东亚海陆热力差指数及其与环流和降水的年际变化关系

利用 196 1～ 1999年海温和地温月平均资料 ,定义了一个海陆热力差指数 ,来表示东亚季风环流的纬向和经向海陆热力差异的变化强度 ,研究了夏季指数与东亚夏季风环流场和中国东部夏季降水的年际变化关系。结果表明 :(1)海陆热力差指数可用来表示东亚夏季风的强弱变化。强指数年东亚季风区低空西南夏季风气流和高层的东风气流明显偏强 ,表明这一年夏季风偏强 ,弱指数年反之。 (2 )海陆热力差指数能较好地反映东部季风区夏季降水的异常状况。强指数年 ,雨带偏北 ,江淮流域和长江中下游明显干旱 ,华南、华北降水偏多 ,弱指数年反之。这一降水异常特征可以从强弱海陆热力差指数年的环流场得到解释。 (3)海陆热力差指数所反映的东亚夏季风具有明显的准 2a和 3～ 6a周期的年际振荡 ,但其振幅和周期具有显著的年代际异常     

未来20年中国气温变化预估

利用大约40余个气候模式和模式集合,考虑多种人类排放情景,预估到2025年前相对于1961－1990年中国的气温变化。只考虑未来人类排放增加多模式集成预估结果表明,中国年平均气温自2006到2025年的20 a期间将继续变暖0.55 ℃,至2010年年平均气温平均变暖大约为1.08 ℃（平均变暖范围为 0.73-1.54 ℃）,至2020年年平均变暖约为1.43 ℃（平均变暖范围为1.10-2.09 ℃）,至2025年平均变暖约为1.39 ℃（平均变暖范围为0.94-2.19 ℃）。 对1990－2005年已经出现观测事实的近16 a气候模式预估结果进行检验表明,多模式考虑多种排放情景集成,一致预估出这16 a的明显变暖趋势,但是变暖幅度略低于实际观测值。经检测证实,对2006－2025年中国气温的预估具有一定的可信度。需要指出的是,目前的预估没有考虑未来的自然变化,只考虑人类排放继续增加的影响。     

两种反映东亚夏季风异常的指数的比较研究

本文利用文献^ [4]提出的一种新的反映东亚夏季风异常的海陆温差指数分析了夏季风异常时我国气温、降水异常以及东亚环流状况，通过分析指出，东亚夏季风偏强，则中国东部夏季气温偏高，江淮干旱，华北多雨；夏季风偏弱则夏季气温偏低，江淮多雨，易涝，华北少雨。通过两种夏季风指数的对比，海陆温差指数能更好地反映东亚夏季环流及天气气候异常。文中还指出，海陆温差指数能更好的反映夏季风异常的原因是它的定义方法更科学，更全面的反映东亚海陆热力差异，既包含了东亚纬向海陆热力差异的影响，又考虑了东亚经向海陆热力差异的因素，并用地表气温和海表温度差来表示海陆热力差，好于以往用海平面气压差来反映海陆热力差。     

东亚海陆热力差指数与中国夏季降水的关系

定义了东亚海陆热力差指数（ＩＬＳＴＤ）,讨论了它与东亚夏季风的强弱年际变化及夏季降水的关系。结果表明：该海陆热力差指数较好地反映了我国东部季风区夏季降水的异常变化、强海陆热力差指数年,华北地区降水偏多,长江、淮河流域明显干旱;弱海陆热力差指数年,长江,淮河流域降水又异常偏多。ＴＬＳＴＤ的异常变化对影响我国东部季风区降水的大气环流型具有较强的识别力,尤其是对夏季西太平洋副热带高压的位置与强度的识别。     

冬季亚洲大陆的热力差异和中国气候的关系

最近的一些研究发现,除了海陆之间的热力差异外,大陆内部也存在热力差异。通过合成及t检验方法分析了亚洲大陆内部区域热力差异的变化特征,探讨了年代际尺度上大陆热力状况的季节变化与东亚初夏和夏季环流、季风活动、中国降水变化的关系。结果表明:正指数年代,在经向上从冬至夏东亚大陆由冷变暖,25°N以北中高纬度对流层高层有气温正距平下传,纬向上高原东侧我国大陆地区春夏季迅速增温。相比之下,海洋上的热力变化不明显,一直维持负距平,海陆热力差异偏大,东亚初夏季风建立偏早,夏季风强度偏强,相应地长江流域初夏降水偏多,夏季降水偏少,华北和西南部分地区夏季降水偏多。相反地,负指数年代海陆热力差异的变化将会减弱海陆之间的热力对比,不利于初夏季风的建立和夏季风加强,上述地区降水的变化大致与正指数年代相反。     

