正压模式中的非绝热波动

应用含有非绝热因子的正压模式方程组,着重分析了对流凝结加热、蒸发－风反馈和ＣＩＳＫ机制等非绝热因子对低纬Ｒｏｓｓｂｙ波和Ｋｅｌｖｉｎ波的影响。既获得了圆频率的表达式,又分析了波的周期与稳定性。结果表明：非绝热因子的存在不但扩大了绝热波的周期,而且改变了波的稳定性。因此,可以认为：所谓季节内振荡（３０—６０天的周期振荡）等低频振荡实际上是一类非绝热波,这类非绝热波是引起中长期天气变化及短期气候演变的重要因素。     

RADIATIVE COOLING AND BROADBAND PHENOMENON IN LOW-FREQUENCY WAVES

In this paper, we analyze the effects of radiative cooling on the pure baroclinic low-frequency waves under the approximation of equatorial β-plane and semi-geostrophic condition. The results show that radiative cooling does not, exclusively, provide the damping effects on the development of low-frequency waves.Under the delicate radiative-convective equilibrium, radiative effects will alter the phase speed and wave period,and bring about the broadband of phase velocity and wave period by adjusting the vertical profiles of diabaticheating. When the intensity of diabatic heating is moderate and appropriate, it is conductive to the development and sustaining of the low-frequency waves and their broadband phenomena, not the larger, the better. The radiative cooling cannot be neglected in order to reach the moderate and appropriate intensity of diabatic heating.     

经圈环流在大气对SSTA强迫响应中的作用

本文建立了一个包括经向Hadley环流作用的简单半谱模式并从1982年欧洲中心的客观分析资料中得到全球纬向平均场。经一系列数值实验发现，当SSTA处于赤道地区时，由它强迫产生的波动可以同时向南北半球传播。但若考虑经向Hadley环流（υ）的作用，波传播的空间位相和振幅就有比较明显的变化，并更接近于实际大气环流异常情况。当非绝热加热源位于偏离赤道的南北半球时，实验结果表明，如果不考虑Hadley环流，南北半球的非绝热加热很难在另一半球产生强的大气响应；考虑了Hadley环流后，则非绝热加热产生的波动可向另一半球传播。数值实验结果还表明，夏季当非绝热加热源的位置改变时，大气对其改变的响应不明显，而冬季大气对非绝热加热源的纬向位置的响应却非常敏感。     

Determination of the momentum flux at the air-sea interface under variable meteorological and oceanographic conditions: Further application of the wind-wave interaction method

Simultaneous observations of wind, wave, and stability parameters made recently by several authors provide an evaluation of the contribution of these factors to the determination of wind stress on the sea surface. It is shown that under diabatic conditions the wind-wave interaction method of determining wind stress is superior to the method utilizing correction for stability. The implication is that the contribution from waves is more important to the stress than that from stability. Thus, the wind-wave interaction method may be applicable under a variety of conditions. For general meteorological-oceanographic applications, a nomograph is also provided for estimating the wind stress from commonly available wind and wave parameters.     

水汽空间分布对大气船舶重力波影响的数 值试验

利用中尺度数值模式ARPS模拟研究了水汽在山脉重力波和大气船波的产生和演变中的作用。研究发现水汽和非绝热效应对大气船波的影响与水汽的空间分布有关,大气船波的产生和演变对水汽的空间分布具有极端的敏感性,在一定条件下水汽的引入有可能减少大气船波的活动。对于3层模式结构的气流过山而言,如果初始的水汽分布在中层大气,则水汽和非绝热效应对大气船波的影响较小,而如果初始的水汽分布在中下层大气,则引入水汽后减少了大气船波的强度,但是如果初始的水汽分布在整个模式大气层,则水汽的引入减少了大气船波的活动。     

Diagnosis of the forcing of inertial-gravity waves in a severe convection system

The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the lhs, and forcing involving three terms—linear and nonlinear terms, and diabatic heating—on the rhs. The equation was applied to a case of severe convection that occurred in East China. The calculation with simulation data showed that the diabatic forcing and linear and nonlinear forcing presented large magnitude at different altitudes in the severe convection region. Further analysis revealed the diabatic forcing due to condensational latent heating had an important influence on the generation of gravity waves in the middle and lower levels. The linear forcing resulting from the Laplacian of potential-temperature linear forcing was dominant in the middle and upper levels. The nonlinear forcing was determined by the Laplacian of potential-temperature nonlinear forcing. Therefore, the forcing of gravity waves was closely associated with the thermodynamic processes in the severe convection case. The reason may be that, besides the vertical component of pressure gradient force, the vertical oscillation of atmospheric particles was dominated by the buoyancy for inertial gravity waves. The latent heating and potential-temperature linear and nonlinear forcing played an important role in the buoyancy tendency. Consequently, these thermodynamic elements influenced the evolution of inertial-gravity waves.     

