Characteristics of Atmospheric Circulation Associated with Cold Surge Occurrences in East Asia:A Case Study During 2005/06 Winter

The characteristics of the upper-level circulation and thermodynamical properties for the period when two distinct cold surges broke out over East Asia during the 2005/06 winter are investigated. From early December 2005 to early January 2006, exceptionally cold weather lasted for approximately one month due to two successive cold surges that took place on 2 December 2005 and 2 January 2006, respectively. This study reveals that both involve the upper-tropospheric circulation, which induces the amplification and expansion of the surface Siberian high toward East Asia, but arose from different causes： the former is caused by the upper-level blocking originated from the North Pacific and the latter is caused by the upper-level wave train across the Eurasian Continent. In particular, it is suggested that the lower-tropospheric anomalous wind caused by upper-level circulation anomalies and a steep meridional temperature gradient amplified by phase-locked annual cycle combined to induce very strong cold advection in East Asia, which resulted in exceptionally cold weather that lasted for several weeks. The present results emphasize that the characteristics of the upper-tropospheric circulation can be considered as important precursors to cold surge occurrences in East Asia.

Improved simulation of the East Asian winter monsoon interannual variation by IAP/LASG AGCMs

The simulation of the East Asian winter monsoon （EAWM） has been a challenge for climate models. In this study, the performances of two versions of the AGCM developed at the lAP, versions 1 and 2 of the Grid-point Atmospheric Model of the IAP/LASG （GAMIL1 and GAMIL2）, are evaluated in the context of mean state and interannual variation. Significant improvements are shown for GAMIL2 in comparison to GAMIL1. The simulated interannual variability of the EAWM, measured by the regional average of 1000 hPa meridional wind over East Asia, has evidently improved; the correlation coefficient with reanalysis data changes from 0.37 in GAMIL1 to 0.71 in GAMIL2. The associated interannual precipitation anomalies are also improved, in terms of both spatial pattern and magnitude. Analysis demonstrates that the improvements result from the better simulation of the El Nino-related Philippine Sea anticyclone （PSAC） in GAMIL2. The improved moist processes, including the stratiform condensation and evaporation in GAMIL2, lead to a reasonable atmospheric heating associated with El Nitro in the tropical Pacific, which further drives the PSAC as a Rossby- wave response.

The Asymmetric Effects of El Ni?o and La Ni?a on the East Asian Winter Monsoon and Their Simulation by CMIP5 Atmospheric Models

E1 Nifio-Southem Oscillation （ENSO） events significantly affect the year-by-year variations of the East Asian winter monsoon （EAWM）. However, the effect of La Nifia events on the EAWM is not a mirror image of that of E1 Nifio events. Although the EAWM becomes generally weaker during El Nifio events and stronger during La Nifia winters, the enhanced precipitation over the southeastern China and warmer surface air temperature along the East Asian coastline during E1 Nifio years are more significant. These asymmetric effects are caused by the asymmetric longitudinal positions of the western North Pacific （WNP） anticyclone during El Nifio events and the WNP cyclone during La Nifia events; specifically, the center of the WNP cyclone during La Nifia events is westward-shifted relat- ive to its El Nifio counterpart. This central-position shift results from the longitudinal shift of remote E1 Nifio and La Nifia anomalous heating, and asymmetry in the amplitude of local sea surface temperature anomalies over the WNP. However, such asymmetric effects of ENSO on the EAWM are barely reproduced by the atmospheric models of Phase 5 of the Coupled Model Intercomparison Project （CMIP5）, although the spatial patterns of anomalous circula- tions are reasonably reproduced. The major limitation of the CMIP5 models is an overestimation of the anomalous WNP anticyclone/cyclone, which leads to stronger EAWM rainfall responses. The overestimated latent heat flux an- omalies near the South China Sea and the northern WNP might be a key factor behind the overestimated anomalous circulations.

WINTER QINGHAI-XIZANG T_(BB) FEATURES IN RELATION TO ATMOSPHERIC CIRCULATION PATTERN AND ASIAN-AUSTRALIAN MONSOONS

Predominantly in the context of Japan GMS-derived T_(BB) data,study is undertaken of the relationship between the winter thermal conditions of the Qinghai-Xizang Plateau(QXP)and anomaly in Asian-Australian monsoons during northern summer.Evidence suggests that anti- correlation of cold air activity of East Asia with that of Mid Asia is responsible for the counterpart of the ground thermal characteristics anomaly on an interannual basis between the SW and NE QXP;the winter thermal pattern bears a closer correlativity with the subsequent summertime Asian-Australian monsoons anomaly;as the thermal distribution is reversed,so are the convection features over North and South China,maritime continent,the NW and SW Pacific at tropical and equatorial latitudes,resulting in vast difference between East-Asian summer and Indonesian-North Australian winter monsoons;the subtropical monsoon-associated rainbelt over the mid-lower Changjiang basins exhibits the discrepancy in vigor and northerly shift timing.Besides,part of the results has been further borne out through analysis of temperature and precipitation records of the eastern portion of the country in monsoon climate.

