黑潮弯曲时的北太平洋冬季海温异常对大气低频振荡的影响

利用中科院大气物理研究所开放实验室ＩＡＰ－ＡＧＣＭ（二层大气环流模式），针对黑潮弯曲时的北太平洋冬季表层海温（ＳＳＴ）异常进行八个月的数值积分试验。试验结果表明：黑潮弯曲时北太平洋冬季ＳＳＴ异常对大气低频振荡的影响具有明显的３０－６０ｄ振荡的特征；在北半球的３０－６０ｄ振荡，大部分地区为向西传播，在南半球则为向东传播；其经向传播较为复杂，在１２０℃剖面上以向南传播为主；热带地区受此ＳＳＴ异常的影响     

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     

西南印度洋海温异常影响亚洲夏季风爆发的数值试验

利用中国科学院大气物理研究所的9层大气环流模式(IAP9—AGCMⅡ)作了西南印度洋海温月异常对亚洲夏季风爆发影响的数值试验。试验结果表明，当该海域1—3月份的海温出现异常增暖时，印度夏季风和东亚夏季风的爆发均较平常晚，反之，二者的建立均较平常早；该海域1—3月份的海温异常对亚洲季风区的降水也有明显的影响。     

西太平洋海温和北极海冰异常对大气环流的影响

利用九层菱形截断１５波的全球大气环流谱模式,对赤道西太平洋海表温度,北极海冰及综合异常精形在北半球夏季大气环流中的作用进行了一系列数值试验和分析。结果表明：赤道西太平洋海表温度的异常变化与北极海冰面呼焦异均可显著影响大气环流,但海冰异常对低纬大气环流的影响远小于西太平洋的海温异常的影响。对全球大气环流异常形成机制的讨论,表二维Ｒｏｓｓｂｙ波开的传播及外强迫引起的大气内部动力学过程虽夏季大气环流异常     

青藏高原隆升影响东亚副热带西风急流的数值试验

利用p-σ九层区域气候模式进行高原隆升对东亚副热带西风急流影响的敏感性试验,分析高原隆升过程中西风急流垂直结构和水平结构的变化,并对其变化的原因进行初步分析.数值试验结果表明,在西风急流垂直结构上,高原隆升后冬季沿90°E高原南侧由低层到高层西风增强,沿115°E经圈在35°N以南中高层西风增强,35°N以北中高层西风减弱,夏季沿90°E高原南侧中高层东风明显减弱,沿140°E在35°N以南中高层西风增强,35°N以北中高层西风减弱.在西风急流水平结构上,冬季沿40°N从100°E到120°E一带200 hPa西风风速显著减弱,而孟加拉湾至华南至日本南部海上一带200 hPa西风风速则显著增强;夏季沿42°N从120°E到150°E一带200 hPa西风风速显著减弱,而沿25°N从120°E到150°E一带200 hpa西风风速则显著增强.冬季高原冷源作用加强和日本西南海上潜热增加所导致东亚500至200 hPa平均温度发生变化以及高原隆起后对西风急流绕流作用的增强共同导致东亚西风急流发生变化,夏季则是高原热源作用加强以及朝鲜半岛和日本西南海上潜热减少导致东亚500至200 hPa平均温度发生变化,进而导致东亚西风急流发生变化.此外,无论冬季还是夏季,对流层中上层温度变化及其所导致的200 hPa风速变化均是在从高原隆升高度为现在高度的1/4至1/2期间变化最为显著.     

近63年中国东部冬季气温异常的时空分布特征

利用中国东部地区115站1951-2013年冬季气温以及美国国家大气科学研究中心和环境预报中心再分析资料,采用经验正交展开和旋转经验正交展开方法,分析中国东部地区近63 a冬季气温变化特征,并基于气候划分的区域分析了其与大气环流异常的关系.结果表明中国东部冬季气温变化在总体一致型的基础上还存在东北一西南反向变化的类型.近63 a冬季气温在1984年前后发生了显著变化,东部冬季气温突变略早于全国,近30 a来中国东部冬季气温明显偏高.中国东部地区冬季气温异常可以分为华南-东南区、东北区、华中区和河套区。西伯利亚高压、东亚大槽和西风急流与中国东部地区冬季气温变化有着显著的相关关系.     

