescale about 60 years was found dominating in both the dry-wet mode index series of the East Asian summer monsoon and the global temperature series after the secular climate states and long-term trend over inter-centennial timescales have been removed.     

Reduction of the East Asian winter monsoon interannual variability after the mid-1980s and possible cause

The East Asian winter monsoon (EAWM) consists of subsystems such as the Siberian high, Aleutian low, East Asian trough, low-level northerly wind and high-level East Asian jet stream. It is revealed that the interannual variation of the EAWM-related atmospheric circulation has exhibited an obvious weakening since the mid-1980s. During 1956-1980, significant negative correlations between the EAWM and sea surface temperature are observed in the oceans along the east coast of East Asia, accompanied by significant positive correlations in the western Warm Pool. However, the significant interannual relationship in the previous period is found to have been disrupted during 1986-2010. Further analysis reveals that the Arctic Oscillation after the mid-1980s tends to suppress the interannual variability of the EAWM. In addition, it was found that the large-scale warming after the mid-1980s is favorable to reduce the land-sea thermal contrast variability on both the interdecadal and interannual time scales.     

Southern Hemisphere mean zonal wind in upper troposphere and East Asian summer monsoon circulation

1 Introduction Variability of the East Asian summer monsoon (EASM) has been detected by considering roles of El Nino and Southern Oscillation (ENSO) cycle, snow cover over Eurasia and Tibetan Plateau, and signals from the soil (namely, the soil temperatur…