Aeolian component records in lacustrine sediments and its atmospheric circulation significance for evolution of Qarhan salt lake,NE Qinghai-Tibetan Plateau

1 Introduction The Qarhan Playa of Qaidam Basin is located at the northeastern QinghaiTibetan Plateau(QTP),in which thick lacustrine and evaporate sediments deposited since the late Pleistocene(Chen et al.,1985,1986).As surrounded by capacious Gobi and yardang fields and suffered strong westerly-northwesterly wind,abundant aeolian materials were trapped in these sediment sequences in the

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 Nio-like SSTanomalies. 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

RESPONSE OF THE ATMOSPHERIC GENERAL CIRCULATION TO WINTER SNOW COVER ANOMALY

In this paper,the response of the atmospheric general circulation to winter anomalous snow cover was investigated through observations studies and model simulation. Results from the observations show that:(1)the anomalous winter snow cover in the extratropics of Eurasian Continent bears an intimate relation to the contemporary atmospheric general circulation.The positive anomaly of winter snow cover is usually accompanied by positive atmospheric EUP teleconnection pattern and stronger East Asian winter monsoon:or vice versa. (2)The linkage between them suggests that the abnormal winter snow cover has an important impact on winter atmospheric general circulation.The anomalous snow cover pattern can lead to the anomaly of winter atmospheric EUP teleconnection pattern and thus influence East Asian Winter monsoon. With NCAR CCM2 including BATS land surface scheme,three groups of experiments were performed to examine the atmospheric response to the anomalous snow cover pattern and explore the relevant mechanism.Simulated results agree well with the observations,which testify the significant response of the atmosphere to snow cover anomaly.It is found that the radiative cooling induced by anomalous snow cover plays an important role in above processes,and the feedback of long-wave radiation can not be neglected.

冬季南北半球际大气质量涛动与东亚冬季风异常联系的模式验证

南北两半球大气中高纬度之间的相互作用与季风等跨半球的天气气候系统存在着密切联系,由于涉及全球范围的大尺度环流与能量变化,其联系途径与机理受到学者们的广泛关注。本文结合ERA5再分析资料以及CMIP6中MPI-ESM1-2-HR模式历史输出资料,验证了冬季南北半球际大气质量涛动(Inter-Hemispheric atmospheric mass Oscillation, IHO)与东亚冬季风异常的联系及其对中国冬季气温的影响。研究表明,再分析资料以及模式结果均表明冬季IHO与东亚冬季风存在显著的正相关关系。IHO通过全球大气质量再分配与东亚冬季风建立起紧密的联系。当IHO为正位相时,大气质量在欧亚大陆北部异常堆积,而在中低纬地区异常亏损,这使得东亚地区海陆气压差明显增大,冬季风增强,同时对中国华中地区冬季地表气温具有显著影响;反之亦然。进一步分析发现,热带低平流层气温可以通过剩余环流调节臭氧含量经向分布进而影响南极对流层气温,从而对IHO年际变化起主要的驱动作用。

Arctic Oscillation and Antarctic Oscillation in Internal Atmospheric Variability with an Ensemble AGCM Simulation

In this study, we investigated the features of Arctic Oscillation （AO） and Antarctic Oscillation （AAO）, that is, the annular modes in the extratropics, in the internal atmospheric variability attained through an ensemble of integrations by an atmospheric general circulation model （AGCM） forced with the global observed SSTs. We focused on the interannual variability of AO/AAO, which is dominated by internal atmospheric variability. In comparison with previous observed results, the AO/AAO in internal atmospheric variability bear some similar characteristics, but exhibit a much clearer spatial structure： significant correlation between the North Pacific and North Atlantic centers of action, much stronger and more significant associated precipitation anomalies, and the meridional displacement of upper-tropospheric westerly jet streams in the Northern/Southern Hemisphere. In addition, we examined the relationship between the North Atlantic Oscillation （NAO）/AO and East Asian winter monsoon （EAWM）. It has been shown that in the internal atmospheric variability, the EAWM variation is significantly related to the NAO through upper-tropospheric atmospheric teleconnection patterns.

