东亚季风区大气季节内振荡经向与纬向传播特征分析

将NECP/NCAR资料中850 hPa纬向风分量进行30～60天带通滤波, 研究东亚季风区大气季节内振荡的传播特征。分析表明, 夏季东亚季风区大气季节内振荡(ISO)的传播分为经向传播和纬向传播, 其中经向传播主要为热带地区ISO的向北传播, 纬向传播则是分别起源于印度季风区的ISO东传和起源于西太平洋海域的ISO西传。东传和西传的ISO在120°E附近汇合后增强自热带地区北传到此的ISO, 使得ISO在经向上可以继续向北传播, 其最北界可达35°N以北, 并对我国长江中下游地区夏季降水产生一定的影响。     

异常东亚冬季风对赤道西太平洋纬向风异常的影响

ENSO由于经常带来大范围的气候异常而倍受关注,赤道西太平洋的纬向风异常对ENSO的发生起着重要作用.首先对赤道西太平洋纬向风异常的发生进行研究,其结果清楚地表明它同东亚冬季风的异常有密切关系.异常强(弱)的东亚冬季风不仅能激发产生赤道西太平洋的西(东)风异常,而且还将在菲律宾以东的西太平洋上导致一个气旋性(反气旋性)环流的形成.研究还表明,上述异常流型产生的物理过程是异常东亚冬季风所造成的气压形势的动力影响,因为在强(弱)东亚冬季风影响下,赤道西太平洋地区会形成向西(东)的气压梯度,即( )p/( )x＜0(( )p/( )x＞0)的异常气压形势.通过赤道太平洋的海-气相互作用,赤道西太平洋的持续西(东)风异常则将进一步导致El Nino(La Ni(n)a)事件的发生.     

亚洲赤道地区大气动能的纬向传播

基于 1980～ 1997年 85 0hPa逐日NCEP/NCAR再分析资料讨论了亚洲赤道地区 (0°～ 5°N)大气动能的纬向传播特征。结果表明 ,在亚洲季风区内 ,赤道地区大气动能 (K)的最强中心位于 75°～ 90°E ,次强中心在索马里急流区 (5 0°E附近 )。在 0°～ 5°N ,90°E以东 ,平均的大气动能扰动和赤道上经向风扰动主要起源于西太平洋 ,并向西经南海传播到孟加拉湾。而在孟加拉湾动能中心与索马里急流区之间 ,动能传播方向比较复杂。以上事实说明赤道地区东亚季风系统确实是存在的 ,与印度季风系统中扰动的传播方向不同 ,东亚季风系统中动能和经向风扰动在东西方向上主要受西太平洋的影响。在亚洲赤道季风区 ,这两个系统的交界处约在 95°～ 10 0°E附近 ,比过去界定的偏西 5～ 10个经度。     

夏季东亚西风急流Rossby波扰动异常与中国降水

利用1958～2003年NCAR/NCEP再分析和中国160 站月降水资料,探讨沿东亚西风急流Rossby波扰动动能异常对东亚夏季风环流和中国夏季（6～8月）降水的影响及其响应机理。研究发现:（1）夏季东亚西风急流Rossby波扰动动能加强（减弱), 东亚西风急流位置偏南（北)、强度偏强（弱）。（2）该扰动动能具有显著的年际和年代际变化特征, 1958～1978年处于年代际偏弱阶段,1979～1998年处于年代际偏强阶段。（3）该扰动动能加强（减弱), 200 hPa 辐合区位于30?N以南（以北）西太平洋地区,此时,500 hPa 西太平洋副热带高压位于30?N以南（以北), 850 hPa 反气旋性距平环流出现在东亚30?N以南（以北）地区,而30?N以北（以南）为气旋性距平环流,东亚热带季风环流加强（减弱), 梅雨锋加强（减弱), 夏季中国东部降水中间多、南北少（中间少、南北多）。（4）东亚高、中、低层大气环流对高层东亚西风急流Rossby波扰动动能强弱响应由对流层上层散度场及垂直速度场变化完成。     

亚洲和南半球大气热源（汇）对亚洲夏季风影响的数值试验

利用NCAR CAM3.1模式及NCEP/NCAR (version 1)再分析资料计算出来的几种大气热源分布情况,分别讨论亚洲各地区和南半球上空夏季大气加热场(热源或冷源)对东亚季风环流系统和印度季风环流系统形成的影响.结果表明:(1)东亚地区上空的大气热源和澳大利亚冷源与东亚夏季风环流关系密切,东亚大陆上空及西太平...     

