南亚高压与西太平洋副热带高压经纬向位置配置对中国东部夏季降水的影响

利用1951—2016年逐月中国160站降水资料、NCEP/NCAR全球大气再分析资料和NOAA_ERSST_V4海表温度资料,分析了南亚高压与西太平洋副热带高压(西太平洋副高)经、纬向位置的关系及其位置配置对中国东部夏季降水的影响,结果表明:(1)南亚高压与西太平洋副高在纬向上的东西进退存在明显的反相关系,在经向上主要存在一致变化的特征,并依此定义了纬向、经向位置指数。纬向位置指数大(小)表示南亚高压与西太平洋副高纬向上距离远(近),经向位置指数大(小)表示两高压经向位置均趋于偏北(南);(2)纬向位置指数与我国华北、华南沿海地区降水呈显著正相关,而与长江中下游、东北北部地区降水呈显著负相关;经向位置指数与我国华北、东北南部地区降水呈显著正相关,而与我国江南、华南地区降水呈显著负相关;(3)南亚高压与西太平洋副高的经向、纬向位置指数与关键海区的前期春季、同期夏季海表温度均有显著的相关,热带太平洋-印度洋、北印度洋、中东太平洋前期春季、同期夏季海表温度与南亚高压东脊点呈显著正相关,与南亚高压脊线及西太平洋副高西脊点均呈显著负相关,而北太平洋海表温度主要与西太平洋副高脊线呈显著正相关。      

Bimodality of the South Asia High simulated by coupled models

The observed South Asia High (SAH) center is characterized by two distinctive equilibrium modes during boreal midsummer, namely the center of SAH is located between 82.5^o--92.5^oE for the Tibetan Plateau mode and between 55^o--65^oE for the Iranian Plateau mode, respectively. The present study describes the ability of 15 coupled general circulation models (CGCM) used in the Intergovernmental Panel on Climate Changes (IPCC) 4th Assessment Report to reproduce the observed bimodality of the SAH. These models reveal a wide range of skill in simulating this bimodality. Nearly half of the models reproduced the bimodality, while the other half of the models did not simulate well these two modes whereas usually preferring one mode. The models that reproduced the bimodality of the SAH present similar horizontal and vertical circulations as those features from the NCEP reanalysis data. The results from these models identify the warm characteristics of the SAH and indicate that these two modes have different dynamic and thermodynamic properties. Different characteristics of the simulated sensible heat and latent heat related to precipitation partly contribute to the difference in the simulations of the SAH bimodality. The majority of these models that prefer to simulate the Tibetan Plateau mode produce a small sensible heat flux difference between the Iranian Plateau and the Tibetan Plateau, and also generally simulate a very strong false precipitation center over the east of the Tibetan Plateau, which indicates strong latent release and thereby contributes to the preference of the SAH center on the Tibetan Plateau. Whereas, the models that reproduce the bimodality of the SAH tend to simulate large precipitation over the southern Himalayas and no obviously false precipitation is produced over the east of the Tibetan Plateau. In addition, the models resolution may also have important impacts on the simulations of precipitation.     

南亚高压的南北偏移与我国夏季降水的关系

该文定义了一个能较好反映南亚高压南北偏移的指数,并发现该指数与我国夏季降水,尤其是华北和长江流域的降水,无论在年际变化上还是长期趋势上都具有十分显著的相关关系。南亚高压位置偏北时,在我国东部至日本上空存在一个显著的异常反气旋,其中心自上而下向南倾斜,在高层给华北地区带来辐散,在低层使得气流在长江流域辐散,在华北地区辐合,造成华北地区降水偏多,长江流域降水偏少。同时,南亚高压偏北对应着高层西风急流以及中层西太平洋副热带高压偏北,使得我国整个雨带偏北。此外,通过与海温的相关分析发现,南亚高压的长期偏南趋势可能受到印度洋增暖的直接影响。南北偏移指数可作为预测我国夏季区域降水的重要指标,在气候预测业务中有一定的应用价值。     