Recognition of two dominant modes of EASM and its thermal driving factors based on 25 monsoon indexes

Based on three reanalysis datasets—ERA-Interim,NCAR–NCEP and JRA-55—the classification of25 commonly used indexes of the East Asian summer monsoon(EASM)was investigated.The physical nature of two categories of monsoon index,together with their circulation pattern,climate anomalies,and driving factors,were investigated.Results suggest that the selected 25 monsoon indexes can be classified into two typical categories(CategoryⅠandⅡ),which are dominated by interannual and decadal variabilities of the EASM,respectively.The anomalous circulation patterns and summer rainfall patterns related to the two categories of index also exhibit evident differences.CategoryⅠis closely linked to the low-latitude circulation system and the anomalous circulation pattern is a typical East Asia–Pacific teleconnection pattern.The summer rainfall anomaly exhibits a typical tripole pattern.However,CategoryⅡmainly reflects the impacts of the middle–high latitude circulation system on the summer monsoon and is closely linked to a typical Eurasian teleconnection pattern,which corresponds to a dipole of summer rainfall anomalies.Further analysis suggests that the underlying thermal driving factors of the two categories of monsoon are distinct.The main driving factors of CategoryⅠare the tropical sea surface temperature anomalies(SSTAs),especially ENSO-related SSTAs in the preceding winter and summer SSTAs in the tropical Indian Ocean.The winter signal of Category II summer monsoon anomalous activity mainly originates from the polar region and the middle and high latitudes of the Eurasian continent.CategoryⅡmonsoon activity is also associated with summer SSTAs in the equatorial central Pacific.

Near-surface wind speed changes in eastern China during 1970-2019 winter and its possible causes

The changes in near-surface wind speed(NWS)have a crucial influence on the wind power industry,and previous studies have indicated that NWS on global and China has declined continuously for decades under global warming.However,recently,the decreasing trend of global NWS has slowed down and even showed a recovery trend.Using the observation data of 831 weather stations of the China Meteorological Administration and the Japanese 55-year reanalysis data from 1970 to 2019,NWS changes in eastern China were analyzed and the possible influencing factors were discussed.Results show that winter NWS presented a decreasing trend from−0.29 m s^(−1) per decade(p<0.001)in 1970-1989 to−0.05 m s^(−1) per decade(p<0.01)in 1990-2019.Moreover,NWS exhibited a significant upward trend of 0.18 m s^(−1) per decade(p<0.1)in 2011-2019,resulting in a 19.6%per decade recovery of the wind power generation.A possible cause is asymmetric changes of the sea level pressure and near-surface air temperature differences between the mid-high latitudes(40°-60°N,80°-120°E)and low latitudes(20°-40°N,110°-140°E)altered the horizontal air pressure gradient.Furthermore,NWS changes were closely associated with the large-scale ocean-atmosphere circulations(LOACs).NWS at 77.4%of the stations in eastern China shows significant correlation(p<0.05)with the East Asian winter monsoon index,besides,the inter/multidecadal variability of NWS was considerably correlated to four LOACs,including Arctic oscillation(AO),North Atlantic oscillation(NAO),Pacific decadal oscillation(PDO),and El Niño-Southern Oscillation(ENSO).The time-series reconstructed by a multiple linear regression model based on above five LOACs matches well with the NWS.Interannual variability of NWS were significantly correlated to AO(−0.45,p<0.01)and NAO(−0.28,p<0.05),while the correlation between NWS and ENSO was weak.

不同类型ENSO对东亚季风的影响和机理研究进展

近十几年来有关热带太平洋存在不同类型的增暖型的研究成为热点课题,其中主要依据海温的空间形态将厄尔尼诺与南方涛动(ENSO)分为两类:一类为传统的东太平洋型ENSO,另一类为中太平洋型ENSO。该两类ENSO的形成机制、演变过程均有不同,产生的气候影响也有差异。本文简要回顾了国内外有关不同类型ENSO及其气候影响的研究进展,特别综述了近年来关于两类ENSO事件对东亚夏季风、东亚冬季风以及东亚冬夏季风关联的影响和机理方面的主要研究进展。文中侧重讨论了年际和年代际时间尺度上ENSO事件对东亚季风的影响,并提出了今后在该领域一些需要进一步研究的科学问题。