CMIP3气候模式对东亚冬季大气环流模拟能力的评估

利用1960—1999年ECMWF月平均再分析资料(ERA40)和耦合模式比较计划(Phase 3 of the CoupledModel Intercomparison Project,简称CMIP3)21个气候耦合模式对20世纪气候模拟试验的模式结果,从气候态和年际变化两个方面,评估了CMIP3气候模式对东亚冬季大气环流的模拟能力。结果表明:(1)模式对东亚地区冬季海平面气压、850 hPa纬向风、经向风和500 hPa高度场气候态的模拟存在不同程度的偏差,但均能较好模拟出上述要素气候态的空间分布特征。总体而言,模式对500 hPa高度场气候态的模拟效果最好,而对850 hPa经向风的模拟效果较差。(2)模式基本上能抓住近40年来东亚地区冬季500 hPa高度场的主要变化特征,但基本上不能模拟出冬季海平面气压、850 hPa纬向风和经向风的变化特征。此外,模式对阿留申低压、蒙古高压和东亚冬季风强度的变化特征几乎没有模拟能力。     

全球变暖形势下中国陆表水分的变化

利用政府间气候变化委员会第四次评估报告（IPCCAR4）中的10个耦合模式CO：加倍试验和控制试验的模拟结果,分析了全球变暖背景下中国水分的变化。结果表明,随着全球变暖,东亚夏季风增强,冬季风减弱,使得冬夏季向中国区域输送的水汽都增强;中国区域降水,夏季除长江流域外基本都增加,冬季除华南外都增加。夏季降水蒸发差（P—E）除了在东北和南方增加外,从长江流域一直到西北有一带状减小带;冬季几乎所有模式的P—E表现为北方增加、南方减小。在全球变暖背景下,降水、蒸发和径流的综合结果以及积雪的作用使得土壤湿度在干旱区增加,且冬季干旱区土壤变湿的强度和范围大于夏季,然而在其他区域土壤湿度减少。上述结论是基于多模式集合平均结果,对未来气候的预估具有一定的参考价值,然而模式间存在较强差异性,仍具有较大不确定性。     

基于IPCC A1B情景的中国未来气候变化预估:多模式集合结果及其不确定性

利用耦合模式比较计划(CMIP3)提供的20世纪气候模拟试验(20C3M)及A1B情景预估试验,讨论了全球增暖情景下21世纪中期中国气候的可能变化。结果表明,A1B情景下,中国夏季降水变化在-0.1～1.1mm/d,冬季降水变化在-0.2～0.2mm/d。模式对降水变化的预估存在较大不确定性。无论冬夏,预估的全国表面气温都将升高,升温幅度在1.2～2.8℃;随纬度升高,增暖幅度相应增大。模式对表面气温变化的预估能力强于对降水变化的预估能力。在A1B情景下,东亚夏季风增强,而冬季风则略为减弱,东亚夏季风雨带到达最北后南撤的时间较之20C3M滞后约一个月。     

近10年全球变暖停滞了吗?

综合分析了与近10年(1999—2008年)全球变暖停滞有关的几个问题。首先,虽然1999—2008年全球平均温度增量接近零,但是这10年仍是30年来平均温度最高的10年。其次,自然变化如火山活动、太阳辐射、ENSO及大洋热盐环流变化可能影响全球平均温度的年际及年代际变化,但是不大可能改变全球变暖的长期趋势。最后,用全球及中国的观测资料证实1999—2008年中国平均温度增量为0.4～0.5℃/10a,即中国的气候变暖仍在继续。     

