冬季平流层热源及其对环流的影响

本文采用一个可用于大气定常波数值试验的线性化原始方程三维谱模式,研究了平流层环流对平流层内各种定常大尺度加热分布的响应.相对于北半球冬季纬向对称的基本状态,讨论了大尺度加热分布对冬季平流层大尺度运动的影响.发现平流层大气除受到对流层的热力强迫作用外,还将受到平流层内热源的影响,由于这种热力强迫作用,在平流层出现了1-2波的环流,但对对流层的环流影响却不大.引入臭氧加热率,使我们进一步证实了臭氧做为平流层中重要的增温因子所起的作用.数值试验的结果表明,臭氧对平流层环流的形成和维持,有着重要的贡献.     

冬、夏平流层定常环流的数值模拟

本文应用一个包括Rayleigh摩擦、Newton冷却及水平涡旋热量扩散准地转34层球坐标模式来模拟北半球冬、夏两季平流层大气环流。利用Lindzen和Kuo所提出的方法来解这样一种复什二阶偏微分方程。 计算结果表明:由模式计算所得到的冬、夏两季北半球实际地形与实际热源强迫所产生的定常行星波振幅与位相的垂直分布及在平流层定常扰动系统的分布均与实际观测得到的分布相一致,这说明平流层的定常扰动分布主要还是由于对流层内地形与热源强迫所产生的定常扰动往平流层传播的结果。     

模式大气对于大尺度地形动力强迫作用的非线性响应

本文与文献[1]相对应,利用一个非线性初始方程谱模式,研究了中、高纬度理想化的大尺度地形以及北半球实际地形的动力强迫作用对于冬季行星尺度的大气定常波的影响。计算结果证实,根据线性模式的数值试验结果所做的定性分析在非线性情形下仍然是成立的,同时,非线性扰动流场也与线性流场有明显的差异,在纬向平场基本气流相对较弱的地区或垂直层次上差异尤为显著。数值试验表明,北半球实际地形强迫的大尺度扰动,在对流层低层以及对流层上部的中、高纬均主要表现出纬向波数为2的行星波,但是在对流层上部的低纬地区3波分量比较明显。中、高纬的大地形动力强迫作用,对于低纬太平洋高空的反气旋和气旋环流的形成有重要的贡献。      

冬季平流层大气环流平均槽脊的形成

本文利用一个π坐标的3层模式描写对流层和平流层的大气运动。由线性化方程的解,讨论了大尺度地形和加热分布的控制作用和定常扰动。 结果得到:(1)地形和对流层热源的超长波扰动,可以传播到平流层中,扰动振幅向上增强,地形波的位相近于垂直,而热源波的位相随高度向西倾斜。(2)地形和热源对平流层平均槽脊的形成都是重要的。但对流层和平流层大气的热源、热汇对30mb阿留申高压的形成起了主要作用。(3)平流层扰动的强大振幅主要是由于平流层大气密度很小所造成的。     

模式大气对于非绝热加热场的线性响应

本文利用一个包含了Newton冷却、Rayleigh摩擦以及▽~4型水平扩散等耗散作用的定常、斜压、线性初始方程三维谱模式,研究了热带和中纬度理想热源以及1979年1月北半球平均非绝热加热场对于冬季行星尺度的大气定常波的影响。数值试验结果表明,热力强迫作用的重要性可以与北半球大地形的动力强迫作用相比拟。利用1979年1月平均加热场作为强迫函数计算得到的强迫扰动,主要表现为纬向波数为2的行星波,并具有明显的斜压结构。热带地区纬向非均匀热源所激发的近似地沿大园路径传播的Rossby波列,对于热带区域与中、高纬大气之间的遥相关现象提供了一种可能的解释,同时,热带外区域的加热场对于整个半球范围内定常波的维持有着更显著的贡献。     