我国冬季气温的年际变化及其与大气环流和海温异常的关系

利用我国160个台站49个冬季（1951／1952-1999／2000年）的气温资料和NCEP／NCAR再分析资料，通过波谱分析的方法提取变量的年际变化分量（周期小于8年部分）进行分析，结果发现：在年际变化的时间尺度上，我国冬季气温表现为全国一致变化型（EOF1）和南北反相变化型（EOF2）两个主要模态，并可以解释总方差60％以上的变化。进一步分析表明，在年际变化尺度上，与气温全国一致变化型相联系的大气环流表现出海陆气压差的改变以及与此相关的东亚大槽强度的变化和东亚高空急流位置的南北移动；赤道中东太平洋的异常海温对这一模态的出现有一定的预示意义，而中国近海的海温则更多的是被动地随气温改变。与南北反相变化型相联系的大气环流表现出显著的北极涛动特征，这一模态的出现会使得次年春季的西北太平洋海温呈现以30°N为界南北反相变化的形态；而北太平洋的海温异常可能对这一模态的形成有一定的作用。这两个模态的空间分布虽然与年代际尺度上的分布非常相似，但它们的相对强弱和对应的环流却有很大的差异。分析显示，全国一致变化型可能更多地表现出年代际变化的特征，而南北反相变化型更多地表现出年际变化的特征；结果还表明，我国冬季气温的变化在不同的时间尺度上是受不同因子影响的。因此，在研究我国冬季气温变化时，将不同的时间尺度分开考虑是十分必要的。

近50年来我国东、西部地面气温和降水变化对比的初步分析

利用1951—2003年我国160个气象站月平均地面气温和降水资料,分析了我国东、西部气温和降水变化趋势的异同,并讨论了其可能原因。结果表明:我国东、西部地区年、季平均气温变化有较好的一致性,降水变化则有一定差异。近50年来,我国东、西部年平均气温均呈升温趋势,降水从1950年代开始减少,至1990年代又增加。东部年平均气温的增暖趋势大于西部,降水受大气环流影响较大。

中国中东部冬季霾日的形成与东亚冬季风和大气湿度的关系

利用1961—2013年中国地面台站长期观测资料和同期NCEP/NCAR再分析资料,以华北、江淮和华南为研究区,分析了中国中东部冬季霾日的形成与东亚冬季风以及大气湿度的关系。结果表明:(1)冬季霾日与东亚冬季风强度成显著的负相关。首先,东亚冬季风强度的减弱使得地面风速减小,进而导致冬季霾日增多。其中,华北7—8 m/s最大风速日数和江淮6—8 m/s最大风速日数的减少,及华南≤2 m/s最大风速日数的增多对各区冬季霾日的增多作用较大。其次,东亚冬季风减弱引起冬季气温的持续升高,易导致冬季霾日的增多,这在华北地区较之在江淮和华南更为明显。(2)由于气候变暖,冬季气温升高,使得近地面相对湿度减小。在江淮和华南地区,冬季霾日的增多与近地面相对湿度的减小显著相关,而在华北地区这种相关较弱。(3)冬季气温升高也有利于大气层结稳定度的增强,3个区域冬季霾日的增多均与大气层结稳定度的增强显著相关,特别是与对流层中低层(850—500 hPa)大气饱和度的降低显著相关。(4)冬季霾日数变化与区域水汽输送关系密切。其中,华北地区的冬季霾日数与水汽总收入成显著正相关,江淮地区与纬向水汽收入成显著正相关,与经向水汽收入成显著负相关,华南地区与经向水汽收入成显著负相关。

关于东亚冬季风指数的一个讨论——东亚中、低纬冬季风的差异

利用NCEP再分析资料和NOAA海表温度等资料,分析了东亚冬季风在不同纬度上的表现。根据我们定义的东亚中纬度冬季风(The mid latitudinal East Asian winter monsoon,简称EAWM-M)和低纬度冬季风(The low latitudinal East Asianwinter monsoon,简称EAWM-L)指数,探讨了它们对应的影响系统,并重点分析了它们与海温异常之间联系的异同。研究主要发现:(1)EAWM-L和EAWM-M指数所反映的东亚冬季大气环流形势不尽相同。在对流层低层,EAWM-L与中国南海、菲律宾附近环流异常的关系密切,EAWM-M与贝加尔湖阻塞高压的关系更为密切;在对流层中层,EAWM-M同样与贝加尔湖阻塞高压异常的联系相对更为紧密,而EAWM-L指数则与东亚大槽的关系更为紧密。在对流层高层,副热带西风急流强度变化通过调制次级环流进而与EAWM-L联系起来,而EAWM-M强弱变化主要与副热带西风急流北界的位置有关。(2)EAWM-L与冬季赤道中东太平洋和热带印度洋海温异常的联系都很紧密,而EAWM-M变化与冬季热带印度洋海温异常的联系更为密切,与赤道中东太平洋海温异常的关系相对偏弱。EAWM-L与冬季赤道中东太平洋和热带印度洋海温异常的紧密联系在年际和年代际尺度上都是存在的,而EAWM-M与冬季热带印度洋海温异常的紧密联系主要体现在年代际尺度上。

