The Relationship between the El Nin o/La Nin a Cycle and the Transition Chains of Four Atmospheric OscillationsPart I: The Four Oscillations简

The first leading modes of the interannual variations in low-level circulation over the North and South Pacific are the Northern Oscillation （NO） and Southern Oscillation （SO）,which are oscillations in sea level pressure anomalies （SLPAs）between the eastern and western Pacific Ocean.The second leading modes are the North Pacific Oscillation （NPO） and the Antarctic Oscillation （AAO）,which reflect oscillations between the subtropics and the high and middle latitudes.The transition chains of these four oscillations were investigated using the National Centers for Environmental Prediction-National Center for Atmospheric Research （NCEP-NCAR） reanalysis data.The general pattern of the transition chain between the NO and NPO was from the negative phase of the NO （NO-） to the positive phase of the NPO （NPO＋）,then from NO＋ to NPO-to NO-.The whole transition chain took about 4-6 years.The general pattern and period of the transition between the SO and AAO were similar to those between the NO and NPO.In addition,the transition chains between the NO and NPO,and the SO and AAO,were almost simultaneous.The transition chains of the four oscillations were found to be closely connected,with the eastward propagations of SLPAs occurring along both sides of the Equator.     

Intraseasonal Oscillation of the South China Sea Summer Monsoon and Its Influence on Regionally Persistent Heavy Rain over Southern China

The intraseasonal oscillation（ISO） in the South China Sea summer monsoon（SCSSM） and its influence on regionally persistent heavy rain（RPHR） over southern China are examined by using satelhte outgoing long wave radiation,NCEP/NCAR reanalysis,and gridded rainfall station data in China from 1981 to 2010.The most important feature of the ISO in SCSSM,contributing to the modulation of RPHR,is found to be the fluctuation in the western Pacific subtropical high（WPSH）,along with a close link to the Madden-Julian oscillation（MJO）.Southern China is divided into three regions by using rotated empirical orthogonal functions（REOFs）for intraseasonal rainfall,where the incidence rate of RPHR is closely linked to the intraseasonal variation in rainfall.It is found that SCSSM ISOs are the key systems controlling the intraseasonal variability in rainfall and can be described by the leading pair of empirical orthogonal functions（EOFs） for the 850-hPa zonal wind over the SCS and southern China.Composite analyses based on the principal components（PCs） of the EOFs indicate that the ISO process in SCSSM exhibits as the east-west oscillation of the WPSH,which is coupled with the northward-propagating MJO,creating alternating dry and wet phases over southern China with a period of 40 days.The wet phases provide stable and lasting circulation conditions that promote RPHR.However,differences in the ISO structures can be found when RPHR occurs in regions where the WPSH assumes different meridional positions.Further examination of the meridional-phase structure suggests an important role of northward-propagating ISO and regional air-sea interaction in the ISO process in SCSSM.     

第四纪两类千年尺度气候振荡现象及机理研究

千年尺度气候突变事件是第四纪冰期普遍存在的气候现象。这些事件可以被分为两类,一类为Dansgaard-Oeschger Event (DO事件),另一类为海因里希(Heinrich Stadial,HS)事件,后者有时也被认为是一种特殊的DO事件,因此也被称为 HS-DO事件。HS事件期间北大西洋冰架的融化一般对应DO振荡的冷相位,这与通常认为的冰架在较冷气候下体积增加并不相符。这两类事件在北大西洋重建数据中表现得最为明显,但其气候影响具有全球性。由于没有显著的外强迫驱动这两类气候突变事件,自20世纪90年代首次被确认以来,HS-DO事件一直是古气候界关注的重点,且人们对其触发机理仍没有定论。本文基于目前对这两类千年事件的研究现状,集中总结了目前已有的可反映千年事件的重建数据,利用已有的模拟工作,重点回顾了现有的机制理论,评述了目前研究DO事件以及HS-DO事件的局限性,并对其后续工作,尤其是模拟部分,进行了展望。     

Resonance of baroclinic waves in the tropical oceans: The Indian Ocean and the far western Pacific

The Indian Ocean has a particularity, its width is close to half the wavelength of a Rossby wave of biannual frequency, this coincidence having been capitalized on by several authors to give the observations a physical basis. The purpose of this article is to show that this is not the case since the resonance of tropical baroclinic waves occurs in all three oceans. This is because the westward-propagating Rossby wave is retroflexed at the western boundary to form off-equatorial Rossby waves dragged by countercurrents before receding and turning back as a Kelvin wave. Thus a quasi-stationary baroclinic wave is formed, whose mean period is tuned to the forcing period. Two independent basin modes resonantly forced are highlighted – 1) a nearly symmetric zonal 1/2-yr period Quasi-Stationary Wave (QSW) that is resonantly forced by the biannual monsoon. It is formed from first baroclinic mode equatorial-trapped Rossby and Kelvin waves and off-equatorial Rossby waves at the western antinode. This QSW controls the Equatorial Counter Current at the node. The Indian Ocean Dipole (IOD) results from a subharmonic mode locking resulting from the coupling of this QSW and the 2nd, 3rd and 4th baroclinic modes - 2) a 1-yr period QSW formed from an off-equatorial baroclinic Rossby wave, which is induced from the southernmost current of the Indonesian Throughflow through the Timor passage, propagating in the southern and northern hemispheres: the drivers are south-easterlies in the southern hemisphere and monsoon wind in the northern hemisphere.     