基于BP-CCA统计降尺度的中亚春季降水的多模式集合模拟与预估

利用中亚地区30个观测台站逐月降水资料及同期ERA-40再分析资料,结合8个CMIP5全球气候模式模拟与未来预估大尺度环流场,使用基于变形典型相关分析的统计降尺度方法（BP-CCA）建立降尺度模型,评估多个气候模式对当前气候下中亚地区春季降水的降尺度模拟能力,并对春季降水进行降尺度集合未来预估。结果表明,建立的降尺度模型能够很好地模拟出交叉检验期内春季降水的时间变化和空间结构：降尺度春季降水与相应观测序列的平均时间相关系数为0.35,最高为0.62,平均空间相关系数为0.87。气候模式对中亚春季降水的模拟能力通过降尺度方法得到了显著提高：8个模式降尺度后模拟的降水气候平均态相对误差绝对值降至0.2%—8%,相比降尺度前减小了10%—60%,模拟的降水量场与相应观测场的空间相关均超过0.77;对比降尺度前多模式集合结果,多模式降尺度集合模拟的相对误差绝对值由64%减小至4%,空间相关系数由0.47增大至0.81,标准化均方根误差降至0.59,且多模式降尺度集合结果优于大部分单个模式降尺度结果。多模式降尺度集合预估结果表明,在RCP4.5排放情景下,21世纪前期（2016—2035年）、中期（2046—2065年）和末期（2081—2100年）的全区平均降水变化率分别为-5.3%、3.0%和17.4%。21世纪前期中亚大部分地区降水呈减少趋势,降水呈增多趋势的站点主要分布在南部。21世纪中期整体降水变化率由减少变为增多趋势,21世纪末期中亚大部分台站降水增多较为明显。21世纪初期和末期可信度高的台站均主要位于中亚西部地区。     

Monsoon Change in East Asia in the 21st Century: Results of RegCM3

The authors investigate monsoon change in East Asia in the 21st century under the Special Report on Emissions Scenarios (SRES) A1B scenario using the results of a regional climate model, RegCM3, with a high horizontal resolution. First, the authors evaluate the model’s performance compared with NCEP-NCAR reanalysis data, showing that the model can reliably reproduce the basic climatology of both winter and summer monsoons over East Asia. Next, it is found that the winter monsoon in East Asia would slightly weaken in the 21st century with spatial differences. Over northern East China, anomalous southerly winds would dominate in the mid-and late-21st century because the zonal land-sea thermal contrast is expected to become smaller, due to a stronger warming trend over land than over ocean. However, the intensity of the summer monsoon in East Asia shows a statistically significant upward trend over this century because the zonal land-sea thermal contrast between East Asia and the western North Pacific would become larger, which, in turn, would lead to larger sea level pressure gradients throughout East Asia and extending to the adjacent ocean.     

Evaluation of spring persistent rainfall over East Asia in CMIP3/CMIP5 AGCM simulations

The progress made fi＇om Phase 3 to Phase 5 of the Coupled Model Intercomparison Project （CMIP3 to CMIP5） in simulating spring persistent rainfall （SPR） over East Asia was examined from the outputs of nine atmospheric general circulation models （AGCMs）. The majority of the models overestimated the precipitation over the SPR domain, with the mean latitude of the SPR belt shifting to the north. The overestimation was about 1mm d-1 in the CMIP3 ensemble, and the northward displacement was about 3°, while in the CMIP5 ensemble the overestimation was suppressed to 0.7 mm d-i and the northward shift decreased to 2.5°. The SPR features a northeast-southwest extended rain belt with a slope of 0.4°N/°E. The CMIP5 ensemble yielded a smaller slope （0.2°N/°E）, whereas the CMIP3 ensemble featured an unre- alistic zonally-distributed slope. The CMIP5 models also showed better skill in simulating the interannual variability of SPR. Previous studies have suggested that the zonal land-sea thermal contrast and sensible heat flux over the southeastern Tibetan Plateau are important for the existence of SPR. These two ther- mal factors were captured well in the CMIP5 ensemble, but underestimated in the CMIP3 ensemble. The variability of zonal land-sea thermal contrast is positively correlated with the rainfall amount over the main SPR center, but it was found that an overestimated thermal contrast between East Asia and South China Sea is a common problem in most of the CMIP3 and CMIP5 models. Simulation of the meridional thermal contrast is therefore important for the future improvement of current AGCMs.     