Response of Atmospheric Low-frequency Wave to Oceanic Forcing in the Tropics

1. IntroductionInvestigations about atmospheric LFW have been a focus of research since Madden andJulian/s outstanding analysis works (1971, 1972). Many dynamical and thermal mechanisms(Chao et al., 1996; Fu et al., 1998; Hendon et al., 1998; Krishnamurti et al., 1988; Lau andChan, 1988) have been advised to explain LFW. Among them are oceanic effects, such as SSTeffect, thermal forcing and others. Usually atmosphere and ocean are taken as a coupled system, which is used to explain ENS…     

青藏高原热力作用下的非绝热Rossby波

从含非绝热项的准地转运动方程组出发，分析了青藏高原大尺度热力作用下非绝热Rossby波的一些性质，从理论上证明当背景西风气流为正压时，冬季高原冷却作用有利于Rossby波的经向传播，夏季高原大尺度热力作用不利于波动的经向传播。非绝热Rossby波的频率方程说明冬季高原的热力作用是中纬季节内振荡的重要激发机制。同时，在背景西风气流为纯斜压条件下，求解了高原热力作用下非绝热Rossby波的频率，并由频率方程说明冬季高原热力作用有利于波动向不稳定方向发展，而夏季高原的大尺度热力作用对波动稳定性的影响存在临界值。     

Generation mechanisms of convectively induced internal gravity waves in a three-dimensional framework

The generation mechanisms of convective gravity waves in the stratosphere are investigated in a three-dimensional framework by conducting numerical simulations of four ideal storms under different environmental conditions: one un-sheared and three constant low-level sheared basic-state winds with the depth of the shear layer of 6 km and the surface wind speeds (U_s) of 8, 18, and 28 m s^?1, using the Advanced Regional Prediction System (ARPS) model. The storms simulated under the un-sheared (U_s = 0 m s^?1), weakly sheared (U_s = 8 and 18ms^?1), and strongly sheared (U_s = 28ms^?1) basicstate winds are classified into single-cell, multicell, and supercell storms, respectively. For each storm, the wave perturbations in a control simulation, including nonlinearity and microphysical processes, are compared with those in quasi-linear dry simulations forced by diabatic forcing and nonlinear forcing that are obtained from the control simulation. The gravity waves generated by the two forcing terms in the quasi-linear dry simulations are out of phase with each other for all of the storms. The gravity waves in the control simulation are represented by a linear sum of the wave perturbations generated by the nonlinear forcing and diabatic forcing. This result is consistent with the results of previous studies in a two-dimensional framework. This implies that both forcing mechanisms are important for generating the convective gravity waves in the three-dimensional framework as well. The characteristics of the three-dimensional gravity waves in the stratosphere were determined by the spectral combination of the forcing terms and the wave-filtering and resonance factor that is determined from the basic-state wind and stability as well as the vertical structure of the forcing.     

层结大气中非线性椭圆余弦波和孤立波的研究

在前文采用半地转近似和行波法来研究层结大气中的非线性波动的基础上,进一步探讨非线性方程及其级数近似方程的解的稳定性,波动解的存在条件和波动的一些特征。研究指出,在平衡点附近,将非线性方程用其级数近似方程代替是可行的、合理的。在初始拟能满足一定的条件下,椭圆余弦波和孤立波是存在的。文中还求得了椭圆余弦波解的周期、ｘ向波长和振幅以及孤立波的宽度和振幅。并指出,孤立波的宽度和振幅不但与波速有关,还与β因子和层结稳定度有关,而且在相同的某条件下,西行的混合Ｒｏｓｓｂｙ－重力孤立波比起东行的惯性重力孤立波来,宽度要小但振幅却大。     

Enhanced response of an atmospheric flow to a line-type heat sink in the presence of a critical level

