The northern annular mode: More zonal symmetric than the southern annular mode

Fan （2007） recently documented the zonal asymmetry of the Antarctic oscillation （AAO） in the austral winter. In this research, the zonal asymmetry of the northern annular mode, or the Arctic oscillation （AO）, in the interannual variability is studied for the boreal winter. It is shown that there is zonal asymmetry of the AO as well, similar to the case of the Antarctic oscillation （AAO）. However, the zonal asymmetry of the AO is considerably weaker than that of the AAO. This is far beyond the speculation, since the zonal asymmetry of the geography is larger in the Northern Hemisphere than the Southern Hemisphere. The Western and Eastern Hemispheres portions of the AO are correlated at 0.54 for 1959-1998, comparing with 0.23 for the case of the AAO. The authors also discussed the physical reason for this inter-hemispheric difference, and partly attributed it to the El Ni~o and Southern Oscillation （ENSO） cycle which may be represented by the SO index. It is indicated that the SO associated sea-level pressure （SLP） patterns are more zonal symmetric in the high latitudes of the Northern Hemisphere than the Southern Hemisphere.     

Interannual variability of Mascarene high and Australian high and their influences on summer rainfall over East Asia

Based on the reanalysis data from NCEP/NCAR and other observational data,interannual variability of Mascarene high(MH) and Australian high(AH) from 1970 to 1999 is examined.It is shown that interannual variability of MH is dominated by the Antarctic oscillation(AAO),when the circumpolar low in the high southern latitudes deepens,the intensity of MH will be intensified.On the other hand,AH is correlated by AAO as well as EI Nino and South Oscillation(ENSO),the intensity of AH will be intensified when EI Nino occurs.Both correlation analysis and case study demonstrate that summer rainfall over East Asia is closely related to MH and AH.When MH intensifies from boreal spring to summer (i.e.from austral autumn to winter),there is more rainfall over regions from the Yangtze River valley to Japan,in contrast,less rainfall is found over southern China and western Pacific to the east of Taiwan,and most of regions in mid-latitudes of East Asia.Compared with MH,the effect of AH on summer rainfall in East Asia is limited to localized regions,there is more rainfall over southern China with the intensification of AH.The results in this study show that AAO is a strong signal on interannual timescale,which plays an important role in summer rainfall over East Asia.This discovery is of real importance to revealingt the physical mechanism of interannual variability of East Asian summer monsoon and prediction of summer precipitation in China.     

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.     

Hadley环流上升支特征及其与东亚臭氧变化的关系

 利用NCEP/NCAR再分析风场资料和TOMS臭氧总量资料以及ECMWF臭氧混合比资料,用叠加计算方案分析了1992~2002年整10 a的平均经圈环流(MMC)气候态特征;在此基础上定义了Hadley环流上升支强度指数(HAI),研究Hadley环流上升支与东亚地区臭氧的相关关系.结果表明:南、北半球的2个Hadley环流圈的公共上升支具有明显的季节特征;冬、夏HAI(WHAI/SHAI)均表现出明显的年变化,WHAI在2月最强,SHAI在8月最强,WHCI与其所处高度的负相关性较夏季好.分析还指出,Hadley环流上升强度越强,同期东亚相对应的Hadley环流上升极值高度处对流层臭氧浓度越小.     

Multi-spatial variability modes of the Atlantic Meridional Overturning Circulation

The multi-spatial variability modes of the Atlantic Meridional Overturning Circulation (MOC) are identified in the natural coupled simulation of two climate models, the MOC either oscillates at decadal scales with strong cross- equatorial flow or fluctuates locally at interannual scales with weaker cross-equatorial flow. Former studies mainly emphasize the paleo-environmental and paleo-climatic impacts of the meridional overturning states transition; this analysis indicates the existence of the multi-spatial variability modes of the MOC at interannual to decadal scales. Further analysis indicates that the conventionally used MOC index, which is defined as the maximum zonal mean meridional stream-function of the North Atlantic, cannot properly describe the multi-spatial variability characteristics of the MOC.     

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.     

