热带和中高纬地区季节内振荡的特征及其动力学诊断

使用5年低阶全球谱模式资料,对中高纬大气和热带大气季节内振荡的动力学性质和传播特征进行了诊断研究。分析发现模式再现了大气中季节内振荡在热带和中高纬地区的传播特性以及它们之间的差异。热带大气30—60天振荡在速度势场上表现为纬向—波结构和行波特性,而在散度风场上反映了赤道西太平洋—印度洋东西向偶极子型的振荡。中高纬大气30—60天振荡表现为定常波位相和振幅的变化,即波包络的传播特征。它与中高纬地区遥相关型的转换有关,通过遥相关位相和振幅的变化,不仅完成了热带和中高纬地区之间以及热带不同区域之间的能量输送,而且通过这种能量输送过程把南、北半球中高纬地区季节内振荡联系起来。      

Medium-range oscillations in the summer tropical easterlies at 200 hPa

By the use of space-time spectral analysis and band-pass filter, some of the features of the medium-range Oscillations in the summer tropical easterlies (10oS-20o) at 200 hPa are investigated based on a two-year (1980 and 1982) wind (u, v) data set for the period from May to September. Space-time power spectral analysis shows that the total energy of the westward moving waves was the largest and that of the standing waves and eastward moving waves was relatively small in the 200 hPa easterlies; the total energy of the eastward moving waves was at minimum at 10oN. Three kind of the medium-range oscillations with about 50 day, 25 day and quasi-biweekly periods were found in the easterlies, which all show a remarkable interannual variation and latitudinal differences in these two years. The wave energy of zonal wind is mainly associated with the planetary waves (1-3), which all may make important contributions to the 50 day and 25 day oscillations in different years or different latitudes. The quasi-biweekly oscillation is mainly related to the synoptic waves (4-6). In equatorial region, the 50 day oscillation was dominant with a eastward phase propagation in 1982 while the dominant oscillation in 1980 was of 25day period with a westward phase propagations in 1980. Both of them are of the mode of zonal wavenumber 1. Strong westward 50 day oscillation was found in 10oN-20oN in these two years. Regular propagations of the meridional wind 50 day oscillation were also found in the easterlies.The 50 day and 25 day oscillation of zonal wind all demonstrate southward phase propagation over the region of the South Asia monsoon and northward phase propagation near interational date line, where are the climatic mean position of the tropical upper-tropospheric easterly jet and the tropical upper tropospheric trough (TUTT), respectively.     

A NUMERICAL STUDY OF SHORT-RANGE CLIMATIC OSCILLATION WITH VARIOUS TIME SCALES FORCED BY EL NINO DURING THE NORTHERN SUMMER

The normal mode method is adopted to decompose the differences between simulations with SST(seasurface temperature)anomahes over centra-eastern Pacific and normal SST by use of a nine-layer global spec-tral model in order to investigate short-range climatic oscillation with various time scales forced by ElNino during the northern summer.Investigation shows that El Nino may have the following influence onatmosphere on various space-time scales.Extra-long wave components of Rossby mode forced by convectiveanomaly over equatorial western Pacific resulting from El Nino produce climatic oscillation on monthly(sea-sonal)time scale in middle-high latitudes of Southern and Northern Hemispheres;extra-long wave componentsof Kelvin mode forced by SST anomalies propagate along the equator,resulting in 30—60 day oscillation oftropical and subtropical atmosphere;and its long waves move eastward with westerly,resulting in quasi-biweekoscillation.     

大气季节内振荡的活动与El Nino

用广东省４７个测站１９５４－１９９０年各月的平均气温、降水、日照时数的标准化资料分别作按时间点分解的主分量分析,取其前６个主分量作为各测站的气候特征量,用相关系数－重心法作聚类分析,作出各月、全年综合要素的气候分区。结果表明：（１）将广东各月分为有较显著差异的５个区,则冬半年（１０－翌年４月）各月的分区形式较类似且规律性明显,夏半年（５－９月）各月的分区逐月变化明显,且分区形式差别较大。（２）若用６个自然季节的平均气温、降水、日照时数标准化资料分别作主分量分析,各取前３个主分量作为全年气候分区的特征量,则广东全年的气候区可分为东南沿海、西南沿海、西北内陆３个区。     