冬季低纬度热源异常在北半球对流层大气环流异常中的作用

本文首先从理论上讨论了北半球冬季低纬度强迫源与中纬度强迫源强迫所产生的准定常行星波在实际基本气流中传播路径及其振幅分布的差异,指出冬季低纬度热源异常将对北半球中、高纬度对流层大气环流的异常起很大影响,而中纬度热源异常将对平流层环流异常起很大作用。 本文应用一个包括Rayleigh摩擦、Newton冷却及水平涡旋热力扩散准地转34层球坐标模式分别计算了冬季低纬度热源异常与中纬度热源异常所造成北半球扰动系统的异常情况,计算结果表明了冬季低纬度热源异常将对中、高纬度对流层大气环流异常起很大作用,热带太平洋上空热源异常将产生PNA型环流异常。     

夏季青藏高原动力和热力的强迫定常扰动

本文应用一个球面和σ坐标原始方程线性定常模式,模拟夏季青藏高原的动力和热力强迫作用下的定常扰动.计算得到的定常扰动,在对流层上层槽脊分布和实况基本相符,但南亚高压的位置稍偏东,中太平洋高空槽较弱.在对流层中层计算的扰动振幅较实况强,特别是西太平洋副高.对偏差的可能原因进行了讨论.文中比较了不同基本气流、热源的垂直分布和热力耗散的影响,结果表明不同的热源垂直分布可以影响定常扰动的位相分布;还指出线性模式中,随高度增强的热力耗散机制对解释定常扰动的位相和结构可能是重要的.     

夏季西藏高原与落基山脉对北半球定常行星波形成的动力作用

本文应用一个包括Rayleigh摩擦、Newton冷却与水平涡旋热力扩散准地转34层球坐标模式来研究夏季西藏高原与落基山脉地形强迫对于夏季北半球定常行星波形成的作用. 计算结果表明:夏季北半球地形强迫所产生的定常行星波的振幅与位相分布与冬季的分布是很不一样的,夏季地形强迫所产生的定常行星波主要集中在亚热带的对流层,并且可以发现纬向波数k=1与k=2的振幅在高纬度存在着第二峰值.计算结果还表明了夏季西藏高原与落基山对于夏季定常行星波的形成起了重要作用.     

平流层臭氧变化对对流层气候影响的研究进展

平流层对对流层的作用是准确评估、预测对流层气候变化的一个重要方面。其中平流层成分尤其是臭氧的变化,可以改变平流层乃至对流层的辐射平衡,从而影响平流层、对流层的热动力过程。本文从辐射、动力2个角度介绍了平流层臭氧影响对流层气候变化的若干研究进展。平流层臭氧可以通过长短波辐射的方式对对流层大气造成辐射强迫,利用大气化学气候模式可以定量计算平流层臭氧变化引起的辐射强迫,但是辐射强迫的估算受模式中辐射传输模块本身缺陷的影响存在不确定性。动力方面,平流层臭氧变化产生的辐射效应可以改变温度的垂直和经向梯度,造成波折射指数的变化,进而影响平流层甚至对流层内波的折射与反射,通过上对流层下平流层区域内的波—流相互作用,对对流层气候产生影响。另外,南极臭氧损耗可通过大气环状模影响冬春季中高纬度对流层的天气气候,但是其影响的强度大小以及物理机制仍需进一步的确认。值得注意的是,北极平流层臭氧的变化与北半球中高纬度气候变化之间的关系相比南半球要更加复杂,需要更为深入的研究。     

平流层-对流层相互作用研究进展：等熵位涡理论的应用及青藏高原影响

系统介绍了近年来应用等熵位涡理论研究平流层-对流层动力相互作用所发现的一些新的事实和机理,包括平流层冬季极涡振荡过程中平流层、对流层环流异常的时空传播特征,以及等熵质量理论框架下的平流层-对流层动力耦合机理,还介绍了影响平流层环流年际尺度异常的因子及影响过程。回顾了夏季青藏高原的热力作用所激发的负位涡强迫源对东亚及全球大气环流的影响。并基于对夏季高原周边等熵位涡经向输送垂直分布的诊断进一步说明,夏季青藏高原的存在使高原东缘及东亚地区成为平流层和对流层物质交换的独特区域,探讨了夏季青藏高原影响平流层-对流层动力耦合的一种重要途径及其影响全球气候的重要意义。     

Planetary stationary waves in the atmosphere Part II: Thermal stationary waves

The contribution of thermal forcing to the planetary stationary waves will be studied also by assuming that heat balance in stationary waves over zonally asymmetric thermal forcing must be maintained over a long time period. Us-ing the same model of geostrophic waves introduced in Part I, we may explain successfully the observed and simulated responses to the thermal forcing in the atmosphere, such as the wave 1 structure at high levels of middle latitudes, the seasonal changes of the stationary waves in the Northern Hemisphere, the opposite phase distributions of stationary waves at high and low levels of the subtropical regions in both hemispheres and so on.     

