对称扰动与纬向基流的相互作用 I. 倾斜E-P通量理论

该文对对称扰动与纬向基流的相互作用理论进行了深入的研究。这里是该文的第一部分,将E-P通量理论引入到中尺度对称扰动的动力学模型中,重新定义E-P通量为“倾斜E-P通量”。采用“倾斜E-P通量”的新概念,详细讨论了影响平均基流的几个因子作用。特别在中尺度系统对动量、热量的垂直输送项改变影响环境风场、温度场方面进行了讨论。     

对称扰动与纬向基流的相互作用I.倾斜E-P通量理论

该文对对称扰动与纬向基流的相互作用理论进行了深入的研究。这里是该文的第一部分,将Ｅ－Ｐ通量理论引入到中尺度对称扰动的动力学模型中,重新定义Ｅ－Ｐ通量为“倾斜Ｅ－Ｐ通量”。采用“倾斜Ｅ－Ｐ通量”的新概念,详细讨论了影响平均基流的几个因子作用。特别在中尺度系统对动量、热量的垂直输送项改变影响环境风场、温度场方面进行了讨论。     

非纬向非平行基流中的对称不稳定

文中讨论了非纬向非平行基流中的对称不稳定,得到了新的非纬向基流下对称不稳定的判据条件。在存在横向切变时,无旋层结流体中扰动的不稳定条件为Ｒｉ＜１４ｓｉｎ２（β－α）;而在有旋层结流体中,弱的横向切变在取一级近似时并不能改变对称不稳定的增长率,但扰动必定传播,传播方向是顺切变方向,波长越短,传播速度越快。     

近四百年北半球气温变化的分析:EMD方法的应用

利用一个二维非弹性非静力的数值模式，讨论了初始扰动的尺度对于对称不稳定发展的影响。结果表明：虽然对称不稳定是β-中尺度的不稳定，但其不一定必须由β-中尺度的扰动来激发；由不同水平尺度的扰动所激发的倾斜环流有不同的特点；对称不稳定倾斜环流可能存在最小临界尺度；对称不稳定的发展存在最优扰动水平尺度，而扰动的垂直尺度对于对称不稳定的发展影响不大。     

中尺度对称不稳定和横波不稳定的波动性质

使用纬向线性以及非线性切变基流下中尺度扰动的Boussinesq近似方程组，讨论了两种典型的中尺度扰动发生对称不稳定或者横波不稳定时，其不稳定的一些特征以及扰动的波动性质。研究结果表明：（1）对于扰动的等位相面平行于基本气流方向的对称性扰动来说，对称不稳定的波动实质是沿着与基本气流方向相垂直的方向传播的重力惯性内波的不稳定。基流二次切变对于中尺度对称扰动来说是一个不稳定因子，并且驱动不稳定的中尺度对称扰动在南北方向传播；（2）对于扰动的等位相面垂直于基本气流方向的横波性扰动来说，在基本气流为常数或者只具有线性切变的情况下，此时根本不存在涡旋Rossby波，横波不稳定的波动实质则是沿着基本气流方向双向传播的重力惯性内波的不稳定。如果考虑基本流场的风速存在二次切变或者非线性切变时，此时就会产生一支新的波动（涡旋Rossby波），涡旋Rossby波相对于基本气流^-U0是单向传播的，涡旋Rossby波产生的物理根源是基本流场的风速^-U二次切变（β＊=^-Uzz≠0），此时横波型不稳定可能是混合的涡旋Rossby——重力波的不稳定。实际大气中，涡旋Rossby波对于中够尺度对流云核、暴雨团等天气系统的发生、发展和演变的物理机制具有极其重要的意义。     

对称扰动与纬向基流的相互作用 II. 粘性波包的发展与弥散

该文对对称扰动与纬向基流的相互作用理论进行了深入的研究。这里是该文的第二部分,主要讨论粘性波包的发展与弥散。在对称扰动波包的动力学方程组中引进粘性作用(Pr=1)可以发现,粘性耗散及扩散导致了“虚群速度(Cigy, Cigz)”的产生,它对波包的发展有着比较重要的影响。此外,各种稳定度参数的时空变化对扰动波包的发展具有重要作用。在一定的条件下,还可以产生波包的不稳定现象。     