Summary Response of the atmosphere to a line-type heat sink, which represents a cold pool induced by evaporative cooling in falling precipitation, is investigated. Two-dimensional, steady-state, linear perturbations forced by the diabatic cooling in the presence of a critical level are solved analytically. The ambient flow is assumed to have a three-layer structure which is the same as that in Lindzen and Tung (1976, denoted as LT hereafter) except that an isolated diabatic cooling is specified in the lower layer. The shear layer with a critical level is assumed to be either dynamically stable or unstable. A steady-state solution is possible even for a dynamically unstable flow in the middle layer because the wave energy is allowed to propagate to infinity in the upper layer.Thermally induced wave response near the critical level depending on the stability and wind shear in terms of the Richardson number exhibits the same behavior as the eigenvalue problem solved by Jones (1967) and LT because the source mechanism does not change the critical level behavior. That is, when the shear layer is dynamically stable, almost all of the wave energy is absorbed near the critical level, while for dynamically unstable case waves can be partially-or over-reflected from the critical level depending on the Richardson number. Waves can be over-reflected and over-transmitted simultaneously as they travel through the critical level in the process of the energy extraction from the unstable mean shear flow.Using the duct condition proposed by LT, it is found that the magnitude of the perturbation vertical velocity in the lower layer is 6 times larger than that for a nonducting case with the same cooling rate. This implies that under a proper choice of the critical level height and stability profile, the response of the atmosphere to a line-type heat sink can be significantly enhanced through the over-reflection process.With 7 Figures     

Wave dynamics of super cloud clusters over the tropical region

A wave dynamics for the super cloud clusters associated with the tropical intraseasonal oscillation is constructed. Under the present framework, the basic state of super cloud clusters is considered to be a large-scale convergence of the zonal wind. This convergence is created by a nonlinear diabatic Kelvin wave front, which moves eastward slowly without change of shape. When interacting with free equatorial waves with n=−1, 0, 1 and 2, this basic flow will suppress those waves which move eastward except for free Kelvin waves, and permit westward propagating modes such as the mixed Rossby-gravity wave, the inertio-gravity waves with n=1 and 2 to appear in the large-scale convergent region. Among these waves, only fast modes, that is, inertio-gravity waves with n=1 and 2 are regarded to be responsible for the presence of cloud clusters which move westward within a super cloud cluster, while the multiplicity of the occurrences of super cloud clusters, which move eastward within the large-scale convergent region, is due to the superposition of free Kelvin wave upon these inertio-gravity waves.     

Observations of an internal gravity wave in the lower troposphere at Halley,Antarctica

Observations of internal gravity waves in the stably-stratified atmospheric boundary layer at Halley, Antarctica are presented. These were made on 1 February, 1986 and take the form of temperature measurements from a 30 m mast and a Sodar record. The temperature record shows a clearly defined, dominant wave period of around 11 min. A high-resolution radiosonde ascent made during the period of wave activity exhibits thin layers of low Richardson number and it is suggested that these are regions of dynamic instability where the waves are generated. A linear stability analysis of the radiosonde data supports this idea. It is argued from simple theoretical ideas and by means of a numerical model that only waves with a wavelength greater than a certain critical value are likely to be observed at the surface. The observations are shown to be consistent with this hypothesis.     

Analysis of the Characteristics of Inertia-Gravity Waves during an Orographic Precipitation Event

A numerical experiment was performed using the Weather Research and Forecasting(WRF) model to analyze the generation and propagation of inertia-gravity waves during an orographic rainstorm that occurred in the Sichuan area on 17 August 2014. To examine the spatial and temporal structures of the inertia-gravity waves and identify the wave types, three wavenumber-frequency spectral analysis methods(Fourier analysis, cross-spectral analysis, and wavelet cross-spectrum analysis)were applied. During the storm, inertia-gravity waves appeared at heights of 10–14 km, with periods of 80–100 min and wavelengths of 40–50 km. These waves were generated over a mountain and propagated eastward at an average speed of 15–20 m s~(-1). Meanwhile, comparison between the reconstructed inertia-gravity waves and accumulated precipitation showed there was a mutual promotion process between them. The Richardson number and Scorer parameter were used to demonstrate that the eastward-moving inertia-gravity waves were trapped in an effective atmospheric ducting zone with favorable reflector and critical level conditions, which were the primary causes of the long lives of the waves. Finally, numerical experiments to test the sensitivity to terrain and diabatic heating were conducted, and the results suggested a cooperative effect of terrain and diabatic heating contributed to the propagation and enhancement of the waves.     