The combined effects of the ENSO and the Arctic Oscillation on the winter climate anomalies in East Asia

With the warm/cold phases of the El Ni o and Southern Oscillation (ENSO) as a background, the impacts of monthly variation in the Arctic Oscillation (AO) on the winter climate anomalies in East Asia are studied with the NCEP/DOE Reanalysis 2 data and the Chinese station data regarding temperature and rainfall. The combined effects of ENSO and the AO indicate that the winter climate anomalies are mainly influenced by the AO in northern China and the ENSO in southern China, when an El Ni o couples with a negative AO month or a La Ni a couples with a positive AO month. These climate anomalies in China are consistent with the mechanisms proposed in previous studies. However, most of China presents a different pattern of climate anomalies if an El Ni o couples with a positive AO month or a La Ni a couples with a negative AO month, with the exception of the temperature anomalies in northern China, which are still affected dominantly by the AO. Further analysis suggests that the causes are attributed to the differences in both the stratosphere-troposphere interaction and the extratropics-tropics interaction. In the former cases, zonal symmetric circulation prevails in the winter and the extratropics-tropics interaction is weakened. Thus, the influences of the ENSO and the AO on the East Asian climate mainly present linear combination effects. On the contrary, an annular mode of atmospheric circulation is not favored in the latter cases and the extratropics-tropics interaction is strong. Hence, the combined effects of the ENSO and the AO on the winter climate in East Asia present nonlinear characteristics.     

Influence of mean climate change on climate variability from a 155-year tropical Pacific coral record

Today, the El Ni?o/Southern Oscillation (ENSO) system is the primary driver of interannual variability in global climate, but its long-term behaviour is poorly understood. Instrumental observations reveal a shift in 1976 towards warmer and wetter conditions in the tropical Pacific, with widespread climatic and ecological consequences. This shift, unique over the past century, has prompted debate over the influence of increasing atmospheric concentrations of greenhouse gases on ENSO variability. Here we present a 155-year ENSO reconstruction from a central tropical Pacific coral that provides new evidence for long-term changes in the regional mean climate and its variability. A gradual transition in the early twentieth century and the abrupt change in 1976, both towards warmer and wetter conditions, co-occur with changes in variability. In the mid-late nineteenth century, cooler and drier background conditions coincided with prominent decadal variability; in the early twentieth century, shorter-period (approximately 2.9 years) variability intensified. After 1920, variability weakens and becomes focused at interannual timescales; with the shift in 1976, variability with a period of about 4 years becomes prominent. Our results suggest that variability in the tropical Pacific is linked to the region's mean climate, and that changes in both have occurred during periods of natural as well as anthropogenic climate forcing.     

四川南部秋季降水变化及相应大气环流异常特征

利用1961—2014年全国756站的降水资料和美国NOAA-CIRES的20CR月平均再分析资料,研究了四川南部秋季(9～11月)降水变化及其相应的大气环流异常特征。结果表明,四川南部秋季降水具有显著的年际和年代际变化特征,其年际周期以2～4 a和准6 a为主,年代际周期以9～15 a为主。它与黄淮流域同期降水存在显著的负相关关系,与四川南部秋季降水关系密切的大气环流结构是北大西洋—俄罗斯西部—蒙古西部—东亚(NRMA)遥相关波列,NRMA遥相关波列在东亚地区激发出一个气旋性环流,与此同时,中南半岛西侧存在一个反气旋性环流,以上环流型有利于北方冷空气和来自孟加拉湾的暖湿气流在四川南部地区汇合,从而容易导致该地区降水的产生,反之亦然。     

Decadal variability of the IOD-ENSO relationship

Using three kinds of over 100-year sea surface temperature （SST） datasets as well as three-dimensional wind data from NCEP/NCAR, this paper documents the decadal variability of the Indian Ocean Dipole （IOD）-EI Nino/Southern Oscillation （ENSO） relationship. During 1948--1969, positive （negative） IOD and warm （cold） ENSO events were more independent of each other. But after 1970, they tended to occur in the same year. ENSO would influence the whole life span of IOD, and IOD also affects the developing phase of ENSO. Considering the climatological background SST, low-level winds and also equatorial vertical circulations, it is revealed that the decadal variability of the IOD-ENSO relationship may be caused by the enhanced Walker circulation with increased rising motion over the Maritime Continent after 1970. Warmer SST around the Maritime Continent gives rise to anomalous low-level convergence and intensified convection there, which apparently increases the SST linkage between the eastern Indian Ocean and the western Pacific and thereby the interaction between the IOD and ENSO event.     