热带对流层大气低频振荡机制的初步研究

本文从赤道β平面近似下的线性化扰动方程组出发,基于第二类条件不稳定(CISK)理论,研究了热带对流层大气准40天低频振荡的动力机制。研究发现,当对流层中、上层存在较大的对流凝结加热时可激发出纬向波数为1、周期为40天左右的不稳定Kelvin波,它以每天8到11个经度的相速缓慢向东移动。由此指出,观测到的热带对流层大气30—50天的低频振荡可能正是这种由对流凝结加热所驱动的缓慢东移的Kelvin波的具体表现。这可对热带对流层大气30—50天低频振荡现象的动力机制给以初步的物理解释。      

热带积云对流加热在全球大气遥响应中的重要作用──数值试验结果

利用ＩＡＰ两层大气环流模式模拟研究了热带地区积云对流加热在大气对赤道东太平洋海温正异常响应中的作用。通过对积分结果进行分析发现：热带地区积云对流在大气对赤道东太平洋海温正异常的响应过程中起着非常重要的作用。若热带地区的积云对流加热减弱则大气中的遥响应（相关）型也减弱。同时我们还发现，热带地区的积云对流加热加强则响应场的３０—６０ｄ低频振荡也得到加强。     

30—60天大气振荡的全球特征

利用ECMWF格点资料,分析研究了大气季节内(30—60天)振荡的全球特征。30—60天振荡动能的分布表明高纬度地区要比赤道地区大得多。说明那里有较突出的30—60天振荡。中高纬度地区的30—60天振荡与热带有明显不同,垂直结构为正压模态,以纬向2—4波为主,多为向酉传播。30—60天振荡存在明显的低频遥相关,北半球主要为欧亚—太平洋(EAP)型和PNA型,南半球主要有澳洲—南非(ASA)型和环南美(RSA)型,并且在全球范围构成南北半球相互衔接的低频波列,即EAP-ASA波列和PNA-RSA波列。南北半球30—60天大气振荡有明显的相互影响,本文研究了南北半球30—60天振荡相互影响的3种主要过程。     

POSSIBLE INFLUENCES OF THE TROPICAL INDIAN OCEAN DIPOLE ON THE EASTWARD PROPAGATION OF MJO

Based on multiple datasets, correlation and composite analyses, and case studies, this paper investigated possible influences of the Indian Ocean dipole （IOD） mode on the eastward propagation of intraseasonal oscillation in the tropical atmosphere. The results showed that （1） the 30-60 day outgoing longwave radiation anomalies in the southeastern Indian Ocean and the 30-60 day 850-hPa zonal wind anomalies over the equatorial central Indian Ocean were significantly correlated with the IOD index; （2） during positive IOD years, the anomalously cold water in the southeastern Indian Ocean and the 850-hPa anomalous easterlies over the equatorial central Indian Ocean might act as barriers to the continuously eastward propagation of the intraseasonal convection, which interrupts the Madden-Julian oscillation （MJO） propagation in the eastern equatorial Indian Ocean and western Pacific; and （3） during negative IOD years, the anomalously warm water in the southeastern Indian Ocean and the low-level westerly anomalies over the equatorial central Indian Ocean favor the eastward movement of MJO.     

CISK-rossby wave and the 30-60 Day Oscillation in the Tropics

The 30-60 day oscillation is an important aspect of the atmospheric variance in the tropical area. A number of works have been done on this phenomenon, this article is a further one. A quasi-geostrophic linear model that consists of a two-layer free atmosphere and a well-mixed boundary layer is used to investigate the instability of intraseasonal oscillation, its propagation and vertical structures. Results show that the dynamical coupling and interaction between the barotropic and baroclinic components via boundary layer convergence / divergence are responsible for the appearance of a new kind of low-frequency wave. Such wave is very different from the traditional tropical Rossby wave. It can propagate westward and eastward. Some behaviours of it appear to resemble the observed 30-60 day oscillation mode in many aspects, such,as vertical structures, zonal and meridional propagations. Now many researchers emphasize the direct relationship between CISK-Kelvin mode and the tropical atmospheric 30-60 oscil     