A new model of tropical waves incorporating momentum mixing by cumulus convection

A comparison is made between the magnitudes of observed large-scale weather waves over the tropical Pacific and the magnitudes of the corresponding waves, predicted by wave-CISK theories, which are driven by the observed amount of latent heating (i.e., precipitation). The theoretical wave fields of meridional velocity, vorticity, and temperature rate are shown to exceed the observed quantities by an order of magnitude. An attempt is made to simulate the observed balance between the diabatic heating and adiabatic cooling within the context of the inviscid theories. For a broad class of heating profiles, geometries and basic states, it is found that this compensation without temperature change cannot be satisfactorily modelled, regardless of the vertical shape of the heating, when the vertical wavelength of the disturbance exceeds about 6 km.Scale analysis demonstrates that an important dynamical term has been neglected in the inviscid models, viz., the vertical transport of horizontal momentum by cumulus clouds. When this process is included in the wave model, velocities, relative vorticity, and the time rate of temperature change are all comparable to the observed values. The general behavior of a system where both forcing and cumulus “friction” are proportional to each other has not been previously examined. We find the behavior of such a system to have several novel features. For example, we find that for a wide range of precipitation amplitudes (from 1/4 to 4 times the precipitation amplitudes of waves in the western Pacific) we get essentially constant amplitudes for wind. The implications of this and other features for various aspects of tropical wave modelling are discussed.     

理想基流中大气波动多折射的数值试验

利用含非绝热加热的准地转正压涡度方程全球谱模式,采用４种热带海表温度异常作为热源和１６种理想基流,进行了理想基流中大气波动多折射的数值试验,积分时间为３０ｄ。得到：热源所激发的扰动通常能产生二支或三支波列,并由第一支波列分支出第二,三支波列,或第二支分支出第三支波列;对于有些基流,第一支波列维持两周或更长时间后消失,而留下其他波列;第二支波列往往最强,对于某些基流,两支流列有汇合聚集的趋势。     

青藏高原大地形的动力、热力作用与低频振荡

在对青藏高原大地形的动力和热力作用作物理分析的基础上, 着重分析了青藏高原大地形的高度、地形坡度和非绝热加热对中高纬低频振荡的影响, 指出:青藏高原大地形的高度、合适的地形坡度和地形加热都可以促进低频振荡的形成, 而且, 这些因子都会影响低频Rossby波的稳定性.     

强迫耗散正压大气中四波共振

本文首次研究了含Ekman摩擦和非绝热加热的四波共振动力学．使用新的双时间尺度和新的时间变换式，由四波共振的广义Landau方程，导得普遍的非线性低频周期解，Ekman摩擦使得低频周期具有滞后和突变返回两个重要特征，而非绝热加热作用与中高纬准双周振荡有关，中高纬的30－50天振荡则与自由Rossby波准共振有关．本文还研究了四波共振产生的爆发性不稳定，指出较大振幅波产生的爆发性不稳定可能是阻塞迅速形成的又一重要原因，还首次得到在正压大气中Ekman摩擦能够激发爆发性不稳定．本文结果纠正了Craik于1985年提出的在流体力学中广泛应用的两个错误论断．     

七月中、低纬地区定常波动和加热场的模拟特征

本文利用P-σ混合坐标原始分程球带模式的最新版本,对七月中、低纬地区的定常波动及非绝热加热场进行了数值模拟。结果表明,模式成功地模拟出了北半球夏季对流层中波数为2的定常波动。高层波峰出现在大陆,波谷出现在海洋上,低层则相反。南半球的副热带高压带也模拟出来了。降水量的模拟也是成功的,特别是位于ITCZ中的积云对流性降水。加热场的模拟结果指出,七月份的热源区除了主要分布在北半球的几个主要大陆上,还分布在热带海洋上ITCZ所在区;其余的广大洋面则显示出冷源的性质。其中热带海洋的热源以潜热加热为主(主要分布于大气的中高层),大陆上的热源有的以感热为主(主要分布于大气的低层),有的仍以潜热加热贡献较大。海洋的冷源是由长波辐射冷却造成的。