Decadal change of the East Asian summer monsoon and its related surface temperature in Asia-Pacific during 1880–2004

The East Asian summer monsoon （EASM） and its related change of surface temperature in the past century were not clearly ad- dressed due to absence of atmospheric reanalysis data before 1948. On the benchmark of station-observed sea level pressure （SLP） in China, we utilized multiple SLP datasets and evaluated their qualities in measuring the SLP-based EASM index （EASMI）. It is found that the EASMI based on the SLP of the Hadley center version 2 （HadSLP2） has shown the best performance on the inter- annual and decadal time scales. Instead of showing a linear weakening trend pointed out by the previous study, the EASMI has likely exhibited the decadal variability, characterized by weakened trends during 1880-1906, 1921-1936, and 1960-2004, and with enhanced trends during 1906-1921 and 1936-1960, respectively. Corresponding to the weakened and enhanced periods of EASMI since the 1920s, the surface air temperature （SAT） index （SATI） averaged in eastern China has likely shown a warming and a cooling trend, respectively. However, the decadal abrupt transitions between the two indices do not occur concurrently, which results in a weak correlation between two indices on the decadal time scale. Further analysis indicates that there are four key regions where the SAT is significantly correlated with the EASMI, suggesting the joint impact of surface temperature in Asia-Pacific on the EASM during 1880-2004. In which, the decadal change of SAT near the Lake Baikal plays an important role in the linear trends of the EASM before and after 1960.     

Differences between dynamics factors for interannual and decadal variations of rainfall over the Yangtze River valley during flood seasons

The prediction of rainfall in the Yangtze River valley, especially, during flood seasons is the main means for scientists in China working on and the understanding of rainfall-associated processes is a crucial component of this effort. It can be derived f…     

Spatial-temporal variability of thermohaline intrusions in the northwestern tropical Pacific Ocean

Using repeated hydrographic measurements at 137°E,spatial-temporal variability of thermohaline intrusions in the northwestern tropical Pacific are investigated.Intrusions can be found in the main thermocline throughout the section,with their strength decreasing rapidly poleward.The strongest intrusions exist at the North Equatorial Countercurrent(NECC) where North/South Pacific thermocline water converges.These intrusions also exhibit temporal variations in strength which are closely associated with the meridional displacement of the NECC.Intrusion strength peaks in boreal winter when the NECC reaches its northernmost position of the year.At interannual time scale,intrusions tend to be weak(strong) during El Ni o(La Ni a) episodes.Variations in intrusion strength also lead to prominent fluctuation of lateral diffusivity K L and cross-front temperature flux F Θ.F Θ exhibits significant year-to-year changes which are well correlated with ENSO index,suggesting a possible role of intrusions in the low-latitude Pacific climate variability.     

A continuous 3000—year precipitation record of ENSO variability during LGM from a stalagmite in Nanjing

A glacial stalagmite chronology from Nanjing has been established by the TIMS-U series dating and annual band counting methods. The annually layering sequence spanning the 3000-year period from 18179 to 14900 calendar years before the present (aBP) was analyzed for evidence of East Asian summer monsoon precipitation variability during the Last Glacial Maximum (LGM). Power spectral analysis of the sequence shows a distinct interannual (2—7 years) band of enhanced variability suggestive of El Ni駉-Southern Oscillation (ENSO) teleconnections into East China during the LGM when climatic boundary conditions were different from those of today. The lower frequency bands (4—7 years) variability becomes weaker from 18179 to 14900 aBP, sup-porting the precession forcing model. The reappearance of the ENSO band in the coldest climatic boundary conditions during the Heinrich Event 1, however, suggests the stimula-tion of the enhanced East Asia winter monsoon to the El Ni駉 events.     

Weakening relationship between East Asian winter monsoon and ENSO after mid-1970s

The East Asian winter monsoon(EAWM) is characterized by the frequent cold surges and associated closely with the Siberia High,East Asian Trough,and high-level westerly jet stream.The ENSO cycle can modulate the EAWM since it has co-variability with the sea surface temperature over the Indo-Western-Pacific which can tune the land-sea thermal contrast for the EAWM.This paper,by analyzing the EAWM,ENSO,and associated atmosphere-ocean variability,documents the weakening of the EAWMENSO relationship after the 1970s.The significant out-of-phase inter-relationship is found to be diminished after the 1970s.Further study in this work suggests that the weakened co-variability of the tropical Indo-Western-Pacific climate associated with ENSO after the 1970s is partly responsible for the weakened inter-relationship.Meanwhile,the reduced EAWM interannual variability and northward retreat of the EAWM-associated climate variability are favorable to the weakened ENSO-EAWM connection.     

