The Propagation and Transport Effect of Planetary Waves in the Northern Hemisphere Winter

Based on the transformed Eulerian-mean equations, the dynamics of planetary waves are discussed. Both observations and simulations indicate that in the Northern Hemisphere winter there are two waveguides for the meridional propagation of quasi-stationary planetary waves. One is the high latitude waveguide, and the other is the low latitude waveguide. These results are in good agreement with theoretical analysis. Moreover, the convergence of EP flux indicates that the stratospheric sudden warming is the result of anomalous planetary wave propagation along the high latitude waveguide and its interaction with mean flows. The tropical quasi-biennial oscillation (QBO) winds, which represent one significant variation of zonal flow in the lower stratosphere at low latitudes, can influence the low latitude waveguide of planetary wave propagation. Our results of the wave-mean flow coupled model show that these tropical winds can also modulate the high latitude waveguide significantly in the case of wave-mean flow interaction.The transport effect of planetary waves on ozone is also analyzed. The residual mean circulation forced by planetary waves indicates that there is strong transport circulation for the dissipative planetary waves. Under the forcing of northward eddy heat transport, a positive transport circulation can result which rises at low latitudes and sinks at high latitudes. At the same time, the modification of planetary wave propagation by the equatorial QBO winds is shown to have an important impact on the transport circulation. The model results indicate that the meridional transport is amplified during the easterly phase of the QBO. This mechanism may explain the interannual variability of ozone in the stratosphere at high latitudes.

ANALYSES OF THE DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE——Ⅱ.VERTICAL PROPAGATION OF PLANETARY WAVES

A linear,hemispheric and stationary spectral model with multilayers in the vertical was employed to simulate the vertical propagation of waves triggered by mountains.Results show that,in cooperation with the East Asia zonal mean flow,Tibetan Plateau can excite a strong wavenumber 1 perturbation in the stratosphere with its ridge and trough lo- cated over the Pacific and Atlantic Oceans respectively.On the other hand,the stratospheric wavenumber 1 perturbation caused by the mechanical forcing of the Rocky Mountains in cooperation with the North America zonal mean flow is very weak.Calculations from observational data of the vertical profile of critical wavenumber for vertically propagating waves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North America tropopause up- wards,whereas it can freely propagate through the East Asia tropopause into the stratosphere.Two-dimensional E-P cross-sections obtained from both observational data and simulated results also demonstrate that waves excited by the Rocky Mountains are refracted towards low latitudes in the troposphere during their upward propagation:whereas,in addition to the above mentioned equatorward leaning branch,the wavenumber 1 and 2 planetary waves excited by the Tibetan Plateau possess another branch which is refracted to high latitudes during upward propagation and penetrates the tropopause into the stratosphere.It is therefore concluded that the difference in the horizontal and vertical wave propagations in the two hemispheres is a result of the different dynamical forcing induced by the two main mountains in the Northern Hemisphere.

Quasi-stationary planetary wave-mean flow interactions in the Northern Hemisphere stratosphere and their responses to ENSO events

Based on the ERA-40 reanalysis data from the European Centre for Medium-Range Weather Forecasts and the output of ECHAM5/MPI-OM, this study investigated the interactions between the quasi-stationary planetary wave （SPW） and mean flow, and their responses to E1 Nifio-Southern Oscillation （ENSO） events in the northern hemispheric stratosphere. Results show that the activity of SPW is the strongest in winter, when the SPW propagates along the polar waveguide into the stratosphere and along the low-latitude waveguide to the subtropical tropopause. The analysis of three dimensional SPW structure indicates that the main sources of SPW activity are located over the Eurasian continent and the North Pacific north of 45°N. On the one hand, the two waveguides of the SPW reflect the influence of mean flow on the propagation of the SPW. On the other hand, the upward propagating SPW can interact with the stratospheric mean flow, leading to deceleration of the zonal mean westerly. Furthermore, the SPW exhibits clear responses to ENSO events. During E1 Nifio winters, the SPW in the strat- osphere tends to propagate more upward and poleward. Its interactions with mean flow can induce a dipole pattern in zonal mean zonal winds, with accelerated westerly winds at low-middle latitudes and decelerated westerly winds at high latitudes. The ECHAM5/MPI-OM model reproduces the climatology of the SPW well. Although the simulated SPW is slightly weaker than the observations in the stratosphere, the model＇s performance has significant improvements compared with other GCMs used in previous studies. However, there are still some problems in the responses of the SPW to ENSO in the model. Although the model reproduces the responses of both the amplitude and the SPW-mean flow interactions to ENSO well in the troposphere, the stratospheric responses are quite weak. Therefore, further studies are needed to improve the simulation of the stratospheric atmospheric circulation and related dynamical processes.

