Testing the ability of RIEMS2.0 to simulate multi-year precipitation and air temperature in China

RIEMS2.0 （Regional Integrated Environment Modeling System, Version 2.0） is now being developed starting from RIEMS1.0 by the Key Laboratory of Regional Climate Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, China. In order to test RIEMS2.0’s ability to simulate long-term climate and its changes, as well as provide a basis for further development and applications, we compare simulated precipitation and air temperature from 1980 to 2007 （simulation duration from Jan. 1, 1979 to Dec. 31, 2007） under different cumulus parameterization schemes with the observed data. The results show that RIEMS2.0 can reproduce the spatial distribution of precipitation and air temperature, but that the model overestimates precipitation with the rainfall center moving northwestward and underestimates air temperature for annual simulations. Annual and interannual variations in precipitation and air temperature for different climate subregions are well captured by the model. Further analysis of summer and winter simulations shows that precipitation is overestimated, except for the Jianghuai-Jiangnan subregions in the winter, and the air temperature bias in the summer is weaker than in the winter. There are larger biases for precipitation and air temperature in semiarid subregions. Anomalies in precipitation and air temperature are also well captured by the model. Although a similar distribution can be found between observed data and simulated results under different cumulus parameterization schemes, these show differences in intensity and location. In sum, RIEMS2.0 shows good stability and does well in simulating the long-term climate and its changes in China.     

东亚夏季风异常的研究

本文运用经验正交函数分析方法,对10～65°N,90°E～175°W范围内近30年逐年7月和8月平均海平面气压场进行了分析研究.结果表明,第一、第三特征向量与东亚季风异常有关,第二特征向量与西风环流异常有关.讨论了东亚季风异常与大气环流的关系,以及季风异常对华北东部地区降水时空分布的影响.     

Spatial and temporal variations of light rain events over China and the mid-high latitudes of the Northern Hemisphere

Based on observed daily precipitation data, monthly gridded radiosonde upper air temperature and sea surface temperature data from the UK Met Office Hadley Centre, monthly surface air temperature from the Climatic Research Unit at the University of East Anglia and the NCEP/NCAR monthly reanalysis data, this study investigates the spatial and temporal variations of light rain events over China and the mid-high latitudes of the Northern Hemisphere during 1961-2010, and discusses the relationship between the change of light rain events and atmospheric stability, sea surface temperature and atmospheric circulation. The light rain events over East China display a decreasing trend of 3.0%/10 a in summer and winter half years. Over Northwest China, an increasing trend of 4.1%/10 a is found in winter half years, but there is no trend in summer half years. Using empirical orthogonal function (EOF) analysis, it is found that the first two principal components of light rain events over the mid-high latitudes of the Northern Hemisphere show long time scale variations in summer and winter half years. The first EOF modes (EOF1s) for summer and winter half years both depict a long-term increase in light rain events over North America and Southern Europe as well as Northwest China (except in summer half years), and a long-term decrease over most of the Eurasia (Central Europe, Eastern Europe, North Asia and East China). The second EOF mode (EOF2) for summer half year shows that light rain events increase over North America, Southern Europe and South China, but decrease over Eurasia north of 45°N from 1961 to early 1980s, while the trends reverse from late 1980s to 2010. The second EOF mode (EOF2) for winter half years indicates that light rain events increase over North America and South and North China, but decrease over Eurasia north of 40°N from 1961 to early 1980s, while the trends reverse from late 1980s to 2009. Correlation analysis and linear regression analysis suggest that EOF1s may be related to the change in atmospheric static stability associated with global warming, and EOF2s are possibly linked to the AMO.     

An virtual numerical experiment to understand the impacts of recovering natural vegetation on the summer climate and environmental conditions in East Asia

By applying a regional integrated environmental model system (RIEMS), a virtual numerical experiment is implemented to study the impacts of recovering natural vegetation on the regional climate and environmental conditions. The results show that recovering the natural vegetation in large scale could have significant influence on summer climate in East Asia. Not only would it be able to change the surface climate, but also to modify to certain extent the intensity of monsoon circulation. Although this is a virtual experiment at an extremely ideal condition, the implication of the simulating results is that the on-going nation-wide activities to recover the crop land for forest and pasture must be managed according to the local natural climate, hydrological and soil conditions. Only under such a condition, would the recovering of natural vegetation bring about significant climate and environmental benefits at regional scale.     