大气季节内振荡对夏季登陆广东台风的影响

基于热带气旋最佳路径资料和向外长波辐射数据,结合高斯滤波、经验正交函数分解和合成分析等方法,探讨了20~90 d周期的MJO(Madden-Julian Oscillation)和10~20 d周期的QBWO(Quasi-Biweekly Oscillation)两类大气季节内振荡对夏季(5-9月)登陆广东台风的影响。结果表明:MJO和QBWO对登陆广东台风个数、强度、位置和运动方向均有显著影响:当MJO和QBWO的对流中心(抑制中心)靠近广东沿岸时,登陆广东的台风数量多(少)、强度大(小)、登陆位置偏东(西)、登陆后东向运动的台风数量偏多(少)。在此基础上,还进一步探讨了MJO和QBWO对生成于南海和西北太平洋的这两类登陆广东台风的影响及两者对登陆广东台风的共同影响。     

Comparison of the Structure and Evolution of Intraseasonal Oscillations Before and After Onset of the Asian Summer Monsoon

High-resolution satellite-derived data and NCEP-NCAR reanalysis data are used to investigate intraseasonal oscillations （ISO） over the tropical Indian Ocean.A composite evolution of the ISO life cycle is constructed,including the initiation,development,and propagation of rainfall anomalies over the tropical Indian Ocean.The characteristics of ISO over the tropical Indian Ocean are profoundly different before and after the onset of the Indian summer monsoon.Positive precipitation anomalies before monsoon onset appear one phase earlier than those after monsoon onset.Before monsoon onset,precipitation anomalies associated with ISO first initiate in the western tropical Indian Ocean and then propagate eastward along the equator.After monsoon onset,convective anomalies propagate northward over the Indian summer monsoon region after an initial eastward propagation over the equatorial Indian Ocean.Surface wind convergence and air-sea interaction play critical roles in initiating each new cycle of ISO convection.     

应用MJO制作长江流域月降水预测的试验研究

用MJO指数RMM1、RMM2、振幅 1—25日平均代替月平均,用上月月平均RMM1和RMM2、振幅构造为右场,下月长江流域降水场为左场,SVD分析两场的关联,借助最优化技术,在降水场预测距平与实况距平同号总站数最大意义下确定系数,建立估计公式,由右场时间系数估计左场时间系数,最后反演降水场。尽管多数的月第一模态相关并不显著,但实际预测效果较好。     

Intraseasonal Oscillation in Global Ocean Temperature Inferred from Argo

The intraseasonal oscillation(ISO;14-97-day periods) of temperature in the upper 2000 m of the global ocean was studied based on Argo observations from 2003-2008.It is shown that near the surface the ISO existed mainly in a band east of 60 E,between 10 S and 10 N,and the region around the Antarctic Circumpolar Current(ACC).At other levels analyzed,the ISOs also existed in the regions of the Kuroshio,the Gulf Stream,the Indonesian throughflow,the Somalia current,and the subtropical countercurrent(STCC) of the North Pacific.The intraseasonal signals can be seen even at depths of about 2000 m in some regions of the global ocean.The largest amplitude of ISO appeared at the thermocline of the equatorial Pacific,Atlantic and Indian Ocean,with maximum standard deviation(STD) exceeding 1.2 C.The ACC,the Kuroshio,and the Gulf Stream regions all exhibited large STD for all levels analyzed.Especially at 1000 m,the largest STD appeared in the south and southeast of South Africa-a part of the ACC,with a maximum value that reached 0.5 C.The ratios of the intraseasonal temperature variance to the total variance at 1000 m and at the equator indicated that,in a considerable part of the global deep ocean,the ISO was dominant in the variations of temperature,since such a ratio exceeded even 50% there.A case study also confirmed the existence of the ISO in the deep ocean.These results provide useful information for the design of field observations in the global ocean.Analysis and discussion are also given for the mechanism of the ISO.     

The excitation mechanism of the interstellar 6.7 GHz methanol maser

We notice that the second kind of astronomical methanol maser with strong emission always coexists at both 6.7 GHz and 12.2 GHz and in association with compact H II regions and we are led to propose a new excitation mechanism —maser amplification of the 6.7 GHz maser wothout population inversion. We show that this mechanism is compatible with the astronomical conditions and that it and other mechanisms are not mutually exclusive, rather it may serve as a useful complement.     

南极长城站地区气象要素的中期振荡特征

本文用多维谱分析的方法研究了1985年1月-1987年12月南极长城站地面气象要素的谱特征。该地区的气象要素与北半球一样,也普遍存在3-5天、准一周、准二周和3-4周振荡周期。在长城站所在的乔治王岛地区,从地面到平流层中下部,气压系统都存在着显著的准二周振荡,这种振荡是由上往下传播的。无论冬、夏季,准二周和准一周振荡都是由西往东传播的,而扰动的南北传播方向则与季节及振荡周期长度有关。南极地区的中期振荡特征与500hPa极地涡旋的活动和强度变化有密切关系。