Atmospheric oscillations over the last millennium

The variations of global atmospheric oscillations over the last millennium, including the North Atlantic Oscillation (NAO), the North Pacific Oscillation (NPO) highly associated with the Pacific Decadal Oscillation (PDO), the Southern Oscillation (SO) and the Antarctic Oscillation (AAO), are studied and compared in this paper based on observations and reconstructed data. The cross correlation analysis of AAO, NAO and NPO shows that there is no significant relationship on interannual variation among them. However, the consistency on decadal variability is prominent. During A.D.1920–1940 and A.D.1980–2000, the positive (strong) phase was dominant and the negative (weak) one noticeable during A.D.1940–1980. In addition, the reconstructed atmospheric oscillations series demonstrate that the positive phase existed in the early of the last millennium for NAO and in the late of the last millennium for AAO, respectively; while it occurred in the mid-late of the last millennium for PDO and ENSO.     

Decadal northward shift of the Meiyu belt and the possible cause

The feature of the decadal movement of the Meiyu belt and their association with East Asia atmospheric circulation for the period of 1979―2007 is examined in this study. It is shown that the Meiyu belt of China has a decadal shift in the late 1990s. There is a remarkable difference between the periods before and after 1999, with the Meiyu belt mainly located to the south of the Yangtze River valley before 1999, but afterward mainly located in the Huaihe River valley. At the same time, a distinctive tropospheric warming and stratospheric cooling trend is found in the mid-latitudes of East Asia, which causes the upper tropospheric pressure surfaces upward bulging and the tropoause elevated in the subtropics and associated widening of the subtropical area over East Asia. Accompanying the subtropics widening, the subtropical westerly jet over East Asia shifts northward and the East Asia tropical Hadley circulation expands poleward, which results in the northward shift of the Meiyu belt.     

近50年开封市降水变化特征的小波分析

利用Morlet小波分析了1961—2010年开封市年降水量距平的小波变化特征,揭示开封市降水量变化的多时间尺度结构.结果表明:开封市年降水量存在多时间尺度的周期变化特征,有6个特征明显的时间尺度,分别是1~2 a、3~4 a、5 a、7 a、9~12 a和15~18 a.其中5 a、7 a、9~12 a和15~18 a的时间尺度在整个时域内都很明显,年际尺度的主周期为7 a,年代际尺度主周期为10 a;开封市降水变化还表现出突变的特点;近50年来,开封市年降水量气候倾向率为6 mm/10 a,年降水量呈增多趋势,未来2~3年内年降水量将处于一个偏多期.     

Propagation of planetary-scale zonal mean wind anomalies and polar oscillations

Global atmospheric variables can be physically decomposed into four components:(1) the zonal time averaged climate symmetric component,(2) the time averaged climate asymmetric,(3) the zonal-mean transient symmetric anomaly,and (4) the transient asymmetric anomaly.This study analyzes the relationships between the intra-seasonal and inter-annual variability of planetary scale decomposed zonal and meridional winds in the tropopause,and oscillations such as those from the El Ni o-Southern Oscillation (ENSO),the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO).The tropical inter-annual zonal mean wind anomalies in the tropopause are linked with the ENSO cycle and can propagate into the subtropics,mid-latitudes,and polar front regions via abnormal meridional vertical cells.Similarly,tropical intra-seasonal (40-60-d) zonal wind anomalies can reach the subtropics and mid-latitudes.The polar intra-seasonal zonal wind anomalies in the tropopause can propagate toward high-latitude areas.Thus,the AO and the AAO are the result of the interaction and propagation of these planetary scale zonal wind anomalies.     

南海海表温度的低频变化及影响因素

利用1950-2010年HadISST1海表温度分析了1950-2010年南海海表温度的季节、年际、年代际变化规律和空间分布,并探讨了太平洋年代际振荡、厄尔尼诺/南方涛动、表面风和EI Nino Modoki对南海海表温度的影响.结果表明:南海海表温度存在显著的季节、年际和年代际变化,1975年左右发生1次由低到高的跃...