2016/2017年冬季北半球大气环流及对我国冬季气温的影响

2016/2017年冬季(2016年12月至2017年2月),东亚冬季风强度较常年同期异常偏弱,西伯利亚高压偏弱。北极涛动(AO)在冬季以正位相为主。冬季北半球500 hPa高度距平场上,亚洲中高纬地区以纬向环流为主,我国为异常正高度距平控制。受其影响,我国各地气温普遍较常年同期偏高,全国平均气温为-1.5℃,较常年同期(-3.4℃)偏高1.9℃,为1961年以来最暖的冬季。季内各月冬季风指数和西伯利亚高压均偏弱,相应我国气温各月均偏高。冬季风的异常偏弱与夏季北极地区大气环流异常状态有关。2016年夏季北极大气环流的热力和动力状态影响了秋季北极海冰偏少的滞后影响效果,不利于冬季风的偏强。

东亚冬季风强度的统计预测方法研究

利用1961～2008年NCEP再分析和NOAA延长重构的月平均海温资料,基于海气系统关键区的前期信号分析,建立了一个东亚冬季风强度的统计预测方法。东亚冬季风强度与前期(9～10月)黑潮及其延伸区和热带西印度洋海温异常(SSTA)密切相关。强东亚冬季风活动与黑潮及其延伸区正SSTA和热带西印度洋负SSTA相对应。东亚冬季风强度还和一个前期(10月)北半球环流型存在显著相关,其中环流型的活动中心分别位于北太平洋中部、太平洋东北部、北美和北大西洋。文中探讨了这三个预测因子对东亚冬季风强度的预测意义,并揭示了其影响东亚冬季风活动的可能物理过程。该预测方法的历史拟合率和试报准确率较高,可用于东亚冬季风强度的定性预测。

我国冬季气温年代际变化及其与大气环流异常变化的关系

利用我国160个台站50年（1951-2000年）的月平均温度资料和NCEP／NCAR再分析资料，对我国从1951／1952-1999／2000共49个冬季（11月至次年3月平均）的气温进行经验正交函数（E（）F）分解。第1模态表现为全国一致的增温或者降温，20世纪70年代中期以后，我国冬季气温增暖明显，发生了显著的年代际变化；第2模态则表现为南北温度的反相关系，20世纪80和90年代，我国北部地区，特别是东北和西北的温度增加，而我国南部则温度降低。采用频谱分析方法提取我国冬季气温的年代际变化信号更清楚地反映出这些变化。而且这两种模态从20世纪80年代开始的正位相叠加使得我国冬季持续偏暖，在降水场没有显著变化的情况下，加剧了华北地区的干旱程度。对气温的年代际变化与大气环流的回归分析表明，我国冬季气温年代际变化的第1模态与半球尺度上的北极涛动（A0）的变化有密切的关系，它在高度场上表现为一个准正压的南北环状模态；而第2模态则与中高纬大气环流中的一波结构联系密切，它在高度场上表现为一个准正压的太平洋和大西洋上反相的振荡模态。这就表明，我国冬季气温的年代际变化与大气环流中的基本气流及其扰动有密切的关联。作者还讨论了大气环流影响我国冬季气温年代际变化的可能机理，并指出进一步需要研究的问题。

东亚冬季风指数的定义及其年际年代际异常

利用NCAR/NCEP再分析资料,通过相关分析方法分析了多种可以表征东亚冬季风活动的气象要素指数的相关性特征,选取地面温度、海平面海陆气压差和500hPa高度3个要素,综合定义了一个东亚冬季风指数。结果表明,该指数表征的东亚冬季风有明显的QTO和QFO周期振荡特征,这一特征与冬季风年代际背景有关,强冬季风年代背景下的振荡比弱冬季风年代背景下的振荡显著,同时该指数能很好地表征东亚冬季风活动的各个方面。对强弱冬季风年的大气环流的结构及其相应的低纬度对流活动、海洋和高低层大气热力状况的分析表明,强弱冬季风活动不仅表现在中高纬度高低层大气环流变化的差异,在局地Hadley环流和赤道附近Walker环流、低纬度对流活动、海洋和大气的热力状况的变化方面也表现出了显著的差异。