亚洲南部地区海陆分布和南半球陆地对亚洲夏季风影响的数值试验

利用CCM3/NCAR模式,设定了几种海陆分布状况,将亚洲25°N以南地区以90°E为界分为东西两个部分,讨论东部陆地(中南半岛、海洋大陆和澳大利亚)和西部陆地(非洲大陆和印度半岛)存在对东亚季风环流系统和印度季风环流系统的影响,结果表明:(1)西部陆地的存在是印度季风环流系统形成的主要机制,而对东亚季风环流系统影响不大;(2)东部陆地的存在是东亚季风环流系统形成的主要机制,但它对印度季风系统也能产生影响;(3)孟加拉湾季风环流及其北部强降水中心是印度半岛和中南半岛存在联合造成的;(4)南半球的非洲和澳大利亚的存在所造成的环流是相互影响的;(5)中南半岛的存在是南海夏季风季节变化的主要机制,澳大利亚的存在有利于盛夏时强西风推进到南海.     

亚洲和南半球大气冷(热)源对亚洲冬季风影响的数值试验

利用NCAR CAM3.1模式及NCEP/NCAR(version 1)再分析资料计算了几种现实大气热源分布情况,讨论了亚洲各地区和南半球上空冬季1月大气冷(热)源对东亚冬季风环流系统和印度冬季风环流系统形成的影响.结果表明:(1)冬季1月东亚地区和澳大利亚上空大气冷(热)源与东亚冬季风环流关系密切,南半球澳大利亚附近的非绝热加热可以激发出澳大利亚北部的热低压系统,东亚大陆东部的大气冷源可以使东亚大陆低空出现冷高压,基本上模拟出东亚季风系统冬季主要环流成员;(2)亚洲地区西部及其对应的南半球印度洋非绝热加热与印度冬季风环流关系密切,同样对东亚冬季风也有一定的影响,特别是亚洲大陆西部副热带地区的非绝热加热可以加强冬季南海的越赤道气流并能调整阿留申低压的位置.     

来自印度季风区的水汽输送与东亚上空水汽输送和中国夏季降水的关系

诊断分析了北半球夏季来自印度季风的水汽输送与东亚上空水汽输送的关系，发现二者之间具有反相变化的特征。印度季风水汽输送偏强（偏弱）时，东亚上空的水汽输送偏弱（偏强），长江中下游降水偏少（偏多）。印度夏季风水汽输送与西太平洋副热带高压强度有显著的相关关系，印度季风水汽输送偏强（偏弱）时，西太平洋副热带高压强度偏弱（偏强），由此导致副高西侧东亚上空向北的水汽输送减弱（增强），使得长江中下游降水偏少（偏多）。对反映热带对流活动的外逸长波辐射（OLR）的分析表明，印度洋上空的对流加热异常不仅能够显著地影响印度季风，也可能对东亚季风产生直接的影响。     

Impact of Ocean-Continent Distribution over Southern Asia on the Formation of Summer Monsoon

Using the CCM3/NCAR, a series of numerical experiments are designed to explore the effect of ocean-land interlaced distributions of Africa-Arabian Sea-India Peninsula-Bay of Bengal (BOB)-Indo-China Peninsula-South China Sea on the formation of the Asian summer monsoon circulation (ASMC). The results show that the thermal difference between African or Indian Subcontinent and nearby areas including the Indian Ocean, Arabian Sea, and part of BOB is the primary mechanism that maintains the Indian monsoon circulation. In the experiment getting rid of these two continents, the Indian monsoon system (IMS) members, i.e., the Somali cross-equatorial jet (40°E) and the southwesterly monsoon over the Arabian Sea and BOB, almost disappear. Moreover, the Hadley circulation weakens dominantly. It also proves that Africa has greater effect than Indian Subcontinent on the IMS. However, the existence of Indo-China Peninsula and Australia strengthens the East Asian monsoon system (EAMS). The thermal contrast between Indo-China Peninsula and SCS, Australia and western Pacific Ocean plays an important role in the formation of the tropical monsoon to the south of the EAMS. When the Indo-China Peninsula is masked in the experiment, the cross-equatorial flow (105°E and 125°E) vanishes, so does the southwesterly monsoon usually found over East Asia, and EAMS is enfeebled significantly. In addition, the impacts of these thermal contrasts on the distribution of the summer precipitation and surface temperature are investigated.     