NUMERICAL SIMULATION OF THE TROPICAL INTRASEASONAL OSCILLATION AND THE EFFECT OF WARM SST

An atmospheric general circulation model is used in a series of three experiments to simulate the intraseasonaloscillation in the tropical atmosphere.Analyses of the model daily data show that various physical variables,from sever-al different regions,exhibit fluctuations with a spectral peak between 30 and 60 days.This represents a 30—60 dayoscillation in the tropical atmosphere and possesses several features which are consistent with observations.These in-clude a horizontal structure dominated by zonal wavenumber 1 and a vertical structure which is predominantlybaroclinic.The effect of warm SST (sea surface temperature) anomalies on the 30—60 day oscillation in the tropical atmos-phere is also simulated by prescribing global SST as observed in 1983.This has the effect of weakening the oscillationwhile at the same time the vertical structure becomes less baroclinic.The importance of cumulus convection to the propagational characteristics of this oscillation is demonstrated by acomparison of results based on different parameterizations for convection.In one case,where the maximum convectionover the Pacific is simulated to be too far east,the simulated 30—60 day oscillation shows evidence of westward propa-gation.In the second case,where the convection maximum is located near the observed position in the western Pacific,there is more clearly evidence of eastward propagation.Both results suggest that the location of maximum convection in the Pacific can have an important influence on thestrength,structure and propagation of the 30—60 day oscillation.     

青藏高原春季500 hPa纬向风季节内振荡特征及其与我国南方降水的关系

利用NCEP/NCAR日平均再分析资料及中国753个测站日降水资料,采用带通滤波、小波功率谱、合成分析等方法研究了青藏高原春季500 hPa纬向风季节内振荡特征及其与我国南方降水的关系.结果表明,青藏高原春季500 hPa纬向风存在明显的10~30 d季节内振荡特征,该低频振荡主要表现为自西向东和自北向南的传播特征.通过位相合成分析发现,这种季节内振荡对我国南方春季降水有重要影响.当高原500 hPa纬向风季节内振荡处于2~3位相时(即高原上盛行西风异常),对应于我国南方地区春季降水明显偏多;反之,当季节内振荡处于相反位相时(6~7位相,即高原上盛行东风异常),对应于我国南方春季降水明显偏少.南方春季最大正(负)异常降水的出现滞后于高原季节内振荡的峰值(谷值)位相,其滞后时间为2 d.分析结果还表明,高原上空纬向风的季节内振荡活动主要通过中纬度大尺度环流异常对我国南方春季降水产生影响.     

长江中游和下游夏季降水季节内振荡的差异

利用1979~2013年中国站点逐日降水资料和NCEP/NCAR再分析资料,对长江中下游夏季降水的季节内振荡最显著周期进行了分析研究。结果表明长江中游最显著周期为10~30天,长江下游最显著周期为30~60天。为了揭示这种差异产生的物理原因,进一步利用位相合成的方法对这两个区域不同周期的季节内振荡降水、高低空风场和高度场以及垂直结构和水汽等循环过程的演变特征进行分析。在200 hPa环流场上,长江中游的降水主要受到高纬度自西向东传播的波列影响,而长江下游的降水与鄂霍次克海的高度场的变化相关。在风场的垂直涡度和散度的位相结构演变过程中,10~30天的垂直涡度和散度有自北向南的移动,30~60天的垂直涡度和散度在长江以南地区有自南向北的传播。水汽输送的位相发展过程表明,长江中游的水汽分别来自于南海的向北输送和长江以北地区向南的水汽输送;长江下游地区的水汽则主要来自于热带东印度洋经孟加拉湾的向东输送并在南海的北向输送,以及西太平洋水汽向西输送到南海再向长江下游的输送。从高层大尺度环流场和整层积分的水汽通量输送上解释了长江中游10~30天降水的自北向南移动,和长江下游30~60天降水自南向北传播的原因。     

