斜压大气波动准共振与中高纬低频振荡

从准地转两层模式出发，可能产生两种情况准共振：（１）纯正压波；（２）两个斜压波和一个正压波。本文对（２）求得准共振三波振幅的解析解和波能量变化周期的近似式。此近似式和数值计算结果两者都表明，斜压情况能量变化周期比正压情况更容易趋于准共振频率偏离Δω自身周期，从物理上指出，波的位相与波振幅之间存在着一个反馈机制，由正压波与斜压波之间的慢变相差引起的动能与有效位能的互相转换，形成了正压波和斜压波交替增强和减弱的低频振荡，其振荡周期与上述近似式一致。当Δω～（０．１－０．０２）。（ωｊ）时，平均能量周期为１２－４３ｄ，而当Δω＝０时，平均周期为３６６ｄ．因此，频率偏离Δω出现仍可能是产生料压大气中高纬低频振荡的一种新的重要机制。     

非绝热加热对中高纬大气低频振荡的调频作用

用诊断方法和数值试验两种方法,研究了非绝热加热对中高纬大气低频振荡的调频作用,首先应用１９７９～１９８９年欧洲中心资料进行功率谱分析,得到：（１）夏季与冬季相比,波动的主周期有有缩短的趋势,（２）ＥｌＮｉｎｏ事件和ＬａＮｉｎａ事件期间,冬夏两季的波动主要周期分别有缩短和变长的趋势,然后,应用强迫耗散准地转正压涡度方程的全球谱模式,考虑三个行星波准共振,积分９０ｄ,得到：（１）三个行星波之间存在的很     

印度洋海温异常对中高纬大气低频振荡影响的数值试验

用数值试验的方法,应用强迫耗散准地转正压涡度方程的全球谱模式,在方程中考虑了偶（单）极子的热力强迫作用,并在三个行星波准共振的条件下,模式共积分90d,得到：在偶、单极强迫热源和基本气流强度的共同作用下,三个行星波之间存在很强的波．波相互作用,且波动振荡呈现准双周和季节内振荡。同时偶、单极强迫源及基本气流的强度变化对中高纬大气的低频振荡调制作用不同。在准共振三波流函数场随时间变化的试验结果中,进一步证实了中高纬大气存在较好的低频振荡。     

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.     

对流凝结加热的垂直分布与低纬大气的30～60天低频振荡

运用一个包含Wave-CISK机制的斜压半地转8层模式和本征函数展开方法，研究了三种不同的对流凝结加热廓线对低纬大气的30—60天低频振荡的影响。研究表明，不同的加热廓线分布时30～60天低频振荡具有不同的相速和周期，并且低频振荡特征相速的量级都是o(10m／s)，由Wave-CISK机制激发的低频CISK—Kelvin波和CISK—Rossby波都是稳定的。同时，还进一步揭示了不同加热廓线对低纬大气30～60天低频振荡垂直结构的影响。     

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。     

正压大气中地形波与自由Rossby波的四波准共振

本文研究了正压大气中一个地形波与三个自由Rossby波的四波准共振动力学特征。由含大地形的准地转正压涡度方程，引入双时间尺度，导得了地用波与自由Rossby波的四波准共振耦合方程组，并求得其低频周期解．由数值计算表明，对于Charney所用地形高度，此解正是准双周振荡。大地形强迫是激发三个自由Rossby波相互输送能量的重要物理机制，使得二个自由Rossby波同时向第3个2波型自由Rossby波输送能量以形成准双周振荡或阻塞。这一结果与观测事实也比较一致。     

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。      

正压大气波动的4波共振和准共振

从准地转正压涡度方程，提出新的双时间尺度，首次导得了正压大气波动的４波准共振耦合方程，即广义Ｌａｎｄａｕ方程，利用新的守恒量，求得其甚低频周期解，其周期为一年左右，这可认为是实际大气中年际振荡的一种新的物理机制。并可求出４波准共振波矢。     

中高纬大气30—60天低频振荡的一种动力学机制

本文着重考虑非均匀基本流的正压局地不稳定性，研究中高纬低频振荡产生的动力机制。基本流是取1980年冬、夏300 hPa的位势场。结果表明正压局地不稳定性能较好地解释中高纬大气30—60 d天振荡。这似乎表明，低频振荡是大尺度大气运动和扰动相互作用的一种固有特征，而不是外源强迫的结果。本文还讨论了适于激发季节内低频振荡的基本流场。初值问题的研究发现中高纬大气30—60 d振荡呈纬向三波模态发展，与初始扰动和基本气流的冬、夏差别无关。     