"1998年二度梅"暴雨与非线性亚临界对称不稳定的初步研究

对1998年7月20日00时8月1日12时这段梅雨暴雨过程进行诊断分析，并利用MM5V3中尺度模式作梅雨暴雨的数值试验，结果表明：(1)本次梅雨暴雨分为3大段过程，非线性亚临界对称不稳定可能是3段梅雨暴雨形成的重要机制；(2)扰动风场增长与降水增长关系密切，扰动风场的增长会超前于降水的增长，非线性亚临界对称不稳定的增强可能使降水增强；(3)非线性亚临界对称不稳定主要发生在高层200hPa，中层500hPa也有发生。非线性亚临界对称不稳定使线性对称稳定的大气变为不稳定。降水区和暴雨中心主要位于高层200hPa和中层500hPa扰动风场极大值南侧与低层850hPa扰动风场极大值北侧之间。(4)非线性亚临界对称不稳定扰动的P折时间和空间尺度，分别为5～8h和200～300km。     

南海夏季风爆发前后扰动演变及其数值研究

以球面正压涡度方程为数学模型，建立了线性和非线性的数值积分模式，通过在模式中设置不同的基本流场和初始扰动场，研究基流和初始场对扰动发展的作用，揭示在球面正压大气中扰动发展的动力学机制。数值试验结果表明:在线性模式中，扰动的移动和发展与基流的分布有着很密切的关系，基流影响着扰动纬向传播的速度和方向； 在非线性模式中，当基流稳定时，扰动的移动以及传播与线性模式的结果相同，但与线性情况的最大区别在于，此时扰动能量的增长存在上限。同时发现，扰动的发展既依赖于基本气流的分布，也依赖初始扰动的结构；南海夏季风爆发前后的基本流场是正压不稳定的，且这种不稳定在季风爆发时达到最强，这可以成为季风爆发的动力学解释。     

最敏感扰动的演变与夏季乌拉尔地区的持续性异常环流

通过数值实验对初始扰动不稳定发展建立异常环流型的过程进行了分析。选择了东亚夏季风异常的１９９１年和１９８５年两个典型年份的平均环流作为基流,以共轭敏感性分析得到的最敏感扰动作为初始扰动,分析其在不同的环流背景下的发展情况。结果说明,１９９１年欧亚地区的基流不稳定性较强,且初始扰动结构有利扰动发展,因而通过能量频散在乌拉尔地区激发扰动并强烈发展,建立起阻塞形势。而１９８５年的扰动在乌拉尔地区形成正涡度距平,不利于阻高的建立。从而导致１９９１年和１９８５年夏季乌拉尔地区几乎相反的异常环流。一系列对比实验说明,异常环流型的建立,不仅依靠能量的频散,更依靠扰动通过正压不稳定过程从基流吸收能量而发展。它既有赖于基流自身的不稳定,又取决于初始扰动的结构以及相对于基流的位置。基流选择了具有特定结构的初始扰动型,只要在有利位置上给予扰动,就能够激发出扰动波列,建立强的持续异常环流型。不论初始波列的位相在一定范围内如何改变,扰动总是倾向于在基流的特定不稳定区域发展。     

线性与非线性对称不稳定的数值试验

设计了一个准二维非静力数值模式，用该模式研究了对称不稳定的发展和演变特征。线性和非线性对称不稳定的数值试验结果表明。线性和非线性对称环流的演变特征及其结构有很大差异。在基本状态是对称不稳定的情况下，线性对称不稳定在其发展过程中始终维持着向冷区倾斜的对称环流；而非线性对称不稳定在其发展初期与线性情况相同，当扰动增长到一定程度时非线性平流项的作用不可忽略，原来对称的环流则被破坏。     