Simulation of East Asian Summer Monsoon with IAP CGCM

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2003年夏季异常天气与西太副高和南亚高压演变特征的分析

通过入梅前后东亚环流与多年平均的对比,表明2003年夏季我国东部旱涝分明、长江以南高温少雨、淮河流域持续多雨、强降水过程频繁等特点是与西太平洋副热带高压(下称西太副高)活动特征有关。该年副高偏强、位置异常偏西,垂直结构呈现较强的动力性特征,即低层为辐散下沉运动、高层为辐合,脊线随高度向北倾斜。副高西北侧的梅雨锋区强,且风切变明显。动力和热力诊断结果表明,200 hPa南亚高压脊线以北东传的负涡度平流产生的辐合下沉运动,有利于对流层中下层副高的加强西伸。500 hPa副高西北侧的雨带位置与对流层上层副热带急流的位置和东伸的南亚高压对应。高层西风带和南亚高压的动力作用也会引发副高短期的东西振荡。降水区对流层高层产生的潜热释放,使副高西北侧加热率垂直方向的非均匀分布增加,导致了副高加强西进。热带天气系统的活动,对副高维持和加强也有不可忽视的作用。正是西风带、副热带和热带系统相互作用,动力和热力因素的综合影响,造成了该年副高及其所带来的天气异常。     

NCAR RegCM2对1991年夏季江淮流域异常降水事件中关键物理过程的模拟能力检验

选取1991年夏季江淮流域发生的持续性特大暴雨洪涝个例,利用NCAR第二代区域气候模式RegCM2对逐日降水过程及其关键物理因子进行了数值模拟.模式的侧边界条件由ECMWF的大尺度分析资料提供,模拟时间为1991年5-8月.模式范围包括东亚地区及相邻海域,水平分辨率为60 km×60 km,垂直方向为23层.试验结果显示,该模式能够合理地模拟出1991年夏季东亚地区的逐日降水过程,特别是在江淮流域发生的异常降水事件.对一些关键物理变量和过程时空结构的分析表明,大气垂直速度和水平散度的时间演变与江淮流域的5次降水事件一致;形成异常降水的水汽来源主要是大气的水平运动输送。西太平洋副热带高压控制着东亚夏季季风的进退,RegCM2能够模拟出西太平洋副高的南北位置移动。而且,模式能够较好地再现出对水汽输送至关重要的低空急流的逐日变化。     

夏季东亚西风急流扰动异常与副热带高压关系研究

利用1979—2003年NCEP/NCAR月平均再分析资料, 探讨夏季 (6—8月) 200 hPa东亚西风急流扰动异常与南亚高压和西太平洋副热带高压的关系。研究指出:夏季200 hPa东亚西风急流扰动动能加强 (减弱), 东亚西风急流位置偏南 (偏北)、强度偏强 (偏弱); 东亚西风急流扰动动能强弱不仅与北半球西风急流强弱和沿急流的定常扰动有关, 而且还与东亚地区高、中、低纬南北向的扰动波列有关, 亚洲地区是北半球中纬度环球带状波列异常最大的区域。夏季200 hPa东亚西风急流扰动动能加强 (减弱), 南亚高压的特征为位置偏东 (偏西)、强度加强 (减弱); 西太平洋副热带高压的特征为位置偏南 (偏北)。东亚环流特别是500 hPa西太平洋副热带高压对东亚西风带扰动异常的响应由高空东亚西风急流南侧的散度场及其对流层中下层热带和副热带地区的垂直速度距平场变化完成。     

Diversity of the Coupling Wheels in the East Asian Summer Monsoon on the Interannual Time Scale: Challenge of Summer Rainfall Forecasting in China

Two types of three-dimensional circulation of the East Asian summer monsoon(EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the interaction between the Mongolian cyclone over North Asia and the South Asian high(SAH) anomalies over the Tibetan Plateau at 200 hPa. The second mode presents the coupling between the anomalous low-level western Pacific anticyclone and upperlevel SAH via the meridional flow over Southeast Asia. These two modes are responsible for the summer rainfall anomalies over China in 24 and 7 out of 37 years, respectively. However, the dominant SST anomalies in the tropical Pacific, the Indian Ocean, and the North Atlantic Ocean fail to account for the first coupling wheel's interannual variability, illustrating the challenges in forecasting summer rainfall over China.     