COMPARISON OF LINEAR AND NONLINEAR WAVES ASSOCIATED WITH STEADY-STATE FORCING SOURCES

Low-frequency phenomena in the atmosphere are intimately related to stationary waves and, in a sense, the former may even be viewed as the time-varying part of the quasi-stationary waves themselves, Much attention has been focused on nonlinear interactions in the conceptual study on stationary waves. Linear and nonlinear primitive-equation baroclinic spectral models are adopted to investigate the response of stationary waves to largescale mechanical forcing and steady-state thermal forcing, both idealized and realistic, followed by calculations of the EP fluxes and three-dimensional wave activity fluxes(Plumb, 1985) for both the linear and nonlinear solutions. Results show that when the forcing source grows intense enough to be comparable to the real one, non-linear interaction becomes very important, especially for the maintenance of tropical and polar stationary waves. Care should be taken, however, in using the EP flux and Plumb's 3-D flux for diagnostic analysis of observational data as they are highly sensitive to nonlinear interaction.     

经圈环流对定常波传播的影响

在一般斜压大气中，基本气流中包含经圈环流时，定常波传播不仅能穿过东风带，而且明显增强。在基流含有经圈环流的情况下，北半球中纬度地形强迫可引起低纬大气的显著响应，这表明经圈环流在中低纬定常响应的相互联系中起着重要作用；北半球中纬度热力强迫可产生类似北半球夏季季风环流的波列分布，这说明经圈环流在夏季季风环流的形成中起着一定的作用；在赤道东太平洋加热强迫情况下，在冬半球可引起ＰＮＡ型的定常波传播波列，而在夏半球却没有明显的ＰＮＡ特征。这表明经圈环流对冬、夏半球的定常波传播路径有着显著的影响。     

THE ROLE OF THE MERIDIONAL CIRCULATION IN STATIONARY WAVE PROPAGATION

In a general baroclinic atmosphere,when the basic state includes meridional circulation,the sta-tionary waves might not only pass through the equatorial easterlies,but also strengthen significantly.The orographic forcing in the Northern Hemisphere mid-latitude might cause marked responses in thelow latitude atmosphere.This suggests that the meridional circulation plays an important role in theconnection of stationary responses in mid and low latitudes,and so does the heating forcing in theNorthern Hemisphere mid-latitude.Forced by the heating forcing in the Northern Hemisphere mid-latitude,the features similar to the Northern Hemisphere summer monsoon circulation can be ob-tained.It appears that the meridional circulation plays certain role in the formation of summer mon-soon circulation.The heating anomaly forcing located at the eastern equatorial Pacific makes the sta-tionary waves present PNA(Pacific-North America)pattern in the winter hemisphere,but it doesnot in the summer hemisphere.It suggests that the meridional circulation has a marked influence onthe route of stationary wave propagation both in the winter and summer hemispheres.     

东西风廓线特征与大气运动平衡态定常波的相关关系及共振条件的研究

本文采用简化数学模型探讨了东、西风廓线特征与外源强迫下大气环流平衡态定常波结构的相关关系。文中采用实际观测资料研究了西风廓线特征与大气环流型季节特征之间的联系。研究表明,西风廓线冬、夏季节差异与中、高纬度西风槽“冬三夏四”波数差气候特征有关,且低纬强东风切变可作为赤道东风波周期振荡成因之一。冬夏西风廓线季节特征可导致大地形强迫效应、海陆加热因子影响作用的显著季节差异。研究还揭示了大气环流型优势波转换的基流特征影响效应,并导出了流场与纬向加热强迫源共振状态的西风廓线特征函数与临界曲线。     