全球环流异常特征及其与中国气候变化的关系

采用球谐函数展开方法对1948—2009年NCEP/NCAR(美国国家环境预报中心/美国国家大气研究中心)高度距平场再分析资料进行分析,通过"时间-高度"的二维坐标方式考察环流异常的立体结构特征,发现南、北半球大气环流在1980年前后发生了明显的正负位相(槽脊)突变.与中国冬季温度和夏季降水的相关分析表明:前期春、夏、秋季的北半球环流纬向正异常越强,华北地区的冬季气温越高,反之越低;前一年冬季环流异常与华北—河套地区的夏季降水呈现反相关,春季北半球均匀异常环流与华北及西南夏季降水呈现反相关;大气环流的纬向异常与华北—河套地区的夏季降水呈现正相关,而同期环流异常与华北东部、西南及江南北部的降水呈现负相关.     

豫北安阳区域性夏季大旱成因分析及预测

首先对1957—2009年共53年豫北安阳区域夏季降水资料进行统计分析,确定安阳区域性夏季大旱的标准,然后分析安阳区域性夏季大旱的成因,并利用这些分析结果进行预测.分析结果如下:利用大气环流分析大旱成因,主要表现在东亚沿海低槽较常年异常深厚和偏东以及西太平洋副高异常偏东、偏南和偏弱.利用太阳黑子分析大旱的形成,可以发现当年6—8月份太阳黑子相对平均数处于谷点或从谷点开始上升时就容易造成安阳区域性夏季大旱.厄尔尼诺现象对安阳区域夏季降水有明显的影响,尤其是较强的厄尔尼诺事件是造成安阳区域性夏季大旱的主要因子.利用亚洲中纬度地转西风急流分析研究,可以看出地转西风急流轴异常偏北,也可造成安阳区域性夏季大旱.     

江淮流域夏季降水异常及与全球中低纬海温异常关系的诊断研究

对1951－1999年中国夏季江淮流域降水异常与海温异常关系的分析表明,前期及同期各季节三大洋海表温度异常（SSTA）与长江流域降水异常的关系是非常显著的,而对淮河流域降水异常总体上的影响较小,前期冬季SSTA的影响显著区主要有：热带印度洋、黑潮、热带中东太平洋和大西洋,各关键区海温异常对亚洲夏季风的影响特征为：当前期冬季赤道印度洋、黑潮、赤道大西洋和热带东太平洋海表温度异常升高（降低）,当年夏季印度西南季风和东亚热带辐合带减弱（加强）,副热带高压位置偏南（北）,副热带辐合带加强（减弱）,长江流域易发生洪涝（干旱）,相关显著性分析表明,前冬赤道印度洋和黑潮区的海温异常对中国夏季降水的影响更为显著。     

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.     

Linkage between winter sea surface temperature east of Australia and summer precipitation in the Yangtze River valley and a possible physical mechanism

The relationship between winter sea surface temperature (SST) east of Australia and summer precipitation in the Yangtze River valley and a possibly related physical mechanism were investigated using observation data. It is found that winter SST east of Australia is correlated positively to summer precipitation in the Yangtze River valley. When the SST east of Australia becomes warmer in winter, the western Pacific subtropical high and the East Asian westerly jet tend to shift southward the following summer, concurrent with low-level southwesterly anomalies over eastern China. These conditions favor precipitation increase in the Yangtze River valley, whereas the opposite conditions favor precipitation decrease. The influence of winter SST east of Australia on East Asian summer atmospheric circulations may occur in two ways. First, by an anomalous SST signal east of Australia in winter that persists through the following summer, thus affecting East Asian atmospheric circulations via the inter-hemispheric teleconnection. Second, when the SST east of Australia is warmer in winter, higher SST appears simultaneously in the southwest Indian Ocean and subsequently develops eastward by local air-sea interaction. As a result, the SST in the Maritime Continent increases in summer, which may lead to an anomalous change in East Asian summer atmospheric circulations through its impact on convection.     