东亚地区人为气溶胶直接辐射强迫及其气候效应的数值模拟

利用耦合化学过程的区域气候模式RegCM3,模拟研究3种主要人为排放气溶胶(硫酸盐、黑碳、有机碳)对东亚区域气候的影响.计算分析近20 a来3种气溶胶的时空分布、综合辐射强迫作用及其对地面气温和降水的影响.模拟结果表明:3种气溶胶冬夏季分布有所不同,冬季气溶胶大值区主要分布在南方地区,而夏季大值区北移;气溶胶短波辐射强迫在大气层顶和地面均为负值;气溶胶的加入对东亚地区地表气温有明显影响,冬季降温中心位于四川盆地,夏季降温大值区位于华北地区.气溶胶直接气候效应使得冬季东亚大部分地区降水减少,夏季东亚地区降水与中国南方地区夏季气溶胶浓度有较好的相关关系,中国东部雨带有南移趋势.     

Seasonal Variation of the East Asian Subtropical Westerly Jet and Its Association with the Heating Field over East Asia

The structure and seasonal variation of the East Asian Subtropical Westerly Jet （EAWJ） and associations with heating fields over East Asia are examined by using NCEP/NCAR reanalysis data. Obvious differences exist in the westerly jet intensity and location in different regions and seasons due to the ocean-land distribution and seasonal thermal contrast, as well as the dynamic and thermodynamic impacts of the Tibetan Plateau. In winter, the EAWJ center is situated over the western Pacific Ocean and the intensity is reduced gradually from east to west over the East Asian region. In summer, the EAWJ center is located over the north of the Tibetan Plateau and the jet intensity is reduced evidently compared with that in winter. The EAWJ seasonal evolution is characterized by the obvious longitudinal inconsistency of the northward migration and in-phase southward retreat of the EAWJ axis. A good correspondence between the seasonal variations of EAWJ and the meridional differences of air temperature （MDT） in the mid-upper troposphere demonstrates that the MDT is the basic reason for the seasonal variation of EAWJ. Correlation analyses indicate that the Kuroshio Current region to the south of Japan and the Tibetan Plateau are the key areas for the variations of the EAWJ intensities in winter and in summer, respectively. The strong sensible and latent heating in the Kuroshio Current region is closely related to the intensification of EAWJ in winter. In summer, strong sensible heating in the Tibetan Plateau corresponds to the EAWJ strengthening and southward shift, while the weak sensible heating in the Tibetan Plateau is consistent with the EAWJ weakening and northward migration.     

On the origin of equatorial Atlantic biases in coupled general circulation models

Many coupled ocean–atmosphere general circulation models (GCMs) suffer serious biases in the tropical Atlantic including a southward shift of the intertropical convergence zone (ITCZ) in the annual mean, a westerly bias in equatorial surface winds, and a failure to reproduce the eastern equatorial cold tongue in boreal summer. The present study examines an ensemble of coupled GCMs and their uncoupled atmospheric component to identify common sources of error. It is found that the westerly wind bias also exists in the atmospheric GCMs forced with observed sea surface temperature, but only in boreal spring. During this time sea-level pressure is anomalously high (low) in the western (eastern) equatorial Atlantic, which appears to be related to deficient (excessive) precipitation over tropical South America (Africa). In coupled simulations, this westerly bias leads to a deepening of the thermocline in the east, which prevents the equatorial cold tongue from developing in boreal summer. Thus reducing atmospheric model errors during boreal spring may lead to improved coupled simulations of tropical Atlantic climate.     