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。     

Atmospheric Circulation Cells Associated with Anomalous East Asian Winter Monsoon

Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon (EAWM) were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface temperatures from 1950 to 2000. Several atmospheric cells in the Pacific [i.e., the zonal Walker cell (ZWC) in the tropic, the Hadley cell in the western Pacific (WPHC), the midlatitude zonal cell (MZC) over the central North Pacific, and the Hadley cell in the eastern Pacific (EPHC)] are associated with anomalous EAWM. When the EAWM is strong, ZWC, WPHC, and MZC are enhanced, as opposed to EPHC. The anomalous enhanced ZWC is characterized by air parcels rising in the western tropical Pacific, flowing eastward in the upper troposphere, and descending in the tropical central Pacific before returning to the tropical western Pacific. The enhanced MZC has characteristics opposite those of the enhanced ZWC in the central North Pacific. The anomalous WPHC shows air parcels rising in the western Pacific, as in the case of ZWC, followed by flowing northward in the upper troposphere and descending in the west North Pacific, as in the case of the enhanced MZC before returning to the western tropical Pacific. The anomalous EPHC is opposite in properties to the anomalous WPHC. Opposite characteristics are found during the weak EAWM period. The model simulations and the observations show similar characteristics and indicate the important role of sea surface temperature. A possible mechanism is proposed to link interannual variation of EAWM with the central-eastern tropical Pacific sea surface temperature anomaly (SSTA).     

南海夏季风爆发迟早与赤道纬向风关系的诊断研究

利用ECMWF和NCEP(1958～1999年)的再分析资料，研究南海夏季风与前期气象要素的关系，结果表明:南海夏季风建立日期与当年2月份赤道印度洋地区的纬向风存在高层(200～100 hPa)为正、低层(1000～700 hPa)为负的显著相关分布，类似于偶极子的分布特征；而在赤道中太平洋地区(160°E～160°W)则存在高层为负、低层为正的另一个显著相关“偶极子”。分析这种相关特征的持续性，发现上述形势从2月份到5月份一直存在，且赤道印度洋地区高低层相反的相关分布从3月份开始逐渐东移，到5月份维持在印度洋东部至南海一带。从5月份的相关系数分布图可发现，南海地区低层为负相关，高层为正相关，说明低层西风异常、高层东风异常的赤道纬向风分布有利于南海夏季风早爆发。针对南海夏季风建立日期与赤道地区(10°S～10°N平均)纬向风的“偶极子”型相关分布特征，定义了一个用于诊断南海夏季风爆发迟早的前期因子。该因子与大部分学者定义的南海夏季风建立日期存在着显著的相关，说明该因子对南海夏季风爆发迟早有一定的反映能力和预测作用。根据Gill(1980年)理论分析发现，上述2月份赤道地区纬向风异常是同期赤道印度洋-大陆桥地区异常强对流活动造成热带赤道大气环流显著异常变化的结果。     

印度洋偶极子对东亚季风区天气气候的影响

利用NCEP/NCAR 40年再分析资料和中国科学院大气物理研究所的IAPAGCM-Ⅱ大气环流模式,分析和模拟了印度洋偶极子对东亚季风区天气气候的影响.结果表明,印度洋偶极子对东亚季风区天气气候,特别是夏季,影响显著.印度洋正偶极子位相期间,东亚地区的西南季风爆发偏晚,强度增强,我国大陆降水增多;而印度洋负偶极子位相期间,东亚地区的西南季风爆发偏早,强度减弱,我国的东南部地区有丰富的降水.     

2019年夏季东亚大气环流异常及对我国气候的影响

为更好了解2019年夏季（6—8月）我国主要气候异常特征及成因,利用气象要素站点资料和NCEP/NCAR再分析大气环流资料分析了2019年夏季降水、气温的时空分布和东亚大气环流特征,并初步诊断了长江中下游降水偏少的可能原因。结果显示,2019年夏季全国气温偏暖明显,降水总量接近常年,但旱涝分布有明显的空间差异,东部主要多雨区位于江南至华南及东北地区,云南和黄淮等地气象干旱长时间持续。东部季风区降水还呈现出明显的季节内变化,尤其是江南等地在夏季前期降水过程密集,涝灾严重,但后期急速减少,高温事件迅速爆发。华南前汛期和江南梅雨开始早结束晚。2019年夏季,欧亚中高纬度地区两槽一脊的环流形势非常明显。其中黄海至日本海持续维持的低槽造成夏季西太平洋副热带高压强度偏强,位置略偏西偏南。这一低槽也是长江中下游少雨和江南多雨的直接原因。其在夏季前期位置明显偏南,和副热带高压脊线南北位置的演变非常一致。但在夏季后期,随着这一低槽的减弱北移,副热带高压迅速北跳,也造成雨带从江南快速移动到北方地区。     

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.     