Wave Sources, Energy Propagation and Conversion for Anomalous Rossby Wave Activities Along the West Asian Jet Stream

Characteristics of the wave sources, energy propagation and conversion for anomalous Rossby wave activities （RWAs） along the West Asian jet stream （WAJS） in summer are examined based on the NCEP/NCAR （National Centers for Environmental Prediction/National Center for Atmospheric Research） reanalysis data from 1958 to 2003, using the vorticity source equation, the Eliassen-Palm （EP） flux, and the wave energy equation under diabatic heating. The study aims to find the dynamical causes for RWA anomalies along the WAJS and to improve the understanding of mid-high latitude circulation anomalies. The results show that the negative vorticity source and the strong EP flux divergence over the Mediterranean Sea and the North Atlantic Scandinavian Peninsula area act as the wave sources for RWA anomalies along the WAJS. When the intensity and position of the wave sources are anomalous, the excited eastward-propagating RWA along the WAJS also behaves anomalously. In strong （weak） years of RWA, Rossby waves excited by the strong divergence of EP fluxes over the Iceland Scandinavian Peninsula area （east to the Scandinavian Peninsula） propagate eastward and southeastward. The eastward propagating waves become strengthened （weakened） after turning southeastward near the Ural Mountains and then entering the Asian subtropical westerly jet stream （ASWJS） over the Caspian Sea-Aral Sea-Xinjiang. The southeastward propagating waves also strengthen （weaken） after directly entering the ASWJS over the eastern Mediterranean-the Black Sea. Furthermore, the divergence of EP fluxes over the Mediterranean also strengthens （weakens） in the strong （weak） years, so they jointly bring about the strong （weak） RWA along the WAJS. Finally, the perturbation available potential energy （PAPE） along the WAJS （15°- 60°E） produced by diabatic heating, is far greater than the conversion from the kinetic energy of the basic flow into the perturbation kinetic energy and from the available potential energy of the basic flow into PAPE. The RWA along the WAJS looks stronger （weaker） than normal when the PAPEs produced by diabatic heating over the Iranian Plateau and West Asia significantly strengthen （weaken）, and therefore they are also the energy sources of RWA anomalies.

2009年秋至2010年春我国西南地区严重干旱的成因分析

我国西南地区从2009年秋季到2010年春季发生了严重干旱,这次干旱无论持续时间和发生区域或降水减少程度都是近50年来所罕见的,因而本文利用ERA-40再分析资料和海温资料从热带西太平洋和热带印度洋热力异常对热带西太平洋和南亚上空大气环流的影响来分析了这次西南地区干旱发生的成因。分析结果表明:从2009年秋到2010年春季,热带西太平洋和热带印度洋处于升温状态,它使得热带西太平洋上空产生反气旋异常环流,造成了西南气流异常在我国东南沿海加强,而华南和华中地区上空处于低槽控制,因而在高原东部为槽后西北气流和下沉气流所控制,造成了从孟加拉湾来的水汽很难到达云贵高原,从而引起了此区域降水长期偏少。并且,分析结果还表明了中高纬度地区的环流异常对此次严重干旱也有重要影响。由于从2009年冬季到2010年春季中高纬度准定常行星波传播的极地波导偏强,而低纬波导偏弱,这导致波的E-P通量在60°N附近对流层和平流层为辐合,而在35°N附近对流层中、上层为辐散,从而引起纬向平均西风在60°N附近对流层和平流层减弱,而在35°N附近对流层中、上层加强,造成了北极涛动(AO)为很大的负值。由于AO为负值,东亚冬季冷空气活动强且路径偏东,使得到达西南地区冷空气偏弱,从而引起西南地区持续性严重干旱的发生。