Intermodel Diversity in the Zonal Location of the Climatological East Asian Westerly Jet Core in Summer and Association with Rainfall over East Asia in CMIP5 Models

The East Asian westerly jet(EAJ), an important midlatitude circulation of the East Asian summer monsoon system,plays a crucial role in affecting summer rainfall over East Asia. The multimodel ensemble of current coupled models can generally capture the intensity and location of the climatological summer EAJ. However, individual models still exhibit large discrepancies. This study investigates the intermodel diversity in the longitudinal location of the simulated summer EAJ climatology in the present-day climate and its implications for rainfall over East Asia based on 20 CMIP5 models. The results show that the zonal location of the simulated EAJ core is located over either the midlatitude Asian continent or the western North Pacific(WNP) in different models. The zonal shift of the EAJ core depicts a major intermodel diversity of the simulated EAJ climatology. The westward retreat of the EAJ core is related to a warmer mid–upper tropospheric temperature in the midlatitudes, with a southwest–northeast tilt extending from Southwest Asia to Northeast Asia and the northern North Pacific, induced partially by the simulated stronger rainfall climatology over South Asia. The zonal shift of the EAJ core has some implications for the summer rainfall climatology, with stronger rainfall over the East Asian continent and weaker rainfall over the subtropical WNP in relation to the westward-located EAJ core.     

The Impacts of Moisture Transport of East Asian Monsoon on Summer Precipitation in Northeast China

By using the ECMWF reanalysis daily data and daily precipitation data of 80 stations in Northeast China from 1961 to 2002, the impacts of moisture transport of East Asian summer monsoon on the summer precipitation anomaly in Northeast China, and the relationship between the variation of moisture budget and the establishment of East Asian summer monsoon in this region are studied. The results demonstrate that the moisture of summer precipitation in Northeast China mainly originates from subtropical, South China Sea, and South Asia monsoon areas. East China and its near coastal area are the convergent region of the monsoonal moisture currents and the transfer station for the currents continually moving northward. The monsoonal moisture transport, as an important link or bridge, connects the interaction between middle and low latitude systems. In summer half year, there is a moisture sink in Northeast China where the moisture influx is greater than outflux. The advance transport and accumulation of moisture are of special importance to pentad time scale summer precipitation. The onset, retreat, and intensity change of the monsoonal rainy season over Northeast China are mainly signified by the moisture input condition along the southern border of this area. The establishment of East Asian summer monsoon in this area ranges from about 10 July to 20 August and the onset in the west is earlier than that in the east. The latitude that the monsoon can reach is gradually northward from west to east, reaching 50°N within longitude 120°-135°E. In summer, the difference of air mass transport between summers with high and low rainfall mainly lies in whether more air masses originating from lower latitudes move northward through East China and its coastal areas, consequently transporting large amounts of hot and humid air into Northeast China.     

Simulation of Precipitation in Monsoon Regions of China by CMIP3 Models

The output of 25 models used in the Coupled Model Intercomparison Project phase 3 （CMIP3） were evaluated, with a focus on summer precipitation in eastern China for the last 40 years of the 20th century. Most models failed to reproduce rainfall associated with the East Asian summer monsoon （EASM）, and hence the seasonal cycle in eastern China, but provided reasonable results in Southwest （SW） and Northeast China （NE）. The simulations produced reasonable results for the Yangtze-Huai （YH） Basin area, although the Meiyu phenomenon was underestimated in general. One typical regional phenomenon, a seasonal northward shift in the rain belt from early to late summer, was completely missed by most models. The long-term climate trends in rainfall over eastern China were largely underestimated, and the observed geographical pattern of rainfall changes was not reproduced by most models. Precipitation extremes were evaluated via parameters of fitted GEV （Generalized Ex- treme Values） distributions. The annual extremes were grossly underestimated in the monsoon-dominated YH and SW regions, but reasonable values were calculated for the North China （NC） and NE regions. These results suggest a general failure to capture the dynamics of the EASM in current coupled climate models. Nonetheless, models with higher resolution tend to reproduce larger decadal trends and annual extremes of precipitation in the regions studied.     

