热带大气运动的长波和超长波(一)

对热带干大气运动的长波、纬向超长波(纬向扰动尺度L_1～10~4公里,经向扰动尺度L_2～10~3公里)和经向超长波(L_1～10~3公里,L_2～10~4公里)进行了尺度分析,得到了适合这些运动的近似方程。对于纬向超长波,与长波的情况一样为正压无辐散运动;但在经向超长波时,则涡度方程中存在辐散项,这一结果与Matsuno得到的在热带存在Rossby波和惯性-重力波混合的情况是一致的。同时,在存在基本气流切变的情况下,对线性化扰动方程进行了频率分析,结果指出,当n≥1时,Rossby波和惯性-重力波是可分的;当n=0,而纬向尺度L_1～1000公里时,存在混合Rossby-重力波,这就证实了上述尺度分析的结果是正确的。于是,把尺度分析的结果与热带波动运动中Rossby波和惯性-重力波是可分的或混合的特性统一了起来。     

台风麦莎的正压特征波动结构及其稳定性

利用中尺度WRF模式对2005年8月西北太平洋台风麦莎（Matsa）进行了精细的数值模拟。使用模式输出资料,对正压浅水方程组进行了数值差分计算,分析它在最大强度时刻的正压特征波动结构和稳定性。结果表明,台风麦莎内部包含有沿逆时针方向传播的重力惯性外波和涡旋Ross-by波,两种波动的结构和稳定性存在显著性差异。前者主要存在于台风外围,增长率随波长的减小而增加,台风外围的波动相速度为48．9～68．5m／s;后者主要位于距离台风中心200km内,表现为3波最不稳定,半径100km处相速度约为5m／s。此外,重力惯性外波的扰动风场与高度场基本相垂直,扰动散涡比值大于3倍,甚至达到10＾3倍,运动以辐合、辐散为主;涡旋Rossby波的扰动风场基本平行于高度场,扰动散涡比值为10＾-1～10＾-2,涡旋运动是其主要运动,与内螺旋雨带沿着切向圆周方向的传播具有密切关系。     

青藏高原上空一次重力波过程的识别与天气影响分析

应用再分析资料、多套卫星反演资料和WRF中尺度数值模拟资料,识别了2005年1月10日青藏高原上空一次重力波过程,以及重力波对青藏高原西部降雪的影响。结果表明,此次重力波位于急流出口区的左方,以西南-东北走向覆盖青藏高原大部分地区。大尺度的冷暖平流相间分布和不断增强的非平衡流为重力波的形成提供了有利背景场。小波交叉谱分析显示垂直涡度与水平散度在对流层中层满足重力波的极化性质,在青藏高原西部的上升支对应有降雪过程发生。WRF可以较好地再现这一过程,并且能够模拟出再分析资料中无法分辨的中尺度重力波。数值模拟表明,青藏高原近地面强烈非绝热加热使得低层大气静力不稳定,在近地面暖区触发对流后引起高层凝结释放潜热,低层融化冷却,有利于激发重力波,并在其上升支产生固态凝结物,随后到来的冷气团提供了有利的水汽输送条件,大范围的弱抬升运动取代了原间隔进入降雪区的强对流上升支,使得固态凝结物得以落至地面,最终在青藏高原西部形成本次降雪过程。      

一个全球大气格点模式和超长波预报问题

本文是作者在“一个修改的σ坐标初始方程”北半球模式的基础上发展全球大气模式的第一个报告.文中给出了这个全球格点模式方程组的基本计算方案;并对一个全球大气形势预报的实例进行了分析,与半球模式预报的结果作了比较,讨论了有关超长波的预报问题.     

Study on Atmospheric Travelling Wave Solutions and Review of Its Present Developments

The scientific achievements of travelling waves in a barotropic atmosphere are introduced, including i) the existence conditions of periodic solutions (wavetrain solutions) and solitary wave solutions (pulse solutions), together with the solution finding methods and a series of related problems, ii) seeking solutions of monotonous wave (wave front) and of nonmonotonous travelling wave (oscillatory wave) by using phase plane shooting technique and hi) progress in the study of travelling wave solution at home and abroad. The investigation of travelling wave solutions in recent years has been found in mathematics, physics, chemistry, biology and other sciences. Over the past decade the problem has been the subject of much interest and become an important area of research. So it is no doubt of great significance to investigate the travelling wave solutions and thereby explain phenomena of weather.     