East Asian summer monsoon circulation structure controlled by feedback of condensational heating

The East Asian summer monsoon (EASM) features strong humid low-level southerly flows and abundant rainfall over the subtropical East Asia. This study identified how condensational heating generated by the EASM rainfall can affect the EASM circulation by contrasting two 10-member ensembles of atmospheric General Circulation Model experiments with Community Climate Model version 3/National Center for Atmospheric Research respectively with and without feedback of condensational heating over the East Asian domain. Major results inferred from the experiments are as follows. Condensational heating is found to absolutely dominate diabatic heating over East Asia. Exclusion of the feedback of condensational heating leads to a significant weakening of summertime tropospheric warming over land and thus a large reduction of the land-sea thermal contrast between entire Asian continent and surrounding oceans. Associated with this, the lower-level EASM flows are weakened, South Asian High at 200 hPa migrates southward with reduced intensity and breaks over East Asia with southerly flows prevailing in the upper troposphere, in contrast to northerly flows in reality. Consequently, local EASM meridional cell disappears and the baroclinic structure featured by the EASM circulation that is dynamically determined by convective condensational heating over East Asia is altered to a barotropic structure. Therefore, it is concluded that the feedback of condensational heating acts to largely enhance lower-level flows of the EASM and essentially determine its baroclinic structure and meridional cell, once the solar radiation and inhomogeneity of the Earth’s surface form low-level monsoon flows in East Asia by enhancing land-sea thermal contrast.     

Weakening of Indian summer monsoon in recent decades

The analysis of 43 years of NCEP-NCAR reanalysis data and station observations reveals the connections between tropospheric temperature variations and the weakening of the Indian summer monsoon circulation. The Indian summer monsoon variation is strongly linked to tropospheric temperature over East Asia, showing significant positive correlations of mean tropospheric temperature with all-Indian summer rainfall and the monsoon circulation intensity. The result shows that Indian summer monsoon circulation underwent two weakening processes in recent decades. The first occurred in circa the mid-1960s, and the other occurred in circa the late 1970s. The finding indicates that the mean tropospheric temperature may play a crucial role in the weakening of the Indian summer monsoon intensity via changing land-sea thermal contrast. The role of the tropospheric temperature contrast between East Asia and the tropical area from the eastern Indian Ocean to the tropical western Pacific is to weaken the Indian summer monsoon circulation.     

印度夏季风的减弱及其与对流层温度的关系

对43aNCEP/NCAR再分析资料和台站实际观测资料的分析,揭示了对流层温度变化和印度夏季风环流减弱之间的联系。印度夏季风的变化与东亚上空对流层温度具有密切的关系,主要表现为对流层平均温度与整个印度夏季降雨和季风环流强度之间存在显著的正相关。结果表明:印度夏季风环流在近几十年经历了两次减弱过程,第一次减弱约发生在20世纪60年代中期,第二次减弱则发生在20世纪70年代后期;通过改变海陆热力对比,对流层平均温度在印度夏季风减弱过程中可能起着重要作用,东亚地区与东印度洋至西太平洋热带地区之间的对流层温度差异导致了印度夏季风环流的减弱。     

RELATIONSHIP BETWEEN WINTERTIME THERMAL CONTRAST OVER THE ASIAN CONTINENT AND THE CLIMATE IN CHINA

Recent studies indicated that except for the land-sea thermal contrast,there also existed the land-land thermal contrast.The composite analysis and t-test method are used to further study the local thermal contrast variation over the Asian continent,and to discuss the association of seasonal variation of land thermal state with circulation over East Asia,the early summer and summer monsoon activity,and the precipitation anomaly in China in the decadal scale.Results show that the positive meridional temperature anomaly transports downward from upper tropospheric layers in middle-high latitudes north of 25°N in the positive years.In the zonal direction,the Tibetan Plateau heating in the successive spring acts as a force to influence the atmosphere,leading to the rapid temperature warming over eastern Chinese continent,which could increase the land-sea thermal contrast with the negative SSTA.Accordingly,the monsoon activity in early summer over East Asian establishes earlier and the summer monsoon intensity becomes stronger.The early summer precipitation is more-than-normal over the Yangtze River,and the summer precipitation is more-than-normal over the north China and the southwest China.The situation is contrary in the negative years.     