夏季南亚高压两类东—西振荡过程的联系及其天气效应对比

夏季南亚高压（SAH）中心呈青藏高原和伊朗高原双模态分布,表现为东—西振荡的形式。同时,SAH的东缘还存在规律性的向东亚地区东伸或西退至青藏高原,表现为另一种形式的东西振荡。本文利用NCEP1逐日再分析资料、APHRODITE逐日降水数据以及印度地区逐日降水数据,研究了SAH这两类东—西振荡的联系以及它们对亚洲地区环流和天气影响的差异。结果表明,SAH中心的双模态东—西振荡位相可显著影响其东缘东伸/西退的发生及其幅度。尽管在SAH中心呈青藏高原和伊朗高原模态时,均可以出现SAH东缘的向东亚东伸,但青藏高原模态下发生东伸的频率明显高于伊朗高原模态;在伊朗高原模态时则更容易出现SAH东缘的西退。而且,在青藏高原模态下发生的SAH东缘东伸的幅度也比伊朗高原模态时更大。进一步研究发现,SAH中心的双模态东—西振荡主要与印度北部及整个青藏高原地区的降水异常型密切联系,并与异常降水有关的热力和动力作用变化相耦合。而SAH东缘的东伸/西退则通过引起西太副高的西进/东退,与东亚地区偶极子型的降水异常（青藏高原中东部、长江与黄河之间的中下游地区的降水异常与长江以南地区的相反）相联系。此外,SAH中心为青...     

厄尔尼诺衰减年东亚夏季大气环流和降水异常的耦合模式后报试验

利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)新一代耦合气候模式(FGOALS)进行了气候异常季节后报试验,通过对1982—2005年7个个例的分析,探讨了厄尔尼诺衰减年夏季东亚大气环流和降水异常发生的物理机制。分析结果表明:FGOALS可以模拟出厄尔尼诺衰减年夏季相关气候场的异常态特征,表现为在西北太平洋为负海温异常,在热带印度洋为正海温异常,从而导致西北太平洋地区大气中低层异常反气旋环流的维持,其反气旋的西南部及西部的偏南及西南气流造成中国长江中下游地区降水的异常增多。在提前3—9个月的预测模拟中,模式可以模拟出气候场的异常演变,随着预测时间的延长,产生局地耦合的西北太平洋海表温度异常信号变弱,使得模拟出的西北太平洋反气旋异常偏弱、中心东移,从而导致影响东亚降水的气候场的异常变弱,降水异常区偏东。模拟结果也揭示出,西北太平洋海表温度负异常是厄尔尼诺异常信号的转换模态,并且,由于局地海-气相互作用,热带海温异常信号可以持续到第2年夏季,从而引起东亚大气环流和降水异常。对于东亚降水的季节预测出现误差可能是模式对ENSO的模拟偏差造成的,随着预测时间延长,模式模拟的厄尔尼诺信号偏弱,这将使得海表温度异常偏弱,同时相关物理场的异常响应也减弱。     