摩擦和非线性对斜压初始扰动发展的影响

通过一个二维非线性斜压Eady波模式,讨论了斜压系统中初始扰动快速发展的动力学机制.由于斜压切变气流存在,其对扰动位涡的平流作用可引起初始扰动位涡的"位涡非屏蔽"(potential vorticity unshielding),导致线性系统初始扰动的快速增长.摩擦作用主要通过耗散局地扰动位涡,改变扰动位涡异常结构,特别是水平方向的位涡异常分布,从而减弱初始扰动位涡的"位涡非屏蔽"作用,抑制系统初始扰动动能的快速增长.非线性作用可以抑制较大振幅扰动的增长,同时引起扰动位涡异常丰富的垂直结构产生,导致初始扰动位涡的"位涡非屏蔽"的减弱,从而抑制初始扰动的快速增长.不同的初始扰动结构,可以产生不同的扰动位涡异常结构,相应存在不同的"位涡非屏蔽"作用,导致初始扰动的快速增长过程不同.位涡异常水平结构为"正负正"或"负正负"分布时,有利于初始扰动的快速增长,而上下层异号的扰动位涡异常在垂直方向间隔的距离越大,越有利于初始扰动的快速发展,这些结果进一步深化了对"位涡非屏蔽"的理解.     

Nonlinear planetary wave instability and blocking

The instability of geostrophic wave circulations related to the nonlinear processes involved in the zonal mean heat balance equations is studied. It is found that the planetary waves may be destabilized by thermal forcing in spe-cific baroclinic layers, called the breaking layers. The critical conditions of the instability will be given. In the troposphere, these conditions may be provided in blocking regions and the development of planetary perturbations is characterized distinctly by the unset, maintenance and decay of observed blocks. The whole blocking episode cannot be described as either the barotropic or baroclinic process only. The limitations on the study of wave-wave interaction using spectral models or spectrum analyses will be discussed also.     

小振幅背风波的非线性特征及水汽敏感性试验

从Scorer的背风波发生理论条件出发,首先考虑3层均匀干空气,利用WRF模式模拟出干空气条件下的小振幅拦截背风波动,波动主要发生在2~5 km的高度范围,波长为8 km左右,这与之前的观测和模拟结果相一致。分析表明:形成平稳背风波动过程中,存在能量波包向下游传播的性质,各位置振动的强度会发生周期性的增强和衰减。引入水汽进行的敏感性试验表明:随着水汽增多,背风波动的波长会增加,且波动传播中所能达到的最大垂直速度有变小趋势。     

地形对热带大气超长尺度Rossby波动的影响

应用赤道β平面近似，建立一个简单的正压大气半地转浅水线性模式，在连续方程中引入地形的作用，讨论地形对热带大气超长尺度Ｒｏｓｓｂｙ波的影响。结果分析表明，起伏不平的于形动力抬升作用导致热带大气超长尺度Ｒｏｓｓｂｙ波动不稳定并且影响波动的特性。     

青藏高原地形重力波拖曳的初步分析及数值模拟研究

针对目前对青藏高原大地形激发的重力波拖曳相关问题还不十分清楚,在GRAPES_Meso模式中引入次网格地形重力波拖曳参数化方案,通过数值试验初步研究了青藏高原地区次网格地形重力波拖曳的一些相关参数,结果指出:(1)沿30°N地形重力波拖曳的垂直分布显示,阻塞拖曳主要存在于模式的低层(第1—5层),重力波拖曳主要存在于模式的第5—10层;从水平分布看,模式第3层以阻塞拖曳为主,主要位于青藏高原边缘地区,阻塞拖曳大值区沿喜马拉雅山脉走向和青藏高原东坡;模式第5层以重力波拖曳为主,主要位于青藏高原东部地区和云贵高原的北部边缘。(2)弗劳德数和气流绕流高度分析表明,在青藏高原喜马拉雅山脉一带和高原东部边缘地区,气流爬坡能力强,同时在这一地区绕流高度最高;弗劳德数越大的地区绕流高度距离地表越高。(3)采用次网格地形重力波拖曳参数化方案后,对于低层和高层地形重力波破碎的发生有更准确的描述,地形重力波是向上垂直传播的。(4)个例和批量试验检验结果表明,采用次网格地形重力波拖曳参数化方案对于风场和降水模拟有正效果,提高了模式预报的准确率。     