波与波的相互作用对阻塞高压的形成、维持和衰退的影响

采用波数域的动能方程和定常波与瞬变波的波数域动能方程计算了阻塞高压形成、维持和衰退阶段的波与波相互作用项和波与平均运动相互作用项。计算结果表明波与波的非线性相互作用项在阻塞高压形成阶段是促使阻塞高压形成的能源,在维持阶段,是维持其稳定的能源,在衰退阶段又是促使其崩溃的能汇。波与平均运动的相互作用项在衰退阶段也起着促使阻塞高压崩溃的重要作用。定常波与瞬变波的非线性相互作用起着在具体时段使阻塞高压形成、维持和衰退的重要作用。     

台风暴雨过程中不同尺度系统的相互作用

采用数值模拟和带通滤波相结合的方法,对一次台风暴雨过程中的大中尺度系统进行了分离;推导出一个包含大中尺度系统相互作用机制的涡度方程,对中尺度系统发生发展的主要影响因子和大中尺度系统之间的相互作用机制进行了定量诊断分析.结果表明:大中尺度系统之间的相互作用是中尺度系统发展增强、进而造成强降水的一种重要机制;当中尺度系统发展到一定阶段后,由中尺度涡度场、散度场和垂直速度场之间的相互配置所决定的散度项和扭曲项又会引起中尺度系统的减弱消散,这种中尺度系统发展演变的内在调节机制使得强降水在时间上也呈现出中尺度特征.     

不同尺度涡旋相互作用对台风的结构和移动的影响

根据大气运动原始方程组导出一个支配台风中心移动的基本方程，方程中包括了非绝热加热，温度场分布，地形与摩擦等各中能影响台风移动的强迫因子。对非绝热加热与水平温度分布的使用所作分析表明，非轴对称的非绝热引导作用可使台风加速、减速或转向运动；温度场上的准区对台风有吸收作用。     

Kinetic energy exchanges between the time scales of ENSO and the Pacific decadal oscillation

This paper examines the non-linear kinetic energy interactions of the atmospheric ENSO and decadal oscillations over the Pacific. The calculations are based on a 54-year dataset of tropospheric winds from NCEP reanalysis. We verify that the decadal oscillations have two dominant modes, corresponding well to the pentadecadal and bidecadal modes reported in the literature. Energy interactions involving the range of decadal oscillations and the range of ENSO oscillations are considered in the context of kinetic energy exchanges in the frequency domain. We quantify the relative amplitudes and spatial structures of the quadratic and triplet terms of the kinetic energy exchanges over the Pacific and conclude that quadratic interactions with the mean flow are the dominant term in the kinetic-to-kinetic energy exchanges. Additionally, we show that triplet interactions provide a non-trivial contribution to the total. The interactions between the range of decadal oscillations and the range of ENSO oscillations are found to be the strongest near the regions of maximum oscillation amplitude and of the maximum oscillation amplitude gradient. Due to their similar spatial structures, the two dominant ENSO modes and the bidecadal mode are found to interact in a resonant way. The interactions among the range of ENSO modes and the range of decadal modes are found to strengthen the ENSO modes in the equatorial, subtropical and midlatitude belts, and to weaken the decadal modes in all but the equatorial belt.     

Chaos of a simple coupled system generated by interaction and external forcing

Summary ?This paper is concerned with the chaotic behavior of a coupled system consisting of two components, one representing the atmosphere and the other representing the ocean. The system is expressed as a highly truncated spectral model and for each component, the spectral model is similar to that of Lorenz (1963). Interactions between the two components are permitted, which lead to the temporal variation of surface temperature and hence that of a critical model parameter (the Rayleigh number). The emphasis of the paper is placed upon the chaotic behavior arising from the interactions between the two components and from periodic external forcing. Numerical tests are carried out to show that through interactions, the chaotic behavior of one component may result in chaos of the other even if the latter is otherwise stationary or periodic. It is shown that chaos may also occur if the system is forced periodically at certain frequencies. This study indicates that a new mechanism for chaos exists for coupled systems which are subject not only to internal fluid dynamic nonlinear interactions, but also to interactions between different components and external forcing. Received July 24, 2001; revised March 25, 2002     