Impacts of Coastal SST Variability on the East Asian Summer Monsoon

The impacts of the seasonal and interannual SST variability in the East Asia coastal regions （EACRSST） on the East Asian summer monsoon （EASM） have been examined using a regional climate model （PδRCM9） in this paper. The simulation results show that the correlation between the EACRSST and the EASM is strengthened after the mid-1970s and also the variability of the EACRSST forcing becomes much more important to the EASM interannual variability after the mid-1970s. The impacts of the EACRSST on the summer precipitation over each sub-region in the EASM region become weak gradually from south to north, and the temporal evolution features of the summer precipitation differences over North and Northeast China agree well with those of the index of EASM （IEASM） differences.
The mechanism analyses show that different EACRSST forcings result in the differences of sensible and latent heat flux exchanges at the air-sea interface, which alter the heating rate of the atmosphere. The heating rate differences induce low level air temperature differences over East Asia, resulting in the differences of the land-sea thermal contrast （LSTC） which lead to 850 hPa geopotential height changes. When the 850 hPa geopotential height increases over the East Asian continent and decreases over the coast of East China and the adjacent oceans during the weakening period of weakens consequently. On the contrary, the EASM enhances during the strengthening period of the LSTC.     

春季西太平洋海表面温度对我国江南春雨的影响

利用NCAR提供的第5代全球大气环流模式CAM3.1探讨了春季西太平洋副热带地区海表面温度对我国江南春雨的影响。数值试验结果表明:春季西太平洋副热带地区海表面温度升高可引起同期东亚—西太平洋副热带纬向海陆热力差异减弱,进而引起3—4月青藏高原东南侧的低涡强度减弱,该低涡与西太平洋副热带高压之间的位势梯度减小,中低纬度西太平洋副热带高压强度减弱,其北侧的850 hPa西南风强度相应减弱,因此西南暖湿气流输送也随之减弱,造成江南地区的水汽通量辐合强度明显减弱,这种环流分布状况将不利于出现较强的江南春雨,导致江南春雨强度明显减小。     

ASIAN-PACIFIC OSCILLATION IN AUTUMN AND ITS RELATIONSHIPS WITH THE SUBTROPICAL MONSOON IN EAST ASIA

Based on the 1961-2010 NCEP/NCAR reanalysis, this work uses empirical orthogonal function(EOF) and composite analysis to study the distributions of zonal land-sea thermal contrast between Asia and the Pacific during transitions from the summer monsoon to the winter monsoon in East Asian subtropics, and investigates the interannual variations of the thermal contrast and their relationships with circulation systems over the East Asian subtropics. The findings are as follows. 1) In autumn, the interannual variations of the temperature deviation in the middle and upper troposphere show significant east-west out-of-phase teleconnection over Asia and the central and eastern Pacific, i.e. the Asian-Pacific Oscillation, or APO. 2) While not as significant as in summer with regard to coverage and intensity, the APO shows interannual variations in autumn that well depicts the change in the intensity of the subtropical monsoon. In the high(low) APO year, the current subtropical summer monsoon is strong(weak) and the winter monsoon is weak(strong) in East Asia as derived from the general circulation and wind field of the East Asian-Pacific region.     

Seasonal scale variability of the East Asian winter monsoon and the development of a two-dimensional monsoon index

This study investigates the seasonal scale variability of the East Asian winter monsoon (EAWM), which is distinguished from the seasonal cycle with temporal variation throughout winter. Winters lasting 120 days (Nov. 17–Mar. 16) for a period of 64 years from the NCEP daily reanalysis data set are used to study the seasonal scale variability of the EAWM. Cyclostationary empirical orthogonal function (CSEOF) analysis is adopted to decompose the variability of the EAWM. The second CSEOF mode of 850-hPa temperature exhibits a seasonal scale variation, the physical mechanism of which is explained in terms of physically consistent variations of temperature, geopotential height, sea level pressure, wind, and surface heat fluxes. The seasonal-scale EAWM exhibits a weak subseasonal and a strong interannual variability and has gradually weakened during the 64 years. In a weak EAWM phase, the land-sea contrast of sea level pressure declines in East Asia. Consistent with this change, low-level winds decrease and warm thermal advection increases over the eastern part of mid-latitude East Asia. Latent and sensible heat fluxes are reduced significantly over the marginal seas in East Asia. However, during a strong EAWM phase, the physical conditions in East Asia reverse. A large fraction of the variability of the EAWM is explained by the seasonal cycle and the seasonal scale variation. A two-dimensional EAWM index was developed to explain these two distinct components of the EAWM variability. The new index appears to be suitable for measuring both the subseasonal and the interannual variability of the EAWM.