Characteristics of Soliton with Dynamic Constraints on its Existence/Propagation in Tropical Easterly Wave

The study concerns the propagation of easterly wave (EW) at tropics as west-moving soliton more steady both in ionn and velocity as evidenced in the dynamic framework.Under the impact of different circulation patterns over the regions of western Pacific trade wind,South-Asia monsoon and their transition,such a soliton becomes tapering off during its westward movement and degrading to a common dispersive wave on the whole,followed by dismtegra-non when striking the South-China Sea monsoon segment,thereby indicating that the sea sector is inaccessible to the soliton When no monsoon trough is present over the South Asian monsoon area around 30癗 or the monsoon depression ]S shallow,it is likely to have west-travelling soliton,which suggests the incursion of the EW into the South-Asian monsoon region.     

Maintenance and development of the Ural high and its contribution to severe cold wave activities in winter 2020/21

2020年底至2021年初,连续两次强寒潮入侵中国东部地区,导致大范围强降温.本文研究这两次寒潮的特征和形成机理.主要结果如下:从2020年12月中旬到2021年1月中旬,乌拉尔山地区维持一宽阔的高压脊.脊前北风的维持和加强导致局地斜压性增加,导致下游横槽槽底等高线梯度加大,冷平流加强,西伯利亚高压加强和向南扩张.准定...     

Nonlinear generation of harmonics through the interaction of an internal wave beam with a model oceanic pycnocline

The interaction of an internal wave beam (IWB) with an idealized oceanic pycnocline is examined using two-dimensional fully nonlinear direct numerical simulations based on a spectral multidomain penalty method in the vertical direction. The phenomenon of focus is the nonlinear generation of harmonics. A total of 24 simulations have been performed, varying the normalized pycnocline thickness and the ratio of peak pycnocline Brunt-Väisälä frequency to that of the stratified lower layer. Harmonics at the point of IWB entry into the pycnocline increase in amplitude and number with a measure of the maximum gradient of the Brunt-Väisälä frequency, suggesting refraction as an important factor in harmonic generation. Among the simulations performed, two distinct limits of pycnocline thickness are identified. For thin pynoclines, whose thickness is 10% of the incident IWB's horizontal wavelength, harmonics trapped within the pycnocline have maximum amplitude when their frequency and wavenumber match those of the natural pycnocline interfacial wave mode. Results in this case are compared with weakly nonlinear theory for harmonic generation by plane wave refraction. For thicker pycnoclines, whose thickness is equal the incident IWB's horizontal wavelength, IWB refraction results in harmonic generation at multiple locations in addition to pycnocline entry, giving rise to complex flow structure inside the pycnocline.     

Criteria for the stability of steady flows induced by diabatic heating

By use of the Liapunov direct method, criteria for the stability of a general steady flow induced by heating are derived for a barotropic model with heating and dissipation. Among these criteria, necessary conditions for the instabilities are identified with the rises of supercritically high speed instability, barotropic instability and some other instabilities.     

影响化州的寒潮强冷空气特征及其与ENSO事件的关系

利用化州1959年以来的气温资料与ENSO资料,分析了化州近54a中寒潮及强冷空气爆发的天气气候特征和在全球大气环流和天气气候异常的大背景下,ENSO事件对影响化州的寒潮及强冷空气异常活动产生的作用,得到一些相关性的结论.统计分析表明,化州出现寒潮的拉尼娜影响年,其时拉尼娜事件爆发型均为东部型,强度中等或偏强,而化州出现寒潮的厄尔尼诺影响年,其时厄尔尼诺事件爆发型均为中部型,强度中等或偏弱.化州寒潮和强冷空气活动多的年份一般出现在中等或弱的厄尔尼诺事件期间或非ENSO年期间.少寒潮和强冷空气活动容易发生在拉尼娜事件影响年期间以及非ENSO事件影响年期间.     