Four-wave resonance in a forced-dissipative barotropic atmosphere

Summary This paper investigates four-wave resonance dynamics containing Ekman friction and diabatic heating. A general nonlinear low-frequency-period (LFP) solution is derived by a new time transformation from the equation of quasigeostrophic vorticity for the forced-dissipative barotropical atmosphere. The solution shows that the friction tends to prolong the LFP and the heating tends to shorten it. For a given time interval, because the effect of the friction exceeds that of the heating it is responsible for the LFP lengthening and v.v. The fact that frictional impact may be either stronger or weaker for a particular period of time leads to a longer or shorter LFP, suggesting a chaotic state of atmospheric motion. For statistical averaging on a long-term basis, however, the effects of both types are in balance so that the LFP is more or less fixed, thereby providing a new kind of physical mechanism for the predictability of climate on monthly/seasonal timescales. Furthermore, the extra-tropical quasi biweekly and 30–50 days oscillations are related to external forcing, and free Rossby wave quasi-resonance, respectively. For the first time it is found that the Ekman friction is able to excite explosive instability in a barotropical atmosphere. These results will be of use to the improvement of the two conclusions reported in Craik (1985).Project supported by the National Natural Science Foundation of China.     

经典Ekman流,Ekman层的平衡风场及其扰动稳定性

本文首先利用变分方法,考察了边界层运动能量的变化,指出经典Ekman流是在不可压缩条件下,能量积分达最小值时的一种平衡运动。这对Ekman层运动的物理本质有了进一步的认识。其次,讨论了Ekman动量近似下的Ekman层的平衡风场特征,研究了该平衡风场附近扰动的稳定性问题,结果表明,在自由大气气压场不发生扰动条件下,Ekman层中存在一类新的与惯性不稳定相类似的动力不稳定,且其不稳定性可与Ekman抽吸相联系,还讨论了一般性条件下的扰动不稳定性问题。     

Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift

Recent technological advances in current measuring devices has resulted in a large observational database related to wind-driven motions in the upper ocean mixed layer. This has served to highlight the fact that transient motions make up a substantial contribution of the resulting Ekman currents. At the same time, certain discrepancies have emerged between the observed angular deflections of the steady-state currents from the surface wind stress, both at the surface and at sub-surface depths, which cannot be reconciled using the classical Ekman model. This paper seeks to tackle these two issues.First a general analytical method is presented for solving the time dependent horizontal momentum Ekman equations. Analysis of the unsteady terms that arise from simple special cases shows how the evolution proceeds through three stages. At early times, the Coriolis acceleration is insignificant, and the current is unidirectional and deepens through downward diffusion of momentum. Later Coriolis acceleration deflects the current vectors in the upper layers, whilst downward diffusion of momentum continues to deepen the layer. Finally, once diffusion has penetrated down to the depth of the steady-state current, then the transients decay on the inertial or diffusive timescale, depending upon the boundary conditions of the particular problem.In the second half of the paper, a new steady-state model is developed that includes the effects of wind-generated waves, through the action of their Stokes drift on the planetary vorticity. Comparisons between observations and the theoretical predictions, demonstrate that inclusion of the Stokes drift is the key to reconciling the discrepancies in the angular deflections of the steady-state currents. This leads to the conclusion that Ekman layer currents are significantly influenced by the surface waves.     

斜压性与非线性Ekman抽吸的动力特征

本文利用Ekman动量近似研究了斜压性对Ekman层动力学的影响,得到了一些新的结果。大气斜压性对Ekman层的水平风速分布及近地面的风速矢的水平分量夹角有重要的改变作用。斜压边界层顶部的非线性Ekman抽吸(垂直运动)由三个不同的物理因子决定,第一、正压性的地面地转涡度,第二、斜压性作用产生的热成风涡度,第三、正压性的地面地转涡度与斜压性的热成风涡度的非线性相互作用。这些理论结果为边界层的参数化及数值模拟结果的解释提供物理基础。     

Tides and Turbulent Mixing in the North of Taiwan Island

Microstructure and hydrological profiles were collected along two cross-shelf sections from the deep slope to the shallow water in the north of Taiwan Island in the summer of 2006. While the tidal currents on the shelf were dominated by the barotropic tide with the current ellipse stretched across the shelf, significant internal tides were observed on the slope. The depth-mean turbulent kinetic energy(TKE) dissipation rate on the shelf was 10~(-6)W kg-1, corresponding to a diapycnal diffusivity of 10~(-2)m~2s~(-1). The depth-mean TKE dissipation rate on the slope was 1 × 10~(-7)W kg-1, with diapycnal diffusivity of 3.4 × 10~(-4)m~2s~(-1). The shear instability associated with internal tides largely contributed to the TKE dissipation rate on the slope from the surface to 150 m, while the enhanced turbulence on the shelf was dominated by tidal or residual current dissipations caused by friction in the thick bottom boundary layer(BBL). In the BBL, the Ekman currents associated with the northeastward Taiwan Warm Current were identified, showing a near-bottom velocity spiral, which agreed well with the analytical bottom Ekman solution.     