副热带高压南侧双台风相互作用的数值研究

用一个正压原始方程模式 ,对 Carr和 Elsberry于 2 0世纪 90年代后期提出的双台风相互作用的概念模式进行了数值研究。结果证实了该概念模式的合理性。同时指出 :在一定的参数范围 ,副热带高压南侧东风气流中的双台风作用 ,可以激发出台风路径的移向突变和移速突变     

Substructure layers and modes in the stratified boundary layer

Geophysical flows include small-scale substructures that support shear instabilities where the smoothed mean profiles indicate only stability. The substructures must draw their energy from the mean flow, probably through wave interactions, and it is shown that the substructures themselves give rise to a type of mode that is well suited for nonlinear interactions with the flow in and around them. The study indicates that substructures and their associated modes form a dynamically interacting system that may contribute to the chaotic nature of a stably stratified region.     

ENERGY-INERTIAL SCALE INTERACTIONS FOR VELOCITY AND TEMPERATURE IN THE UNSTABLE ATMOSPHERIC SURFACE LAYER

Triaxial sonic anemometer velocity and temperature measurements were used to investigate the local structure of the velocity and temperature fluctuations in the unstable atmospheric surface layer above a grass-covered forest clearing. Despite the existence of a 2/3 power law in the longitudinal velocity (2 decades) and temperature (1 decade) structure functions, local isotropy within the inertial subrange was not attained by the temperature field, although a near-isotropic state was attained by the velocity field. It was found that sources of anisotropy were due to interactions between the large-scale and small-scaleeddy motion, and due to localvelocity-thermal interactions. Statistical measures were developed and used to quantify these types of interactions. Other types of interactions were also measured but were less significant. The temperature gradient skewness was measured and found to be non-zero in agreement with other laboratory flow types for inertial subrange scales. Despite these interactions and anisotropy sources in the local temperature field, Obukhovs 1949hypothesis for the mixed velocity-temperature structure functions was found to be valid. Finally, our measurements show that while a 2/3 power-law in the longitudinal velocity structure function developed at scales comparable to five times the height from the ground surface (z), near-isotropic conditions wereachieved at scales smaller than z/2.     

冬季亚澳季风环流的低频耦合过程

利用1982—1983年和1984—1985年两个冬季的欧洲中期预报中心格点资料研究了冬季东亚西风急流与澳大利亚夏季风在低频尺度上的相互作用与可能的传播方式。结果表明,我国北部上空的西风急流(及相应的锋区)与澳大利亚的夏季风的低频变化有很好的一致性。它们的联系和相互作用表现为:东亚西风急流通过改变西北太平洋地区的越赤道气流影响澳大利亚夏季风的低频变化,而澳大利亚夏季风则通过增强或减弱的高空辐散向北气流影响东亚西风急流。将这种相互作用称为亚澳季风环流的“低频耦合过程”。     

Persistence and long-term memories of daily maximum and minimum temperatures in southern South America

The persistence and long-term memories in daily maximum and minimum temperature series during the instrumental period in southern South America were analysed. Here, we found a markedly seasonal pattern both for short- and long-term memories that can lead to enhanced predictability on intraseasonal timescales. In addition, well-defined spatial patterns of these properties were found in the region. Throughout the entire region, the strongest dependence was observed in autumn and early winter. In the Patagonia region only, the temperatures exhibited more memory during the spring. In general, these elements indicate that nonlinear interactions exist between the annual cycles of temperature and its anomalies. Knowledge of the spatiotemporal behaviour of these long-term memories can be used in the building of stochastic models that only use persistence. It is possible to propose two objective forecast models based on linear interactions associated with persistence and one that allows for the use of information from nonlinear interactions that are manifested in the form of forerunners.