热带准两年振荡影响北半球冬季大气环流的诊断分析

利用NCEP/NCAR再分析资料 ,首先讨论了热带纬向风准两年振荡 (QBO)的东、西风位相的划分标准。结果发现 ,赤道 5 0hPa的风与西风深厚度关系最密切 ,即赤道 5 0hPa的纬向平均风为西 (东 )风时往往代表平流层下层为一层深厚的西 (东 )风。在此基础上诊断分析了 1 95 8/1 95 9～ 1 997/1 998年共 40个冬季中热带纬向风QBO对北半球中高纬度地区纬向平均环流和准定常行星波传播的影响。诊断分析表明 ,热带QBO对北半球冬季大气环流的影响主要表现在平流层和对流层上层。热带QBO的东风位相年与西风位相年相比 ,中高纬地区的绕极西风环流明显减弱 ,中低纬地区则出现相反变化 ,从而在平流层的纬向平均环流分布上呈现偶极子形式。纬向平均流的这种年际变化可以很好地用中高纬度准定常行星波传播的异常加以解释 ,QBO的东风位相年和西风位相年相比 ,中高纬准定常行星波向极地的传播更强 ,从而在高纬度平流层产生异常的E P通量辐合 ,波 -流相互作用的结果使得西风减弱。但是热带纬向风QBO的影响在 1 95 8/1 95 9～ 1 997/1 998年的前后 2 0年有所差异。后 2 0年相对于前 2 0年而言 ,东西风位相的差异有所减小 ,Holton Tan振荡明显减弱 ;就行星波传播而言 ,东风位相年下 ,前 2 0年行星波向上传播较弱 ,而后 2 0年则以?

水平非均匀基流中行星波的传播

行星波传播理论虽然已有很多研究,但是大多以纬向对称基流为主,无法解释东西风带之间相互作用的事实.鉴于此,本文从理论上系统讨论了纬向对称和水平非均匀基流中定常和非定常波动的传播特征.首先,对纬向对称基流中波动传播的周期特征进行分析后发现,西风中位相东传超长波周期大于30d,而东风中位相西传超长波的周期则小于30d.之后,从传播的空间以及周期特征等方面系统研究了水平非均匀基流中球面波动传播理论,得到以下结论:经向基流使得定常波可以穿越东风带,在南北两半球间传播,为东西风带之间的相互作用提供了理论解释;强的经向流使得波动传播具有单向性;亚澳季风区低层纬向1波呈低频特征.

低电离层中的行星波扰动及其垂直传播

根据武昌电离层观象台接收的罗兰－ＣＬＦ无线电波的传播资料，利用小波分析方法，研究了１９８５年和１９８６年冬季的低电离层中的行星波扰动及其垂直传播．结果表明：（１）两个冬季中，在７５ｋｍ和９５ｋｍ高度上，均存在明显的行星波扰动，主要成分是５—１０天和１０—２０天周期的波动，扰动幅度随高度增长，但增长值小于理论增长值；（２）在７５ｋｍ高度上的扰动和９５ｋｍ高度上的扰动，具有十分相似的扰动形态．根据行星波的垂直传播理论和实验资料，得到它们的垂直传播速度为２．７—３．７ｋｍ／ｄ，垂直波长为４０—６０ｋｍ．

大气Rossby波动力学的研究进展

Rossby波是旋转大气和海洋中的一类重要波动,在天气和气候演变中起有重要的作用。该文介绍了北半球中纬度地区的两类重要Rossby波——斜压不稳定波和准定常行星波,在最近20余年来取得的一些重要研究进展。文中涉及的主要研究领域有:斜压不稳定波包动力学、湿斜压过程对斜压不稳定波的作用、北半球风暴轴动力学、斜压波包与高影响天气的预报、准定常行星波的形成机理、准定常行星波的水平传播与能量频散、准定常行星波的垂直传播与能量频散、三维准定常行星波的传播与能量频散。

中层大气行星波的跨赤道传播

使用一个全球原始方程半谱模式，模拟了行星波的跨赤道传播．结果指出：冬半球对流层顶附近准定常行星波的幅度起伏和相位变化，可以造成中层大气行星波的跨赤道传播，并且在夏半球形成瞬变行星波．所得结果为中层大气行星波的跨赤道传播、夏半球行星波的形成和南北半球之间的耦合提供了一种物理机制．

南半球对流层大气对热带太平洋—印度洋海温异常综合模的响应及其机制解释

利用NOAA SST及NCEP/NCAR再分析资料,研究了热带太平洋—印度洋海温异常综合模和南半球对流层大气之间的遥相关模态并对其进行了机制解释。首先通过相关和合成分析,给出了遥相关的空间模态,结果表明：北半球秋、冬季,在南半球对流层大气存在和热带太平洋—印度洋海温异常综合模密切联系的遥相关作用中心,该中心的分布构成一列明显的从赤道中太平洋出发,最终到达非洲中南部及赤道印度洋的Rossby波列,将赤道太平洋、印度洋与南半球中高纬度大气连接起来,起到了类似＂大气桥＂的作用。而单纯IOD和单纯EN-SO均难以在南半球对流层激发出遥相关波列,进一步证实了两者共同作用的影响。其次,利用行星波能量传播理论对两者之间的遥相关进行了机制分析,发现纬向波数为1~3的大气行星波的能量传播是热带太平洋—印度洋海温异常综合模与南半球对流层大气之间遥相关的一种可能的联系方式。