Interannual variation of North China rainfall in rainy season and SSTs in the equatorial eastern Pacific

The rainfall in North China during rainy season （July and August （JA）） exhibits a strong interannual variability. In this study, the atmospheric circulation and SST anomalies associated with the interannual variation of JA North China rainfall are examined. It is found that on the interannual timescale, the JA North China rainfall is associated with significant SST anomalies in the equatorial eastern Pacific, and the North China rainfall and SST anomaly in the equatorial eastern Pacific correspond to the similar variation of the upper-level westerly jet stream over East Asia. A possible mechanism is proposed for the influence of the SST anomalies in the equatorial eastern Pacific on the North China rainfall.     

Positive feedback of winter ocean-atmosphere interaction in Northwest Pacific

Associated with East Asia Trough in the upper layer in winter, the Aleutian Low is the predominant atmos- pheric activity center in North Pacific. Previous re- searches on interannual or decadal variability of Aleu- tian Low[1―4] found that the Aleutian …     

Tropospheric biennial oscillation of the western Pacific subtropical high and its relationships with the tropical SST and atmospheric circulation anomalies

There is the significant period of tropospheric biennial Oscillation(TBO)over East Asian monsoon region at the interannual timescales,which has the important influences on East China climate.Based on a set of reconstructed indices which describes the western Pacific subtropical high(WPSH)objectively,this paper focuses on the TBO component of WPSH,one of the key members of the East Asian Monsoon system,and its relationships with the tropical SST and atmospheric circulation anomalies.It is found that(1)As an important interannual component of WPSH,the time series of TBO has the obvious transition in the late1970s,and the variability of the WPSH’s TBO component is more significant after the late 1970s.(2)The time-lag correlations between the WPSH’s TBO and the tropical sea surface temperature(SST)anomalies in several key ocean regions are more significant and have longer correlation duration than the raw data.The response of the western boundary index to ENSO is earlier than the intensity index,and the time-lag correlations of them are up to maximum when lagging ENSO by 3–5 months and 5–6months,respectively.(3)In the course of the WPSH’s TBO cycle,the occurrence of the El Ni o-like anomaly in the tropical central-eastern Pacific in winter is always coupled with the weak East Asian winter monsoon,with the most significant enhancing phase of the WPSH’TBO.In contrast,the La Ni a-like anomaly in the central-eastern Pacific in winter is coupled with the strong East Asian winter monsoon,with the most weakening phase of the WPSH’s TBO.(4)The distribution of the tropical SST and atmospheric circulations anomalies are asymmetric in the TBO cycle.The WPSH’s TBO is more significant in the period of the developing El Ni o-like anomaly in central-eastern Pacific than in the period of the developing La Ni a-like anomaly.Therefore,during the period of developing El Ni o-like anomaly,more attention should be paid to the interannual component of TBO signal in the short-term climate prediction.     

Covarying modes of the Pacific SST and northern hemispheric midlatitude atmospheric circulation anomalies during winter

The interannual-to-interdecadal relationship between the Pacific sea surface temperature （SST） and the northern hemispheric midlatitude＇s atmosphere represented by the circumpolar vortex was documented with the global oceanic and atmospheric reanalysis data of recent 50 years. Two covarying modes of the Pacific SST and northern circumpolar vortex anomalies during winter were examined using the singular value decomposition and wavelet analysis techniques. One is the interannual, ENSO-related mode and the other is the interdecadal, North Pacific SST-related mode with a period of around 20 years. The two modes exhibit distinct spatial structures. For the interannual mode, the SST anomaly is characterized by a typical ENSO pattern with the principal signature in the tropical eastern Pacific and secondary one in the central North Pacific, while the atmospheric anomaly is regional, characterized by a Pacific-North American pattern. For the inter- decadal mode, large SST anomaly is located in the central North Pacific, while the atmospheric anomaly is zonally global, associated with the midlatitute＇s standing long-wave variations. When the central North Pacific is colder, the long-wave is stronger, and vice versa. Further investigations suggest that the interdecadal mode could involve an interaction between ＂two oceans and an atmosphere＂.     