Characteristics of decadal-centennial-scale changes in East Asian summer monsoon circulation and precipitation during the Medieval Warm Period and Little Ice Age and in the present day

Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450?C1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pattern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400?C1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.     

Identifying the northernmost summer monsoon location in East Asia

An integrated index which can be used to indicate the advance of subtropical summer monsoon in East Asia has been proposed in this paper.The index was comhined by three variables including precipitation,wind and pseudo-equivalent potential tempera- ture.The northernmost summer monsoon location(NSML)was identified by using this index annually.It was found that the NSML ex- perienced an interdecadal shift in the period 1977—1979 based on the annual index analysis from 1961 to 2001.A comparison of the NSML with other four summer monsoon indices has also been made.The result showed that the NSML could well represent the interan- nual and interdecadal variability of summer monsoon precipitation in North China(beyond 35°N),while other four indices could well indi- cate the precipitation anomalies of East Asian summer monsoon along the Yangtze River valley(around 30°N).     

Modeling impacts of East Asian Ocean-Land thermal contrast on spring southwesterly winds and rainfall in eastern China

Using the National Centers for Environmental Prediction–National Center for Atmospheric Research （NCEP–NCAR） reanalysis dataset, the NOAA’s Climate Prediction Center’s merged analysis of precipitation, and the MM5v3 Meso-scale Model, the impacts of surface temperature differences between the East Asian land and its adjacent oceans on spring southwesterly winds and rainfall over eastern China are studied. The modeling results show that the temperature differences exert strong influence on the occurrence of the southwesterly winds and rainfall over southern China and their northward advances. When surface temperature increases over the land and decreases over the oceans, the temperature gradient with a winter feature earlier changes toward the gradient with a summer feature. Both the low-pressure system east of the Tibetan Plateau and the subtropical high-pressure system over the western Pacific strengthen, accompanying with the strengthening of the lower-tropospheric southwesterly winds over eastern China. Accordingly, the upward motion increases over the Yangtze-Huaihe River （YHR） valleys and decreases over southern China, leading to an increase of spring rainfall over the YHR valleys and a decrease over southern China. Thus, the rain belt over eastern China appears over the YHR valleys but not over southern China. Under a weaker condition of the spring thermal contrast, the rain belt does not occur over eastern China. When the spring thermal contrast pronouncedly strengthens, the rain belt over southern China may advance northward into the YHR valleys during spring, though there is no onset of the tropical monsoon over the South China Sea. This forms a rain belt similar to that of the YHR valleys during the summer Meiyu period.     

东亚地区汛期OLR季节内振荡型的年际变化特征

 分析了1979—2005年5—8月东亚地区向外长波辐射（OLR）主要的空间模态和季节内振荡（ISO）强度的年际变化特征,并研究了各个模态主要ISO型之间的联系。结果表明,5—8月东亚地区OLR存在3种主要的空间模态：西太平洋偶极型（WPD）,西太平洋经向型（MWP）和东亚中纬太平洋波列（MEAP）,其时间变化表现为10～20,20～30和30～70d的周期振荡,其强度均存在极显著的年际变化,由东亚夏季风区加热强迫和大气内部非线性相互作用引起。WPD的主要ISO型之间相互独立,MWP和MEAP的不同ISO型之间存在强的相互作用。深入研究这3个模态的20～30和10～20d振荡变化特征,对于东亚地区夏季10～30d延伸期预报具有重要意义。     

East Asian monsoon change for the 21st century: Results of CMIP3 and CMIP5 models