Planetary wave reflection and its impact on tropospheric cold weather over Asia during January 2008

Reflection of stratospheric planetary waves and its impact on tropospheric cold weather over Asia during January 2008 were investigated by applying two dimensional Eliassen-Palm （EP） flux and three-dimensional Plumb wave activity fluxes.The planetary wave propagation can clearly be seen in the longitude-height and latitude-height sections of the Plumb wave activity flux and EP flux,respectively,when the stratospheric basic state is partially reflective.Primarily,a wave packet emanating from Baffin Island/coast of Labrador propagated eastward,equatorward and was reflected over Central Eurasia and parts of China,which in turn triggered the advection of cold wind from the northern part of the boreal forest regions and Siberia to the subtropics.The wide region of Central Eurasia and China experienced extreme cold weather during the second ten days of January 2008,whereas the extraordinary persistence of the event might have occurred due to an anomalous blocking high in the Urals-Siberia region.     

垂直切变流中非线性重力波及其相互作用

利用多重尺度摄动法，推导出斜压大气中(基本风场具有垂直切变)两个非线性重力波相互作用方程，这两个方程联立组合为耦合非线性schrǒdīnger方程组。两个重力波相互作用时可激发出重力驻波。数值计算表明：两个孤立重力波相遇，相追会使波振幅增大，波宽变窄。强烈对流天气突然爆发的可能原因之一是中尺度重力波非线性相互作用的结果。     

低纬大气Kelvin波和Rossby波的非线性相互作用

利用多重尺度摄动法,对低纬大气Kelvin波和Rossby波的波包演变进行了分析,得到两波的非线性相互作用方程为耦合的非线性复系数Landau方程组。数值计算表明两波相遇将使波振幅变化,波宽变窄;两波非线性相互作用可能是低纬强烈天气突然爆发的原因之一。     

Lamb波相控阵结构健康监测成像技术

在分析相控阵波束指向的控制过程与介绍相控阵结构健康监测原理的基础上,利用相控阵原理控制Lamb波的时间延迟使其在结构损伤处聚焦.通过比较结构健康状态与损伤状态的传感器响应信号,获取Lamb波损伤散射信号;采用相控阵技术控制损伤散射信号时间延迟得到不同方向的信号,进而实现对结构的多方位扫描,根据扫描信号特点,将各方向的监测结果信号采用灰度图像显示.该方法在铝板结构中实现损伤的定位成像,其不仅能够精确定位损伤位置,而且能够直观清晰显示结构损伤.     

时-空二维波传播分解方法及其在季节内振荡分析中的应用

大气季节内振荡最显著的特征之一就是其复杂多变的传播特征。为了进一步分析大气季节内振荡的传播特征及其不同传播方向分量的不同作用,基于波的传播理论,对时-空谱分析进行了发展,提出了时-空二维波传播分解方法,并用理想函数验证了其正确性和可行性。结果表明:对任一时-空二维序列,采用此方法均可正确地分解得到空间上具有不同传播方向的3部分分量:前进波、后退波和驻波分量。之后,对向外长波辐射(OLR)、200和850hPa纬向风的东传、西传分量以及驻波分量分别进行联合经验正交函数(CEOF)分析。结果表明,在东传分量上,热带大气季节内振荡主要表现为纬向1波的向东传播,与对流层高、低层纬向风呈现反位相的斜压结构,和未分解的情况相比,前两个主要模态重要性的排序出现了颠倒,说明通过时-空二维波传播分解,避开了各分量之间的相互影响,进一步揭示了前两个模态的物理意义及其在季节内振荡中的重要性;在西传分量上,热带大气季节内振荡主要表现为纬向2—3波的向西传播;驻波分量主要表现出印度洋和太平洋的反位相结构。对热带地区大气季节内振荡的东、西分量的分析,深化了对热带大气季节内振荡东传、西传特征的了解,这对于热带大气季节内振荡更加准确预报及其...