对流层及平流层低层全球动能的季节性急变

利用１９８０－１９８８年ＥＣＭＷＦ的资料，分析对流层５００ｈＰａ，３００ｈＰａ和平流层低层１００ｈＰａ全球范围的纬向平均动能和涡动动能的季节过渡，比较不同层次不同纬度带动能模态的季节性急变，得到如下结论：（１）北半球热带与温带各层次的ＫＺ都有季节性急变，发生在３－４月和１０月附近，而南半球仅在热带有急变。（２）北半球热带地区ＫＺ在６月还有一次季节性急变，出现有１００ｈＰａ和５００ｈＰａ．（３）１０     

东亚季风系统的时空变化及其对我国气候异常影响的最近研究进展

本文回顾了关于东亚季风系统的时空变化及其对我国气候异常影响的最近研究进展。许多研究说明,东亚季风系统无论风场的垂直结构、年循环或是水汽输送和降水特征都明显不同于南亚和北澳季风系统,它是亚澳季风系统中一个相对独立的季风系统。并且,研究结果表明了东亚季风系统有明显的时空变化:其中夏季风系统在年际时间尺度上存在着一个准两年周期振荡和具有极向三极子异常的空间分布特征,并从20世纪70年代中后期起至今发生了明显变弱的年代际变化,这个变化在华北尤其显著;而东亚冬季风在年际时间尺度上存在一个准四年周期振荡,从20世纪80年代中后期起也发生了明显变弱的年代际变化,它引起了我国的持续暖冬。进一步的研究还揭示了东亚季风系统的变异是与海–陆–气耦合系统变异及其相互作用密切相关,因而,东亚季风系统可以看成是一个大气–海洋–陆地的耦合气候系统,即称之为东亚季风气候系统。此外,本文还从上述东亚季风气候系统的年际和年代际变异提出了长江流域严重洪涝灾害发生的气候学概念模型和华北持续干旱的气候背景。     

夏季南亚高压和印度低压环流指数及其与大气热源的关系

利用NCEP/NCAR再分析资料计算了1950-2006年夏季(6-8月)南亚高压(SAH)和印度低压(IL)的面积、强度和中心位置指数,并定量分析了SAH、IL的气候和异常特征及其与亚洲季风区大气热源的同期相关关系,结果表明:(1)夏季SAH 7月最强、6月最弱,中心位置6月偏东南,7、8月偏西北;IL 7月最强,中心位置偏西。(2)SAH、IL的年际异常与亚洲季风区热源异常显著相关,但IL与热源的相关明显强于SAH。(3)青藏高原(下称高原)的影响主要表现在SAH、IL中心位置的经度指数异常与同期高原及亚洲内陆与东亚、东北亚间的热源异常型;SAH、IL中心偏东年,热源异常型为西正、东负。高原主体及其邻近地区的热源异常与SAH强度异常无显著相关,而与IL强弱呈显著正相关。     

Interdecadal Variability of the East Asian Summer Monsoon and Associated Atmospheric Circulations

Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.     

Meridional Propagation of the 30- to 60-day Variability of Precipitation in the East Asian Subtropical Summer Monsoon Region: Monitoring and Prediction

The meridional propagation of the 30- to 60-day intraseasonal variability (ISV) of precipitation in the East Asian subtropical summer monsoon (EASSM) region and its monitoring and prediction are investigated in the current study. Based on a multivariate empirical orthogonal function (MV-EOF) analysis of precipitation and relative vorticity at 700?hPa in East Asia, a bivariate index referred to as the EASSM-ISV index is designed using the two leading MV-EOF modes, with the objective of real-time monitoring of the 30- to 60-day variability of precipitation in the EASSM region. It is found that this index, with its eight phases, can explain the meridional propagation of the 30- to 60-day ISV in precipitation and circulation in the EASSM region. Based on a singular value decomposition technique, a statistical forecast model is developed in which the EASSM-ISV indices from the preceding five pentads are used to predict the indices in five pentads in the future. Meanwhile, the indices are used to predict the meridional propagation of the 30- to 60-day precipitation anomaly in the EASSM region. This model thus provides a useful tool for intraseasonal prediction of precipitation during the rainy season in China.