Forty-two climate models participating in the Coupled Model Intercomparison Project Phases 3 and 5 were first evaluated in terms of their ability to simulate the present climatology of the East Asian winter (December-February) and summer (June-August) monsoons. The East Asian winter and summer monsoon changes over the 21st century were then projected using the results of 31 and 29 reliable climate models under the Special Report on Emissions Scenarios (SRES) mid-range A1B scenario or the Representative Concentration Pathways (RCP) mid-low-range RCP4.5 scenario, respectively. Results showed that the East Asian winter monsoon changes little over time as a whole relative to the reference period 1980-1999. Regionally, it weakens (strengthens) north (south) of about 25°N in East Asia, which results from atmospheric circulation changes over the western North Pacific and Northeast Asia owing to the weakening and northward shift of the Aleutian Low, and from decreased north- west-southeast thermal and sea level pressure differences across Northeast Asia. In summer, monsoon strengthens slightly in East China over the 21st century as a consequence of an increased land-sea thermal contrast between the East Asian continent and the adjacent western North Pacific and South China Sea.     

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…     

Preliminary results of a regional air-sea coupled model over East Asia

We have established a regional air-sea coupled model over East Asia and conducted a 20-year integration to evaluate its performance in reproducing the present climate. The coupled model consists of RegCM3 and HYCOM controlled by the OASIS3 coupler with resuolution of 60 km for the atmosphere and 33 km for the ocean, respectively. Unlike some other regional air-sea coupled models, a one-way nesting method is employed in the oceanic component and a heat flux adjustment for solar radiation is used to remove an about 2°C cold bias in SST. The primary analysis for this 20-year integration shows that the coupled model successfully reproduces the main features of the circulations over East Asia, both in the atmosphere and the ocean, including climatology, seasonal and interannual variations. Improvements are seen in the coupled model compared to the uncoupled one, especially in the simulation of precipitation, the most important element of the East Asian monsoon, although there are still obvious discrepancies that come mainly from the model components themselves. Further analyses show that the rainfall simulation benefits from the enhancements of the Northwest Pacific Subtropical High in summer, which leads to the improvement of the moisture flux simulation at the middle-lower atmospheric circulation. The results indicate that the regional air-sea coupled model is more suitable for the East Asia monsoon simulation.     

青藏高原对亚洲季风平均环流影响的数值试验

利用垂直方向具有９层σ面、水平方向菱形截断波数为１５的全球大气环流谱模式和有、无青藏高原大地形两种情况下１０年积分的模拟结果，研究了青藏高原大地形对亚洲季风平均环流的影响。结果表明：有、无青藏高原大地形，亚洲冬、夏季季风平均环流均存在很大的差异。去除地形，使夏季高层的南亚高压、低层的大陆热低压、副热带高压及冬季的大陆冷高压在位置或强度上发生了改变；地形的有、无决定着冬季东亚大槽的强度；索马里越赤道气流有地形时明显较无地形时强；地形的有无还影响着降水强度和雨带的分布。另外，副热带高压中心及雨带的季节性移动与高原大地形的存在与否亦有很大的关系     

中国西部绿化对东亚季风气候影响的数值模拟

中国西部大开发战略中的生态环境建设将在西部地区引起显著的地表覆盖变化。根据最新的全球地表特征数据库资料和21世纪初中国西部生态环境三大重点建设工程的具体规划，得出两种植被，即现实植被和虚拟植被。并利用RIEMS—TEA模式，通过一次敏感性试验，发现西部地区绿化明显影响东亚的季风系统和中国东部季风区气候。模拟试验显示，中国西部绿化会明显增强东亚夏季风，这将会加强中国东部由南向北的水汽输送，并有利于输送邻近海洋的水汽到大陆，使得中国大陆东部季风区整体出现降温、增湿和降水增加。而且，温度、湿度、气压和风速受影响的程度在垂直方向上都已超出了边界层之外。     

冬春海温异常对东亚初夏季风环流的影响

用ＯＳＵ的两层大气环流模式进行了热带西太平洋冬春海温异常对东亚初夏（５月）季风环流影响的数值试验．结果表明：①海温的负距平引起西太平洋副热带高压脊南落和西伸，东亚热带季风环流减弱，我国西南和华南地区的降水增加；②海温的正距平引起西太平洋副热带高压明显减弱，西太平洋的赤道西风加强，我国西南和华南地区的降水减少     

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.     