东亚夏季风异常活动的空间多模态特征

利用ERA40再分析资料,采用相关、合成、自然正交函数展开（EOF分析）等方法,探讨了东亚地区夏季风活动的多空间模态特征及其与大气环流异常的可能联系。结果表明：1）东亚夏季风活动存在3种差异明显的典型空间模态。第一模态反映了夏季风活动在我国东部沿海及以东洋面与其以西地区的反相变化,主要体现了夏季风活动主体位置的东西变动;第二模态反映了自我国华南,经长江中下游、山东半岛、渤海湾至我国东北及朝鲜半岛一带夏季风活动的一致性变化,体现了东亚夏季风活动的整体强弱;第三模态主要反映了夏季风活动在中国以东洋面、朝鲜半岛、东北亚一带与我国华南地区的反相变化,主要体现了夏季风活动主体位置的南北移动。2）东亚夏季风活动的多空间模态对应的大气环流异常存在显著差异。东亚夏季风第一空间模态与亚洲南部区域以及鄂霍次克海上空的SLP呈负相关,而与北极极区、贝加尔湖地区及日本以东洋面的SLP呈正相关;而与同期500hPa高度场的相关分布主要表现为自极地经鄂霍次克海至日本以东洋面的“＋-＋”的波列分布特征。第二模态与SLP和500hPa高度场的相关分布具有非常相似的空间分布形势,均表现为东北、朝鲜半岛、日本海一带与菲律宾洋面、鄂霍次克海地区的反位相分布,自低纬向高纬呈现“＋-＋”的波列分布特征。第三模态与SLP和500hPa高度场的相关分布,主要表现为菲律宾附近洋面、日本及以东洋面、贝加尔湖到亚洲北部的负正相间的分布形势。     

夏季东亚季风与西太平洋副高对福建旱涝影响的诊断分析

利用NCEP/NCAR发布的850 hPa风场和OLR场以及福建38个站月降水资料, 分析了福建夏季旱涝与东亚夏季风及西太平洋副高的关系。结果表明夏季旱涝与夏季风强弱及副高南北位置密切相关。涝 (旱) 年在东亚季风系统中的热带季风环流出现异常加强 (减弱), 副热带季风环流则出现异常减弱 (加强); 涝年副高平均脊线位置偏北于27°N附近, 旱年则偏南于24°N附近; 由春入夏, 再由夏入秋副高南北位置的季节位移, 涝年先是急速北跳, 而后又急速南撤, 旱年却进退平缓。旱涝年东亚中高纬度环流亦表现出不同特征, 涝 (旱) 年一般没有 (有) 出现阻塞形势, 中纬度纬 (经) 向环流发展, 副热带锋区北抬 (南压), 研究还进一步揭示了夏季副高位置南北偏离影响夏季各月降水及其分布的不同形式。     

东亚夏季风指数的年际变化与东亚大气环流

文中从夏季东亚热带、副热带环流系统特点出发 ,定义了能较好表征东亚夏季风环流年际变化的特征指数 ,并分析了东亚夏季风指数的年际变化与东亚大气环流及夏季中国东部降水的关系。文中定义的东亚夏季风指数既反映了夏季东亚大气环流风场的变化特征 ,也较好地反映了夏季中国东部降水的年际变化特征。此外 ,还探讨了东亚夏季风指数变化的先兆信号     

Summertime land–sea thermal contrast and atmospheric circulation over East Asia in a warming climate—Part I: Past changes and future projections

Land–sea surface air temperature (SAT) contrast, an index of tropospheric thermodynamic structure and dynamical circulation, has shown a significant increase in recent decades over East Asia during the boreal summer. In Part I of this two-part paper, observational data and the results of transient warming experiments conducted using coupled atmosphere–ocean general circulation models (GCMs) are analyzed to examine changes in land–sea thermal contrast and the associated atmospheric circulation over East Asia from the past to the future. The interannual variability of the land–sea SAT contrast over the Far East for 1950–2012 was found to be tightly coupled with a characteristic tripolar pattern of tropospheric circulation over East Asia, which manifests as anticyclonic anomalies over the Okhotsk Sea and around the Philippines, and a cyclonic anomaly over Japan during a positive phase, and vice versa. In response to CO₂ increase, the cold northeasterly winds off the east coast of northern Japan and the East Asian rainband were strengthened with the circulation pattern well projected on the observed interannual variability. These results are commonly found in GCMs regardless of future forcing scenarios, indicating the robustness of the East Asian climate response to global warming. The physical mechanisms responsible for the increase of the land–sea contrast are examined in Part II.