大尺度行星波跨赤道传播的E-P通量诊断

利用Nimbus－7卫星温度探测资料，计算了平流层和中间层的风场、位势高度扰动场，进行了行星波E－P通量分析．结果表明，中层大气中的准定常行星波，其定常分量不能跨过赤道上空的零风线，由于其幅度的起伏和相位的变化，激发的瞬变行星波分量不受赤道零风线的限制，可以从冬半球向夏半球传播，也可以从夏半球向冬半球传播．这种跨赤道传播为夏半球行星波的能量来源提供了一种解释．

大气准两年振荡对赤道行星波上传的影响

本文讨论了热带大气行星波在ＱＢＯ风场中向上传播的规律，并运用数值模拟的方法，得到了开尔文波和混合罗斯贝重力波在ＱＢＯ不同相位下交替上传的结果．

1980—2019年夏季东亚大槽减弱及其与北极海冰变化的关系

利用1979—2019年NECP/DOE(NCEP2)月平均500 hPa位势高度数据,基于各季节东亚大槽的频率分布特征,客观地确定了东亚大槽的槽区范围和东亚大槽强度指数。在此基础上,分析了夏季东亚大槽减弱与北极海冰变化的关系,结果表明:1980—2019年各季节东亚大槽强度均存在年代际减弱趋势,其中夏季减弱趋势最显著,可能与全球变暖导致的北极海冰快速融化有关。在年际尺度上,夏季东亚大槽强度减弱主要受前期夏秋季海冰的影响。当前一年夏季北极涛动为负位相时,受北极高压异常影响,海冰分布呈现格陵兰岛东部和加拿大群岛高密集度冰区海冰增加,欧亚-太平洋扇区季节性冰区海冰减少的偶极子型分布特点。在海冰反照率正反馈机制的作用下,秋季融冰区范围扩大,有利于极区的行星波1波异常信号上传至平流层。春季平流层的位势高度正异常信号在有利的行星Rossby波垂直传播条件下向南扩张并在东亚一侧下传,且一直持续到夏季,直接影响到东亚中纬度地区,使得东亚大槽减弱。

Three-Dimensional Dynamic Features of Two Arctic Oscillation Types

We investigated the differences between stratospheric （S-type） and tropospheric （T-type） Arctic Oscillation （AO） events on the intraseasonal time scale, in terms of their influences on surface air temperature （SAT） over the Northern Henfisphere and the dynamic features associated with their spatial structures. S-type AO events showed a stratosphere-troposphere coupled structure, while T-type events exhibited a stratosphere-troposphere uncoupled structure. The annular SAT anomalies over the Northern Hemisphere were found to be associated with S-type AO events, whereas such an annular feature was substantially de- structed in T-type AO events. The different horizontal structures in the troposphere of the two types could mainly be attributed to transient eddy feedback forcing. As for the vertically uncoupled structure of T- type events, the underlying dynamical features that differentiate them from S-type events lie in the vertical propagation of zonally confined Rossby waves. In T-type events, the zonally confined Rossby wave packets can emanate from the significant height anomalies over Northeast Asia, where one vertical waveguide exists, and then propagate upward into the stratosphere. In contrast, such a vertical propagation was not evident for S-type events. The stratospheric anomalies associated with the upward injection of the zonally confined Rossby waves from the troposphere in T-type events can further induce the anomalous vertical propagation of planetary waves （PWs） through the interference between the climatological-mean PWs and anomalous PWs, leading to the final stratosphere troposphere uncoupled structure of T-type events.

A dynamic view of the tropospheric teleconnection between IOD and the Pacific Ocean

The tropospheric teleconnection pattern be-tween the Indian Ocean Dipole (IOD) and the Pacific Ocean was studied using GISST and NECP/NCAR reanalysis data. Results show that a structure of Rossby wave train extends from the tropical Indian Ocean over southern subtropical regions of Australia and Pacific Ocean to the tropical Pacific Ocean, where a strong correlation between IOD and geo- potential height (GH) anomaly of Pacific Ocean exists. En-ergy propagating pathways of the planetary wave with wave numbers 1―3 are qualitatively in agreement with the Rossby wave train, which implies that the energy propagation of the stationary planetary wave could be responsible for the tro-pospheric teleconnection between IOD and tropical Pacific Ocean.