大气季节内振荡及其重要作用

大气季节内振荡(ISO)是上世纪80年代以来大气科学的重要前沿研究课题.作者系统地回顾和总结了十多年来在大气季节内振荡(ISO)及其对其他气候系统的重要作用方面的主要研究工作和成果,尤其是新近的研究成果.主要包括热带大气ISO的基本特征和主要活动规律;中高纬度大气ISO的基本特征和活动规律,以及与热带大气ISO的主要差别;全球大气低频(30～60天)遥相关特征;大气季节内振荡的动力学机制;大气季节内振荡对南海(亚洲)夏季风爆发,以及对南海(东亚)夏季风异常的重要作用;热带大气季节内振荡与El Nino(L     

夏季青藏高原热源低频振荡对我国东部降水的影响

利用NCEP/NCAR逐日再分析资料及长江中下游降水资料, 诊断和分析了长江中下游地区旱年1978年、涝年1999年青藏高原东部大气热源与降水季节内振荡的关系, 并着重讨论了青藏高原低频热力过程的经、纬向传播, 结果表明:1978年夏季青藏高原东部大气热源存在10~20 d周期为主的振荡, 交叉谱分析表明:青藏高原东部热源与长江中下游降水在10~20 d频段存在显著相关, 且青藏高原激发的周期为10~20 d的低频振荡热源在纬向上呈现出驻波形式; 1999年夏季青藏高原东部热源存在30~60 d周期为主的振荡, 热源与长江中下游降水在30~60 d频段存在显著相关。     

热带东风急流的气候学和中期振荡

本文用13年夏半年(5—10月)月平均风场和两年逐日风场资料研究了200hPa南亚热带东风急流的气候学特征和中期振荡过程。研究表明,南亚夏季热带东风急流显著的非季节性变动和年际差异与低纬对流层高层大尺度环流变化和南亚夏季风活动密切相关,相对于多年平均而言,存在5类异常的东风急流。 各种分析表明,热带东风带存在三种主要的中期振荡。准50天周期振荡与夏季南亚对流层上部大尺度散度场的变化相关联,表现为十分显著的向南的位相传播。准50天和25天振荡均存在显著的年际变化。准50天周期振荡系统性不强的年份,准25天周期振荡是低纬行星波的主要振荡,在东风急流区除表现为系统性向西传播外也表现为向南的位相传播。准双周振荡在东风带一般向西传播。      

1983与1985年夏季北半球500hPa高度场大气低频波的振荡特征

本文利用观测资料分析了1983与1985年夏季半球500hPa高度场大气低频波的振荡特征。结果表明，1983年（厄尔尼诺年）夏季热带中、东太平洋和印度洋以及东亚季风区上空的低频振荡比1985年（反厄尔尼诺年）夏季的低频振荡强，而热带西太平洋的情况恰好相反。这是由于反厄尔尼诺年夏季热带西太平洋对流活动强盛所致。分析结果还表明：1983年夏季低频波基本上是东传的；1985年夏季，在中高纬度地区低频波主要还是东传，热带是西传。西藏高原是大气低频振荡的汇区。     

热带大气季节内振荡的进一步分析

利用ＥＣＭＷＦ的格点资料对热带大气季节内振荡作了进一步分析研究,表明热带大气季节内振荡既有Ｋｅｌｖｉｎ波型扰动,也有Ｒｏｓｓｂｙ波型扰动;影响热带大气季节内振荡移动的主要因素有扰动波型和积云对流活动的异常;伴随ＥｌＮｉｎｏ事件的发生,热带大气季节内振荡的动能急剧减小,而准定常扰动动能急剧增大,既反映了热带大气季节内振荡对ＥｌＮｉｎｏ的激发作用,也说明了在ＥｌＮｉｎｏ期间热带大气季节内振荡偏弱的原因。     

Quasi-two weeks oscillation in the tropical atmosphere

Summary Based on analysis of ECMWF data (1981–1987) and numerical simulations using a general circulation model (GCM), a quasi-two-week (10–20 day) oscillation in the tropical atmosphere is studied in this paper. It is shown that the kinetic energy of the quasi-two-week oscillation is larger than that of the intraseasonal oscillation, and is another important low-frequency system in the tropical atmosphere. By comparing it with the intraseasonal oscillation, some obvious differences can be found. For example, the zonal scale of the quasi-two-week oscillation is dominated by perturbations with wavenumber 2–4; its vertical structure mainly shows barotropic features; the zonal propagation is basically westward; and its meridional and zonal components the same size.With 10 Figures