Projected change in the relationship between East Asian summer rainfall and upper-tropospheric westerly jet

The authors analyzed the interannual variability in summer precipitation and the East Asian upper-tropospheric jet (EAJ) over East Asia under the Historical and Representative Concentration Pathways Scenarios (RCPs, including RCP4.5 and RCP8.5), using outputs of 17 Coupled Model Intercomparison Project phase 5 (CMIP5) coupled models. The analyzed results indicate that the models can reasonably reproduce relatively stronger interannual variability in both East Asian summer rainfall (EASR) and EAJ. These models can also capture the relationship between the rainfall anomaly along the East Asian rain belt and meridional displacement of the EAJ. Projected results suggest that the interannual variabilities in precipitation along the East Asian rain belt and in the EAJ are enhanced under the scenarios RCP4.5 and RCP8.5 in the 21st century, which is consistent with the previous studies. Furthermore, it is found that the relationship between the East Asian rainfall and the meridional displacement of the EAJ is projected to be stronger in the 21st century under the global warming scenarios, although there are appreciable discrepancies among the models.     

Palaeoclimate simulation of Little Ice Age

Promotedbytheinternationalresearch projectsofPAGESandCLIVAR ,thestudiesonclimaticandenvironmentalchangesinthepast 2 0 0 0yearshavedrawntheattentionofgeologistsandpalaeoclimato logistsallovertheworld[1,2 ] .AmongthemthecoldeventoftheLittleIceAge (LIA)isparticularlythemostattractiveone[3～ 10 ] ,whichisthenearesttypicalcoldperiodintheglobalrangefrommodernage ,andhadaprofoundimpactuponhumansociety[11] .Addi tionally ,moreknowledgeaboutthecauseoforiginanddynamicmechanismofLIAmayenrichandpe…     

Stalagmite-inferred Holocene precipitation in northern Guizhou Province,China, and asynchronous termination of the Climatic Optimum in the Asian monsoon territory

An absolute-dated, bi-decadal-resolution, stalagmite oxygen-isotopic time series from Shigao Cave reveals the evolution of summer monsoon precipitation over the past 9.9 ka BP in northern Guizhou Province, Southwest China. The  18O-inferred climate conditions are divisible into three distinct stages: (1) a maximum humid era from 9.9-6.6 ka BP; (2) a gradual declining precipitation interval between 6.6-1.6 ka BP; and (3) a relatively low precipitation time window after 1.6 ka BP. Consistency of contemporaneous stalagmite Holocene 18O records between Shigao and other caves in the Indian and East Asian monsoon realms support the effect of primary orbital solar forcings on monsoonal precipitation. However, statistical analysis shows a significant spatial asynchroneity of the Holocene Optimum termination in the Asian monsoon territory. The Holocene Optimum ended at 7.2-7.4 ka BP in Oman, located in the Indian monsoon region, and at 5.6-5.8 ka BP in Central China, in the East Asian monsoon zone. In Southwest China, the termination occurred between these periods, at 6.6-7.0 ka BP, and was influenced by both monsoon systems. We propose that this spatially asynchronous ending of Holocene Optimum in Asia may be attributed to sea surface temperature changes in the western tropical Pacific, which is a primary moisture source for the East Asian monsoon.     

Seven million-year iron geochemistry record from a thick eolian red clay-loess sequence in Chinese Loess Plateau and the implications for paleomonsoon evolution

Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe₂O₃ ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe₂O₃ ratio record from the red clay-loess sequence indicates that (ⅰ) variations of the free to total Fe₂O₃ ratios of the loess can correlate generally with the alternations of the loess and paleosol horizons; (ⅱ) the East Asia summer monsoon was stronger as a whole in Neogene than that in Quaternary; (ⅲ) the strongest East Asia summer monsoon may occur between 4.0 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.     

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.