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 Nino-like SST anomalies. 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 EAWM activity. The tropical Pacific SSTA pattern related closely to the strong EAWM activity differs significantly from that of the La Nina year.     

Interdecadal variations of the East Asian winter surface air temperature and possible causes

Using the NCEP/NCAR and JRA-25 monthly analysis data from 1979 to 2011, this paper analyzes the interdecadal variations of winter (Dec.–Feb.) mean surface air temperature (SAT) over East Asia by means of the empirical orthogonal function (EOF) analysis method. Two dominant modes were extracted, with the leading mode basically depicting a sign consistent SAT variation and the second mode describing a meridional dipole structure between the northern and southern parts of East Asia. These two modes can explain more than 60% of the variance. The leading mode is closely related to the intensity of Siberian high and the East Asian winter monsoon. The second mode exhibits a notable interdecadal shift in the late 1990s, with a turning point around 1996/1997. Winter SAT in the northern (southern) part of East Asia tends to be cooler (warmer) since the late 1990. Winter sea level pressure (SLP) differences between 1997–2011 and 1979–1996 show negative (positive) anomalies over southern (northern) Eurasia. At 500-hPa, an anomalous blocking high occurs over northern Eurasia, while a cyclone anomaly appears over northern East Asia. In addition, the upper-level East Asian jet stream tends to shift northward and become stronger after the late 1990. Indeed, the interdecadal shift of winter SAT over East Asia is dynamical consistent with changes of the large-scale atmospheric circulation in the late 1990s. The result indicates that previous autumn sea surface temperature (SST) in the North Atlantic Ocean, the Northern Indian Ocean and the western North Pacific Ocean, as well as sea ice concentration (SIC) in the northern Eurasia marginal seas and the Beaufort Sea also experienced obvious changes in the late 1990s. In particular, the interdecadal shifts of both SST in the North Atlantic Ocean and SIC in the Arctic Ocean and its marginal seas are well coherent with that of the winter SAT over East Asia. The results indicate that the interdecadal shift of East Asian winter SAT may be related to changes in the North Atlantic SST and the Arctic SIC in the late 1990s.     

Observed oceanic feedback to the atmosphere over the Kuroshio Extension during spring time and its possible mechanism

High-resolution satellite measurements are used to study the air-sea interaction over the Kuroshio Extension （KE） region during spring time. There are two oceanic fronts in the KE region off the east coast of Japan. These fronts are generally associated with strong ocean currents, which may display unstable meander, resulting in remarkable warm sea surface temperature （SST） ridges and cold SST troughs. Analyses of these satellite observations reveal a significantly positive correlation between sea surface wind speed and its underlying SST along these fronts. This positive SST-wind correlation becomes even more significant when strong meanders occur along the fronts. This positive SST-wind correlation indicates an ocean-to-atmosphere feedback over the KE region during spring time. A high-resolution regional atmospheric model is used to investigate the atmospheric response to SST changes along the two fronts.     

2002： The extra-strong warm winter event in North Asia and its accompanying anomalous atmospheric circulation

Features of an extra-strong warm winter event in North Asia in 2002 and its accompanying anomalous atmospheric circulation were studied through diagnosis on the atmospheric reanalysis data set. Results show that the winter of 2002 is of the warmest in the recent 54 years in North Asia, which was caused by both decadal scale and interannual scale variability. The interannual variability is proved to be as the main cause for the event, and it is related to the global scale atmospheric circulation anomalies, with the strongest of them in the Eastern Hemisphere and in the middle and high latitude region of the Southern Hemisphere.