Growing interfacially coupled oscillations of the ocean–atmosphere

A stability analysis of the coupled ocean–atmosphere is presented which shows that the potential energy (PE) of the upper layer of the ocean is available to generate coupled growing planetary waves. An independent analysis suggests that the growth of these waves would be maintained in the presence of oceanic friction. The growing waves are a consequence of relaxing the rigid lid approximation on the ocean, thus allowing an upward transfer of energy across the sea surface. Using a two and a half layer model consisting of an atmospheric planetary boundary layer, coupled with a two layer ocean comprising an active upper layer and a lower layer in which the velocity perturbation is vanishingly small, it is shown that coupled unstable waves are generated, which extract PE from the main thermocline. The instability analysis is an extension of earlier work [Tellus 44A (1992) 67], which considered the coupled instability of an atmospheric planetary boundary layer coupled with an oceanic mixed layer, in which unstable waves were generated which extract PE from the seasonal thermocline. The unstable wave is an atmospheric divergent barotropic Rossby wave, which is steered by the zonal wind velocity, and has a wavelength of about 6000 km, and propagates eastward at the speed of the deep ocean current. It is argued that this instability, which has a multidecadal growth time constant, may be generated in the Southern Ocean, and that its properties are similar to observations of the Antarctic Circumpolar Wave (ACW).     

The effect of barotropic shear on baroclinic instability Part I: Normal mode problem

The effect of barotropic shear in the basic flow on baroclinic instability is investigated using a linear multilevel quasi-geostrophic β-plane channel model and a nonlinear spherical primitive equation model. Barotropic shear has a profound effect on baroclinic instability. It reduces the growth rates of normal modes by severely restricting their structure, confirming earlier results with a two-layer model. Dissipation, in the form of Ekman pumping and Newtonian cooling, does not change the main characteristics of the effect of the shear on normal mode instability.Barotropic shear in the basic state, characterized by large shear vorticity with small horizontal curvature, also effects the nonlinear development of baroclinic waves. The shear limits the energy conversion from the zonal available potential energy to eddy energy, reducing the maximum eddy kinetic energy level reached by baroclinic waves. Barotropic shear, which controls the level of eddy activity, is a major factor which should be considered when parameterizing the eddy temperature and momentum fluxes induced by baroclinic waves in a climate model.     

台风的数值模拟研究——积云动量输送作用

本文用一个考虑积云动量垂直输送作用的二维轴对称原始方程模式,模拟了台风的生成和发展过程。数值试验所得到的“模式台风”比考虑Ekman抽吸作用所得结果在其结构上更接近实际台风。因此,同Ekman抽吸一样,积云动量垂直输送作用也可以激发第二类条件不稳定(CISK),促使台风的生成和发展。而且,积云动量垂直输送作用,在台风的形成和维持中可能比Ekman抽吸更为重要。     

爆发性气旋的合成诊断及形成机制研究

该文对发生在太平洋和大西洋的16个爆发性气旋作了合成分折, 对强弱爆发性气旋作了对比及诊断.研究发现, 基本场上存在不少明显的差异.分析得出, 强爆发性气旋的形成与高空急流的非纬向性以及反气旋性弯曲密切相关.非纬向高空急流为爆发性气旋提供了强的辐散、斜压性、斜压不稳定场.高层强爆发性气旋前部的反气旋曲率易造成重力惯性波在能量北传时发展, 促使气旋快速加深.暖平流及非绝热加热可使反气旋曲率加强.一般情况下, 当气旋西部位涡的大值区与北部位涡的大值区叠加下沉时, 有利于气旋爆发性发展.     

稳定的和不稳定的斜压行星波

本文采用两层模式,初步地应用“时空同化”的自然观,引进空间不稳定性观点,把空间不稳定性和时间不稳定性结合起来,研究振幅随纬度变化的斜压行星波的存在范围和其稳定性;得出了稳定的和不稳定的斜压行星波及其空间不稳定判据,并对传统的斜压行星波不稳定理论和判据作出鉴定,重新提出了斜压行星波时间不稳定判据,并讨论其物理含义;还得出了高层和低层斜压行星波相互强迫振动的机制以及不同纬度间扰动振幅的关系。