平流层大气动力学及其与对流层大气相互作用的研究:进展与问题

本文综述了近年来关于平流层大气动力学及其与对流层大气相互作用动力过程的研究进展,特别是回顾了近年来关于平流层大气环流和行星波动力学、热带平流层大气波动及其与基本气流相互作用、平流层大气环流变异对对流层环流和气候变异的影响及其动力过程、平流层大气数值模拟以及在全球变暖背景下平流层大气的长期演变趋势预估等的研究进展。最近的研究揭示了大气准定常行星波传播波导的振荡现象、重力波在热带平流层准两年振荡和全球物质输送中的作用、平流层长期的变冷趋势变化、平流层在对流层天气和气候变化中的作用等现象,表明了平流层大气动力学研究的重要性。平流层大气动力学的深入研究,以及对数值模式中平流层模拟性能的提高,最终都会推动整个大气科学和气候变化研究的进一步发展。     

冬季北半球地形与定常热源强迫所产生的定常行星波及其动量通量、热量通量的计算

本文应用一个包括Rayleigh摩擦、牛顿冷却、水平涡旋热量扩散、定常、准地转、34层球坐标模式来研究冬季北半球地形与定常热源强迫所产生的定常行星波。 本文计算了强迫所产生的定常行星波引起的动量通量与热量通量。计算结果与观测结果比较一致。 计算结果表明:最大向北的动量通量与热量通量位于平流层。     

Upscale effects in simulations of tropical convection on an equatorial beta-plane

A cloud-resolving model is configured to span the full meridional extent of the tropical atmosphere and have sufficient zonal extent to permit the representation of tropical cloud super-clusters. This is made computationally feasible by the use of anisotropic horizontal grids where one horizontal coordinate direction has over an order of magnitude finer resolution than the other direction. Typically, the meridional direction is chosen to have the coarser resolution (40 km grid spacing) and the zonal direction has enough resolution to ‘permit’ crude convective squall line ascent (1 km grid spacing). The aim was to run in cloud-resolving model (CRM) mode yet still have sufficient meridional resolution and extent to capture the equatorial trapped waves and the Hadley circulation. The large-scale circulation is driven by imposed uniform tropospheric cooling in conjunction with a fixed sea surface temperature distribution. At quasi-equilibrium the flow is characterized by sub-tropical jetstreams, tropical squall line systems that form eastward-propagating super-clusters, tropical depressions and even hurricanes.Two scientific issues are briefly addressed by the simulations: what forces the Hadley circulation and the nature of stratospheric waves appearing in the simulation. It is found that the presence of a meridional sea surface temperature gradient is not sufficient on its own to force a realistic Hadley circulation even though convection communicates the underlying temperature gradient to the atmosphere. It is shown in a simulation that accounts for the observed time and zonal-mean momentum forcing effect of large-scale eddies (originating in middle latitudes) that the heaviest precipitation is concentrated near the equator in association with moisture flux convergence driven by the Trade winds.A spectral analysis of the stratospheric waves found on the equator using the dispersion relation for equatorially-trapped waves provides strong evidence for the existence of a domain-scale Kelvin wave together with eastward and westward propagating inertia-gravity waves. The eastward-propagating stratospheric waves appear to be part of a convectively coupled wave system travelling at about 15 ms⁻¹.     

NUMERICAL STUDY OF TROPICS-EXTRATROPICS INTERACTION

A nonlinear steady-state baroclinic primitive-equation numerical model of atmospheric forced stationarywaves is used to investigate the tropics-extratropics interactions.Newtonian cooling,Rayleigh friction andbiharmonic horizontal diffusion are included in the model.The Eliassen-Palm (EP) cross-section and three-dimensional wave activity flux,which was derived by Plumb (1985) for linear quasi-geostrophic stationarywaves on a zonal flow,are used as diagnostics for the vertical and horizontal propagation of the waves.Results of the numerical experiments and diagnostics analyses suggest that the extratropical influenceon the tropical large-scale motion is important.The mid-latitude orographic forcing,especially of the Qing-hai-Xizang Plateau,and the extratropical thermal forcing make substantial contribution to the main-tenance of the cyclonic circulation over the eastern tropical and subtropical Pacific as well as the inversecirculation over the western Pacific in the upper troposphere.In addition,the longitudinal variation ofdiabatic heating in tropics has a significant influence on the wintertime stationary waves at higher latitudes.